Minimize Landsat-8

Landsat-8 / LDCM (Landsat Data Continuity Mission)

Spacecraft    Launch    Mission Status    Sensor Complement    Ground Segment    References

The Landsat spacecraft series of NASA represents the longest continuous Earth imaging program in history, starting with the launch of Landsat-1 in 1972 through Landsat-7 with the ETM+ imager (launch April 15, 1999). With the evolution of the program has come an increased emphasis on the scientific utility of the data accompanied by more stringent requirements for instrument and data characterization, calibration and validation. This trend continues with LDCM, the next mission in the Landsat sequence. The enhancements of the Landsat-7 system, e.g., more on-board calibration hardware and an image assessment system and personnel, have been retained and improved, where required, for LDCM. Aspects of the calibration requirements are spread throughout the mission, including the instrument and its characterization, the spacecraft, operations and the ground system. 1) 2)

The following are the major mission objectives: 3)

• Collect and archive moderate-resolution, reflective multispectral image data affording seasonal coverage of the global land mass for a period of no less than five years.

• Collect and archive moderate-resolution, thermal multispectral image data affording seasonal coverage of the global land mass for a period of no less than three years.

• Ensure that LDCM data are sufficiently consistent with data from the earlier Landsat missions, in terms of acquisition geometry, calibration, coverage characteristics, spectral and spatial characteristics, output product quality, and data availability to permit studies of land cover and land use change over multi-decadal periods.

• Distribute standard LDCM data products to users on a nondiscriminatory basis and at no cost to the users.

Background: In 2002, the Landsat program had its 30th anniversary of providing satellite remote sensing information to the world; indeed a record history of service with the longest continuous spaceborne optical medium-resolution imaging dataset available anywhere. The imagery has been and is being used for a multitude of land surface monitoring tasks covering a broad spectrum of resource management and global change issues and applications.

In 1992 the US Congress noted that Landsat commercialization had not worked and brought Landsat back into the government resulting in the launches of Landsat 6 (which failed on launch) and Landsat 7. However there was still much conflict within the government over how to continue the program.

In view of the outstanding value of the data to the user community as a whole, NASA and USGS (United States Geological Survey) were working together (planning, rule definition, forum of ideas and discussion among all parties involved, coordination) on the next generation of the Landsat series satellites, referred to as LDCM (Landsat Data Continuity Mission). The overall timeline foresaw a formulation phase until early 2003, followed by an implementation phase until 2006. The goal was to acquire the first LDCM imagery in 2007 - to ensure the continuity of the Landsat dataset [185 km swath width, 15 m resolution (Pan) and a new set of spectral bands]. 4) 5) 6) 7) 8) 9) 10) 11)

The LDCM project suffered some setbacks on its way to realization resulting in considerable delays:

• An initial major programmatic objective of LDCM was to explore the use of imagery purchases from a commercial satellite system in the next phase of the Landsat program. In March 2002, NASA awarded two study contracts to: a) Resource21 LLC. of Englewood, CO, and b) DigitalGlobe Inc. of Longmont, CO. The aim was to formulate a proper requirements set and an implementation scenario (options) for LDCM. NASA envisioned a PPP (Public Private Partnership) program in which the satellite system was going to be owned and operated commercially. A contract was to be awarded in the spring of 2003. - However, it turned out that DigitalGlobe lost interest and dropped out of the race. And the bid of Resource21 turned out to be too high for NASA to be considered.

• In 2004, NASA was directed by the OSTP (Office of Science and Technology Policy) to fly a Landsat instrument on the new NPOESS satellite series of NOAA.

• In Dec. 2005, a memorandum with the tittle "Landsat Data Continuity Strategy Adjustment" was released by the OSTP which directed NASA to acquire a free-flyer spacecraft for LDCM - thus, superseding the previous direction to fly a Landsat sensor on NPOESS. 12)

However, the matter was not resolved until 2007 when it was determined that NASA would procure the next mission, the LDCM, and that the USGS would operate it as well as determine all future Earth observation missions. This decision means that Earth observation has found a home in an operating agency whose mission is directly concerned with the mapping and analysis of the Earth's surface allowing NASA to focus on advancing space technologies and the future of man in space.

Overall science objectives of the LDCM imager observations are:

• To permit change detection analysis and to ensure consistency of the LDCM data with the Landsat series data

• To provide global coverage of the Earth's land surfaces on a seasonal basis

• To acquire imagery at spatial, spectral and temporal resolutions sufficient to characterize and understand the causes and consequences of change

• To make the data available to the user community.

The procurement approach for the LDCM project represents a departure from a conventional NASA mission. NASA traditionally specifies the design of the spacecraft, instruments, and ground systems acquiring data for its Earth science missions. For LDCM, NASA and USGS (the science and technology agency of the Department of the Interior, DOI) have instead specified the content, quantity, and characteristics of data to be delivered.

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Figure 1: History of the Landsat program (image credit: NASA) 13)

Legend to Figure 1: The small white arrow within the Landsat-7 arrow on this timeline indicates the collection of data without the Scan Line Corrector.

"The Landsat series of satellites is a cornerstone of our Earth observing capability. The world relies on Landsat data to detect and measure land cover/land use change, the health of ecosystems, and water availability," NASA Administrator Charles Bolden told the Subcommittee on Space Committee on Science, Space and Technology U.S House of Representatives in April 2015.

"With a launch in 2023, Landsat-9 would propel the program past 50 years of collecting global land cover data," said Jeffrey Masek, Landsat-9 Project Scientist at Goddard. "That's the hallmark of Landsat: the longer the satellites view the Earth, the more phenomena you can observe and understand. We see changing areas of irrigated agriculture worldwide, systemic conversion of forest to pasture – activities where either human pressures or natural environmental pressures are causing the shifts in land use over decades."

Landsat-8 successfully launched on Feb. 11, 2013 and the Landsat data archive continues to expand. — Landsat-9 was announced on April 16, 2015. The launch is planned for 2023. 14)

Dec. 31, 2015: NASA has awarded a sole source letter contract to BACT (Ball Aerospace & Technologies Corporation), Boulder, Colo., to build the OLI-2 (Operational Land Imager-2) instrument for the Landsat-9 project. 15)

 


 

Spacecraft:

In April 2008, NASA selected GDAIS (General Dynamics Advanced Information Systems), Inc., Gilbert, AZ, to build the LDCM spacecraft on a fixed price contract. An option provides for the inclusion of a second payload instrument. LDCM is a NASA/USGS partnership mission with the following responsibilities: 16) 17) 18) 19)

• NASA is providing the LDCM spacecraft, the instruments, the launch vehicle, and the mission operations element of the ground system. NASA will also manage the space segment early on-orbit evaluation phase -from launch to acceptance.

• USGS is providing the mission operations center and ground processing systems (including archive and data networks), as well as the flight operations team. USGS will also co-chair and fund the Landsat science team.

In April 2010, OSC (Orbital Sciences Corporation) of Dulles VA acquired GDAIS. Hence, OSC will continue to manufacture and integrate the LDCM program as outlined by GDAIS. Already in Dec. 2009, GDAIS successfully completed the CDR (Critical Design Review) of LDCM for NASA/GSFC. 20) 21)

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Figure 2: Artist's rendition of the LDCM spacecraft in orbit (image credit: NASA, OSC)

The LDCM spacecraft uses a nadir-pointing three-axis stabilized platform (zero momentum biased), a modular architecture referred to as SA-200HP. The SA-200HP (High Performance) bus is of DS1 (Deep Space 1) and Coriolis mission heritage. The spacecraft consists of an aluminum frame and panel prime structure.

The spacecraft is 3-axis stabilized (zero momentum biased). The ADCS (Attitude Determination and Control Subsystem) employs six reaction wheels, three torque rods and thrusters as actuators. Attitude is sensed with three precision star trackers (2 of 3 star trackers are active), a redundant SIRU (Scalable Inertial Reference Unit), twelve coarse sun sensors, redundant GPS receivers (Viceroy), and two TAMs (Three Axis Magnetometers).

- Attitude control error (3σ): ≤ 30 µrad

- Attitude knowledge error (3σ): ≤ 46 µrad

- Attitude knowledge stability (3σ): ≤ 0.12 µrad in 2.5 seconds; ≤ 1.45 µrad in 30 seconds

- Slew time: 180º any axis: ≤ 14 minutes, including settling; 15º roll: ≤ 4.5 minutes, including settling.

Key aspects of the satellite performance related to imager calibration and validation are pointing, stability and maneuverability. Pointing and stability affect geometric performance; maneuverability allows data acquisitions for calibration using the sun, moon and stars. For LDCM, an off nadir acquisition capability is included (up to 1 path off nadir) for imaging high priority targets (event monitoring capability).
Also, the spacecraft pointing capability will allow the calibration of the OLI using the sun (roughly weekly), the moon (monthly), stars (during commissioning) and the Earth (at 90° from normal orientation, a.k.a., side slither) quarterly. The solar calibration will be used for OLI absolute and relative calibration, the moon for trending the stability of the OLI response, the stars will be used for Line of Sight determination and the side slither will be an alternate OLI and relative gain determination methodology. 22) 23)

C&DH (Command & Data Handling) subsystem: The C&DH subsystem uses a standard cPCI backplane RAD750 CPU. The MIL-STD-1553B data bus is used for onboard ADCS, C&DH functions and instrument communications. The SSR (Solid State Recorder) provides a storage capacity of 4 Tbit @ BOL and 3.1 Tbit @ EOL.

The C&DH subsystem provides the mission data interfaces between instruments, the SSR, and the X-band transmitter. The C&DH subsystem consists of an IEM (Integrated Electronics Module), a PIE (Payload Interface Electronics), the SSR, and two OCXO (Oven Controlled Crystal Oscillators).

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Figure 3: Photo of the EM SSR (Solid State Recorder), image credit: NASA

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Figure 4: Block diagram of the C&DH subsystem (image credit: NASA, USGS, Ref. 229)

- The IEM subsystem provides the command and data handling function for the observatory, including mission data management between the PIE and SSR using FSW on the Rad750 processor. The IEM is block redundant with cross strapped interfaces for command and telemetry management, attitude control, SOH (State of Health) data and ancillary data processing, and for controlling image collection and file downlinks to the ground.

- The SSR subsystem provides for mission data and spacecraft SOH storage during all mission operations. The OCXO provides a stable, accurate time base for ADCS fine pointing.

- The C&DH accepts encrypted ground commands for immediate execution or for storage in the FSW file system using the relative time and absolute time command sequences (RTS, ATS respectfully). The commanding interface is connected to the uplink of each S-band transceiver, providing for cross-strapped redundancy to the C&DH. All commands are verified onboard prior to execution. Real-time commands are executed upon reception, while stored commands are placed in the FSW file system and executed under control of the FSW. Command counters and execution history are maintained by the C&DH FSW and reported in SOH telemetry.

- The IEM provides the command and housekeeping telemetry interfaces between the payload instruments and the ADCS components using a MIL-STD-1553B serial data bus and discrete control and monitoring interfaces. The C&DH provides the command and housekeeping interfaces between the CCU (Charge Control Unit), LCU (Load Control Unit) , and the PIE boxes.

- The PIE is the one of the key electrical system interfaces and mission data processing systems between the instruments, the spacecraft C&DH, SSR, and RF communications to the ground. The PIE contains the PIB (Payload Interface Boards ) for OLI (PIB-O) and TIRS (PIB-T).

Each PIB contains an assortment of specialized FPGAs (Field Programmable Gate Arrays) and ASICs, and each accepts instrument image data across the HSSDB for C&DH processing. A RS-485 communication bus collects SOH and ACS ancillary data for interleaving with the image data.

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Figure 5: Block diagram of PIB (image credit: USGS, NASA)

- Data compression: Only the OLI data, sent through the PIB-O interface, implements lossless compression, by utilizing a pre-processor and entropy encoder in the USES ASIC. The compression can be enabled or bypassed on an image-by-image basis. When compression is enabled the first image line of each 1 GB file is uncompressed to provide a reference line to start that file. A reference line is generated every 1,024 lines (about every 4 seconds) to support real-time ground contacts to begin receiving data in the middle of a file and decompressing the image with the reception of a reference line.

- XIB (X-band Interface Board): The XIB is the C&DH interface between the PIE, SSR, and X-band transmitter, with the functional data path shown in Figure 6.

The XIB receives real-time data from the PIE PIB-O and PIB-T and receives stored data from the SSR via the 2 playback ports. The XIB sends mission data to the X-band transmitter via a parallel LVDS interface. The XIB receives a clock from the X-band transmitter to determine the data transfer rates between the XIB and the transmitter to maintain a 384 Mbit/s downlink. The XIB receives OLI realtime data from the PIB-O board, and TIRS real-time data from the PIB-T board across the backplane. The SSR data from the PIB-O and PIB-T interfaces are multiplexed and sent to the X-Band transmitter through parallel LVDS byte-wide interfaces.

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Figure 6: X-band mission data flow (image credit: USGS, NASA)

- SSR (Solid Ste Recorder): The SSR is designed with radiation hard ASIC controllers, and up-screened commercial grade 4GB SDRAM (Synchronous Dynamic Random Access Memory) memory devices. Protection against on-orbit radiation induced errors is provided by a Reed-Solomon EDAC (Error Detection and Correction) algorithm. The SSR provides the primary means for storing all image, ancillary, and state of health data using a file management architecture. Manufactured in a single mechanical chassis, containing a total of 14 memory boards, the system provides fully redundant sides and interfaces to the spacecraft C&DH.

The spacecraft FSW (Flight Software) plays an integral role in the management of the file directory system for recording and file playback. FSW creates file attributes for identifier, size, priority, protection based upon instructions from the ground defining the length of imaging in the interval request, and its associated priority. FSW also maintains the file directory, and creates the ordered lists for autonomous playback based upon image priority. FSW automatically updates and maintains the spacecraft directory while recording or performing playback, and it periodically updates the SSR FSW directory when no recording is occurring to synchronize the two directories (Ref. 229).

TCS (Thermal Control Subsystem): The TCS uses standard Kapton etched-foil strip heaters. In general, a passive, cold-biased system is used for the spacecraft. Multi-layer insulation on spacecraft and payload as required. A deep space view is provided for the instrument radiators.

EPS (Electric Power Subsystem): The EPS consists of a single deployable solar array with single-axis articulation capability and with a stepping gimbal. Triple-junction solar cells are being used providing a power of 4300 W @ EOL. The NiH2 battery has a capacity of 125 Ah. Use of unregulated 22-36 V power bus.

The onboard propulsion subsystem provides a total velocity change of ΔV = 334 m/s using eight 22 N thrusters for insertion error correction, altitude adjustments, attitude recovery, EOL disposal, and other operational maintenance as necessary.

The spacecraft has a launch mass of 2780 kg (1512 kg dry mass). The mission design life is 5 years; the onboard consumable supply (386 kg of hydrazine) will last for 10 years of operations.

Spacecraft platform

SA-200HP (High Performance) bus

Spacecraft mass

Launch mass of 2780 kg; dry mass of 1512 kg

Spacecraft design life

5 years; the onboard consumable supply (386 kg of hydrazine) will last for 10 years of operations

EPS (Electric Power Subsystem)

- Power: 4.3 kW @ EOL (End of Life)
- Single deployable solar array with single-axis articulation capability
- Triple-junction solar cells
- NiH2 battery with 125 Ah capacity
- Unregulated 22 V - 36 V power bus
- Two power distribution boxes

ADCS (Attitude Determination &
Control Subsystem)

- Actuation: 6 reaction wheels and 3 torque rods
- Attitude is sensed with 3 precision star trackers, a redundant SIRU (Scalable Inertial Reference Unit),
12 coarse sun sensors, redundant GPS receivers (Viceroy), and 2 TAMs (Three Axis Magnetometers)
- Attitude control error (3σ): ≤ 30 µrad
- Attitude knowledge error (3σ): ≤ 29 µrad
- Attitude knowledge stability (3σ): ≤ 0.12 µrad in 2.5 seconds
- Attitude jitter: ≤ 0.28 µrad, 0.1-1.0 Hz
- Slew time, 180º pitch: ≤ 14 minutes, inclusive settling
- Slew time, 15º roll: ≤ 4.5 minutes, inclusive settling

C&DH (Command & Data Handling)

- Standard cPCI backplane RAD750 CPU
- MIL-STD-1553B data bus
- Solid state recorder provides a storage capacity of 4 TB @ BOL and 3.1 TB @ EOL

Propulsion subsystem

- Total velocity change of ΔV = 334 m/s using eight 22 N thrusters
- Hydrazine blow-down propulsion module

Table 1: Overview of spacecraft parameters

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Figure 7: Two views of the LDCM spacecraft (without solar arrays) and major components (image credit: NASA, USGS)

RF communications: Earth coverage antennas are being used for all data links. The X-band downlink uses lossless compression and spectral filtering. The payload data rate is 440 Mbit/s. The X-band RF system consists of the X-band transmitter, TWTA (Travelling Wave Tube Amplifier), DSN (Deep Space Network) filter, and an ECA (Earth Coverage Antenna). The serial data output is set at 440.825 Mbit/s and is up-converted to 8200.5 MHz. The TWTA amplifies the signal such that the output of the DSN filter is 62 W. The DSN filter maintains the signal's spectral compliance. An ECA provides nadir full simultaneous coverage, utilizing 120º half-power beamwidth, for all in view ground sites below the spacecraft's current position with no gimbal or actuation system. The system is designed to handle up to 35 separate ground contacts per day as forecasted by the DRC-16 (Design Reference Case-16).

The X-band transmitter is a single customized unit, including the LDPC FEC algorithms, the modulator, and up converter circuits. The transmitter uses a local TXCO (Thermally Controlled Crystal Oscillator) as a clock source for tight spectral quality and minimum data jitter. This clock is provided to the PIE XIB to clock mission data up to a 384Mbit/s data rate to the transmitter. The X-band transmitter includes an on-board synthesized clock operating at 441.625 Mbit/s coded data rate using the local 48 MHz clock as a reference. Using the on-board FIFO buffer, this architecture provides a continuous data flow through the transmitter (Ref. 229).

The S-band is used for all TT&C functions. The S-band uplink is encrypted providing data rates of 1, 32, and 64 kbit/s. The S-band downlink offers data rates of 2, 16, 32, RTSOH; 1 Mbit/s SSOH/RTSOH GN; 1 kbit/s RTSOH SN. Redundant pairs of S-band omni's provide transmit/receive coverage in any orientation. The S-band is provided through a typical S-band transceiver, with TDRSS (Tracking and Data Relay Satellite System) capability for use during launch and early orbit and in case of spacecraft emergencies.

Onboard data transmission from an earth-coverage antenna:

• Real-time data received from PIE (Payload Interface Electronics) equipment

• Play-back data from SSR (Solid State Recorder)

• To three LGN (LDCM Ground Network) stations

- NOAA Interagency Agreement (IA) to use Gilmore Creek Station (GLC) near Fairbanks, AK

- Landsat Ground Station (LGS) at USGS/EROS near Sioux Falls, SD

- NASA contract with KSAT for Svalbard; options for operational use by USGS (provides ≥ 200 minutes of contact time)

• To International Cooperator ground stations (partnerships of existing stations currently supporting Landsat).

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Figure 8: Photo of the EM X-band transponder (left) and AMT S-band transponder (right), image credit: NASA

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Figure 9: Alternate view of the deployed LDCM spacecraft showing the calibration ports of the instruments TIRS and OLI (image credit: NASA/GSFC)

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Figure 10: The LDCM spacecraft with both instruments onboard, OLI and TIRS (image credit: USGS) 24)

 

Launch: The LDCM mission was launched on February 11, 2013 from VAFB, CA. The launch provider was ULA (United Launch Alliance), a joint venture of Lockheed Martin and Boeing; use of the Atlas-V-401 the launch vehicle with a Centaur upper stage. 25) 26)

Note: Initially, the LDCM launch was set for July 2011. However, since this launch date was considered as too optimistic, NASA changed the launch date to the end of 2012. This new launch delay buys some time for an extra sensor with TIR (Thermal Infrared) imaging capabilities.

Orbit: Sun-synchronous near-circular orbit, altitude = 705 km, inclination = 98.2º, period = 99 minutes, repeat coverage = 16 days (233 orbits), the nominal LTDN (Local Time on Descending Node) equator crossing time is at 10:00 hours. The ground tracks will be maintained along heritage WRS-2 paths. At the end of the commissioning period, LDCM is required to be phased about half a period ahead of Landsat 7. 27)

 

Minimize Mission Status

Mission status:

• November 6, 2018: Orbit Logic Inc. of Greenbelt, Maryland delivered their mission planning and scheduling system, the STK (Systems Tool Kit) SchedulerTM, for the Landsat program. 28)

Orbit Logic announced today that they have delivered their STK Scheduler software and CPAW (Collection Planning & Analysis Workstation) software to General Dynamics Mission Systems for mission planning and scheduling for the LMOC (Landsat Mission Operations Center) for Landsat-8 and -9. Orbit Logic is now in the process of integrating the software into the Landsat ground system. The U.S. Geological Survey (USGS) awarded the Landsat Multi-satellite Operations Center (LMOC) contract to the General Dynamics team to develop and carry out operations of the Landsat-9 Mission Operations as well as assuming operations of the on-orbit Landsat-8 observatory.

Landsat-9 will be the next satellite in the Landsat series that images the Earth's surface. It is currently scheduled for launch in December 2020. Orbit Logic software will streamline and modernize the mission planning and collection planning process, taking over for the Generic Mission Planning System and the Collection Activity Planning Element (CAPE) that was previously developed and operated by USGS. Orbit Logic's STK Scheduler will produce a deconflicted schedule for satellite communications between the Landsat satellites, U.S. and international ground stations, and TDRSS satellite communication nodes. Orbit Logic's CPAW software will be used for Landsat-8 and -9 to generate validated, deconflicted, and optimized high fidelity imagery collection plans. A significant number of requirements were satisfied out of the box with Orbit Logic's COTS software products. Plus, Orbit Logic provided engineering services to integrate with other elements of the ground system and develop models of the Landsat spacecraft bus and sensors. Additionally, Orbit Logic's planning software solution provides a multi-mission planning system to support LS-8 and LS-9 simultaneously.

Table 2: Orbit Logic delivers their Landsat Mission Planning System

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Figure 11: Sample Landsat collection plan built using CPAW (image credit: Orbit Logic)

• November 5, 2018: After making landfall in northwestern Mexico, Hurricane Willa quickly weakened over rugged, dry terrain. But the remnants of that category 3 storm pushed a stream of moisture and rain northeast toward Texas. 29)

- While Willa did not bring overwhelming rain to Texas, the infusion of moisture was unwelcome in a state already in the grips of severe flooding. Since September 2018, a series of storms have delivered historic amounts of rain to central Texas. One particularly potent cold front in mid-October dropped more than a foot of rain in some areas.

- The deluge saturated soils, overfilled lakes and reservoirs, and pushed rivers over their banks. One river even flowed backwards. In a series of proclamations issued throughout October, the Texas governor declared a state of disaster for 111 counties because of the flooding and severe weather.

- Storm after storm rolled through and dumped record rainfall in parts of Texas. Several satellites observed the deluge and its aftermath.

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Figure 12: OLI map of the Nueces River region in Texas acquired on 1 October 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

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Figure 13: On 1 November 2018, OLI on Landsat-8 captured a false-color view (bands 7-6-4) of flooding along the Nueces River near Calallen. At the time, a stream gauge in nearby Mathis showed the river had risen to 9 m putting it 1 m above flood stage (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- The map of Figure 14 depicts spaceborne measurements of rainfall from 1-31 October 2018. The brightest areas reflect the highest rainfall amounts, with many places receiving 25 to 45 cm or more during this period. The measurements are a product of the NASA/JAXA GPM (Global Precipitation Measurement) mission. These rainfall totals are regional, remotely-sensed estimates. Each pixel shows 0.1 degrees of the globe (about 11 km at the equator), and the data are averaged across each pixel. Therefore, individual ground-based measurements within a pixel can be significantly higher or lower than the satellite average.

- The Dallas Fort Worth Airport recorded 39.77 cm of rain in October 2018, making it the wettest October on record there, according to the National Weather Service. While the statistics are still being finalized statewide, it is likely that October will go down as the second wettest month in Texas on record.

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Figure 14: This IMERG map depicts GPM satellite-based measurements of rainfall from 1-31 October 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens using IMERG data provided by NASA/GSFC)

• October 30, 2018: As Rebecca Trinh cruised around Santa Monica Bay, just a mile offshore from Los Angeles, the smell of chlorine and sewage flooded her nostrils. Seagulls fed on debris in the ocean, while a plume of wastewater bubbled to the surface. Most people would turn and cruise away from the scene, but the stench was precisely what brought the microbial oceanographer here. 30)

- Trinh and a team from NASA's Jet Propulsion Laboratory were part of an effort to help LA Sanitation monitor water quality during maintenance of the city's oldest and largest wastewater treatment plant. The Hyperion Water Reclamation Plant serves around 4 million people, treating wastewater from sinks, showers, toilets, and surface runoff from storm drains. From September 21 to November 2, 2015, plant operators had to shut down Hyperion's main discharge pipe in order to make repairs to the internal structure.

- The main outflow pipe normally transports wastewater five miles offshore, a distance where the seawater is deep enough so that waste (effluent) can be naturally diluted before reaching the surface—"The solution to pollution is dilution," Trinh noted. During the repair, plant operators were forced to use their one-mile backup discharge pipe, which releases effluent much closer to the shore. Researchers like Trinh worked to observe and learn from the event. They published their findings in the scientific journal Frontiers. 31)

- "The one-mile pipe is closer to shore and in much shallower water," said Trinh, "so there were a lot of human health impacts and ecological impacts that people were worried about." Using satellites, the team was able to monitor the area in near-real-time and provide LA Sanitation with insight on potential biological hazards.

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Figure 15: OLI on Landsat-8 acquired a natural-color image of Santa Monica Bay on October 10, 2015, midway through the shutdown. The green patches near the coast are phytoplankton blooms likely caused by an excess of nutrients from the nearshore wastewater discharge (image credit: NASA Earth Observatory)

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Figure 16: These maps show the sea surface temperature of Santa Monica Bay before, during, and after wastewater was transported through the shorter pipe. The data was acquired by the Thermal Infrared Sensor (TIRS) on the Landsat-8 satellite. During the diversion, a cooler pool of water formed near the mouth of the one-mile pipe, as the plume of wastewater also brought colder water from the depths to the surface. (image credit: NASA Earth Observatory)

- "We knew that along with the change in temperature, we were going to get all the excess nutrients and the potentially harmful bacteria and chemicals associated with the pipe's effluent," said Trinh. Researchers had two main worries about the excess nutrients. First, that they would stimulate toxic phytoplankton blooms. Second, that they could lead to eutrophication—when extreme growth, and subsequent death, of algae, phytoplankton, or other plant life severely depletes the oxygen supply for other marine animals.

- Measuring chlorophyll-a concentrations in coastal environments is challenging. Water temperatures fluctuate quite a bit, waters are often rich with sediment and land runoff, and there is usually a higher concentration of phytoplankton than in offshore waters. Trinh's team developed a new satellite algorithm to decrease the "signal-to-noise" ratio in tricky coastal waters and to provide more accurate chlorophyll-a measurements. The improved algorithm integrates data collected by Trinh and her team from ship-based instruments with data from Landsat-8 (Figure 17).

- "The satellite component gave a new perspective on the situation because usually Hyperion just monitors from the ship in a very small area around the pipes," said Trinh. "We're showing that these wastewater diversions can have wide spatial impacts, and you wouldn't know that without something like a satellite data set."

- Trinh and colleagues helped guide LA Sanitation on where to collect water samples to test for harmful bacteria. For instance, satellite data showed higher chlorophyll concentrations along the southern shoreline of Santa Monica Bay, so water quality monitors collected samples from Topanga Canyon to Malaga Cove. In this area, they found that 10 percent of the samples contained fecal bacteria in amounts that exceeded state water quality standards. Multiple beaches were temporarily closed as a result.

- Trinh said this study was a good demonstration of how satellites can aid in monitoring water quality, especially in coastal areas with a lot of human activity and near wastewater outflows. "If a plant's pipes don't stay functional or have a catastrophic blowout," she said, "we already know what type of instruments and satellites we can use to make water quality monitoring as efficient as possible."

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Figure 17: These maps show chlorophyll-a concentrations—a proxy for the amount of phytoplankton in the water—over the six-week pipe diversion period. Four phytoplankton blooms occurred during the diversion (including the one at the top of this page). Researchers who took water samples identified the phytoplankton as non-toxic euglenoids, a type of green algae (image credit: NASA Earth Observatory, images by Joshua Stevens, using data courtesy of Rebecca Trinh/Columbia University, and Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- A NASA team was able to use satellite imagery to observe effects of a repair of Los Angeles' largest wastewater treatment plant.

• October 19, 2018: As the Neuquén River winds its way from the Andes through west-central Argentina toward the Atlantic Ocean, it passes a spectacular series of rock formations in the Neuquén Basin. For paleontologists, the basin is a great place to find fossils, particularly dinosaurs. And for those in the oil business, it is fertile ground for gas and oil exploration. 32)

- From space, boundaries between some of the major groups of sedimentary rock formations are visible. In the first image, the deep reds of the Candeleros Formation—a sequence of sandstones formed roughly 90 to 100 million years ago in a braided river system—dominate the landscape. These rocks are flanked in some areas, especially near the river, by a green-yellow sequence of rocks that are part of the younger Hunical Formation, formed during drier times. The older Royosa Formation, meanwhile, peeks through in some areas where erosion has scraped away overlying rock layers (see Figure 19).

- Paleontologists have uncovered quite a menagerie of fossilized fauna in Candeleros rocks, including ancient species of fish, frogs, snakes, turtles, small mammals, and several types of dinosaurs. Few of the fossilized creatures have received the notoriety of Giganotosaurus carolinii—a carnivorous theropod thought to be larger and faster than Tyrannosaurs Rex.

- Petroleum geologists are more interested in what lies beneath the Candeleros Formation. Several layers of rock, formed when the area was covered by an ocean, contain gas and oil. While drilling has been ongoing here since 1918, the recent discovery of a large deposit of shale gas and oil in the Vaca Muerta Formation has made the Neuquén Basin one of the few regions outside of the United States where companies are pursuing horizontal drilling and hydraulic fracturing.

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Figure 18: The distinctive sedimentary rock formations in west-central Argentina make for a geological and paleontological wonderland. OLI on Landsat-8 acquired this image showing part of the basin on September 3, 2018 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 19: The older Royosa Formation, meanwhile, peeks through in some areas where erosion has scraped away overlying rock layers (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

• October 17, 2018: Satellites captured a rare image of a plume of dusty glacial flour streaming from eastern Greenland. Dust is probably the last thing that comes to mind when you think about Greenland, an island mostly covered by ice. Though Greenland's dust events are nothing like the massive clouds of dust and sand that can darken skies over the Sahara Desert for days, winds in Greenland are occasionally strong enough to send plumes of sediment streaming from dried-out lakes, river valleys, and outwash plains along the coasts. The dust in Greenland is mainly glacial flour, a fine-grained silt formed by glaciers grinding and pulverizing rock. 33)

- For more than a century, researchers have sporadically reported high-latitude dust events in expedition logs and scientific publications. But only during the past decade have scientists attempted to study them systematically. The Arctic and high-latitudes can be tough to study even with satellites, and a recent study noted a dearth of Greenland dust observations.

- No longer. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite and a sensor on the European Space Agency's Sentinel-2 collected imagery on September 29, 2018, of a sizable silt plume streaming from Greenland's east coast. The source was a braided stream valley about 130 kilometers (80 miles) northwest of Ittoqqortoomiit, a village at a latitude of 73 degrees North. That puts the village north of the northern coast of Alaska.

- "This is by far the biggest event detected and reported by satellites that I know about," said Santiago Gassó, an atmospheric scientist at NASA's Goddard Space Flight Center. He first noticed the storm on October 3.

- "We have seen a few examples of small dust events before this one, but they are quite difficult to spot with satellites because of cloud cover," said Joanna Bullard of Loughborough University. "When dust events do happen, field data from Iceland and West Greenland indicate that they rarely last longer than two days."

- The glacial flour was likely made by several glaciers farther up the valley, then carried south by meltwater streams and deposited in the floodplain. As stream water levels dropped in autumn, the floodplain dried out and became susceptible to scouring by the wind. In this case, Bullard noted, the winds were triggered by the combination of a low-pressure system crossing the Greenland ice sheet followed closely by a ridge of high pressure.

- Since high-latitude dust events are poorly understood, they are typically not included in atmospheric and climate models. Gasso hopes that eventually they will be included because they could have effects on air quality, the reflectivity of snow, and even marine biology.

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Figure 20: A series of Landsat-8 images captured on September 21, 23, 29, and 30—shows the floodplain where the stream flows into Scoresby Sound. As the soil on the floodplain dried out (first two images), the floodplain became increasingly gray. Northwesterly winds on September 29 were strong enough to lift glacial flour into the air (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

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Figure 21: The Copernicus Sentinel-2 satellite of ESA collected imagery on September 29, 2018, of a sizable silt plume streaming from Greenland's east coast. Northwesterly winds on September 29 were strong enough to lift glacial flour into the air (image credit: NASA Earth Observatory image by Joshua Stevens, using Copernicus Sentinel data (2018) processed by the European Space Agency. Story by Adam Voiland)

• October 02, 2018: The powerful, shallow earthquake of magnitude 7.5 that rattled the northern coast of Sulawesi island on September 28, 2018, caused tremendous damage. Homes throughout Palu, Indonesia, have been flattened. A series of tsunami waves decimated the coastline. Destructive flows of mud and soil destroyed several inland areas in the city of 300,000 people. 34)

- While coastal areas took heavy damage because of the tsunami, the image also reveals three large inland flows of mud that caused severe damage in densely populated areas. Intense shaking from the earthquake may have triggered liquefaction and lateral spreading, processes in which wet sand and silt takes on the characteristics of a liquid. These processes, which are especially common near streams and on reclaimed land, can produce destructive mudslides even in relatively flat areas.

- Scientists were surprised that the earthquake generated such a big tsunami. Normally, large tsunamis occur after megathrust earthquakes that cause vertical displacement. But the Sulawesi earthquake occurred along a strike-slip fault, meaning the motion was horizontal. Some scientists suspect that a submarine landslide, shaken loose by the earthquake, may have provided the energy that fueled the destructive tsunami. In addition, the narrow, finger-like shape of Palu Bay likely amplified the fast-moving surge of water and made it even more dangerous.

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Figure 22: OLI on Landsat-8 captured a natural-color image of Palu on October 2, 2018. The false-color (bands 6-5-2) images make it easier to distinguish between urban areas (purple-gray), vegetation (green), and upturned soil (brown and tan), image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland

• September 27, 2018: The capital of India, New Delhi, has been experiencing one of the fastest urban expansions in the world. Vast areas of croplands and grasslands are being turned into streets, buildings, and parking lots, attracting an unprecedented amount of new residents. By 2050, the United Nations projects India will add 400 million urban dwellers, which would be the largest urban migration in the world for the thirty-two year period. 35)

- These images show the growth in the city of New Delhi and its adjacent areas—a territory collectively known as Delhi—from December 5, 1989, (Figure 23) to June 5, 2018 (Figure 24). These false-color images use a combination of visible and short-wave infrared light to make it easier to distinguish urban areas. The 1989 image was acquired by the Thematic Mapper on Landsat 5 (bands 7,5,3), and the 2018 image was acquired by Operational Land Imager on Landsat-8 (bands 7,6,4).

- Most of the expansion in Delhi has occurred on the peripheries of New Delhi, as rural areas have become more urban. The geographic size of Delhi has almost doubled from 1991 to 2011, with the number of urban households doubling while the number of rural houses declined by half. Cities outside of Delhi—Bahadurgarh, Ghaziabad, Noida, Faridabad, and Gurugram—have also experienced urban growth over the past three decades, as shown in these images.

- With a flourishing service economy, Delhi is a draw for migrants because it has one of India's highest per capita incomes. According to the latest census data, most people (and their families) move into the city for work. The Times of India reported that the nation's capital grew by nearly 1,000 people each day in 2016, of which 300 moved into the city. By 2028, New Delhi is expected to surpass Tokyo as the most populous city in the world.

- The increased urbanization has had several consequences. One is that the temperatures of the urban areas are often hotter than surrounding vegetated areas. Manmade structures absorb the heat and then radiate that into the air at night, increasing the local temperature (the urban heat island effect). Research has shown that densely built parts of Delhi can be 7°C (45°F) to 9°C (48°F) warmer in the wintertime than undeveloped regions.

- Additionally, sprawling cities can have several environmental consequences, such as increasing traffic congestion, greenhouse gas emissions, and air pollution. From 2005 to 2014, NASA scientists have observed an increase in air pollution in India due to the country's fast-growing economies and expanding industry.

- India is one of many countries with fast-growing cities. By 2050, China is projected to add 250 million people in its urban areas, and Nigeria may add 190 million urban dwellers. In total, India, China and Nigeria are expected to account for 35 percent of the world's urban population growth between 2018 and 2050.

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Figure 23: False-color image of New Delhi acquired with the TM (Thematic Imager) of Landsat-5 on 5 December 1989 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

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Figure 24: False-color image of New Delhi acquired on June 5 2018 with the OLI (Operational Land Imager) on Landsat-8 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

• September 26, 2018: The last big eruption at Hokkaido's Kuttara volcano happened roughly 40,000 years ago, about the time Neanderthals were going extinct and a bit before people had begun to domesticate dogs. 36)

- Earlier eruptions at the Japanese stratovolcano had produced thick andesitic lavas that flowed into two large tongue-shaped lobes immediately north of the volcano. Silica-rich, viscous magma blocked the vent, so pressure built up in much the same way it does in a soda bottle after it is shaken. When the pressure grew intense enough, it blasted a vent at the top of the volcano and sent a large plume of ash shooting into the air. Fast-moving jumbles of ash, gas, and other debris—known as pyroclastic flows—swept down the southwestern slope of the volcano.

- That explosive eruption—and the slumping of rock into the emptied-out lava chamber—sculpted the bowl-shaped caldera that now sits at the top of the mountain and holds Lake Kuttara, one of the roundest and clearest lakes in Japan.

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Figure 25: OLI on Landsat-8 acquired an image on 15 September 2015 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, Story by Adam Voiland)

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Figure 26: For the three-dimensional view, the Landsat-8 image was draped over a global digital elevation model built from data acquired by NASA's SRTM (Shuttle Radar Topography Mission), image credit: NASA Earth Observatory, image by Joshua Stevens, using topographic data from SRTM, story by Adam Voiland

- Following that explosive eruption, volcanic activity at the caldera calmed and geothermal activity shifted to the southwestern slope of the volcano. About 15,000 to 20,000 years ago, viscous lava began to bulge upward into a lava dome, and a series of small steam explosions gouged several craters into a valley of fumaroles, geysers, streams, and ponds.

- This exotic, steaming landscape persists today. Known in Japanese as Jigokudani (Hell Valley) for its rusty red and black terrain, visitors can follow a walking path through the treeless valley, along a hot creek with a popular natural foot bath. They eventually arrive at sulfurous Lake Oyunuma, which has a surface temperature of 50ºC (122ºF).

- The lingering volcanic activity in the area has fueled the development of several onsens, or hot spring spas, that have made Noboribetsu one of the most famous spa towns in Hokkaido. Millions of people visit each year to soak in the natural mineral-rich waters from Lake Oyunuma and Hell Valley.

• September 4, 2018: Scattered in a sea of sand, inselbergs in Namibia host ecology uniquely influenced by fog. The Namib Sand Sea stands at the heart of Namib-Naukluft National Park, which is located on the coast of Namibia. Most of the terrain is dominated by sand, but one percent features inselbergs, or isolated raised hills. 37)

- According to a UNESCO World Heritage Center report, the inselbergs receive more rainfall than the surrounding lower-elevation dunes. That is because warm air gets pushed up the mountains from winds blowing past, causing water vapor to condense into clouds. Also, the raised land catches more fog coming from the ocean. Fog is the primary source of water for the Namib Sand Sea, which is the only coastal desert in the world to contain large dune fields influenced by fog.

- The wetter microclimate results in more abundant and diverse vegetation on inselbergs than sand dunes. Hauchab primarily has vegetation found in the palaeotropical Nama Karoo biome, which fosters shrubs and grasses, and the temperate Succulent Karoo biome, which is famous for its spring flowers.

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Figure 27: This image shows two inselbergs in the sand sea: Uri-Hauchab and Hauchab. The OLI (Operational Land Imager) on Landsat-8 acquired the image on 5 July 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

- The sand sea of Figure 28 covers over three million acres (1,215,000 hectare) inside the Namib-Naukluft Park. The national park is the combination of the Namib Desert, thought to be the world's oldest desert, and the Naukluft Mountains, which serve as a sanctuary for endemic Hartmann zebras.

- The sand sea consists of two dune seas, one on top of the other. The foundation is an ancient sand sea that has existed for about 21 million years. That has been covered over with younger sand that has been active for the past 5 million years. Sand seas in other parts of the world are generally formed through erosion of hard bedrock underneath, but the Namib Sand Sea is unique because the materials were transported from thousands of kilometers away. Carried by river, ocean current, and wind, sediments were transported along the Orange River to the coast, where they were lifted by winds and deposited inland.

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Figure 28: This image was acquired by the Moderate Resolution Imaging Spectroradiometer instrument (MODIS) on NASA's Terra satellite on August 10, 2018 (image credit: NASA Earth Observatory images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, story by Kasha Patel)

• September 1, 2018: The world's oldest and largest known impact structure shows some of the most extreme deformation conditions known on Earth. About two billion years ago, an asteroid measuring at least 10 km across hurtled toward Earth. The impact occurred southwest of what is now Johannesburg, South Africa, and temporarily made a 40-kilometer-deep and 100-kilometer-wide dent in the surface. Almost immediately after impact, the crater widened and shallowed as the rock below started to rebound and the walls collapsed. The world's oldest and largest known impact structure was formed. 38)

- Scientists estimate that when the rebound and collapse ceased, Vredefort Crater measured somewhere between 180 and 300 kilometers wide. But more than 2 billion years of erosion has made the exact size hard to pin down.

- "If you consider that the original impact crater was a shallow bowl like you would serve food in, and you were able to slice horizontally through the bowl progressively, you would see that the bowl's diameter will decrease with each slice you take off," said Roger Gibson of University of the Witwatersrand and an expert on impact processes. "For this reason, we are unable to categorically fix where the edge now lies."

- According to Gibson, the uplift at the center of the impact was so strong that a 25-kilometer section of Earth's crust was turned on end. The various layers of upturned rock eroded at different rates and produced the concentric pattern still visible today. Vredefort Dome, which measures about 90 km across, was observed on June 27, 2018, by OLI (Operational Land Imager) on Landsat-8.

- Notice that only part of the ring is visible. That's because areas to the south have been paved over by rock formations that are less than 300 million years old. The young rock formations have begotten fertile soils that are intensely cultivated.

- The darker ring in the center of this image, known as the Vredefort Mountainland, has shallow soils with steep terrain not suitable for farming, so the area remains naturally forested. Along the ridges in the Mountainland you can see white lines: these are the hardest layers of rock, such as quartzite, which resist erosion. The outer part of Mountainland has exposed rocks that are roughly 2.8 billion years old; this is the Central Rand Group, source of more than one-third of all gold mined on Earth.

- Visitors to the impact site today can witness geologic time by traversing just 50 km from Potchefstroom toward Vredefort. The journey would take you from shallow crustal sedimentary rocks deposited between 2.5 and 2.1 billion years ago, ending with 3.1- to 3.5-billion-year-old granites and remnants of ocean crust that were once about 25 km below Earth's surface.

- "Such exposed crustal sections are incredibly rare on Earth," Gibson said. "The added bonus here is that the rocks preserve an almost continuous record spanning almost one-third of Earth's history."

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Figure 29: The image of the Vredefort Crater was acquired on 27 June 2018 with OLI on Landsat-8 (NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• August 28, 2018: The Padma is one of the major rivers of Bangladesh, flowing across the rich, fertile, flat land of South Asia. Sometimes the river acts as a pathway for transportation, but other times it has more destructive effects that displace farms, homes, and lives. Every year, hundreds (sometimes thousands) of hectares of land erode into the Padma River. Since 1967, more than 66,000 hectares (660 km2) have been lost—roughly the area of Chicago. 39)

- For the past 30 years, satellites have observed how the river has grown in size, transformed in shape, and changed in location. These natural-color satellite images show the Padma River in 1988, 1992, and 2018. The images were acquired by Landsat satellites: the Thematic Mapper on Landsat 5, the Enhanced Thematic Mapper Plus on Landsat 7, and the Operational Land Imager on Landsat 8. All images were acquired in January and February during the dry season.

- Over the past three decades, the river has changed from a relatively narrow, straight line to meandering to braided and, most recently, back to straight. The upper region has experienced the most erosion, but noticeable change has also taken place near Char Janajat.

- The erosion is indicated by the presence of meandering bends, or the tendency of the river to snake back and forth in an S-shape. Such formations evolve as the river's flow wears away the outer banks, widening the channel.

- In the 1988 image, the river course was narrower and the right bank was slightly convex. A curve started to develop in 1992 and lasted for eight years. The bend then began straightening and has since disappeared. Padma's meandering bends subsided due to chute-off—when the water flows across the land instead of following the curve of the river.

- Researchers are particularly interested in the Char Janajat area because it is the site of a new bridge crossing. As one of Bangladesh's biggest construction projects, the Padma River Bridge will connect the eastern and western parts of the country and shorten travel times between some locations from thirteen hours to three. There have been some concerns that erosion could threaten the construction of the bridge, although other researchers believe it could actually stabilize the banks and reduce erosion once it is finished. The bridge is scheduled to open by the end of 2018.

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Figure 30: The lower portion of the Padma River has wide meandering curves, an indicator of extensive erosion, shown in these Landsat January images acquired from 2 January, 1988 -20 January 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Kasha Patel)

• August 21, 2018: The Surkhandarya province in southern Uzbekistan was once the heart of Bactria, a prosperous kingdom that flourished along the Amu River between 600 B.C.E. and 600 C.E. 40)

- Teams of archaeologists from the Soviet Union began visiting the province in the 1950s to catalogue its archaeological riches—remnants of towns, irrigation networks, burial mounds, pottery, weapons, and many other items. In the past decade, satellites have made a contribution from above as well. Since 2008, Ladislav Stančo of Charles University (Prague, Czech Republic) has led a team that used satellite imagery to systematically survey the area for archaeological sites.

- The researchers relied mainly on declassified spy satellite imagery from the Corona program, but they also gleaned insights from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite, from Landsat satellites, and several commercial satellites. Stančo and colleagues identified dozens of new sites and followed up with field expeditions to several new sites (Figures 31 and 32).

- The Pashkhurt Basin—the area between the colorful ridges and the Kugitangtau Range—has a handful of villages situated around natural oases, including Pashkhurt, Zarabag, and Gos. The scientists discovered several archaeological sites around these villages, as well as several near Sherabad. Archaeologists think people living in Bactria were attracted to the area partly because of the presence of desirable minerals and metals in the foothills of the Kugitangtau Range. The small white areas are potash deposits, some of which continue to be mined today. People have long used potash to produce glass, soaps, and textiles.

- In current times, cotton is the primary crop grown along the Sherabad River, with much of the river's water getting diverted for the thirsty plant. Intensive irrigation like this is common along rivers that flow toward the Aral Sea, and it has caused that large lake to shrink dramatically in recent decades.

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Figure 31: The image centers on a colorful sequence of sedimentary ridges in southern Uzbekistan near several of the sites. The image was acquired by the Operational Land Imager (OLI) on Landsat 8 on June 27, 2018. The ridges are sandwiched between croplands flanking the Sherabad River and the Kugitangtau Range. Note: the image has been flipped to minimize relief inversion. The ridges rise roughly 1,000 meters above sea level (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland, with information from Franz T. Fürsich, Petra Tuŝlová, and Ladislav Stančo)

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Figure 32: This image shows the Landsat data draped over topographic data from NASA's SRTM (Shuttle Radar Topography Mission), image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the USGS and topographic data from SRTM, story by Adam Voiland, with information from Franz T. Fürsich, Petra Tuŝlová, and Ladislav Stančo

• July 17, 2018: After nearly running dry six months ago, Cape Town's reservoirs have risen dramatically. Rain has poured down on southern Africa on several occasions in recent months. According to Cape Town's Department of Water Affairs, water levels in the city's main reservoirs stood at 55 percent of capacity on July 16, 2018. 41)

- The largest reservoir—Theewaterskloof—holds 40 percent of Capetown's total water storage capacity, so the state of that reservoir serves as a good barometer for the amount of water available to the city. OLI (Operational Land Imager) on Landsat-8 acquires new imagery of the reservoir every two weeks.

Figure 33: After nearly running out of water in early 2018, the city's reservoirs are being replenished by rain, conservation efforts, and engineering fixes. The animation based on Landsat imagery, shows the condition of the reservoir at two month intervals between 1 July 2015 and 9 July 2018. Parts of the reservoir with standing water appear dark blue; areas where the bottom of the reservoir was dry and exposed are light blue (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

- Water levels changed changed significantly between 2015 and 2018. While Theewaterskloof was 55 percent full in 2015, it dropped to 40 percent capacity in 2016 following a year of light rainfall. As the drought worsened, the reservoir shrank to 20 percent capacity by July 2017 and 13 percent by January 2018. With the arrival of heavier rains in April 2018, the reservoir bounced back to 40 percent capacity by July 16, 2018.

- In June 2018, Cape Town authorities credited voluntary water conservation by residents, water use restrictions and tariffs, the installation of a city-wide pressure management system, a leak repair program, and the favorable rains for averting Day Zero, when most of the taps would have been shut off. Despite the recent increase in water stored in the reservoirs, the city plans to keep water-use restrictions in place until reservoirs are 85 percent full.

• July 16, 2018: In July 2017, a huge iceberg dramatically broke away from the Larsen C Ice Shelf on the Antarctic Peninsula. But the aftermath has been a bit more drawn-out, as the berg hasn't moved very far. 42)

- In a year, iceberg A-68A moved a relatively short distance from the edge of the ice shelf into the Weddell Sea (Figure 34). In the right image, the berg's western edge is roughly 45 km from the shelf. A-68B, the much smaller fragment of the original berg, is more than twice that distance from its prior location.

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Figure 34: The left image shows Iceberg A-68 on July 30, 2017, soon after it broke away from the shelf and then fractured into two pieces known as A-68A and A-68B. The right image shows the same area on July 1, 2018. Both images are false-color, acquired with the Thermal Infrared Sensor (TIRS) on Landsat-8. Colors indicate the relative warmth or coolness of the landscape, from orange (warmest) to light blue and white (coldest), image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS. Story by Kathryn Hansen with image interpretation by Chris Shuman.

- A-68A's sluggishness is not surprising. When it calved, the berg was about the size of Delaware and weighed more than a trillion tons. Dense sea ice in the Weddell Sea has made it harder for currents, tides, and winds to move all of that mass. The iceberg has also become stuck at times when its north end encounters the shallow water near Bawden Ice Rise, an ice-covered rock outcrop.

- Still, Iceberg A-68A has seen plenty of motion. Throughout the year, tide cycles have shuffled the berg back and forth like a driver trying to get out of a tight parallel-parking spot. Its north end has been repeatedly smashed against Bawden Ice Rise, fracturing and reshaping its northern edge. Also notice how the southeastern edge appears to have grown in area. This is not part of the original iceberg; it is fast ice that has come fastened to the edge of the berg as it shoves through the ice pack.

- A-68A will continue this dance in moonlight, as the darkness of austral winter continues through early August. Thermal images offer one way that scientists can "see" the iceberg during polar night. Radar imagery from the Sentinel-1 satellite also has been an important tool for Adrian Luckman and the UK-based Project MIDAS, which has been monitoring the iceberg and how its calving affects the Larsen C Ice Shelf.

- There's no telling how much longer A-68A will stay "stuck" in the Weddell Sea. The smaller A-68B is a good example of the path taken by many Antarctic bergs, as they are carried by currents out of the Weddell and northward toward South Georgia and the South Sandwich Islands.

• July 9, 2018: The High Plains Aquifer, also known as the Ogallala Aquifer, is under stress. Farmers today have to drill ever deeper wells in order to pump water for irrigation, and one recent study found the aquifer to be under more strain than any other in the United States. About 30 percent of the water once stored beneath Kansas is already gone, and another 40 percent will be gone within 50 years if current trends continue. 43)

- Nonetheless, pumping continues. Data collected by the MODIS sensors on Aqua and Terra satellites and other sources show that irrigation is increasing in some parts of the aquifer. One study found that 519,000 more hectares were irrigated in 2007 compared to 2002—97 percent of the total added in the United States during that period.

- While MODIS can monitor regional trends, it cannot easily examine irrigation patterns at the level of individual fields. "The higher resolution of the sensors on Landsat give us a more nuanced understanding of the annual and seasonal rhythms of irrigation than is possible with MODIS," explained Jillian Deines, a hydrologist at Michigan State University. Deines and colleagues David Hyndman and Anthony Kendall authored a study in which they compiled nearly two decades of Landsat data to study irrigation trends along the Republican River Basin, which runs through Colorado, Kansas, and Nebraska.

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Figure 35: Using Landsat-5, -7 and -8 data to track patterns in irrigation may help water managers sketch out a more sustainable future for the Ogallala Aquifer in the central United States. This map shows irrigation frequency in the basin between 1999 and 2016. Areas watered nearly every year are purple; those watered only rarely are yellow. The extent of the Ogallala Aquifer is shown with gray (image credit: NASA Earth Observatory, maps by Lauren Dauphin, using data from Deines, Jillian, et al. (2017), story by Adam Voiland)

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Figure 36: This image highlights the variability in irrigation between center-pivot irrigation fields in an area along the Colorado-Nebraska border. The most widely grown crops in the basin are corn and wheat (image credit: NASA Earth Observatory, maps by Lauren Dauphin, using data from Deines, Jillian, et al. (2017), story by Adam Voiland)

- Water use in the Republican River Basin is a sensitive issue. While there is a compact in place that details how the states should share water, litigation about water use is common. Given the legal context, Deines says it would be helpful for hydrologists and water managers to have a good understanding of exactly when and where irrigation occurs. Ground-based irrigation statistics tend to be decentralized and of varying quality, so Deines looked to Landsat for a more consistent view.

- Examining natural-color and infrared imagery, the team produced high-resolution annual irrigation maps for the entire basin. The maps detail how frequently a field was irrigated, as well as the first and last year it was irrigated.

- After analyzing some economic data, Deines and her colleagues believe some of the variability in irrigation they found was driven by crop prices. (Farmers expand irrigation when prices are high to increase yields and profits.) Rainfall also played a role in the variability. "Farmers ended up irrigating more intensely on a smaller number of fields during drought years," noted Deines.

- Landsat also detected an increase in the number of fields irrigated over the study period. Most of the increase was centered on the eastern part of the basin near the Platte and Republican Rivers, an area where irrigation depends more on drawing water from rivers than drilling groundwater from the aquifer.

• July 6, 2018: From milky white to vibrant turquoise to blood red, the three lakes at the summit of the Kelimutu volcano are known to unpredictably change color— a phenomenon unique to this volcano on the Indonesian island of Flores. 44)

- The changing colors have been a source of supernatural folklore. Locals say the lakes are the resting place for departed souls. Depending on the good or bad deeds performed in their life, the deceased get placed into the various lakes.

- The westernmost lake known as Tiwu Ata Mbupu (meaning Lake of the Old People) is usually blue. Tiwu Nuwa Muri Koo Fai (Lake of the Young Men and Women) is usually turquoise. The southeastern lake called Tiwu Ata Polo (Bewitched Lake) is usually red or brown. It is believed to be the home of those who have been evil in life. Depending on when you visit, the colors can range from white, green, blue, brown, or black. In 2016, the lakes changed colors six times.

- While other lakes can be colored by species of bacteria, the changing colors at Kelimutu are thought to be caused by fumaroles, or volcanic vents that release steam and gases such as sulfur dioxide. The fumaroles produce upwelling in the lakes, such that denser, mineral rich water from the bottom is brought towards the surface. All of the lakes contain relatively high concentrations of zinc and lead.

- While minerals play a part in the coloring, another key factor is the amount of oxygen present in the water. Like your blood, these lake waters appear bluer (or greener) when low in oxygen. When they are oxygen-rich, they appear blood red or even cola black.

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Figure 37: These images, acquired by OLI on Landsat-8, show the various colors of the crater lakes on three different days. All three crater lakes appear on the crest of the volcano with the eastern two lakes sharing a common crater wall (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

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Figure 38: Photograph of the Kelimutu crater lakes (image credit: Tom Casadevall, U.S. Geological Survey via Wikimedia Commons, story by Kasha Patel)

• June 18,2018: Estuaries near the coast of Guinea–Bissau on the west coast of Africa branch out like a network of roots from a plant. With their long tendrils, the rivers meander through the country's lowland plains to join the Atlantic Ocean. On the way, they carry water, nutrients, but also sediments out from the land. 45)

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Figure 39: This natural–color image captures the movement of the sediments as the rivers move east to west. The image was acquired on May 17, 2018, by the Operational Land Imager (OLI) on Landsat 8. The discoloration is most apparent in Rio Geba, which runs past the country's capital city of Bissau (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the USGS. Story by Kasha Patel)

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Figure 40: This map shows a more detailed look at how colored dissolved organic matter (CDOM) discolors the water. Organic matter—such as leaves, roots, or bark—contain pigments and chemicals that can color the water when they dissolve. Depending on the amount of dissolved particles, the water in natural–color imagery can appear blue, green, yellow, or even brown as the CDOM concentration increases. In this data visualization, the amount of CDOM is represented in yellows, greens, and blues (with blue indicating clearer water). Note the difference in water clarity as the streams flow from inland towards the ocean (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS. Story by Kasha Patel)

- These estuaries play an important role in agriculture. This small west African country is mostly made up of flat terrain that only stands 20 to 30 m above sea level. The coastal valleys flood often, especially during the rainiest part of the year (summer), and can have damaging effects on infrastructure, agriculture, and public health. But at non–devastating levels, the rains make the valleys good locations for farming, especially rice cultivation.

- Much of the agricultural land is created by destroying mangroves, which acts as a natural barrier between the land and the water. For instance, a lot of rice production occurs along the Rio Geba, which is surrounded by broad valleys and a low, rolling plain carved out of woodlands. As a result, coastal areas have been eroding, which is expected to worsen with rising sea levels. A few projects are focused on restoring mangrove populations, and researchers have been seeing regrowth.

• June 13, 2018: Steaming fissures first began to crack open and spread lava across Hawaii's Leilani Estates neighborhood on May 3, 2018. Since then, more than 20 fissures have opened on Kilauea's Lower East Rift Zone, though most of the lava flows have been small and short-lived. 46)

- Not so for fissure number 8. That crack in the Earth has been regularly generating large fountains of lava that soar tens to hundreds of feet into the air. It has produced a large, channelized lava flow that has acted like a river, eating through the landscape as it flows toward the sea.

- While the fissure 8 lava flow initially remained in relatively narrow channels, it began to widen significantly as it neared the coastline and passed over flatter land. It evaporated Hawaii's largest lake in a matter of hours, and devastated the communities of Vacationland and Kapoho, destroying hundreds of homes.

- On June 3, 2018, lava from fissure 8 reached the ocean at Kapoho Bay on Hawaii's southeast coast. When the Multi-Spectral Instrument (MSI) on the European Space Agency's Sentinel-2 satellite captured a natural-color image on June 7, the lava had completely filled in the bay and formed a new lava delta. For comparison, the Landsat-8 image shows the coastline on May 14.

- Since May 3, 2018, Kilauea has erupted more than 110 million cubic meters of lava. That is enough to fill 45,000 Olympic-sized swimming pools, cover Manhattan Island to a depth of 2 meters, or fill 11 million dump trucks, according to estimates from the U.S. Geological Survey. However, that is only about half of the volume erupted at nearby Mauna Loa in a major eruption in 1984.

- The new land at Kapoho Bay is quite dynamic, fragile, and dangerous. "Venturing too close to an ocean entry on land or the ocean exposes you to flying debris from sudden explosive interaction between lava and water," USGS warns. Since lava deltas are built on unconsolidated fragments and sand, the loose material can abruptly collapse or quickly erode in the surf.

- The plumes that form where lava meets seawater are also hazardous. Sometimes called "laze," these white plumes of hydrochloric acid gas, steam, and tiny shards of volcanic glass can cause skin and eye irritation and breathing difficulties. When Sentinel-2 captured this image, the laze plume streamed west and mixed with clouds.

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Figure 41: Landsat-8 image of Hawaii's Kapoho Bay costline acquired on 14 May 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS and modified Copernicus Sentinel data (2018) processed by the European Space Agency. Story by Adam Voiland)

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Figure 42: Landsat-8 image of Hawaii's costline acquired on 7 May 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS and modified Copernicus Sentinel data (2018) processed by the European Space Agency. Story by Adam Voiland)

• May 16, 2018: Every year, seven million flower bulbs are planted in the Keukenhof Garden in the Netherlands. When the final winter chill disappears and springtime arrives, the bulbs sprout to produce beautiful rows of reds, oranges, and yellows—including 800 varieties of tulips. 47)

- The season begins in March with purple crocuses, followed by hyacinths and daffodils. It ends with tulips reaching peak bloom in April. The vivid display draws more than a million tourists, who line up for a glance before the flowers are harvested and disappear.

- The landscape in this image—known as the "bulb region"—lies about 20 km from Amsterdam. It contains numerous gardens, including Keukenhof, one of the world's largest flower gardens. The Netherlands is the largest producer of tulip bulbs in the world, providing 4.2 billion annually and exporting half.

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Figure 43: The colorful floral spectrum can also be seen from space. OLI (Operational Land Imager) on Landsat-8 captured the scene on April 21, 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kasha Patel)

• May 1, 2018: The sparsely populated Gran Chaco plain in South America is home to a dry forest of thorny trees, shrubs, and grasses. The second largest forest in Latin America—behind only the Amazon rainforest—stretches across parts of Paraguay, Argentina, and Bolivia and supports thousands of plant types and hundreds of species of birds, mammals, and reptiles. 48)

- However, the region also has one of the highest rates of deforestation in the world. Observations by Landsat satellites indicate that roughly 20 percent—142,000 km2—of Gran Chaco's forest has been converted into farmland or grazing land since 1985. That's an area roughly the size of New York state.

- Deforestation has been particularly widespread in Paraguay in recent years. Between 1987 and 2012, the forests in Paraguay lost nearly 44,000 km2, mainly because of the expansion of cattle farms in the western part of the country.

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Figure 44: OLI on Landsat-8 captured this natural-color image of pastures in Boquerón on August 14, 2016. The image is centered just east of the Pilcomayo River near Tezén. Unlike the "fishbone" pattern of deforestation in the Amazon, deforestation in the Gran Chaco tends to leave large rectangular clearings that reflect careful surveying by large-scale cattle-ranching operations (image credit: NASA Earth Observatory, image by Michael Taylor, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

• April 30, 2018: In February 2018, the average extent of sea ice in the Arctic was the lowest of any February on record, thanks to a winter warming event. Then, on March 17, 2018, Arctic sea ice extent reached its annual peak; it was the second-lowest maximum on record. 49)

- By the time the image of Figure 45 was acquired in mid-April, springtime sunlight and warmth had advanced the melting to produce some beautiful patterns and textures in the Beaufort Sea, north of Canada. The natural-color image was acquired by the Operational Land Imager (OLI) on Landsat-8 on April 15, 2018. A small part of the image (lower right) was mosaicked in from an April 17 image in order to show more of Mackenzie Bay. In the days before this image was acquired, the region experienced an extended period of generally sunny days, allowing ample sunlight to reach the ice and melt its surface. The thinnest ice appears blue-gray.

- The favorable weather was a boon for NASA's Operation IceBridge, an airborne mission now in its tenth year making flights over the Arctic. Clear skies meant ample data could be collected by instruments on P-3 research plane when it flew over sea ice in the eastern Beaufort Sea on April 14.

- "The main purpose of these IceBridge flights is to measure the thickness of the sea ice," said IceBridge project scientist Nathan Kurtz. "Ice thickness is an important factor which allows us to assess the health of the pack and its ability to survive the summer melt. It is also an important regulator in the exchange of energy and moisture between the ocean and the atmosphere."

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Figure 45: OLI natural color image of the Beaufort Sea, north of Canada, acquired on 15-17 April 2018 (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

- Sea ice appears static when we view a single satellite image, but in fact, it is almost constantly in motion. The ice pack in the open sea is pushed around by winds and currents, and this fractures it into smaller pieces that are more vulnerable to melting. The animation of Figure 46, composed of images acquired by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra and Aqua satellites between April 4 and 15, captures that motion. Some areas appear to open up and then refreeze. Note how the fast ice—which is still anchored to the shore and more resistant to winds and currents—appears less fractured.

Figure 46: The animation of MODIS instrument on Terra and Aqua, acquired between 4-15 April 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response, with special thanks to Walt Meier, NSIDC, story by Kathryn Hansen)

- As the sea ice thins and fractures, you can also see that warmth is also coming from ocean water below the ice. The TIRS (Thermal Infrared Sensor) on Landsat-8 captured the data for this false-color image on April 15 and 17 (Figure 47). It shows the relative warmth or coolness of the landscape. Orange depicts where surfaces are the warmest—areas of open ocean or thin sea ice. Light blues and whites are the coldest areas, which includes the fast ice and the larger, thicker floes.

- This visual array of thicknesses, textures, and motion in the sea ice are a striking example of Earth's beauty that few people get to witness. "As scientists, we have the privilege of witnessing the beauty and mystery of the cryosphere firsthand, even as we work to collect that data," said IceBridge mission scientist John Sonntag. "Often I look out from the windows of our aircraft and see features that I don't immediately understand, but one of my colleagues in the global community of cryospheric scientists can usually explain the processes behind them."

- "While on the flights, I'll stare out the windows for hours looking at the surface. The movement of the ice leads to huge variability over small scales, with many interesting scenes and patterns visible and a variety of color shades," Kurtz added. "But there's only so much that can be discerned with human eyes. That is why we have the sensitive instrument suite on the plane: to map the intricacies of the ice cover which may otherwise be invisible to us and to quantify parameters for scientific interpretation."

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Figure 47: TIRS on Landsat-8 captured the data for this false-color image on 15-17 April 15, 2018 (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• April 25, 2018:The Russian settlement of Surgut lies on the north bank of the Ob River in the cold, swampy lowlands of West Siberia. Just a small village in the 1960s, Surgut has ballooned into a bustling city of 340,000 people, largely because of the development of the vast gas and oil reserves in the area. 50)

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Figure 48: Detail image. OLI on Landsat-8 collected this natural-color image of the city and its surroundings on August 22, 2016. Gas and oil infrastructure spreads across marshlands northeast of the city, and there is another sizable oil field southeast of the neighboring city of Nefteyugansk (image credit: NASA Earth Observatory images by Mike Taylor and Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

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Figure 49: OLI on Landsat-8 collected this natural-color image of the city and its surroundings on August 22, 2016. Gas and oil infrastructure spreads across marshlands northeast of the city, and there is another sizable oil field southeast of the neighboring city of Nefteyugansk (image credit: NASA Earth Observatory images by Mike Taylor and Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

- By analyzing NDVI measurements collected between 2000 and 2016 (Figure 50), Igor Ezau and Victoria Miles of Norway's Nansen Environmental Remote Sensing Center have identified some interesting changes in this area. Most notably, the taiga forests across the northern part of West Siberia have gradually become less green, a trend the scientists attribute to rising summer temperatures.

- However, the opposite is true in pockets of forest around the towns and cities. When the researchers focused on changes to the vegetation within 40 km of 28 cities in Siberia, they found the vegetation had gotten slightly greener (or browned less) than the rest of the region.

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Figure 50: Over the past two decades (acquired between 2000-2016), NASA satellites (MODIS on Terra) have collected observations of the Normalized Difference Vegetation Index (NDVI)—the "greenness" or health—of the vegetation in the forests and marshlands around the city. Taiga forests (light green) made up of evergreen and deciduous trees grow in the well-drained soils along the Ob River, while marshlands (light brown) with few trees dominate the swampy landscape beyond the river valley (image credit: NASA Earth Observatory images by Mike Taylor and Joshua Stevens using NDVI trend data courtesy of Victoria Miles/NERSC, story by Adam Voiland)

- The effect was particularly pronounced around older cities like Surgut, which have had more time to establish parks and other green spaces to reverse the initial loss of vegetation cover associated with development and urbanization. In the NDVI variability map above, the cities and rivers showed low variability between 2000 and 2016 in comparison to the ring of vegetation surrounding the two cities. The greater variability indicates an increase in greening during the warmer months. Note: to generate the NDVI map, the scientists applied a statistical technique that extracted the local effects from the regional trends.

- The greening trend was driven by other factors, as well. For Surgut and several other cities, development required covering swampy soils with relatively sandy, well-drained soil that was sturdy enough to build on. The sandier soils were not only better for infrastructure, they made it easier for trees to thrive.

- Building materials like concrete and asphalt also created an urban heat island that increased land surface temperatures in the city core compared to rural areas around it. In the Arctic, heat islands warm the soil, which can thaw underlying permafrost and have far-reaching effects on tundra and taiga landscapes. In areas like Surgut with cool and short summers, the added warmth gives many types of vegetation a boost.

- In comparison to other Siberian cities, the intensity of Surgut's heat island is unusual. The city is home to two large gas power plants. One of them, Surgut-2, has an installed capacity of 5597 megawatts, which means it supplies energy to nearly 40 percent of the population in Russia and is among the largest gas-fired power stations in the world.

- "Surgut is now about 10 degrees Celsius above normal, which means that ecosystems around the city have a climate that could otherwise only be found 600 kilometers to the south," noted Ezau.

• April 11, 2018: Like plant life on land, phytoplankton in the water flourish under just the right conditions. For phytoplankton in Louisiana's Lake Pontchartrain, those conditions include a combination of ample sunlight and nutrients, a long stretch of warm weather, and calm winds. 51)

- Lake Pontchartrain and other nearby lakes and inlets compose a huge estuary east of the Mississippi Delta; collectively they drain an area spanning 12,000 km2 (4,600 square miles). Unusually warm temperatures in February and March helped spur the early spring bloom shown in Figure 51, even before nutrients from the Upper Mississippi could pour into the region.

- Blooms become more likely when excess river nutrients reach the lake through the Bonnet Carré Spillway. During flood season, the spillway is occasionally opened to divert excess water from the Mississippi River and relieve pressure on levees near New Orleans.

- On March 8, the U.S. Army Corps of Engineers started to open the spillway in response flooding along the Ohio and Mississippi Rivers. The pulse of sediment-laden water is visible on March 14. Such inputs of nutrients—often fertilizer from the Mississippi watershed—can set the stage for large blooms of algae and cyanobacteria—single-celled organisms that can contaminate drinking water and pose a risk to human and animal health. Satellite imagery can help identify the occurrence of a phytoplankton bloom, but direct sampling is required to discern the species.

- The extra nutrients from the Mississippi helped trigger another bloom around March 25. However, cloud cover impeded satellite views on most days.

- By early April 2018, the blooms appeared less vibrant. John Lopez of the Lake Pontchartrain Basin Foundation reported, that wind on the lake helped to break up the second bloom and suppress its growth. But nutrients from the river can persist in the lake for months, making it possible for more blooms to develop later this year.

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Figure 51: Blooms of phytoplankton appeared in Lake Pontchartrain several times in March 2018. OLI on Landsat-8 acquired this image of a colorful bloom on March 3, 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

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Figure 52: Overview of the Lake Pontchartrain/New Orleans region acquired by OLI on Landsat-8 on March 3, 2018 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• April 8, 2018: Greenland's coastline is anything but smooth. It is punctuated by rocky outcrops and ice-choked fjords, the outlets through which ice from the interior drains into the sea. The myriad "marine-terminating outlet glaciers" along the coast of Prudhoe Land in northwest Greenland may not be the country's largest, but they are retreating fast. 52)

- This image pair shows changes to two of the more prominent glaciers in this region. Figure 53 was acquired on September 28, 1987, by the Thematic Mapper on Landsat-5; Figure 54 was acquired on September 30, 2017, by the Operational Land Imager (OLI) on Landsat-8. Tracy Glacier (north) and Heilprin Glacier (south) are the largest glaciers draining into Inglefield Bredning, a fjord measuring about 20 km wide.

- According to research published in 2018, scientists found that glaciers in this region have retreated significantly in the 21st century due to atmospheric warming. From the 1980s through the 1990s, Tracy and Heilprin glaciers retreated at similar rates, about 38 and 36 meters per year, respectively. But between 2000 and 2014, their rates of retreat diverged dramatically. Tracy retreated by 364 meters per year. That is more than three times the rate of retreat at Heilprin, which lost 109 meters per year over the same span.

- The difference is likely due to the way the glaciers encounter water. Tracy Glacier flows into a deep channel of seawater (as much as 600 meters deep), making it more vulnerable to melting from below by ever-warming seawater. Heilprin, in contrast, flows into shallower water and is not thinning or retreating as quickly.

- NASA's ship-based Oceans Melting Greenland (OMG) field campaign has been studying the role of the oceans in the melting Greenland's ice. At the same time, Heilprin and Tracy glaciers are among those mapped each year by NASA's Operation IceBridge, an airborne mission to map polar ice. During the 2011 IceBridge campaign, scientist Michael Studinger snapped this photograph of Tracy Glacier.

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Figure 53: TM (Thematic Mapper) on Landsat-5 acquired this image on 28 Sept. 1987 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

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Figure 54: OLI (Operational Land Imager) on Landsat-8 acquired this images on 30 Sept. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• April 5, 2018: The transformative power of water, wind, and gravity is on full display in Iraq's Ga'ara Depression. The rim of this large, oval-shaped basin near the Iraq-Syria border rises a few hundred meters along its southern and western edges. 53)

- Geologists call the rock at the bottom of the basin the Ga'ara Formation. It is made up of alternating layers of sandstone and soft claystone that formed roughly 300 million years ago, when the area was covered by a shallow sea. Later, types of carbonate rock (dolomite, limestone, and marl) were layered on top of the Ga'ara Formation, and the entire sequence of rock was gradually pushed up into a dome shape by tectonic forces.

- The dome achieved its maximum height about 30 million years ago. Erosive forces have since chipped away at this layer-cake of rock. The combined effects of water, wind, and gravity wore through the thin carbonate layers at the top of the dome, and then hollowed out the oval-shaped depression from the soft, crumbly rock of the Ga'ara Formation, leaving behind a rim of tougher carbonates. These steep cliffs along the southern rim have played a key role in widening the basin over time. The regular stream of landslides and rockfalls that tumble down the cliffs have caused the southern rim to continue moving south over the years.

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Figure 55: OLI on Landsat-8 acquired this image of the basin on August 27, 2017. It is derived from observations of shortwave infrared, near infrared, and green light (bands 7-5-3), a combination that makes it easier to distinguish different rock and soil types and to detect the presence of moisture (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- While rain is infrequent here, it can fall in intense bursts during the short wet season. These sporadic deluges can transform dried-out channels (known locally as wadis) into roaring rivers that, over time, carve the sharp valleys in the limestone plateaus along the western and southern rim. When the rushing streams drain into the Ga'ara's relatively flat interior, they spread out and become braided streams with multiple, interlacing channels that spread sediment over a wide area.

- As the streams slow, their capacity to carry sediment diminishes, causing sandbars to accumulate along the channels. Over time, the channels migrate back and forth, creating fan-shaped deposits of sediment known as alluvial fans. Some of the fans, especially along the southern rim, are older and dormant; others, mainly along the western rim, are smaller and actively growing.

- While geologists think rockslides and flowing water were especially influential in carving out this depression, wind played a key role as well. During drier periods, fine sand on the basin floor often gets lifted by wind storms and blown out of the basin in an easterly direction.

• March 26, 2018: It is one of the most famous patches of coral outside of the Great Barrier Reef. Stretching a mere 7.5 km by 2.5 km and surrounded by deep ocean, it is barely a speck on world maps. Though uninhabited today, Nikumaroro atoll is noteworthy for someone who likely had a short and ill-fated residence there: Amelia Earhart. 54)

- Nearly 1,600 km from Fiji, halfway between Australia and Hawaii, this South Pacific island is essentially a sandbar atop a coral reef atop a subsiding deep-sea volcano. The Operational Land Imager (OLI) on Landsat-8 acquired a natural-color image of the tiny island on July 28, 2014 (Figure 56).

- Once named Gardner Island by American sailors, Nikumaroro is part of the Phoenix Islands in the island nation of Kiribati. The Americans and the British tried several times to colonize the island, attempting to grow coconuts and considering the spot for weapons testing. Thick scrub and stands of Pisonia and coconut palms hold the sandbar in place around a central lagoon. Kiribati declared the island part of the Phoenix Islands Protected Area in 2006.

- The most famous claim to fame for Nikumaroro is that it may be the final resting place for Amelia Earhart and Fred Noonan. The pair of Americans flew out of New Guinea in July 1937 on one of the last proposed legs in their attempt to circumnavigate the world by airplane. Their intended destination was Howland Island (also part of the Phoenix Island chain), but they never made it. Radio transmissions suggested they might have missed their target by several hundred miles to the southeast.

- For decades, forensic scientists, historians, and aviation aficionados have searched for evidence that Earhart landed the Lockheed Electra 10E on Nikumaroro. Many of those efforts have centered around a crest of land called The Seven Site (named for the shape of a clearing). British colonists in the late 1930s found human bones, a woman's shoe, airplane parts, bottles of cosmetics, and a box that once contained a sextant (for navigation), among other items. Later explorations have turned up evidence of campfires and of shells and fish, turtle, and bird bones that appeared to have been eaten.

- But early forensic studies of the remains and artifacts were crude by today's standards and ultimately proved conflicting and inconclusive. Modern scientists no longer have access to the human bones for DNA testing. A new analysis of the old evidence, published earlier this year, concluded that there is enough evidence to call Nikumaroro the final resting place of Earhart, though the debate continues.

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Figure 56: The OLI instrument on Landsat-8 acquired this natural-color image of the Nikumaroro atoll on 28 July 2014 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Mike Carlowicz)

• March 15, 2018: Where the states of Indiana, Illinois, and Kentucky meet, so do the Wabash and Ohio rivers. At this junction, the Ohio picks up water from the Wabash and continues flowing generally southwest until it joins the Mississippi River near Cairo, Illinois. Here, the Ohio River adds a tremendous amount of water to the Mississippi River, making the Ohio River a major source of freshwater that ultimately reaches the Gulf of Mexico. 55)

- The connections in this drainage system, or watershed, is why the heavy rains that spurred flooding in the Midwestern United States in late February 2018 ultimately led to flooding in Louisiana in early March. What happens downriver is largely affected by what happens upriver. The pulse of floodwater on the Ohio helped deliver freshwater and a sediment plume to the Gulf of Mexico.

- The recent flooding at the confluence of the Wabash and Ohio rivers is visible in this image, acquired by OLI (Operational Land Imager) on the Landsat-8 satellite. The image is a composite, showing floodwater on March 3, 2018, combined with an image acquired on November 7, 2017, that shows the typical widths of the rivers. It is false-color (bands 6-5-3) to better distinguish flooded areas (blue) from the surrounding land (tan).

- John Sloan, a watershed scientist at the National Great Rivers Research and Education Center, pointed out that smaller tributaries on the west side of the image have narrower floodplains that become successively larger as the watershed becomes larger. Major rivers, such as the Ohio, have very wide floodplains. This image shows the widespread flooding that can occur in the area around the confluence of major rivers like the Wabash and Ohio rivers.

- Floods can speed up the processes of erosion and sedimentation, increasing the volume and speed of the water flowing through an existing channel. During a flood, water and sediment can spill over a river's natural banks and flow into the adjacent floodplain. In the image of Figure 57, the blue area shows both the river channel and the portion of the floodplain that was flooded in early March.

- As the floodwaters slow and recede, they usually leave most of their sediments behind on the floodplain. Sometimes these add organic matter and fertility to the floodplain. In other cases, land is scoured and thick sand deposits are left behind-for instance, when a levee breaks and water rushes across the floodplain.

- "River flooding is a natural process," said Lois Morton, a professor (emeritus) at Iowa State University. "Floodplains provide important upstream storage, reducing river flows downstream, recharging groundwater supplies, filtering nutrients, and enriching forest and wetland habitats."

- Major flooding most often occurs when heavy, persistent winter rains coincide with snowmelt because the still-frozen ground makes water run off the landscape rather than soaking into the soil. The flood this winter along the Ohio River was the worst in two decades, according to news reports, but not the worst on record.

- "The winter flood of 1937 on the Ohio River was one of the worst to hit the Ohio River Valley, and the Wabash basin was a big contributor," Morton said. Waters rose to "major" flood stage north of the Ohio-Wabash confluence and inundated Evansville, Indiana. They crested well above major flood stage south of the confluence in Shawneetown, Illinois, and destroyed most of the town.

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Figure 57: Composite image of OLI, showing floodwater on March 3, 2018, combined with an image acquired on November 7, 2017, that shows the typical widths of the rivers. It is false-color (bands 6-5-3) to better distinguish flooded areas (blue) from the surrounding land (tan), image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS. Story by Kathryn Hansen, with image interpretation by John Sloan/National Great Rivers Research and Education Center, and Kenneth Olson and Lois Morton/Iowa State University.

• March 13, 2018: Just over 200 km southwest of Barcelona, Spain's largest river meets the Mediterranean Sea and creates the Ebro Delta. At 350 km2, the delta is the fourth largest on the Mediterranean. It is an important wetland ecosystem and a productive agricultural area. Two large spits flank the delta to the north and south, giving it a distinct shape like a bird in flight. 56)

- The Ebro River drains one-sixth of the Iberian Peninsula (more than 8.5 million hectares) as it makes its way from the Pyrenees and Cantabrian mountains of northern Spain. It winds through the regions of Cantabria, Castile and León, the Basque Country, La Rioja, Navarre, Aragon, and Catalonia, forming portions of those regional boundaries and lending its name to cities and towns throughout. As the Ebro traverses these regions of Spain, it takes pieces of each—sediments, soil, and sand. When the river meets the sea, it loses velocity and deposits its sediment load along the shore, feeding the delta.

- Scientists have estimated that the river first reached the Mediterranean Sea about 13 to 15 million years ago. The peculiar shape of the Ebro Delta reveals that it has had a rich morphologic history, and the delta has experienced tremendous shape-shifting recently.

- Motivated by the complex shoreline, a group of researchers led by Florida State University's Jaap Nienhuis used simple models of river profiles and coastline evolution to understand the delta's development. The authors established that rapid changes to the Ebro Delta began about 2100 years ago, and their results were published in Earth Surface Dynamics.

- "There is a lot of information hidden in that shape complexity that we knew might tell us something about what the delta looked like in the past," Nienhuis said.

- A substantial input of sediments built and shaped the Ebro Delta. Climatic records show that flooding was initially responsible for carrying an abundant amount of river sediments to the coast. But more recent delta growth spurts can be attributed to manmade land-use changes, such as forest clearing and the conversion of land to agricultural fields, which exposed more sediment for runoff into the Ebro River.

- "The Ebro, and many other deltas in the Mediterranean, were some of the first to experience significant human impacts," Nienhuis explains. "Some of the modeling we have done suggests that early land-use changes, like deforestation during the Roman Empire, could have led to its growth. In that sense, we can use the Ebro to learn about coastal response to land-use changes and the longevity of some of these impacts."

- Deltas are categorized into three main groups: river-dominated, tide-dominated, and wave-dominated. Wave-dominated deltas often have a "cuspate" shape, which is created as the sea pushes the river's deposits back towards the shoreline on each side of the main channel. This leads to smooth, curving beaches that extend back to the mainland on both sides. River-dominated deltas are pointy because the river exerts itself into the sea, depositing enough sediment to sustain its river channel and outpacing the ability of waves to push those sediments back to shore. This creates "lobes" of land extending into the sea.

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Figure 58: This natural-color Landsat-8 image was acquired on 31 January 2018. One can see the modern La Banya and El Fangar spits and the southern lagoons that were once bays, as well as the suspended sediment plume exiting the river's mouth (image credit: NASA Earth Observatory, image by Michael Taylor and Joshua Stevens, using Landsat data from the USGS, story by Laura Rocchio)

- More than 1,000 years ago, a river-dominated Ebro Delta formed a pointy lobe known as the Riet Vell. Then, around six centuries ago, the river channel changed course (a process called avulsion) and the Riet Vell lobe was abandoned. A new lobe called the Sol de Riu began to form at the mouth of the new river channel. Meanwhile, the abandoned Riet Vell lobe was slowly pushed landward by waves to form a spit at the southern end of the delta. Like a potter working a piece of clay, the constant wave action slowly transported sediments southwest, forming the long curving La Banya spit.

- An avulsion that occurred about 300 years ago moved the river channel yet again, this time abandoning the Sol de Riu lobe, which was in turn worked by waves into the El Fangar spit to the delta's north. It also formed the Mitjorn-Buda lobe that the channel still runs through today. Nienhuis and colleagues speculate that sometime during this period of rapid delta growth, former unnamed spits closed off their protected bays and created the modern Encanyissada, Clot, and Tancada lagoons.

- Humans, who indirectly drove the growth of the delta over the past 2100 years, are today starving the delta. The waters of the Ebro River have been diverted for irrigation, so sediment dynamics have drastically shifted. There are now 187 dams on the river, and most sediments now settle in front of dams instead of reaching the sea. The loss of sediment deposits from the Ebro River means the modern Ebro Delta is now wave-dominated. River damming, combined with sea-level rise and land subsidence, are predicted to take their toll—40 percent of the delta could be submerged by 2100.

• March 6, 2018: In Sarawak, rivers stem from rivers stemming from even larger rivers. The snake-like nature and sharp turns of these waterways resemble a painting when viewed from space, but the causes of these patterns are rooted in nature. 57)

- On June 16, 2016, the Operational Land Imager (OLI) on the Landsat 8 satellite acquired this image of the Sarawak River Delta on the island of Borneo in East Malaysia (Figure 59). The Rajang River, visible at the bottom of the image, is Malaysia's longest (563 km) and can be navigated from the South China Sea to points far inland.

- The area's unique drainage patterns are most obvious in the top-right quadrant of the image, northeast of Sarikei. Here you can see the Rajang River forking at several sharp T-shaped junctions, heading at times 90 degrees from its previous path, and then turning west and resuming its path toward the sea. According to Robert Gastaldo, a sedimentologist at Colby College, this so called "T-junction splitting" is the result of faults in the Earth's upper crust. The faults cause blocks of land to drop downward, which strongly influences the path that water will take.

- Not all of the rivers pictured here take such sharp turns. According to Gastaldo, the gentle snake-like turns are sculpted by the incoming and outgoing tides, which can be significant in this delta. During a king tide, water can rise and fall by 6 meters within a 12-hour cycle. Tides also influence the shape of a river's mouth. As a tide falls, or "ebbs," seawater rushes seaward. The high speed of that rushing water, combined with the normal seaward flow of river water, sculpts a funnel-shaped mouth. The Batang Paloh is a clear example of this phenomenon, where the mouth is much wider toward the ocean and narrows toward the land.

- You can also see an array of colors in the waters throughout the delta. Light brown "tea-colored" water is caused by humic acids that have leached into the water from the peatlands. (The entire area is blanketed in a layer of thick peat that has been accumulating since about 7,500 years ago.) Yellow-tinged waters contain a mix of this peat and large amounts of suspended sediment. The gradient in color depends on how much sediment remains suspended in the water as it approaches the coast.

- "In the 1960s, the Rajang River flowed clear with a tinge of light-brown tea water," Gastaldo said. "Once logging commenced, the high amount of rainfall in this part of the island could more easily erode the soils, significantly increasing the suspension load."

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Figure 59: The OLI instrument on Landsat-8 acquired this image on 16 June 2016 of the Sarawak River Delta on the island of Borneo in East Malaysia (image credit: NASA Earth Observatory, image by Mike Taylor, using Landsat data from the USGS. story by Kathryn Hansen, with image interpretation by Robert Gastaldo/Colby College)

• February 24, 2018: As recently as 2010, only 3 percent of Cambodia's domestically generated electricity came from hydropower. By 2016, hydropower was the source of 60 percent of it. 58)

- The completion of the Lower Sesan II dam in Stung Treng province will give hydropower yet another boost. At full capacity, the $800 million project is designed to generate 400 MW of electricity, making it the biggest hydropower station in the country. Water levels began to rise in September 2017, when the dam's floodgates were closed. In November 2017, the first turbine began to generate power. By October 2018, all eight turbines are expected to be operating.

- OLI (Operational Land Imager) on the Landsat-8 satellite captured these before and after natural-color images of the dam and reservoir. They were built near the confluence of the Sesan River (Tonlé San in Cambodian) and Srepok River, both tributaries of the Mekong River. The image of Figure 60 was acquired on February 14, 2017; Figure 61 shows the same area on February 1, 2018. The brown and light green areas in the first image, particularly those with straight edges, were likely cleared recently for timber; some of the smaller tan areas were crop fields near villages. Densely forested areas are green.

- In a country where only 50 % of rural communities have access to the electrical grid, the boost in generating capacity will help with a government-led effort to bring electricity to all Cambodians by 2022. The project is also expected to reduce the cost of electricity.

- However, the dam and its 75 km2 reservoir will also have significant impacts on communities near the river. Though some communities have resisted moving, rising waters have forced thousands of people to leave their villages. Scientists have cautioned that the Mekong Basin could see a 9% drop in the availability of fish.

- The dam is likely a harbinger of things to come. Plans are ongoing to add several more dams along the Mekong River and its tributaries, including two on the Mekong River that would dwarf this one. The Stung Treng dam would generate 900 MW and the Sambor Dam would generate 2,600 MW.

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Figure 60: OLI image of the two river region in Cambodia, captured on 14 Feb. 2017, prior to the completion of the dam (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

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Figure 61: OLI image of the same area, acquired on 1 Feb. 2018, showing the partially filled lake (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Adam Voiland)

• February 15, 2018: Several hundred years ago, pre-Inca and Inca civilizations grew corn, potatoes, beans, quinoa, and squash on raised beds in the verdant Cayambe Valley. Now greenhouses dominate this landscape, and most of them are filled with roses and other cut flowers that will be harvested, packed, and shipped to the United States. Located in Ecuador's Northern Highlands, the Cayambe Valley has one of the highest densities of greenhouses for rose production in the world, said Gregory Knapp, a geographer at the University of Texas at Austin and a scholar of Ecuador's booming cut flower industry. 59)

- OLI (Operational Land Imager) on Landsat-8 collected these natural-color images of the valley on September 20, 2017. The image of Figure 62 is a detail nadir view of Figure 63, with Cayambe, a town of 40,000 people. Figure 63 features also three inactive volcanoes, lying to the north, including Imbabura (4,630 m). Bands of cloud forests (dark green) ring the lower slopes of the volcanoes.

- Ecuador exports nearly $1 billion (U.S.) in cut flowers each year; the main product is roses, though baby's breath, carnations, and chrysanthemums are also grown. About one-third of the roses that Americans exchange on Valentine's Day come from Ecuador; almost all of the rest arrive from Colombia. Cayambe's rise as an epicenter of rose production mirrors the growth of Ecuador's cut flower industry. In the mid-1980s, Landsat imagery shows very few greenhouses in Cayambe. By 2000, they had sprung up on the outskirts of the town. By 2017, they were ubiquitous. The greenhouses make it possible for rose growers to precisely control temperature and humidity to minimize diseases and pests.

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Figure 62: OLI nadir natural-color image of Cayambe surrounded by plastic greenhouses, acquired on 20 Sept. 2017 (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

- The valley's location along the equator makes it ideal for growing roses, which benefit from bright light, the roughly equal length of days year round, and the minimal variations in daily and seasonal temperatures. At an elevation of roughly 2,800 m, roses also grow slower than they would if grown at lower elevations, leading to larger blooms and more sugar in the stems (which extends shelf life).

- Wetlands and irrigation systems provide easy access to water; some of the water supply systems date to pre-Columbian times. The valley's fertile volcanic soils are another plus, though the location at the foot of an active volcano comes with the risk of ash falls and destructive mudflows known as lahars.

- "There are certainly questions and concerns about the environmental and health impacts of the pesticides used and the treatment of greenhouse workers (in particular women), but the explosive growth of Cayambe's flower industry—which nobody expected—has had undeniable benefits," said Knapp. "It has created a huge number of jobs in the area and turned Cayambe into a prosperous place."

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Figure 63: An overview of the Cayambe valley and its surroundings with the snow-capped Volcán Cayambe (5790 m) — an active stratovolcano east of the town— which towers over the valley (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

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Figure 64: This image shows the Landsat data draped over topographic data from NASA's SRTM (Shuttle Radar Topography Mission), image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the USGS and SRTM data, story by Adam Voiland

In its five years in space as of 11 February 2018, the Landsat-8 Earth-observing satellite has racked up some impressive statistics: 26,500 orbits around the planet, 1.1 million "scenes" captured, a motherlode of images that represents 16 percent of all the observations in the 45-year Landsat archive. 60)

- But more impressive and important than any set of numbers, Landsat-8 — which makes global measurements of Earth's land surface — strengthened the program's role as a cornerstone among the growing number of government and commercial programs that capture imagery of Earth from space.

- Landsat-8's global coverage and faster data acquisition rates are enabling significant research and opening up new ways in which scientists, businesses, and resource managers can use the data – including water quality mapping, near-realtime ice velocity detection, and improved tracking of crop health and how much water crops use.

- "I am thrilled by the performance of Landsat 8," said NASA Landsat 8 Project Scientist Jim Irons. "And even more so by the adoption of the data by so many people for important, consequential research and applications."

- The Landsat program is a collaboration between NASA and the USGS (U.S. Geological Survey). NASA oversees the design, build, and launch; USGS takes over operations once satellites are in orbit, and manages the expanding data archive. Landsat 8 is the latest success in this nearly 50 year partnership.

- "If we look back over the five years, have we hit our mark?" said Tom Loveland, Chief Scientist at USGS' EROS (Earth Resources and Observation Science) center. "My answer would be that to date, almost all capabilities that we rely on for Landsat-8 are working superbly."

- Landsat-8, which before launch was called LDCM (Landsat Data Continuity Mission), launched into orbit on Feb. 11, 2013. Once it became operational and was renamed Landsat-8, the satellite continued a streak of engineering and science success unmatched in spaceflight: the succession of Landsat satellites has now made 45-plus years of continuous observations of Earth's surface, without any gaps.

- The length of this record is what makes Landsat a "cornerstone" program in the growing field of land imaging. For scientists that want to compare new imagery or data to previous decades, the unbroken Landsat record offers the one, consistent reference point. This role is furthered by USGS's and NASA's commitment to keeping the entire Landsat data archive free and accessible to scientists and the public. Landsat-9 is targeting a launch in 2020 and will continue that role.

- At a time when more commercial imagers are operating, "Landsat-9 will launch into this mix and continue to provide the stability and reliability necessary to systematically study Earth surface dynamics," Irons said.

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Figure 65: Remote Rupert Bay in northern Quebec (Canada) is a place where the majesty and dynamism of fluid dynamics is regularly on display. With several rivers pouring into this nook of James Bay, the collision of river and sea water combines with the churn of tides and the motion of currents past islands to make swirls of colorful fluid that could impress even the most jaded of baristas (image credit: NASA Earth Observatory)

Legend to Figure 65: When OLI on Landsat-8 captured this image of Rupert Bay on July 30, 2016, tannin-stained (dark brown) river water was flowing into the bay at the same time that turbid seawater appeared to be pushing in due to the rising tide. The shallowness of the bay, some suspended mud and sediment kicked up by the tide, and mixing of the stained river water and sea water likely gave the sea water a light brown appearance. Note that the colored plumes and intricate vortices around the islands are pointing inland—an indicator that the tide was likely coming in or that northwesterly winds were affecting the flow of the water. The lowermost image shows a detailed view of von Kármán vortices formed as water flowed past a small island in the bay.

- Landsat-8 benefits from evolutionary technological advances over its predecessors. Landsat- 8's OLI (Operational Land Imager ) collects data in two new spectral bands: a deep blue (coastal/aerosol) band and a cirrus cloud detection band. Both of Landsat-8's science instruments, OLI and TIRS (Thermal Infrared Sensor), can outperform their predecessors' measurement sensitivity due to an improved SNR (Signal-to-Noise Ratio).

- These improvements have been integral to the work of water quality managers who can now use Landsat-8 to map water quality indicators in coastal and inland waters. "We can now pull out detailed maps of water constituents, including chlorophyll, dissolved organic matter, and suspended sediment," says Jeff Masek, the Landsat-9 Project Scientist.

- Landsat-8 has also made mapping the movement of glaciers, ice sheets, and sea ice easier. This in turn has led to the near-realtime global monitoring of glaciers, detailed Antarctic ice sheet velocity maps, and new Antarctic rock outcrop maps, all of which combine to give a better understanding of cryospheric processes.

- Landsat-8 also detects more subtle changes in vegetation health and can help make meaningful measurements of biophysical variables that land managers track, like leaf-area index. And with the launch of the European Space Agency's Sentinel-2 satellites, scientists are now "harmonizing" imagery from multiple missions to observe changes to vegetation on seasonal timescales.

- This five-year launch anniversary also marks an engineering milestone. Landsat-8 was built with a five-year design life. Most missions that survive their first few months on orbit tend to last much longer than their stated design life. Given that Landsat-8 instruments have few moving parts and the OLI instrument in particular has significant redundancy, scientists and engineers think Landsat-8 will continue operating for years to come. "I expect Landsat 8 to last well beyond its design life and continue operations deep into the next decade," Irons said.

- The first three Landsats were built with one-year design lives but the operational life exceeded that by at least four years for all of them. Landsats-4 and -5 were built with three-year design lives, but operated well beyond that – Landsat-5 operated for nearly 29 years (a feat for the record books). And Landsat-7, launched in 1999, was built with a five-year design life and is now in its 19th year of operation, albeit with some degradation.

- Landsat-8's data quality and collection pace add significantly to the Landsat data record. The combined Landsat archive with its depth, quality, and open access has exposed new avenues to better understanding our planet, and this record will continue into the future.

• February 7, 2018: The Cotahuasi Canyon in Peru stands as a potent reminder of the tremendous erosive power of water and ice. Cutting through a towering plateau—a product of repeated volcanic eruptions and tectonic uplift—the canyon is one of the deepest in the world. 61)

- Cotahuasi formed over the course of several million years as rivers and glaciers chiseled into the plateau. The relief from the canyon floor to the rim ranges from 2.5 to 3.5 km (1.5 to 2.2 miles), making Cotahuasi Canyon about twice as deep as the Grand Canyon.

- Evidence of volcanic activity surrounds the canyon. To the south, snow-capped Solimana (Figure 66), an inactive stratovolcano that last erupted about 500,000 years ago, soars above the plateau. Colorful yellow and orange volcanic deposits are visible around the north rim of the canyon.

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Figure 66: On July 3, 2016, OLI on Landsat-8 passed over the canyon. This image shows the Landsat-8 data draped over topographic data from NASA's SRTM (Shuttle Radar Topography Mission) of Feb. 2000 (image credit: NASA Earth Observatory, image by Joshua Stevens using Landsat data from the USGS and topographic data from SRTM, story by Adam Voiland)

- The image of Figure 67 underscores the stark transitions in environmental conditions and vertical ecology of the canyon. The base (elevation 1200–2300 meters) is a warm, lowland zone where fruits, especially grapes, are widely grown. Higher up (2300–3600 meters), the dominant crop is maize. Farmers also raise more traditional crops such as kiwicha, quinoa, and tarwi. Potatoes and other tuber crops are grown in the cooler, upland areas (3600–4000 meters). Not much can be grown in the arid, cold climate (4000–5000 meters) at the top of the plateau, but farmers use the land to raise alpacas, llamas, sheep, and cattle.

- The canyon is so remote—it's a 12-hour bus ride to Arequipa—that relatively few outsiders make it there. Archaeologists and geologists occasionally visit to catalog Incan and pre-Incan archaeological sites or to piece together the geological history of the area. Some adventurous travelers come to the canyon to raft and hike, but the Cotahuasi River's many rapids are known for being extremely dangerous.

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Figure 67: This image is a nadir view from OLI of the area near the town of Cotahuasi, captured on July 3, 2016 (image credit: (image credit: NASA Earth Observatory, image by Joshua Stevens using Landsat data from the USGS)

• February 3, 2018: It is one of Central America's most active volcanos. Volcán de Fuego puffs continuously without notice by nearby communities, punctuated by episodes with explosive activity, huge ash plumes, and lava flows. 62)

- The Guatemalan volcano is at it again, beginning its latest bout of unruly behavior on January 31, 2018. On the next day,OLI (Operational Land Imager) on Landsat-8 captured these natural-color images of the eruption. Ash in a volcanic plume typically appears brown or gray, while steam appears white. You can see a wider view of the volcano here. Fuego is located about 70 km (40 miles) west of Guatemala City.

- According to CNRED (Coordinadora Nacional para la Reducción de Desastres), the plume reached an altitude of 6,500 m above sea level and was carried 40 km to the west and southwest by the winds. Falling ash affected tens of thousands of people, primarily in the provinces of Escuintla and Chimaltenango. Lava from two active conduits flowed through four ravines, leading officials to preemptively close National Route 14 to vehicles.

- In addition to ash, the plume contains gaseous components invisible to the human eye, including sulfur dioxide SO2. The gas can affect human health—irritating the nose and throat when breathed in—and reacts with water vapor to produce acid rain. It also can react in the atmosphere to form aerosol particles, which can contribute to outbreaks of haze and influence the climate.

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Figure 68: OLI image of the eruption of the Fuego volcano, captured on 1 Feb. 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

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Figure 69: Detail image of the Fuego volcano eruption, captured on 1 Feb. 2018 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

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Figure 70: This map shows concentrations of SO2, detected on 1February by OMPS (Ozone Mapper Profiler Suite) on the (Suomi-NPP (Suomi National Polar-orbiting Partnership) satellite (image credit: NASA Earth Observatory image by Joshua Stevens, using OMPS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC), story by Kathryn Hansen)

• January 30, 2018: Cape Town—a cosmopolitan city of 3.7 million people on South Africa's western coast—is on the verge of running out of water. According to the city's mayor, if current consumption patterns continue then drinking water taps will be turned off in April and people will have to start procuring water from one of 200 collection points throughout the city. 63)

- With key reservoirs standing at precariously low levels, the city forecasts that this so-called Day Zero will happen on April 12, 2018, though the exact date will depend on the weather and on consumption patterns in the coming months. The rainy season normally runs from May to September.

- Cape Town's six major reservoirs can collectively store 898 x 106 m3 of water, but they held just 26 percent of that amount as of January 29, 2018. Theewaterskloof Dam—the largest reservoir and the source of roughly half of the city's water—is in the worst condition, with the water level at just 13 percent of capacity.

- In practical terms, the amount of available water is even less than this number suggests because the last 10 percent of water in a reservoir is difficult to use. According to Cape Town's disaster plan, Day Zero will happen when the system's stored water drops to 13.5 percent of capacity. At that point, the water that remains will go to hospitals and certain settlements that rely on communal taps. Most people in the city will be left without tap water for drinking, bathing, or other uses.

Figure 71: This animated image shows how dramatically Theewaterskloof has been depleted between January 2014 and January 2018. The extent of the reservoir is shown with blue; non-water areas have been masked with gray in order to make it easier to distinguish how the reservoir has changed. Theewaterskloof was near full capacity in 2014. During the preceding year, the weather station at Cape Town airport tallied 682 mm (27 inches) of rain (515 mm is normal), making it one of the wettest years in decades. However, rains faltered in 2015, with just 325 mm falling. The next year, with 221 mm, was even worse. In 2017, the station recorded just 157 mm of rain (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and water level data from South Africa's Department of Water and Sanitation, story by Adam Voiland)

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Figure 72: This trio of images shows how the three successive dry years took a toll on Cape Town's water system. Voëlvlei, the second largest reservoir, has dropped to 18 percent of capacity. Some of the smaller reservoirs like the Berg River and Wemmershoek are still relatively full, but they store only a small fraction of the city's water. One of the largest reservoirs in the area—Brandvlei—does not supply water to Cape Town; its water is used by farmers for irrigation (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and water level data from South Africa's Department of Water and Sanitation, story by Adam Voiland)

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Figure 73: This line chart details how water levels in the six key reservoirs have changed since 2013. Though the reservoirs are replenished each winter as the rains arrive, the trend at almost all of them has been downward. The one exception is Upper Steenbras, which holds about 4 percent of the city's water and has been kept full because it is also used to generate electricity during peak demand. Also, the city is likely drawing down the largest reservoirs first to minimize how much water is lost to evaporation.

- Piotr Wolski, a hydrologist at the Climate Systems Analysis Group at the University of Cape Town, has analyzed rainfall records dating back to 1923 to get a sense of the severity of the current drought compared to historical norms. His conclusion is that back-to-back years of such weak rainfall (like 2016-17) typically happens about once just every 1,000 years.

- Population growth and a lack of new infrastructure has exacerbated the current water shortage. Between 1995 and 2018, the Cape Town's population swelled by roughly 80 percent. During the same period, dam storage increased by just 15 percent.

- The city did recently accelerate development of a plan to increase capacity at Voëlvlei Dam by diverting winter rainfall from the Berg River. The project had been scheduled for completion in 2024, but planners are now targeting 2019. The city is also working to build a series of desalination plants and to drill new groundwater wells that could produce additional water.

- In the meantime, Cape Town authorities have put tight restrictions on residential water usage. New guidelines ban all use of drinking water for non-essential purposes, while urging people to use less than 50 liters (13 gallons) of water per person per day.

• January 12, 2018: First there was fire. Then rain. And now deadly debris flows are devastating Montecito, California. More than a dozen people are missing or dead, and at least 400 homes have been damaged or destroyed by fast-moving floods that swept mud, rocks, and charred wood left exposed by the Thomas fire. 64)

- OLI on Landsat-8 acquired natural-color imagery of Montecito before and after the fire and debris flows. Figure 74 shows the town on January 10, 2018, after mud and debris tore through the town. The image of Figure 75 was captured on November 23, 2017, before the fire. Charred, debris-covered areas appear brown; unburned vegetation is green. Trails of mud and debris are visible along streams well south of the burn scar.

- Recent fire activity tends to make flash floods, debris flows, and mudflows much more likely. Plants and trees have numerous protective chemicals with which they coat their leaves to prevent water loss. Many of these substances are similar to wax. Vaporized by the heat from fires, these substances disperse into the air and then congeal over the soil surface when the fire begins to cool. Like the wax on your car, they coat the soil, causing water to bead up and run off quickly. The problem is especially pronounced for intense and long-lived blazes such as the Thomas fire.

- Another key factor that made this event so dangerous was the rate at which the rain fell. While the total rainfall was not that exceptional, unusually intense rain fell in and near the burn scar at the beginning of the storm. In just five minutes, 13 mm (0.54 inches) of rain fell in Montecito. Nearby Carpinteria received 22 mm (0.86 inches) within 15 minutes. According to the U.S. Geological Survey, any storm that has rainfall intensities greater than about 10 mm (0.4 inches) per hour poses the risk of producing debris flows. In Southern California, as little as 7 mm (0.3 inches) of rainfall in 30 minutes has triggered debris flows.

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Figure 74: OLI image of the town of Montecito, acquired on 10 January 2018, after mud and debris tore through the town (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, caption by Adam Voiland)

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Figure 75: OLI image of the town of Montecito, captured on 23 November 2017, before the fire (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, caption by Adam Voiland)

• December 26, 2017: In September 2017, a new iceberg calved from Pine Island Glacier—one of the main outlets where the West Antarctic Ice Sheet flows into the ocean. Just weeks later, the berg named B-44 shattered into more than 20 fragments. 65)

- On December 15, 2017, OLI (Operational Land Imager) on Landsat-8 acquired a natural-color image (Figure 76) of the broken iceberg. An area of relatively warm water, known as a polyna, has kept the water ice free between the iceberg chunks and the glacier front. NASA glaciologist Chris Shuman thinks the polynya's warm water could have caused the rapid breakup of B-44.

- The image of Figure 76 was acquired near midnight local time. Based on parameters including the azimuth of the Sun and its elevation above the horizon, as well as the length of the shadows, Shuman has estimated that the iceberg rises about 49 meters above the water line. That would put the total thickness of the berg—above and below the water surface—at about 315 meters.

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Figure 76: OLI image of the broken iceberg B-44, acquired on 15 Dec. 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the U.S. Geological Survey, caption by Kathryn Hansen)

Figure 77: This animation combines five Landsat-8 views of iceberg B-44 acquired over the past four months ((image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the U.S. Geological Survey, caption by Kathryn Hansen)

• December 24, 2017: Before the opening of the Panama Canal in 1914, Cape Horn was a place that gave mariners nightmares. The waters off this rocky point, at the southern tip of Chile's Tierra del Fuego peninsula, pose a perfect storm of hazards. 66)

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Figure 78: On July 12, 2014, OLI on Landsat-8 captured this image of Cape Horn and the Wollaston and Hermite Islands. The Sun's low position in the sky—the image was captured in mid-winter at 56 degrees South—caused the peaks on the islands to cast long shadows toward the southwest (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS, story by Adam Voiland)

- Southwest of Cape Horn, the ocean floor rises sharply from 4,020 m to 100 m within a few kilometers. This sharp difference, combined with the potent westerly winds that swirl around the Furious Fifties, pushes up massive waves with frightening regularity. Add in frigid water temperatures, rocky coastal shoals, and stray icebergs—which drift north from Antarctica across the Drake Passage—and it is easy to see why the area is known as a graveyard for ships.

- Hundreds of ships have gone down near Cape Horn since Dutchman Willem Schouten, a navigator for the Dutch East India Company, first charted a course around the Horn in 1616. One vessel that narrowly escaped that fate was the HMS Beagle, with naturalist Charles Darwin aboard. In 'The Voyage of the Beagle', Darwin described the harrowing journey as the explorers tried to round the Horn just before Christmas 1832.

December 21st. — The Beagle got under way: and on the succeeding day, favored to an uncommon degree by a fine easterly breeze, we closed in with the Barnevelts, and running past Cape Deceit with its stony peaks, about three o'clock doubled the weather-beaten Cape Horn. The evening was calm and bright, and we enjoyed a fine view of the surrounding isles.

Cape Horn, however, demanded his tribute, and before night sent us a gale of wind directly in our teeth. We stood out to sea, and on the second day again made the land, when we saw on our weather-bow this notorious promontory in its proper form—veiled in a mist, and its dim outline surrounded by a storm of wind and water.

Great black clouds were rolling across the heavens, and squalls of rain, with hail, swept by us with such extreme violence, that the Captain determined to run into Wigwam Cove. This is a snug little harbor, not far from Cape Horn; and here, at Christmas-eve, we anchored in smooth water. The only thing which reminded us of the gale outside, was every now and then a puff from the mountains, which made the ship surge at her anchors.

Table 3: Charles Darwin 'The Voyage of the Beagle'

• December 15, 2017: For more than a hundred years, the fertile and forested patch between the Tennessee and Cumberland rivers was referred to as the "land between the rivers." In the 1960s, it became the "land between the lakes." 67)

- In an attempt to control flooding and to generate electricity in rural Kentucky and Tennessee, the TVA (Tennessee Valley Authority) built Kentucky Dam, thereby impounding the Tennessee River and creating Kentucky Lake in 1944. It became the largest manmade lake east of the Mississippi River.

- Two decades later, the U.S. Army Corps of Engineers blocked the flow of the nearby Cumberland River as well. With the completion of Barkley Dam in 1966, the waters of the Cumberland piled up into Lake Barkley. In the process of creating the two lakes, residents of several small towns along and between the rivers were moved, and parts of some towns were permanently flooded. A few local roads and railways had to be re-routed.

- Engineers also dug out Barkley Canal in order to bring the two rivers and lakes to the same water level. This allowed ships and barges to more easily move goods (without locks) from the Cumberland and Tennessee river valleys toward the mighty Mississippi River. By the time they were done, the TVA and Army Corps had created one of the largest inland peninsulas in the United States.

- In the years after the lakes were created, the new peninsula was slowly converted into a recreation area for hunting, fishing, boating, hiking, and camping. Now managed by the U.S. Forest Service, the Land Between the Lakes National Recreation Area includes one of the largest freshwater recreation complexes in the United States. The parkland and lakes attract roughly two million visitors per year. The Operational Land Imager (OLI) on Landsat 8 acquired this natural-color image of the region on October 7, 2016.

- Near Golden Pond, some forests have been cleared and re-seeded to return the land to what it likely looked in the 19th century. That grassland prairie also has been settled with elk and bison that once roamed the region. Recreational facilities also include a planetarium and a woodlands nature station. At the southern end of Land Between the Lakes, near the town of Dover, a re-creation of an 1850s homestead includes rare breeds of livestock and plants from that era.

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Figure 79: OLI image of the "land between the lakes" in Kentucks, acquired on 7 October 2016 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS, story by Mike Carlowicz)

• December 5, 2017: At 6:50 a.m. on August 14, 2017, the people of Regent heard a low rumbling noise like the hum of a passing airplane. Then there was quiet. A hillside had failed in this mountainous area just beyond Freetown, Sierra Leone (Africa, located on the Atlantic Ocean). 68)

- Ten minutes later, an explosive sound came from the direction of nearby Mount Sugar Loaf. The Earth trembled and began to flow. Trees and boulders of all sizes tumbled chaotically. Sparks lit the morning air as metal and rock collided. A river of rust-colored soil plunged into the swollen stream valleys below, which were already filled with floodwater due to several days of intense rain. A destructive slurry of mud, boulders, and tree parts rushed down toward the stream valley, flowing more than three kilometers before draining into the sea near Lumley.

- When authorities tallied the loss of life and property, the numbers were sobering. More than 1,141 people died and 3,000 people lost their homes, according to a World Bank assessment. Damage to homes in the area totaled more than $14 million.

- Sustained downpours were the immediate trigger for the landslide. Between July 1 and August 14, Freetown received 1,040 mm of rain—about three times the norm for that period. However, decades of rapid urbanization in landslide-prone areas, as well as construction along streams where flooding was common, set the stage for the disaster. Joseph McCarthy, an urban planner at Njala University, went so far as to tell Thompson Reuters that: "The major cause of mudslides and flooding is the chaotic development caused by the rapid urbanization of Freetown."

- This pair of false-color Landsat images (Figures 80 and 81) illustrates the extent of the changes. Forested areas appear red, urban areas are gray, and landslide debris is tan. In 1986, most of the development was in low-lying, coastal areas. By 2017, development had spread widely into mountainous areas. For instance, the town of Regent had just a handful of buildings in 1986. By 2017, it had many more buildings and a population of 28,000 people.

- In addition to the spread of urban areas, the images also highlight the extent of deforestation—one of the factors that helps trigger landslides—to the south of Freetown. According to one analysis of Landsat imagery led by Lamin Mansaray of Zhejiang University, the Freetown region saw its densely forested areas drop from 113 km2 in 1986 to 59 km2 in 2015 — a 52 percent decline.

- The city's population increased from about 500,000 people in 1986 to about 1 million people today. A civil war between 1991–2002 accelerated the city's expansion. "Before 1991, there was minimal rural-urban migration in Sierra Leone. During the conflict, rural areas were most vulnerable to attacks, and Freetown was by far the safest place to be," explained Mansaray. "After the war ended in 2002, migration into the capital remained high because most people in rural areas had lost their homes and sources of livelihoods."

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Figure 80: False-color image of Freetown acquired by Landsat-5 on January 3, 1986 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

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Figure 81: False-color image of Freetown acquired by Landsat-8 on November 8, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

• December 2, 2017: In central Algeria, just above the Tropic of Cancer and about 1200 km south of the Algiers metropolis, lies a land as desolate as it is beautiful. 69)

- In this part of the Sahara, known as the Tanezrouft Basin, the land is especially parched, with annual rainfall measured in mm (less than 5 mm). This is a hyperarid place of soaring temperatures and scarce access to water or vegetation. There are no permanent residents here, only occasional Tuareg nomads. The basin's colloquial name is the "Land of Terror" because, for many, to traverse this land is to stare death in the face.

- The severe conditions that make this basin a barren expanse for life also lay bare its exquisite geology. Wind erosion—caused by constant sandblasting through millennia of frequent sandstorms—has exposed ancient folds in the Paleozoic rocks. This natural-color image, acquired on October 22, 2017, by OLI (Operational Land Imager) on Landsat 8, shows concentric rings of exposed sandstone strata that create stunning patterns across the Tanezrouft Basin. When viewed from 705 km above Earth, the exposed geologic features create an arresting work of abstract art.

- The sandstone canyons in this region have walls that rise as high as 500 m, and salt flats can be found in their lower reaches. The flats indicate that water played a role in sculpting this landscape. "Intermittent flooding has occurred often enough to mold the landscape pretty thoroughly over millions of years," explained P. Kyle House, a geologist with the U.S. Geological Survey. "There are numerous canyons in this region that both follow and abruptly cut directly across the grain of the tilted and folded strata," he added. "These patterns are striking and reminiscent of landscapes formed on folded strata in, for example, the Red Desert of southern Wyoming and even parts of the heavily forested Appalachian Mountains of the Eastern United States."

- On the ground, life is a rare. About 80 km east of this area, the trans-Saharan highway—known as one of the world's most brutal roads—makes its way through the desert.

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Figure 82: Natural color image of OLI, acquired on October 22, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS. Story by Laura Rocchio, Landsat science outreach team)

• November 25, 2017: Lake Chad sustains people, animals, fishing, irrigation, and economic activity in west-central Africa. But in the past half century, the once-great lake has lost most of its water and now spans less than a tenth of the area it covered in the 1960s. Scientists and resource managers are concerned about the dramatic loss of fresh water that is the lifeblood of more than 30 million people. 70) 71)

- Lake Chad sits within the Sahel, a semiarid strip of land dividing the Sahara Desert from the humid savannas of equatorial Africa. The Chad Basin is bordered by mountain ranges and spans more than 2.4 million km2 of Cameroon, Nigeria, Chad, and Niger. The water level is largely controlled by the inflow from rivers, notably the Chari River from the south and, seasonally, the Komodugu-Yobe from the northwest. Rainfall can also reach the lake by way of smaller tributaries and groundwater discharge.

- Inflow fluctuates with the shifting patterns of rainfall associated with the West African Monsoon, making the system very sensitive to drought. Most precipitation in the Sahel falls during the peak of a short rainy season from July through September. The dry season is most intense between November and March. Years with little precipitation can wreak havoc on the water supply.

- Extreme swings in Lake Chad's water levels are not new. The lake has experienced wet and dry periods for thousands of years, according to paleoclimate research. More recently, variations in depth and extent were noted by French explorer Jean Tilho, who reported in 1910 that parts of the lake had dried up. But what is new is the way researchers are studying changes in the lake.

- The images of Figures 83 to 85 highlight the shrinking and growing in the recent life of Lake Chad. The false-color images were acquired by Landsat satellites—Landsat-1 in 1973 and Landsat-8 in 2017. The combination of visible and infrared light helps to better differentiate between vegetation (red) and water (blue and slate gray). The photographs of Figure 85 were captured by the Corona reconnaissance satellite in 1963 and by an astronaut on the International Space Station in 2015.

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Figure 83: False-color image of Lake Chad acquired by Landsat-1 in 1973 (image credit: NASA Earth Observatory, images using Landsat data provided by the USGS, Story by Kathryn Hansen)

- In 1973, the lake was in a phase called "Normal Lake Chad"—a single body of water with an archipelago on the north side of the southern basin. Note how little vegetation was around the lake at that stage. Throughout the 1970s, severe droughts plagued the African Sahel, and water disappeared from the northern basin. Since then, water has come and gone from the northern lobe depending on the year and season. But the two lobes have never reconnected into a single lake.

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Figure 84: False-color image of Lake Chad acquired by OLI on Landsat-8 in 2017 (image credit: NASA Earth Observatory, images using Landsat data provided by the USGS, Story by Kathryn Hansen)

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Figure 85: These two images were captured by the Corona reconnaissance satellite in 1963 and by an astronaut on the International Space Station in 2015 (image credit: NASA Earth Observatory, images using declassified military satellite Corona data provided by the USGS — at right is an astronaut photograph ISS042-E-244403, provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, NASA/JSC, Story by Kathryn Hansen)

• November 2017: A lot happened on the Antarctic Peninsula under the cloak of the 2017 polar night—most notably, the calving of a massive iceberg from the Larsen C ice shelf. At the time (July), scientists had to rely on thermal imagery and radar data to observe the break and to watch the subsequent motion of the ice. 72) 73)

- By August, scientists started getting their first sunlit views of the new iceberg, which the U.S. National Ice Center named A-68. MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured a wide view of the berg on September 11. A few days later, on September 16, the OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) on Landsat-8 captured these detailed images.

- The image on the left of Figure 86 shows the icebergs in natural color. The rifts on the main berg and ice shelf stand out, while clouds on the east side cast a shadow on the berg. The thermal image on the right shows the same area in false-color. Note that the clouds over the ice shelf do not show up as well in the thermal image because they are about the same temperature as the shelf. Thermal imagery has the advantage of showing where the colder ice ends and "warm" water of the Weddell Sea begins. It also indicates differences in the thickness of ice types. For example, the mélange is thicker (has a colder signal) than the frazil ice, but thinner (warmer signal) than the shelf and icebergs.

- Both images show a thin layer of frazil ice, which does not offer much resistance as winds, tides, and currents try to move the massive iceberg away from the Larsen C ice shelf. In a few weeks of observations, scientists have seen the passage widen between the main iceberg and the front of the shelf. This slow widening comes after an initial back-and-forth movement in July broke the main berg into two large pieces, which the U.S. National Ice Center named A-68A and A-68B. The collisions also produced a handful of pieces too small to be named.

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Figure 86: Two Landsat-8 images acquired on 16 Sept. 2017. Left: OLI natural color image of A-68A and A-68B. Right: TIRS false color image of the same scene (image credit: NASA Earth Observatory, images by Joshua Stevens using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

• November 11, 2017: Ushuaia, Argentina, is many things to the growing number of people who live there: the southernmost city in the world, the gateway to Antarctica, and a gorgeous home along a rocky coast. For NASA, the city's southerly location makes it an ideal place to stage science flights to Antarctica. 74)

- The flights are part of Operation IceBridge, NASA's longest-running mission to map polar ice (now in its ninth year in the Southern Hemisphere). For the first time, flights over the icy continent are being staged from Ushuaia, instead of Punta Arenas, Chile. Read more about this campaign on our blog.

- OLI (Operational Land Imager) on Landsat-8 captured this image of Ushuaia on March 28, 2017. Located at the tip of South America, it is the capital city of Tierra del Fuego province. Port Williams lies across the channel from Ushuaia, but the village is too small to be visible in this natural-color image.

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Figure 87: The OLI instrument on Landsat-8 captured this image of Ushuaia on the Beagle Channel on March 28, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS, story by Kathryn Hansen)

- Ushuaia is located about 250 km southeast of Punta Arenas, Chile. The city's proximity to the Antarctic Peninsula means that NASA's IceBridge campaign scientists gain an hour of extra flight time over science targets. That's important because the P-3 aircraft being flown during this campaign has a shorter range than the DC-8 aircraft flown during previous campaigns. The map of Figure 88 represents how flights from Ushuaia might cross the Southern Ocean to observe the Antarctic Peninsula and its surrounding seas and ice.

- Science flights began on October 29, and the spring weather in Ushuaia has been relatively mild for the first few weeks of the campaign. But as the locals say, you can get four seasons in any given day here. Strong winds, cold temperatures, and heavy rain are not out of the question. Living or visiting here means you should be ready for any kind of weather at all times.

- The extent of the urban area visible in the satellite image shows that, indeed, the city covers a sizeable area for such a remote part of the world (23 km2). Census information from 2010 reported the population in Ushuaia to be 56,956—almost double the population in 1991. Still, that's just a small fraction of the country's total population of more than 40 million people, most of whom live in Buenos Aires province.

- Ushuaia's port is partially used for industry; container ships dock here, and cargo boxes are stacked in tidy, colorful rows along the shore. Tourism is also important: People come from around the world to hike in Tierra del Fuego National Park, ski in the mountains, cruise to see penguins on Martillo Island, or catch a cruise ship to Antarctica.

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Figure 88: Map showing the southern tip of South America and the Antarctic Peninsula (image credit: NASA Earth Observatory, map by Jesse Allen, story by Kathryn Hansen)

Improvements to the quality and usability of Landsat satellite data have been made with the release of a new USGS product called Landsat Analysis Ready Data (ARD).

This product will help reduce the time needed to process and analyze data and imagery, a significant advantage to scientists studying landscape changes, including changes from wildfires, hurricanes, vegetation cover, drought and other events.

A fundamental goal for Landsat ARD is to significantly reduce the amount of data processing for scientists, who currently have to download and prepare large amounts of Landsat scene-based data for time-series investigative analysis.

ARD provides users with notable flexibility in how they access customized Landsat data. For example, users will have the ability to tailor requests according to specific needs in terms of geospatial regions, spectral bands and collection dates.

Landsat data are the world's longest continuously acquired collection of space-based land remote sensing data. ARD products represent over 30 years of Landsat data available at the highest scientific quality ever produced.

This initial ARD release includes Landsat 4-8 imagery of the conterminous United States, Alaska and Hawaii. In the future, the USGS plans to add the earlier Landsat 1-5 Multispectral Scanner era imagery to the ARD product suite and eventually expand ARD to include the full global Landsat archive.

ARD will serve many purposes such as the foundational dataset for the recent USGS Land Change Monitoring, Assessment, and Projection (LCMAP) initiative. The initiative aims to characterize historical and near-real time land-cover changes across the United States.

The ARD products are based on the recently released Landsat Level-1 Collection structure. Landsat Level-1 products refer to the most basic level of processing that has been applied to a scene for them to be used in applications. This collection management structure ensures access to Landsat Level-1 products as they are acquired and a consistent archive of known data quality.

The USGS generates ARD products from data acquired by the Landsat 4-5 Thematic Mapper, Landsat 7 Enhanced Thematic Mapper Plus and Landsat 8 Operational Land Imager and Thermal Infrared Sensor instruments.

Landsat ARD is created after processing Landsat Level-1 Collection scenes into Albers Equal Area Conic projection. The USGS processes these products to create top of atmosphere reflectance, brightness temperature and atmospherically corrected surface reflectance. The USGS assembles these products into "tiles" adapted from the Web Enabled Landsat Data tiling scheme. This tiling scheme ensures that each pixel in an ARD tile represents the same location on the Earth's surface through the entire ARD time series record from 1982 to the present.

In addition to this higher-level spectral band processing of geophysical parameters, ARD includes several pixel-level quality assessment bands. These bands document the presence of sensor, solar, atmospheric and topographic conditions and traceability to the Landsat Level-1 input source scenes used in ARD.

Each ARD tile product is accompanied by comprehensive metadata that ensures full traceability to the Level-1 input source scenes as well as the versions of the algorithms and processing software used to generate them. The USGS has documented ARD product characteristics in the Landsat ARD Data Format Control Book.

ARD results from a USGS-NASA decision to make Landsat data more relevant for the next generation of information applications. -Users can access Landsat ARD through the EarthExplorer data portal.

Table 4: USGS releases Landsat ARD (Analysis Ready Data), a revolutionary new product 75)

• November 4, 2017: The Aral Sea and Lake Balkhash have a lot in common. Both lakes are located in an arid part of Central Asia; both are somewhat saline; and neither has an outlet. But after the desiccation of the Aral Sea—once the fourth-largest lake in the world—Balkhash now covers a comparatively larger area. Spanning 17,000 km2 in Kazakhstan, Lake Balkhash is the largest lake in Central Asia and fifteenth-largest in the world (Figures 89 and 91). 76)

- Water in the western part of the lake is almost fresh—suitable for drinking and industrial uses—whereas the eastern side of the basin is brackish to salty. The western side is also murkier; visibility/light penetrates to about 1 meter, compared to more than 5 meters on the eastern side. This murkiness, and the water's milky, yellow-green color, is likely due to sediments suspended in the water. "The lake is very shallow, and it is windy nearly every day, so waves can stir up sediments from the bottom," said Niels Thevs of the University of Greifswald (Germany) and the Central Asia office of the World Agroforestry Center.

- Anywhere between 70 to 80 percent of the lake's water comes from the Ili River, which enters the lake along the eastern shoreline. The surrounding delta (green) is now one of the largest wetlands in Central Asia. "I imagine that the wetlands of the Ili Delta look like the wetlands around Aral Sea 50 years ago," Thevs said.

- Thevs describes large parts of the Ili Delta that are only accessible by boat, where you can cruise for hours amid 3-meter-high reeds. These reeds (Pharagmites australis) are considered invasive in the United States. Not so in the Ili Delta, where the plant is an important part of the ecosystem. Thevs also describes parts of the delta where the water is so crystal clear that you can see fish and water plants up to 7 to 8 meters below.

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Figure 89: OLI on Landsat-8 captured this natural-color image of Lake Balkhash on 9 October 2017. The image shows the southwestern part of the lake (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

- If you were to cruise in a boat in the main part of the lake, you could count 43 islands with a total area of 66 km2, according to Zhanna Tilekova of Kazakh National Technical University, who has published research on the region's geoecology. However, those numbers can change. Tilekova noted that as water levels decline, new islands form and the area of existing islands grows. In the western part of the lake, Tasaral (north of this image) and Basaral islands are the largest. Ortaaral and Ayakaral islands are also relatively large (Figure 90). Vegetation, likely small brown shrubs (Saxaul), can grow on these islands. The white areas are likely salt pans.

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Figure 90: Detail image of Lake Balkhash, acquired on 9 Oct. 2017. (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

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Figure 91: This is a map of the Lake Balkhash drainage basin, including the Ili River and its tributaries (image credit: Wikipedia) 77)

• October 29, 2017: In 1985, this part of Shandong Peninsula in eastern China was an open expanse of tidal mudflats frequented mainly by birds and other wildlife. By 2017, the landscape had been transformed into one that is intensely sculpted by human activity. 78)

- OLI (Operational Land Imager) on Landsat-8 captured this natural-color image on September 8, 2017 (Figure 92). The area falls within Binzhou, a prefecture in northern Shandong Province. Seen from above, the landscape is checkered with squares and rectangles, likely aquaculture ponds and brine pools used to produce salt. Dozens of drill pads for oil pumps are visible on the right side of the image. This area falls within the Shengli oil field, the second largest oil field in China.

- Heavy industry—likely oil-refining facilities—are visible near the center of the image. Landsat imagery shows that construction of these industrial facilities began in 2012. The drill pads were mostly established in the mid-1990s. Other major industrial products produced in Binzhou include garments, a fuel called coke, heavy machinery, and cement.

- In research that uses decades of Landsat imagery to determine where surface water has undergone the most change, this area stands out. Browse the Aqua Monitor and Surface Water Explorer to see how the distribution of surface water has changed in this part of China since the 1980s.

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Figure 92: OLI image of the changing landscapes in eastern China, acquired on 28 September 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

• October 22, 2017: As autumn progresses, so does the trail of color across New England. The reds, yellows, and oranges of the season typically emerge first on the deciduous trees and shrubs at higher latitudes and elevations. That was the case on October 13, 2017, when the Operational Land Imager (OLI) on Landsat-8 captured this natural-color image of foliage in north-central Maine. 79)

- The image of Figure 93 shows the mountainous part of Baxter State Park, an 200,000-acre (809 km2) area of protected wilderness. The summit of Mount Katahdin rises to 1,605 m, the tallest point in the state. Vegetation growth is stunted on the mountain's upper slopes and tablelands, which appear light tan. Moving down from the tree line you start to see evergreens, and then deciduous species with magnificent, colorful foliage. When the image was acquired, leaf color was at its local peak for 2017.

- "Typically, northern Maine reaches peak conditions the last week of September into the first week of October," according to the Maine Foliage Report. "The rest of the state's progression of color will start occurring from north to south in mid-October. Coastal Maine typically reaches peak conditions mid-to-late October."

- Leaf color appears around the same time every year, when daylight grows shorter and triggers plants to slow and stop the production of chlorophyll. But for the best color, leaves need dry weather and cooler temperatures. According to news reports, New England's foliage this year may not be as vibrant as other years. As of early October, many areas had not yet seen temperatures cool off much, causing leaves to go from green to brown.

- The Appalachian National Scenic Trail, generally known as the Appalachian Trail or simply the A.T., is a marked hiking trail in the Eastern United States extending between Springer Mountain in Georgia (Southern terminus) and Mount Katahdin in Maine (Northern Terminus). The trail is about 3500 km in length, claimed to be the longest longest hiking-only trail in the world. More than 2 million people are said to do at least a one day-hike on the popular trail each year. "Thru-hikers" attempt to hike the trail in its entirety in a single season — more than 2,700 people thru-hiked the trail in 2014. 80)

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Figure 93: Landsat-8 image of northern Maine, acquired on 13 Oct. 2017, showing the mountainous part of Baxter State Park, an area of protected wilderness with Mount Katahdin as the highest peak in the state (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, story by Kathryn Hansen)

• October 13, 2017: Devastating wildfires have burned through California's wine country since October 8, 2017, taking dozens of lives and leaving thousands of people homeless. Even communities distant from the fires have been plagued by poor air quality, as the smoke plumes have darkened skies and canceled school and other activities across the region. 81)

- On October 11, OLI on Landsat-8 acquired the data for these false-color images of the fires near Santa Rosa and other communities in Northern California. The images are composites combining shortwave infrared, near-infrared, and green (OLI bands 6-5-3) with natural color (bands 4-3-2) and a thermal infrared signature (TIRS, band 10). These combinations make it easier to see through the smoke to the burn scars and the still-active fires.

- In the past week, 21 wildfires have ignited in Napa, Sonoma, Solano, and Mendocino counties and other communities north and east of San Francisco Bay. Fanned by northeasterly Diablo winds, the fires have collectively consumed at least 170,000 acres (265 square miles) of land—an area about half the size of the city of Los Angeles.

- The most prominent events include the Tubbs fire (between Santa Rosa and Calistoga, Figure 95), which has burned more than 34,000 acres; the Atlas fire (near Lake Berryessa, off the lower right of our image), which torched 44,000 acres; and the Redwood/Potter fires (near Mendocino National Forest, north of this scene) with 32,000 acres burned. Part of the Adobe fire (about 8,000 acres) appears in the lower right of the image, near Kenwood.

- CalFire and local officials reported that at least 3,500 homes and businesses have been destroyed, and thousands more are being threatened. Tens of thousands of people have evacuated, and thousands of firefighters have been sent to stop the spreading flames. As of the morning of October 12, most of the fires had little or no containment, according to CalFire bulletins, and "red flag warnings" were still being raised for fire weather with low humidity and high winds.

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Figure 94: Landsat-8 detail false-color image of the Santa Rosa region, acquired on 11 Oct. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, Story by Mike Carlowicz)

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Figure 95: Landsat-8 false-color image of the north California wine country affected by wildfires, acquired on 11 Oct. 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, Story by Mike Carlowicz)

• September 10, 2017: In early September 2017, ocean scientists noticed something swirling in the waters off the coast of the Brazilian state of São Paulo. The sinuous threads of darkness amid the blue Atlantic Ocean were not caused by oil; they were the result of a phytoplankton bloom. 82)

- OLI on Landsat-8 captured the image of Figure 96 on September 5, 2017. Figure 96 is a wide view showing blooms spanning more than 100 km off of São Paulo state. The image of Figure 97 shows details of the bloom near Caraguatatuba. The dark colors are probably high concentrations of dinoflagellates, according to researchers at the University of São Paulo. Analyzing water samples collected from Caraguatatuba Bay and from the channel between the Ilhabela archipelago and the mainland, they identified the species as likely to be Gymnodinium aureolum.

- "But, this is a complicated species to identify," said Aurea Maria Ciotti, a scientist at the university's Center for Marine Biology. She and others are awaiting the results of additional tests to confirm the identification. "Blooms here are very uncommon—this is the first time for this species as far as we know."

- In January 2014, a bloom of a different species—Myrionecta rubra—appeared as dark patches that spanned about 800 km of the waters near Rio de Janeiro. Both the 2014 and 2017 blooms appear dark in satellite images for the same reason; the high concentration of heavily pigmented cells darken the water and less light is reflected directly back toward the satellite.

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Figure 96: OLI image off the coast of the Brazilian state of São Paulo, captured on Sept. 5, 2017, showing blooms spanning more than 100 km (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS. Story by Kathryn Hansen)

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Figure 97: This image shows details of the bloom near Caraguatatuba (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS. Story by Kathryn Hansen)

• September 8, 2017: The HLS (Harmonized Landsat Sentinel-2) project has released a new and improved version of its data sets. Landsat-8 and Sentinel-2 satellites have spectral and spatial similarities that make using their data together possible. When the data are used together observations can be more timely and accurate. Note: Sensor co-calibration efforts were underway prior to Sentinel-2A's launch. 83)

- Sentinel-2 and Landsat products represent the most widely accessible medium-to-high spatial resolution multispectral satellite data. Following the recent launch of the first out of two Sentinel-2 satellites, the potential for synergistic use of the two sources creates unprecedented opportunities for timely and accurate observation of Earth status and dynamics. Thus, harmonization of the distributed data products is of paramount importance for the scientific community. Activities to harmonize data products are on their way, yet more coordination is needed to allow the majority of users to easily and effectively include both data types into their work.

- The HLS project is an effort to "harmonize" the data of the two satellite programs so that they can be more easily used in unison. The ultimate goal is to obtain seamless 2-3 day global surface reflectance coverage at 30 meters that removes residual differences between the sensors due to spectral bandpass and view geometry. Currently the v1.3 HLS data set encompasses 82 global test sites that cover about 7% of the global land area.

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Figure 98: This map is showing the temporal revisit time of the combined Landsat-8, Sentinel-2A and -2B satellites over the continental US (image credit: NASA)

- Using the processing power of the NASA Earth Exchange (NEX) computer cluster at NASA Ames, the HLS workflow atmospherically corrects data from the satellites, geographically tiles the Landsat data in a manor matching the Sentinel-2 tiling, and then corrects for different sensor view angles BRDF (Bidirectional Reflectance Distribution Function) and does a slight band pass adjustment for the Sentinel-2 data to create the harmonized 30 meter product.

- The new HLS version 1.3 expanded the number of geographic test sites, fixed a bug that was causing incorrectly calibrated coefficients to be used when calculating spectral reflectance and another bug in the BRDF calculation. Version 1.3 also changed the band combination of its quick-look browse images to follow the USGS standard format (SWIR-1, NIR, Red) and it added quality assessments on a per-site basis in addition to the previous per-tile availability.

- Currently, HLS data are only available for dates through April 30, 2017 because the HLS process relies on pre-collection L1T data.

- The next version of HLS will include a wall-to-wall harmonized product for North America, and will migrate to routine weekly processing. The project anticipates releasing the new version (v1.4) by early 2018.

- The HLS team includes researchers from NASA Goddard Space Flight Center, the University of Maryland, and NASA Ames Research Center.

• September 5, 2017: On January 17, 2017, a fire lit by a farmer in a swampy area along the Peruaçu River burned out of control and moved into the Peruaçu Environmental Preservation Area, a national park in the state of Minas Gerais, Brazil. From there, it proceeded to burn amidst grass, bushes, and palm trees (Mauritia flexuosa) for the past eight months. 84)

- Rather than producing big, orange flames and billowing plumes of smoke, this fire smoldered underground in dried out, carbon-rich soil and likely peat. In this part of the world, swampy soils near rivers are often drained to make them more suitable for growing crops. On August 11, 2017, OLI (Operational Land Imager) on Landsat-8 captured this image of the charred landscape (gray) that the fire left behind.

- "The fire spread slowly through soil and roots without any visible flames, but it was able to move up the hollow trunks of the Mauritia flexuosa and jump to the palm tree canopy," explained Jose Eugenio Cortes Figueira, a biologist at the Federal University of Minas Gerais who has been monitoring the fire.

- In mid-August 2017, the burn scar was still smoldering and hundreds of palm trees had toppled over. The photograph of Figure 100, taken by Figueira, shows smoke seeping from the ground with several downed palm trunks behind it. As of mid-August, the fire had burned roughly 600 hectares of palm swamp along the river—in roughly the same area that had burned during a similar fire in 2014.

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Figure 99: The OLI image, acquired on Aug. 11, 2017, shows the burn scar left by a palm swamp fire in Brazil along the Peruaçu River. Rather than producing big, orange flames and billowing plumes of smoke, this fire smoldered underground in dried out, carbon-rich soil and likely peat. The fire spread slowly through soil and roots, but it was able to move up the hollow trunks of palm trees in the area and burn off the canopy [image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS, Story by Adam Voiland, with information from Jose Eugenio Cortes Figueira (Federal University of Minas Gerais) and Geraldo Wilson Fernandes (Federal University of Minas Gerais)].

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Figure 100: This photo of the charred region shows smoke seeping from the ground with several downed palm trunks behind it (image credit: Jose Eugenio Cortes Figueira)

• September 1, 2017: Landsat-8, after collecting data for 4.5 years, has already added over a million images to the archive—this represents 14.8 percent of the entire 45-year Landsat data collection—and each day Landsat-8 adds another ~700 new scenes. 85)

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Figure 101: The data contributions of each Landsat satellite to the USGS Landsat data archive as of Sept. 1, 2017. For Landsat-4 and -5, the darker color on the bars represents MSS (Multispectral Scanner System) data and the lighter color is Thematic Mapper data collected by the mission (image credit: USGS, NASA)

• August 24, 2017: The Kamchatka Peninsula's location along the Pacific Ring of Fire puts the peninsula in one of the most geologically restless areas on the planet. There are more than 100 active volcanoes on the peninsula, one of the highest concentrations of active volcanoes anywhere. 86)

- The most restless of these is Klyuchevskoy (also spelled Kliuchevskoi), a stratovolcano that rises 4,835 meters (15,862 feet) above sea level. According to geological and historical records, Klyuchevskoy has rarely been quiet since it formed about 6,000 years ago. Smithsonian's Global Volcanism Program details a steady stream of activity at Klyuchevskoy punctuated by eruptions every few years that often span months.

- True to form, satellites observed ash and volcanic gases puffing from Klyuchevskoy throughout much of August 2017. The Operational Land Imager (OLI) on Landsat 8 captured this image of a volcanic plume streaming west from the volcano on August 19, 2017. The plume is brown; clouds are white. Note in the broader view that there is also a smaller plume streaming from Bezymianny, a volcano to the south of Klyuchevskoy.

- Fewer than 300 people live within 30 km of Klyuchevskoy, so eruptions do not pose much risk to people on the ground. However, they can represent a hazard to aircraft if ash clouds rise to heights between 8 and 15 km. The ash plume was at a height of roughly 6 km on the day this image was collected, according to the KVERT (Kamchatka Volcanic Eruption Response Team).

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Figure 102: Figure 103 detail image of a volcanic plume streaming west from the volcano on August 19, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

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Figure 103: OLI on Landsat-8 captured this image of a volcanic plume streaming west from the volcano on August 19, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, story by Adam Voiland)

• August 12, 2017: Greenland is best known for its ice, but some remote sensing scientists found themselves closely tracking a sizable wildfire burning along the island's coast in August 2017. The fire burned in western Greenland, about 150 km northeast of Sisimiut. 87)

- Satellites first detected evidence of the fire on July 31, 2017. MODIS (Moderate Resolution Imaging Spectroradiometer) and VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP collected daily images of smoke streaming from the fire over the next week. OLI (Operational Land Imager) on Landsat-8 captured these more detailed images (Figures 104 and 105) of the fire on August 3, 2017.

- While it is not unprecedented for satellites to observe fire activity in Greenland, a preliminary analysis by Stef Lhermitte of Delft University of Technology in the Netherlands suggests that MODIS has detected far more fire activity in Greenland in 2017 than it did during any other year since the sensor began collecting data in 2000.

- Fires detected in Greenland by MODIS are usually small, most likely campfires lit by hunters or backpackers. But Landsat did capture imagery of another sizable fire in August 2015. According to Ruth Mottram of the Danish Meteorological Institute (DMI), neither DMI nor other scientific groups maintain detailed records of fire activity in Greenland, but many meteorologists at the institute have heard anecdotal reports of fires.

- The blaze appears to be burning through peat, noted Miami University scientist Jessica McCarty. That would mean the fire likely produced a sharp increase in wildfire-caused carbon dioxide emissions in Greenland for 2017, noted atmospheric scientist Mark Parrington of the European Commission's Copernicus program.

- It is not clear what triggered this fire, though a lack of documented lightning prior to its ignition suggests the fire was probably triggered by human activity. The area is regularly used by reindeer hunters, and is not too far from a town with a population of 5,500 people.

- The summer has been quite dry. Sisimiut saw almost no rain in June and half of the usual amount in July. That may have parched dwarf willows, shrubs, grasses, mosses, and other vegetation that commonly live in Greenland's coastal areas and made them more likely to burn.

- Fires emit a soot-like material called black carbon. It is likely that winds will transport some of this material east to the ice sheet where it will contribute to a line of darkened snow and ice along the western edge of Greenland's ice sheet. This area is of interest to climate scientists because darkened snow and ice tends to melt more rapidly than when it is clean.

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Figure 104: Wildfires are burning in Greenland, acquired on August 3, 2017 with OLI on Landsat-8 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, Story by Adam Voiland, with information from Ruth Mottram (Danish Meteorological Institute), Jessica McCarty (Miami University), Mark Parrington (COPERNICUS), and Stef Lhermitte (Delft University of Technology)

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Figure 105: Detailed OLI image of wildfires on Greenland (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, Story by Adam Voiland, with information from Ruth Mottram (Danish Meteorological Institute), Jessica McCarty (Miami University), Mark Parrington (COPERNICUS), and Stef Lhermitte (Delft University of Technology)

• July 2017: The Landsat-8 OLI instrument continues to be remarkably stable over its four years on orbit. Significant change is only apparent in the Coastal Aerosol band (band 1) and this approximately 1% change in response is currently being corrected in operational data processing. 88)

- In addition, all the on-board calibration devices are working well, and with the exception of a few small (<1%) degradations in the devices used most frequently, have not degraded. The availability of the multiple devices allows identifying the degrading devices and deciphering instrument change from calibrator change.

• On July 23, 2017, the Landsat Program celebrateed forty-five years of continuous Earth observation. NASA — working in cooperation with the U.S. Department of the Interior (DOI) and its science agency, the USGS — launched the first Landsat satellite (originally named Earth Resources Technology Satellite 1) on July 23, 1972. 89)

• July 18, 2017: Something happened 100 years ago that changed forever the way we fly. And then the way we explore space. And then how we study our planet. That something was the establishment of what is now known as NASA Langley Research Center (LRC), which is commemorating its 100th anniversary in 2017. 90)

- Just three months after the United States entered into World War I, Langley Memorial Aeronautical Laboratory was carved out of coastal farmland near Hampton, Virginia, as the nation's first civilian facility focused on aeronautical research. The goal was, simply, to "solve the fundamental problems of flight." Under the direction of the National Advisory Committee for Aeronautics (NACA), ground was broken for the center on July 17, 1917.

- From the beginning, Langley engineers devised technologies for safer, higher, farther, and faster air travel. More than 40 state-of-the-art wind tunnels and supporting infrastructure have been built over the years, and researchers use those facilities to develop many of the wing shapes still used today in airplane design. Better propellers, engine cowlings, all-metal airplanes, new kinds of rotorcraft and helicopters, faster-than-sound flight—these were among Langley's many groundbreaking aeronautical advances.

- During World War II, Langley tested planes like the P-51 Mustang in the nation's first wind tunnel built for full-sized aircraft. Langley later partnered with the military on the Bell X-1, an experimental aircraft that would fly faster than the speed of sound. Follow-on research would extend the reach of American aeronautics into supersonics and hypersonics. By 1958, NACA would become NASA, and Langley's accomplishments would soar from air into space.

- Over the past half century, LRC has contributed significantly to the development of rockets and to the spacecraft testing and astronaut training of the Mercury, Gemini, and Apollo programs. In particular, astronauts practiced Moon landings here with the lunar lander. Langley also led the unmanned Lunar Orbiter initiative, which not only mapped the Moon, but helped choose the spot for the first human landing. With the Viking 1 landing in 1976, Langley led the first successful U.S. mission to the surface of Mars. All along, the center and its researchers have contributed to the study of Earth via satellite and through instruments flown on the space shuttles, space station, and NASA aircraft.

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Figure 106: OLI (Operational Land Imager) on Landsat-8, acquired these natural-color images of LRC (Langley Research Center), also known as LaRC, and the surrounding Hampton Roads area on April 9, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, Story by Jim Schultz, NASA Langley Research Center, adapted by Mike Carlowicz)

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Figure 107: Location of LRC on the Virginia Peninsula, acquired on April 9, 2017, bound to the north by the York River, to the south by the James River, and to the east by the Chesapeake Bay (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, Story by Jim Schultz, NASA Langley Research Center, adapted by Mike Carlowicz)

- Over the past half century, LRC has contributed significantly to the development of rockets and to the spacecraft testing and astronaut training of the Mercury, Gemini, and Apollo programs. In particular, astronauts practiced Moon landings here with the lunar lander. Langley also led the unmanned Lunar Orbiter initiative, which not only mapped the Moon, but helped choose the spot for the first human landing. With the Viking 1 landing in 1976, Langley led the first successful U.S. mission to the surface of Mars. All along, the center and its researchers have contributed to the study of Earth via satellite and through instruments flown on the space shuttles, space station, and NASA aircraft.

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Figure 108: Though NASA now has major centers and facilities around the country, Langley remains a world leader in aviation and aeronautics research, exploring ideas for new aircraft and looking for ways to make air travel less polluting, more fuel efficient, and quieter (image credit: NASA Earth Observatory, Ref. 90)

• July 12, 2017: The waters off of North Carolina's barrier islands have been called a "graveyard of the Atlantic." Countless ships have wrecked here, due to the area's treacherous weather and currents and its expansive shoals. These shoals are, by definition, usually submerged. But occasionally parts of them can rise above sea level. 91)

- These natural-color images, acquired by OLI (Operational Land Imager) on the Landsat-8 satellite, show the shoal area off of Cape Point at Cape Hatteras National Seashore—the site of a newly exposed shoal nicknamed "Shelly Island." The first image was captured in November 2016. When the second image was acquired in January 2017, waves were clearly breaking on the shallow region off the cape's tip. The site of those breakers is where the island eventually formed, visible in the third image captured in July 2017. The new island measures about a mile long, according to news reports.

- "What exactly causes a shallow region to become exposed is a deep question, and one that is difficult to speculate on without exact observations," said Andrew Ashton, a geomorphologist at the Woods Hole Oceanographic Institution. "A likely process would be a high tide or storm-driven water elevation that piled up sediment to near the surface, and then water levels went down exposing the shoal. Waves then continue to build the feature while also moving it about."

- While the exact mechanism for the formation of Shelly Island this year is mostly unknown, the phenomenon is not uncommon. Cape Lookout, the next cape down the barrier islands (to the southwest, beyond this image) has had several islands form on its shoal over the past decade or two.

- The shoreline and cape tips along North Carolina's barrier islands are constantly in motion. Cape tips are sculpted by waves and currents that hit from all directions. Meanwhile, sediment is carried up and down the coastline and often deposited near the cape tips. Each cape has a so-called "cape-associated shoal" lurking underwater. These submerged mounds of sand can extend for tens of kilometers. They are also very shallow, rising to anywhere from 10 meters to a few meters below the surface in places.

- "Tidal flows moving up and down the coast are diverted by the capes and result in a net offshore current at cape tips and deposition at the shoals," Ashton said. "Occasionally, a portion of the shoal becomes exposed and forms an island."

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Figure 109: Three images of North Carolina's Cape Hatteras, acquired with OLI on Landsat-8, show the changing coastline with the built-up of shoals (image credit: NASA Earth Observatory, images by Jesse Allen and Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

• June 17, 2017: There is an obvious difference between the dark green coniferous forests that dominate the western shore of Tomales Bay and the lighter green grasslands on the east side (Figure 110). But the differences between the two shores run much deeper than the vegetation. - Tomales Bay lies about 50 km northwest of San Francisco, along the edges of two tectonic plates that are grinding past each other. The boundary between them is the San Andreas Fault, the famous rift that partitions California for hundreds of miles. 92)

- To the west of the Bay is the Pacific plate; to the east is the North American plate. The rock on the western shore of the Bay is granite, an igneous rock that formed underground when molten material slowly cooled over time. On the opposite shore, the land is a mix of several types of marine sedimentary rocks. In Assembling California, John McPhee calls that side "a boneyard of exotica," a mixture of rock of "such widespread provenance that it is quite literally a collection from the entire Pacific basin, or even half of the surface of the planet."

- As the plates shift, the ground west of the San Andreas Fault moves northward. On average, movement along the fault averages about 3 to 5 cm per year—about the speed that fingernails grow. However, that movement is anything but steady. The two plates tend to lock together until extreme amounts of pressure build up. When the pressure reaches a breaking point, an earthquake sends the plates lurching. During the Great 1906 San Francisco Earthquake, a road at the head of Tomales Bay was offset by nearly 6 meters.

- In Figure 111, you can see that the direction of the fault follows the orientation of Tomales Bay, running from the head of the Bay through Olema Valley toward Bolinas Lagoon.

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Figure 110: OLI on Landsat-8 captured this natural-color image of part of Tomales Bay on March 1, 2017. Lagunitas Creek, a northward-flowing stream that offers critical habitat for the endangered coho salmon, roughly traces the fault (image credit: NASA Earth Observatory , images by Jesse Allen, using Landsat data from the USGS, story by Adam Voiland)

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Figure 111: Overview of the Tomales Bay as part of the San Andreas fault, about 50 km northwest of San Francisco (image credit: NASA Earth Observatory , images by Jesse Allen, using Landsat data from the USGS, story by Adam Voiland)

• June 7, 2017: Forests, grasslands, deserts, and mountains are all part of the Patagonian landscape that spans more than a million km 2 of South America. Toward the western side, expanses of dense, compacted ice stretch for hundreds of kilometers of the Andes mountain range in Chile and Argentina. Glaciologist Eric Rignot described these icefields as "one of the most beautiful places on the planet." Their beauty is also apparent from space. 93)

- The two lobes of the Patagonian icefields—north and south—are what's left of a much more expansive ice sheet that reached its maximum size about 18,000 years ago. The modern icefields are just a fraction of their previous size, though they remain the southern hemisphere's largest expanse of ice outside of Antarctica.

- "The rapid thinning of the icefield's glaciers illustrates the global impact of climate warming," said Rignot, of NASA's Jet Propulsion Laboratory and the University of California-Irvine. "We have shown that Patagonia glaciers experience some of the world's most dramatic thinning per unit area, more than Alaska or Iceland or Svalbard or Greenland."

- The northern remnant is the smaller of the two icefields, covering about 4,000 km2 (about a quarter the size of the southern icefield). On April 16, 2017, the Operational Land Imager (OLI) on Landsat 8 captured this rare cloud-free image of the entire North Patagonian Icefield (Figure 112).

- While the northern icefield is smaller than its southern counterpart, it still has 30 significant glaciers along its perimeter. Ice creeps downslope through mountain valleys and exits the through so-called "outlet glaciers." Many come to an abrupt end on land, while others terminate in water. The water-terminating glaciers San Rafael and San Quintín are the icefield's largest.

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Figure 112: OLI image on Landsat-8, acquired on April 16, 2017 (image credit: NASA Earth Observatory, images by Jesse Allen and Joshua Stevens, using Landsat data from the USGS, story by Kathryn Hansen)

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Figure 113: The San Rafael Glacier excerpt from Figure 112

- The San Rafael Glacier starts near the western flank of Monte San Valentin—the tallest summit in Patagonia—and drains westward into Laguna San Rafael. The lagoon is ringed by a ridge of debris, called a moraine, shoveled into place by the glacier in the past when it was much larger. Visitors to the area in the late 1800s described the glacier as having a large bulbous front, called a piedmont lobe, that spread out well into the lagoon. Since then, the glacier has receded and is no longer lobe-like, though it still actively sheds icebergs from its front in a process known as calving. San Rafael is one of the most actively calving glaciers in the world.

- Part of the reason why this glacier sheds so many bergs is because of its speed. "Flowing" at a speed of 7.6 km/year, San Rafael is the fastest-moving glacier in Patagonia and among the fastest in the world.

- It is also the icefield's only glacier to come into contact with ocean water. Seawater from the Pacific enters the lagoon through the Golfo Elefantes, which connects to the lagoon via the Rio Tempanos (Iceberg River). At 46.7 degrees south latitude, San Rafael is the closest glacier to the equator in the world to connect to the sea.

- There was a point when seawater did not reach the glacier. "It used to be a lagoon with fresh water," said Rignot. "Then an earthquake in the 1960s lowered the ground and connected the lagoon with the ocean waters (the passage for seawater is only a few meters deep)."

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Figure 114: The San Quintin Glacier excerpt from Figure 112

- San Rafael's "twin" is the San Quintín glacier immediately to the southwest. This glacier currently ends in a piedmont lobe, and illustrates what San Rafael looked like before it receded. Until 1991, the glacier terminated on land, but with the glacier's retreat, the basin has filled in with water to form a proglacial lake. (Note that the lake water is barely distinguishable from the ice due to its milky color).

- San Quintín does not flow as fast (1.1 km/ year) or calve as many bergs as San Rafael, but it is an impressive glacier on its own, standing as the second-largest in the North Patagonian Icefield. Together with San Rafael, the glaciers drain 37 percent of the icefield.

- Like its twin, San Quintín has been receding dramatically. Researchers have shown that between 1870 and 2011, the glacier lost 14.6 percent of its area. For comparison, San Rafael lost 11.5 percent during the same period.

• May 30, 2017: In April 2017, a hillside saturated by melting snow and rainfall collapsed near the village of Kurbu-Tash in southern Kyrgyzstan. Over the following weeks, a slow-moving river of fine-grained soil flowed down a valley and engulfed dozens of homes. 94)

- On May 11, 2017, the OLI (Operational Land Imager) on the Landsat-8 satellite captured an image (right) of the landslide deposit. Freshly exposed soil is tan. For comparison, the image on the left shows the same area on April 25, 2017. The landslide transported 2.8 million m3 of soil, according to Kyrgyzstan's Ministry of Emergency Situations.

- People living in the foothills of the Tien Shan mountains in southern Kyrgyzstan face an unusually high risk of landslides. Several factors contribute to the elevated risk, including the presence of active faults, steep terrain, and the presence of landslide-prone soil types. Loess, for instance, is involved in many landslides in this region because the fine-grained soil becomes quite unstable when saturated with water. Heavy bouts of rain, the melting of snow, and small earthquakes often trigger slides. The risk is particularly high in the spring, when heavy rainfall is most likely. Since the area is densely populated, landslides take lives and destroy many homes each year.

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Figure 115: OLI images of the southern Kyrgyzstan region of Kurbu-Tash, acquired on April 25 (left) and on May 11 (right) after the large landslide (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS, caption by Adam Voiland)

• May 25, 2017: A large landslide has strewn debris over a stretch of California's Highway 1. On the night of May 20, 2017, more than a million tons of rocks and dirt spilled over the roadway, according to the California Department of Transportation. 95)

- OLI ( Operational Land Imager) on Landsat 8, acquired images of the area on April 20 and May 22, 2017. The center image, acquired by a the MSI (Multispectral Imager) on the European Space Agency's Sentinel-2 satellite, shows the same location as it appeared after a previous, smaller landslide this spring.

- "This is a large slide preceded by smaller slides, which is not uncommon," said Thomas Stanley, a geologist and researcher for NASA, in an email. "Much of the California coastline is prone to collapse, so it's fortunate that this landslide happened in an unpopulated location." In 2015, the Monterey County Environmental Resource Policy Department rated parts of the nearby coast as highly susceptible to landslides.

- The latest landslide covered roughly one-third of a mile of the scenic route in 10 to 12 meters of rubble. The highway will remain closed for the foreseeable future, according to Caltrans.

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Figure 116: Documentation of a major landslide on California's Highway 1 observed by OLI on Landsat-8 and by MSI on Sentinel-2 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS and Sentinel-2 data from ESA, story by Pola Lem)

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• May 8, 2017: Not many people venture near the shores of Lake Natron in northern Tanzania. The lake is mostly inhospitable to life, except for a few species adapted to its warm, salty, and alkaline water. 96)

- But you don't need to visit the lake in person to see its stunning, seasonal color. OLI (Operational Land Imager) on Landsat 8 captured these natural-color images of Lake Natron and its surroundings. They show the lake on March 6, 2017, very early in the rainy season that runs from March to May. In these images, you can see the deepest water along the perimeter of the lake bed, the location of lower-elevation lagoons.

- The lake is a maximum of 57 km long and 22 km wide. The climate here is arid. High levels of evaporation have left behind natron (sodium carbonate decahydrate) and trona (sodium sesquicarbonate dihydrate). The alkalinity of the lake can reach a pH level of greater than 12. In a non-El Niño year, the lake receives less than 500 mm of rain. Evaporation usually exceeds that amount, so the lake relies on other sources—such as the Ewaso Ng'iro River at the north end—to maintain a supply of water through the dry season.

- But it's the region's volcanism that leads to the lake's unusual chemistry. Volcanoes, such as Ol Doinyo Lengai (about 20 km to the south), produce molten mixtures of sodium carbonate and calcium carbonate salts. The mixture moves through the ground via a system of faults and wells up in more than 20 hot springs that ultimately empty into the lake.

- While the environment is too harsh for most common types of life, there are some species that take advantage of it. Small, salty pools of water can fill with blooms of haloarchaea—salt-loving microorganisms that impart the pink and red colors to the shallow water. And when the waters recede during the dry season, flamingos favor the area as a nesting site, as it is mostly protected from predators by the perennial moat-like channels and pools of water.

- Lake Natron is a salt and soda lake in the Arusha Region of northern Tanzania. The lake is close to the Kenyan border and is in the Gregory Rift, which is the eastern branch of the East African Rift. The lake is within the Lake Natron Basin, a RAMSAR Site wetland of international significance.

- The lake is the only regular breeding area in East Africa for the 2.5 million lesser flamingoes, whose status of "near threatened" results from their dependence on this one location. When salinity increases, so do cyanobacteria, and the lake can also support more nests. These flamingoes, the single large flock in East Africa, gather along nearby saline lakes to feed on Spirulina (a blue-green algae with red pigments). Lake Natron is a safe breeding location because its caustic environment is a barrier against predators trying to reach their nests on seasonally forming evaporative islands. Greater flamingoes also breed on the mud flats.

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Figure 117: OLI image of Lake Natron in Tanzania, acquired on March 6, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens using Landsat data from the USGS)

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Figure 118: Detail image of Lake Natron (image credit: NASA Earth Observatory, images by Joshua Stevens using Landsat data from the USGS)

• April 19, 2017: The ice atop Greenland is not static. It slowly flows toward the coast and enters the ocean via outlet glaciers that ring the giant island. Petermann Glacier is one such "river" of ice. Like most glaciers that come in contact with the sea, Petermann has been known to periodically shed, or calve, icebergs. A new crack on the glacier has glaciologists watching Greenland's northwest coast closely. 97)

- The new crack, or "rift," is visible in these images acquired on April 15, 2017, with OLI (Operational Land Imager) on Landsat 8. The image of Figure 119 shows a wide view of the glacier, including its front—where the glacier's floating tongue meets the fjord's ice-covered sea water. The image of Figure 120 shows a detailed view of the rift.

- "Rifting and calving are normal," said Kelly Brunt, a glaciologist at NASA/GSFC ( Goddard Space Flight Center). "However, if this new rift crosses Petermann and calves a good chunk of ice, it would be the third such relatively large iceberg from this system in about seven years." It remains to be seen whether that will happen. Brunt points out that the rift currently appears to end at a feature running down the center of the glacier. "That's pretty typical," she said, citing similar occurrences on ice shelves in Antarctica.

- This new rift could eventually work its way through the feature in the center of the glacier. Or, the new rift could be met by an old rift—visible in the upper-right part of the detailed image—as it works its way from the northeast side of the glacier fjord. "But there is really no telling at this point," Brunt said.

- The day before the satellite images were acquired, Brunt flew with NASA's Operation IceBridge, an airborne science mission that conducts important surveys of snow and ice near Earth's poles. The flight had a number of goals, including an overflight of the recently discovered rift.

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Figure 119: OLI image of the Petermann Glacier in Greenland acquired on April 15, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens and Jesse Allen, using Landsat data from the U.S. Geological Survey)

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Figure 120: Detailed view of the new rift on Petermann Glacier (image credit: NASA Earth Observatory, images by Joshua Stevens and Jesse Allen, using Landsat data from the U.S. Geological Survey)

• April 16, 2017: This remote volcanic island has intrigued generations of scholars. Famed for its monolithic statues, Easter Island is shrouded in mystery. Its population, once sizable, collapsed (Figure 121). 98)

- "The clearest example of a society that destroyed itself by overexploiting its own resources," is how University of California Los Angeles geographer Jared Diamond once described it. But the island's history may not be as clear-cut as Diamond suggests. While scientists agree that broad-scale deforestation occurred here at some point, the verdict is still out on what exactly caused the downfall of the Rapanui people.

- Scholars do agree on one thing: the island once looked very different than it does today. Called Rapa Nui by its original inhabitants, it takes its English name from the day Europeans arrived: April 5, 1722—Easter Sunday. Dutch navigator Jacob Roggeveen reported a few thousand people living there at the time. He described this island, more than 3,000 km west of South America, as "exceedingly fruitful, producing bananas, potatoes, sugar-cane of remarkable thickness."

- Unbeknownst to Roggeveen, the indigenous population he encountered was just a fraction of its former size. Scholars estimate that between 15,000 to 20,000 people lived on Rapa Nui at the peak of its habitation. A thick cover of palm trees once shaded its hills, which are now fringed by low-lying vegetation.

- The extinct Terevaka volcano dominates the landscape, which also includes Poike and Rano Kau volcanoes and a number of smaller volcanic features such as lava tubes. Tufts of clouds pepper the sky overhead and a thick white outline along the island's southern edge indicates strong waves crashing against its shores. The Poike Peninsula, which juts out to the east, appears orange in places, a result of erosion exposing the brightly colored volcanic soil. The largest stand of trees, a eucalyptus plantation, was planted by people. Authorities hope reforestation efforts will help protect the island against the scouring wind.

- About 5,000 people live on Easter Island today, and thousands of tourists come to see the anthropomorphic "moai" statues each year. Amid strain from a rising population, the island faces challenges ahead. It has no sewer system and continues to draw on a limited freshwater supply.

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Figure 121: OLI on Landsat-8 captured this image of Easter Island on July 29, 2015 (image credit: NASA Earth Observatory image by Jesse Allen, using Landsat data from the USGS; story by Pola Lem)

• March 31, 2017: This month, 20 Landsat scenes were ingested by the USGS Hazard Data Distribution System to provide data for Charter activations: 99)

- Earthquake in Indonesia

- Cyclone Debbie in Australia

- Flood in Peru

The International Charter is a system that supplies free satellite imagery to emergency responders anywhere in the world. The Charter concept is this: a single phone number is made available to authorized parties providing 24/7 contact to a person who can activate the charter. Once activated, a project manager takes charge. The project manager knows what satellite resources are available, how to task them to collect data, and how to quickly analyze the collected data to create impact maps for first responders. These maps, provided to responders for free, often show where the damage is and where crisis victims are, allowing responders to plan and execute relief support.

You can think of the Charter as a one-stop-shop for impact maps—an essential resource, since in many cases satellite data are the only practical method to assess current ground conditions after a disaster.

• March 18, 2017: Several hundred lakes dot the expansive Tibetan Plateau. With the average plateau elevation exceeding 4,500 meters above sea level, its lakes are among the highest in the world.

- Puma Yumco in Lhozhag County is one of the larger lakes in southern Tibet. A small village along the eastern edge of the lake—Tuiwa—is reportedly one of the highest administered settlements in the world, sitting at an elevation of 5,070 meters. Tuiwa's economy centers on raising livestock (sheep and yaks), tourism, and textiles. Though there are fish in the lake, they are considered sacred and are not eaten by most Tibetans. - Lake Puma Yumco is 32 km long and 14 km wide and covers an area of 880 km2.

- Every winter, villagers herd thousands of sheep across the lake's frozen surface to two small islands, where the soil is more fertile and the forage is better in the winter.

- While the rhythms of life have remained largely unchanged in Tuiwa for many decades, researchers have used satellites to track subtle changes at Puma Yumco and other lakes throughout the plateau. One team has found that the number of lakes on the Tibetan Plateau has increased by 48 percent, and the surface area of the water has increased by 27 percent between the 1990s and 2015. For Puma Yumco, the size of the lake dropped a bit between the 1970s and 1990s, but has risen since then, primarily because of an increase in precipitation.

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Figure 122: Landsat-8 image of the mostly ice-coverd lake Puma Yumco on the Tibetan Plateau, acquired with OLI on March 13, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)

• March 17, 2017: Geographers who have studied the growth of China's cities over the past four decades tend to sum up the pace of change with one word: unprecedented. In 1960, about 110 million Chinese people—or 16% of the population—lived in cities. By 2015, that number had swollen to 760 million and 56%. -For comparison, the entire population of the United States was about 325 million people as of March 2017. 100)

- The surge in urbanization began in the 1980s when the Chinese government began opening the country to foreign trade and investment. As markets developed in "special economic zones," villages morphed into booming cities and cities grew into sprawling megalopolises. Perhaps no city epitomizes the trend better than Shanghai. What had been a relatively compact industrial city of 12 million people in 1982, had swollen to 24 million in 2016, making it one of the largest metropolitan areas in the world.

- For more than four decades, Landsat satellites have collected images of Shanghai. The composite images of Figures 123 and 124 show how cities in the Yangtze River Delta have expanded since 1984. Note how Suzhou and Wuxi have merged with Shanghai to create one continuous megalopolis (Figure 124).

- These "best-pixel mosaics" are made up of small parts of many images captured over five-year periods. The first image is a mosaic of scenes captured between 1984 and 1988; the second shows the best pixels captured between 2013 and 2017. This technique makes it possible to strip away clouds and haze, which are common in Shanghai.

- A 2015 World Bank report noted that 7,734 km2 in the Yangtze River Delta Economic Zone—which includes Shanghai, Suzhou, Wuxi, and several other cities—became urban between 2000 and 2010. That is an area equivalent to 88 Manhattans. During that period, population in that zone increased by 21 million people.

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Figure 123: China's metropolitan region of Shanghai observed with TM on Landsat-5 in 1984 (image credit: NASA Earth Observatory mosaics by Joshua Stevens and Jesse Allen using Landsat data from the USGS, caption by Adam Voiland)

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Figure 124: China's metropolitan region of Shanghai observed with OLI on Landsat-8 in 2017 (image credit: NASA Earth Observatory mosaics by Joshua Stevens and Jesse Allen using Landsat data from the USGS, caption by Adam Voiland)

• March 15, 2017: Along the western border of Virginia, two roughly parallel ridges—one of which is the backbone of Shenandoah National Park and the other part of George Washington National Forest—rise above the rolling lowlands of the Shenandoah Valley. Despite being just a few kilometers apart, the ridges show some marked differences (Figure 125). 101)

- With a perimeter of smooth, straight crests encircling a valley, Massanutten Mountain has the look of a flat-bottomed canoe. Shenandoah National Park's portion of the Blue Ridge, in contrast, has a more textured, irregular, and knobby shape; it looks more like a spine, with a dendritic network of gullies descending from its main crest.

- The two ridges look different due to distinct geological histories. The rock underneath Shenandoah National Park is largely igneous, meaning it was created when magma or lava cooled and solidified. Some of the oldest rocks in the park are granites that formed deep underground about 1.1 billion years ago when continents collided and pushed up a mountain range during the Grenville orogeny. Major outcrops of granite are located east of Shenandoah's highest crest and dominate peaks such as Old Rag and Mary's Rock.

- About 500 million years later, the tectonic tides had shifted. Instead of continents colliding, they were pulling apart. As the crust thinned and rifts formed, volcanoes sprang up and spilled lava across the land surface. This laid down layer upon layer of basalt, a type of igneous rock that cools quickly and thus has small mineral crystals. When exposed later to the high temperatures and pressures associated with the collision of tectonic plates, the basalt metamorphosized into metabasalt. This greenish rock, known in this area as the Catoctin Formation, makes up much of the Blue Ridge's highest crest, including peaks like Hawksbill, Stony Man, Mount Marshall, and Hightop.

- As the rift widened, it eventually connected with the ocean and was filled by a narrow, shallow sea. At its bottom, sedimentary rocks began to form as layers of sand, mud, and material from sea life began to rain down on the sea floor and become sandstone, shale, and carbonate rock.

- The landscape we see today was set up by one more cycle of continents slamming into each other—a collision between North America and Africa about 300 million years ago known as the Alleghanian orogeny. While building mountains that were once as tall as the Himalayas, the Alleghanian orogeny thrust the older igneous rocks (once the root of the Grenville range) upward and squeezed them into a curved bulge called an anticline, putting older rock layers quite close to the surface. The same collision squeezed and folded the nearby rocks of the Shenandoah Valley and Massanutten into a concave depression called a syncline that kept the youngest sedimentary rocks quite close to the surface.

- With the rock layers in place, erosion played the final role in sculpting the modern landscape. Rivers such as the Shenandoah's South Fork wore away relatively soft and weak types of sedimentary rock (the shale and carbonates) to create low-relief areas such as the Shenandoah Valley, Page Valley, and Fort Valley. Erosion-resistant, quartz-rich sandstone remained to give Massanutten Mountain its distinctive shape. To the east, the erosion-resistant igneous-based rocks of the Blue Ridge tower over Shenandoah Valley, Massanutten Mountain, and the rest of the Piedmont.

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Figure 125: OLI on Landsat-8 captured this natural-color image on Oct. 21, 2013 of the neighboring ridges. The Landsat image has been draped over a digital elevation model based on data from ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) on NASA's Terra satellite. The tops of both ridges are brown because fall colors had emerged in these cool, high-elevation areas (image credit: NASA Earth Observatory image by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)

• March 1, 2017: The Caspian Sea stretches about 1,000 km from Kazakhstan to Iran. In the north, temperatures are colder, and the water is fresher (less saline) and shallower. As a result, northern areas are more prone to freezing in wintertime. 102)

- The image of Figure 126 shows the northwestern Caspian where it meets western Kazakhstan. The brown areas are part of the Volga Delta. Just offshore, in the shallowest parts (only meters deep), a well-developed expanse of consolidated ice appears white. Farther offshore, a large field of old, hummocked, white and gray-white ice has detached. (When pieces of ice are pushed together, some ice is forced upward and downward into so-called ‘hummocks.') This ice is slowly drifting in a giant polynya which is covered by young, thin ice (nilas).

- The image of Figure 127 shows a detailed view of the nilas ice, which appears dark. Perhaps most notable, however, is the white, diamond-shaped piece of ice parked right in the middle. "This ‘island' of white ice is most probably a piece that detached from the ice field," said Alexei Kouraev, a scientist at the Laboratory of Geophysical and Oceanographic Studies (France). He notes that a likely point of origin is the "dent" of similar size in the boundary of the white ice (mid-right in the image of Figure 126).

- It might look like that ice diamond is on the move, cutting a path through the thinner cover. But it's more likely that the chunk of ice broke away from the thicker sea ice and became grounded—anchored to the bottom of the sea. The grounded ice (‘stamukha' in Russian) is not moving, according to Kouraev. Instead, the wind is pushing the thin ice around this grounded ice, creating a ‘shadow' of open water behind it.

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Figure 126: On February 4, 2017, OLI on Landsat-8 acquired natural-color images that beautifully demonstrate the variety of ice types that can form in the northern Caspian Sea (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS)

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Figure 127: Detail image showing grounded ice (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS)

• February 16, 2017: In the past few years, the title of "largest solar farm in the world" has been a rather short-lived distinction. For a period in 2014, the Topaz Solar Farm in California topped the list with its 550 MW facility. In 2015, another operation in California, Solar Star, edged its capacity up to 579 MW. By 2016, India's Kamuthi Solar Power Project in Tamil Nadu was on top with 648 MW of capacity. — As of February 2017, Longyangxia Dam Solar Park in China was the new leader, with 850 MW of capacity. 103)

- By January 5, 2017, solar panels covered 27 km2 of the Qinghai province in China (Figure 128). According to news reports, there were nearly 4 million solar panels at the site in 2017. The rapid expansion at Longyangxia coincides with China's fast-growing solar power sector. In 2016, China's total installed capacity doubled to 77 GW. That pushed the country well ahead of other leading producers—Germany, Japan, and the United States—to become the world's largest producer of solar power. However, those three countries (and several others) produce more solar power per person.

- It is unlikely that Longyangxia will remain the largest solar park in the world for long. A project planned for the Ningxia region in China's northwest will have a capacity of 2,000 MW when it is finished, Bloomberg reported.

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Figure 128: Landsat-8 image of the Longyangxia Dam Solar Park in China, acquired with OLI (operational Land Imager) on January 5, 2017 (NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)

• February 5, 2017: Image comparison of Silicon Valley observed by Landsat-1 in 1972 and by Landsat-8 in 2016.

By the middle of the 20th Century, Silicon Valley was already "on the map." This part of California's Santa Clara Valley drew its nickname from the raw material being used in the region's growing semiconductor industry. The area at the south end of San Francisco Bay became a magnet for scientists and for technology companies, so by the time the new Landsat-1 satellite caught a glimpse in 1972, urban sprawl had already replaced many of the valley's orchards. 104)

- While the two images of Figures 129and 130 don't show much change in the development of the landscape, they clearly show the development of the technology behind Landsat's satellite sensors. The false-color image of Figure 129 was acquired on October 6, 1972, with the MSS (Multispectral Scanner System) on Landsat-1; the natural-color image of Figure130 was acquired on November 18, 2016, by the OLI (Operational Land Imager) on Landsat-8.

- The most obvious improvement is the spatial resolution. Over the past 45 years, you have certainly noticed similar improvements in your electronics and imaging products. Better spatial resolution is the reason you can now see blades of grass in a televised football game and the fine lines on your face in a smartphone photo. In short, there is a lot more detail visible in the 2016 image than in the 1972 image. Both are displayed at a resolution of 45 m per pixel. The MSS image is relatively blurry, however, because the sensor's spatial resolution was just 68 x 83 m. The OLI image appears crisper because the instrument can resolve, or "see," objects down to about 30 m (15 m in some cases).

- The 2016 image also has better radiometric resolution, which means the newer instrument is more sensitive to differences in brightness and color. OLI uses 4,096 data values to describe a pixel on a scale from dark to bright. MSS used just 64. More data ultimately translates to the features in the image appearing smoother.

- Finally, the images are very different colors because the wavelengths (color) of light used to compose the images are from different parts of the spectrum. Both images were composed using red and green wavelengths. The image of Figure 129, however, uses near-infrared. False-color images like this one (MSS bands 6, 5, 4) are still produced with modern instruments because they are useful for distinguishing features such as vegetation, which appears red in the top image.

- In contrast, the OLI image does not show near-infrared (although the instrument does have the capability). Instead, it includes blue, a color that MSS was not designed to sense. This combination (OLI bands 4, 3, 2) produces a natural-color image similar to what your eyes would see.

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Figure 129: False color image of the Silicon Valley, acquired with MSS on Landsat-1 (former ERTS) on October 6, 1972 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the U.S. Geological Survey, caption by Kathryn Hansen)

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Figure 130: Natural color image of the Silicon Valley, acquired with OLI on Landsat-8 on Nov. 18, 2016 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the U.S. Geological Survey, caption by Kathryn Hansen)

• January 27, 2017: Mariners have long considered the waters off Africa's southern tip to be treacherous. After decades of failed attempts to navigate around the continent, Portuguese explorers took to calling one of its southerly promontories the Cape of Storms (it was later renamed the Cape of Good Hope). Cape Agulhas , Africa's southernmost point, is Portuguese for Cape of Needles. Historians think the name may be a reference to the needle-like rock formations and reefs along its coast. 105)

- The convergence of two ocean currents—one warm and one cold—in the shallow waters of Agulhas Bank produces turbulent and unpredictable waters. Warm water arrives from the east on the fast-moving Agulhas Current, which flows along the east coast of Africa. Meanwhile, the cooler, slower Benguela Current flows north along Africa's southwestern coast. That means navigating around the tip of South Africa requires mariners to sail against ocean currents on both sides of the continent.

- Eventually, they learned to stay well out to sea as they rounded the Cape of Good Hope and Cape Agulhas, but not before failed attempts had littered the area's reefs with wrecked ships. Even in modern times, shipwrecks are relatively common in the turbulent water of Agulhas Bank, where colliding currents regularly spin off rogue waves, eddies, and meanders.

- The instability and churning does have one benefit. As water masses stir the ocean, they draw nutrients up from the deep, fertilizing surface waters to create blooms of microscopic, plant-like organisms (phytoplankton) in the open ocean. The phytoplankton feed a robust chain of marine life that makes Agulhas Bank one of the richest fishing grounds in southern Africa.

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Figure 131: Landsat-8 image of Cape Agulhas, acquired by OLI (Operational Land Imager) on May 25, 2016 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from USGS)

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Figure 132: Suomi-NPP image of the South Africa Coast, acquired with VIIRS (Visible Infrared Imaging Radiometer Suite) on Jan. 4, 2017. The light blue swirl to the east of Cape Agulhas is a phytoplankton bloom in an area of cool, upwelling water (image credit: NASA Earth Observatory, image caption by Adam Voiland)

• January 4, 2017: Around Lake Thurmond, a large reservoir that straddles Georgia and South Carolina, something is not right with the birds. The lake is full of vegetation — particularly an invasive aquatic plant known as Hydrilla verticillata — and the area is full of birds that are distressed or dying. 106)

- Scientists have deduced that the birds are consuming a toxic cyanobacteria that lives on Hydrilla verticillata. The toxin causes a neurodegenerative disease and ultimately death in the water birds that ingest it. Eagles don't eat the plants, but they do prey on other birds. And many eagles have been found dead in the vicinity of Lake Thurmond.

- Hydrilla is tenacious. It grows in fresh water on every continent except Antarctica, and it has been found in at least 30 states in the U.S. The plant tolerates a wide range of temperature, nutrient, salinity, and turbidity conditions, and it can grow as fast as one inch per day. In Lake Thurmond, the plant can be found in 11,200 of the lake's 71,000 acres. The U.S. Army Corps of Engineers has used herbicides to temporarily control the plant's growth at boat ramps and swimming areas, but the impact on birds has encouraged investigation into treatments that would be more widespread and long-term.

- To help lake managers know where to focus management efforts, researchers at the University of Georgia developed a new way to assess the distribution of Hydrilla across the lake. The project was part of NASA's DEVELOP program, in which recent college graduates and early career professionals use NASA satellite observations to address an environmental or public policy issue. On October 18, 2015, the Operation Land Imager on the Landsat-8 satellite acquired an image (Figure 133) of Lake Thurmond. Blue overlays on the Landsat image show the extent of Hydrilla that month. The map is based on a model developed by the team, derived from Landsat-8 imagery and ground-based measurements.

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Figure 133: The OLI (Operational Land Imager) on Landsat-8 acquired this image of Lake Thurmond on Oct. 18, 2015 (image credit: NASA Earth Observatory, map by Jesse Allen, using Landsat data from the USGS and field observations and model data provided by Abhishek Kumar, University of Georgia; caption by Kathryn Hansen)

- Hydrilla grows best under specific water and light conditions. The model accounts for those parameters, represented in this series of four images (Figure 134). The most important factor is the water's transparency (top left). By lowering a Secchi disk into the water and measuring the depth at which it is no longer visible, scientists can estimate the water's transparency. In this map, the darkest orange areas are transparent and yellow areas are turbid (murky). Highly transparent regions are more suitable for Hydrilla.

Note: a Secchi desk, created by Angelo Secchi in 1965, is a plain white, circular disk 30 cm in diameter used to measure water transparency in bodies of water. The disc is mounted on a pole or line, and lowered slowly down into the water. The depth at which the disk is no longer visible is taken as a measure of the transparency of the water. This measure is known as the Secchi depth and is related to water turbidity.

- From the transparency measurement, the team derived other parameters, including the gradual loss of light at depth, or "light attenuation" (top-right), the percentage of light penetrating the column of water (bottom-left), and the maximum depth at which Hydrilla colonize (bottom-right). The new model integrates all of these parameters to determine the ideal locations for Hydrilla growth. According to the DEVELOP team, the model will "act as the foundation for later models intending to predict future locations in need of Hydrilla management."

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Figure 134: Model representation to estimate the water's transparency, light attenuation, etc. of the Hydrilla influence (image credit: NASA Earth Observatory, map by Jesse Allen, using Landsat data from the USGS and field observations and model data provided by Abhishek Kumar, University of Georgia; caption by Kathryn Hansen)

• December 21, 2016: At first glance, a river's course may seem fixed and unchanging. In truth, the path is a perpetual work-in-progress that, in some cases, can shift dramatically in a short span of time. This is especially true in the Moxos plains of northern Bolivia. In this tropical area east of the Andes, several rivers meander through a swampy landscape of savanna, forests, and ponds. While studying three decades of satellite imagery of this area, geographer Umberto Lombardo of the University Pompeu Fabra in Barcelona, Spain, noticed a particularly striking example of rapid change on a stretch of the Maniqui River. 107)

- OLI (Operational Land Imager) on Landsat-8 captured four false-color images between 2013 and 2016 (Figure 135). These images were assembled using red, green, and shortwave infrared light. The use of infrared light makes it easier to distinguish between silt-laden water and bare land. Water absorbs infrared light, while plants and bare earth reflect it. As a result, areas with standing water appear blue, while bare land appears light brown. Forests are bright green; savanna is pink-brown.

- "Images like this underscore how much and how quickly small- and medium-size rivers in this part of the world change," said Umberto Lombardo. Earlier research on larger rivers in the Amazon had suggested that big shifts in a river's path usually coincide with major flooding associated with La Niña, a cyclical cooling of ocean temperatures in the equatorial Pacific. But after systematically combing through three decades of satellite imagery and the paths of 12 small and medium-sized rivers in the southern Amazon, Umberto found no obvious connection to La Niña. Instead, he found that the course of small rivers tended to be in a regular state of change regardless of La Niña cycles.

- Umberto's findings have on-the-ground implications. Authorities should be prepared for the possibility that indigenous communities living along small rivers may have to be resettled if rivers shift in the coming years. Also, a planned road linking Villa Tunari to San Ignacio de Moxos may be destroyed or regularly flooded without careful planning, he explained.

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Figure 135: The image on the upper left shows the course of the river in September 2013, when it flowed in a northeasterly direction. By August 2014, it had broken through its right bank and began to spill into a swampy depression nearby. By September 2015, the river had broken out of its channel for a second time, this time flowing into a pond a few kilometers south of the first break. By July 2016, sediment deposited by the river had filled in most of the pond and the river was charting a more easterly path. Over those three years, vegetation growth started to cover up the channel that was full of water in 2013 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)

• December 2016: The in-orbit performance of Landsat-8 continues to be outstanding, currently acquiring around 740 scenes per day, and several Antarctic and Arctic off-nadir requests have recently been fulfilled with no impact on routine imaging. Operational and data processing solutions have been implemented to mitigate the impact of the anomaly in Landsat-8's TIRS (Thermal Infrared Sensor) SSM (Scene Select Mirror). All affected data have been reprocessed and nominal TIRS data collection and processing have been restored. 108)

- Landsat MSS (Multispectral Scanner) Improvement Plan: There are efforts to improve the Landsat MSS archive, including MSS reflectance-based calibration, adjustment of minimum and maximum radiance values to minimize saturation, updating of gain-trend models, and derivation of a bulk correction factor to minimize attitude bias. Overall, the processing and model updates being implemented will help increase the number—as well as the geometric and radiometric quality—of MSS Level-1T scenes. Currently, the plan is to begin collection-processing for MSS in the summer of 2017.

- Landsat-8 TIRS Reprocessing Status: Ron Morfitt reported of how image measurements from geometric calibration are being used to correct the SSM issue, which caused TIRS images to be shifted out of alignment with OLI by as much as 500 m. Overall, the new TIRS processing model is working well, with registration accuracy of around 20 m when telemetry and calibration data are available.

- Matt Montanaro and Aaron Gerace provided an update on the stray-light correction algorithm being developed for TIRS on Landsat-8. Montanaro explained how stray light entering the optical path from outside the direct field-of-view is causing significant nonuniform banding in the TIRS bands 10 and 11. The approach to correct this issue uses TIRS data to estimate the out-of-view signal, based on in-scene statistics. Initial validation results based on comparison with underpass data from the MODIS (Moderate Resolution Imaging Spectroradiometer) on Terra are encouraging. Although more testing is planned over land and low-temperature regions of Antarctica, the LST (Landsat Science Team) recommended moving toward operational implementation of the developed stray-light correction algorithm. The current plan is to implement the algorithm during Collection 1 reprocessing, which is slated to begin in the fall of 2016.

The NASA–USGS Landsat mission and European Space Agency's Sentinel-2 missions have collaborated to produce a Harmonized Surface Reflectance Product. The data products from these missions represent the most widely accessible medium-to-high spatial resolution multispectral satellite data in the world. Following the launch of the Sentinel-2A satellite on June 23, 2015, the potential for synergistic use of the two sources creates unprecedented opportunities for timely and accurate observation of Earth status and dynamics. Thus, harmonization of the distributed data products is of paramount importance for the scientific community. Activities to harmonize data products are on their way, yet more coordination is needed to allow the majority of users to easily and effectively include both data types into their work.

Table 5: New harmonized Landsat–Sentinel reflectance product available

• December 14, 2016: Earth's ice is changing, from mountain glaciers to ice sheets to ice shelves. For the most part, land-based ice has been shrinking, and the very definition of a "glacial pace" has changed within our lifetimes. Now researchers have the tools to see those changes every few weeks and at scales as small as 5 meters — the technique is known as feature tracking. 109) 110)

- Using freely available data from the Landsat 8 satellite, scientists are working to provide a near-real-time view of every large glacier and ice sheet on Earth. A group of scientists from the National Snow and Ice Data Center (NSIDC), the University of Alaska–Fairbanks, the University of Bristol, and the Jet Propulsion Laboratory (JPL) have started the GoLIVE (Global Land Ice Velocity Extraction) project , a NASA-funded effort to better understand how ice flow is changing worldwide.

- "We are now able to map how the skin of the ice is moving," said Ted Scambos, senior research scientist at NSIDC and lead for the GoLIVE project. "From now on, we're going to be able to track all of the different types of changes in glaciers. There's so much science to extract from the data." The effort was described at the 2016 fall meeting of the American Geophysical Union.

- Evidence strongly suggests that the loss of ice from glaciers and ice sheets has been the largest contributor to sea level rise over the past three decades, with waters rising at a global average rate of 3.3 mm/year. By examining changes in ice flow in combination with data on ocean and atmospheric changes, the researchers hope to determine what causes ice masses to change and how much ice will flow into the ocean. The satellite-based approach is particularly valuable in remote landscapes, where ground- and airplane-based observations are expensive, dangerous, and intermittent.

- In Alaska and Canada's Yukon Territory, for instance, most glaciers are so remote that speedup events can go unnoticed for months until a pilot flies over the region and reports disrupted ice, notes Mark Fahnestock of the University of Alaska. The map of Figure 136, based on an analysis by GoLIVE investigators, shows the velocity of ice in southeastern Alaska near Malaspina and Hubbard glaciers.

- "By measuring ice flow all the time, we can identify a surge as it starts, providing an entirely new way to follow this phenomenon," Fahnestock said. "We can also follow large seasonal swings in tidewater glaciers as they respond to their environment. Scientists need to see all of this variability in order to identify trends."

- Automation has been key to this ice velocity mapping effort. Landsat 8 collects images of roughly 700 sunlit parcels of the planet every day; over the course of 16 days, it observes the entire land surface of Earth in multiple visible and infrared wavelengths. This means scientists can view changes in the same spot on Earth every 16 days (or 32, 48, 64, etc., as cloud cover allows).

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Figure 136: GoLIVE map of Landsat-8 OLI data showing the velocity of ice in the southeastern Alaska near the Malaspina and Hubbard glaciers (image credit: NASA Earth Observatory, images Landsat-derived ice velocity data courtesy of Alex Gardner, NASA/JPL, California Institute of Technology and ASTER GDEM data from the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team)

- It also means there is a huge amount of data to process and analyze. From 2013 to 2016, Landsat-8 collected thousands of images from Antarctica alone. The globes of Figure 137 show how many times Landsat-8 passed over a given icy parcel in 2015 alone. As many as 150 to 200 images were collected over the brightest yellow and green areas, while purple areas had just a handful of useful images because of frequent cloud cover and fewer orbital passes. Due to the nature of the satellite's polar orbit, areas in the far north and south can be imaged more frequently (when there is sunlight).

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Figure 137: Observation frequency of the polar regions of Earth, Antarctica (left) and the Arctic region (right) by the Landsat-8 satellite (image credit: NASA Earth Observatory, images Landsat-derived ice velocity data courtesy of Alex Gardner, NASA/JPL, California Institute of Technology and ASTER GDEM data from the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team)

- The imaging system on Landsat-8 is far more sensitive than previous Landsat sensors, distinguishing far more subtle differences in shading and surface texture. The GoLIVE team has written software that allows researchers to follow these subtle features, like bumps or dune-like patterns on ice surfaces. By comparing images of the same location on different dates, researchers can track individual features and determine the speed of the surface flow. "The question is: how sensitive are these ice sheets to changes in the atmosphere and the ocean?" said Alex Gardner of JPL. "We could wait and see, or we could look to the past to help inform what is most likely to happen in the future."

- Gardner has been looking closely at Antarctica, with ice velocities represented in the map of Figure 138. He is working to combine the new Landsat 8 ice-flow data with prior maps of the continent's glacier flow in the hopes of understanding decadal changes across the entirety of the ice sheet. Almost 2,000 km3 of ice flows into the Southern Ocean from Antarctica each year.

- Twila Moon, an ice scientist at the University of Bristol, is using the global maps to expand her research in Greenland. With the new database, she can study the movements of more than 240 glaciers, nearly all of the outlets from the ice sheet. And with Landsat-8 making an overpass every 16 days, she has an opportunity to detect seasonal changes and cyclical patterns.

- While most glaciers speed up in the warmer summer months, Moon has found several that slow down dramatically in the mid- to late-summer. "We can group these glaciers by looking at the similarities in their behavior," Moon said. "It's providing an opportunity to get at the underlying drivers of why they change." With measurements of what the seasonal shifts do to glacier speed, scientists can extrapolate what might happen to those glaciers as global temperatures continue to climb.

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Figure 138: GoLIVE map of Landsat-8 OLI data showing the velocity of ice in Antarctica in 2015 (image credit: NASA Earth Observatory, images Landsat-derived ice velocity data courtesy of Alex Gardner, NASA/JPL, California Institute of Technology and ASTER GDEM data from the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team)

• November 19, 2016: In Landsat images of the Tafilalt oasis of southeastern Morocco, dozens of thin lines run across the desert from the Anti-Atlas mountains toward the town of El Jorf. These are qanats (khettaras in Moroccan)—ancient underground water channels designed to transport water down slopes without active pumping. 111)

- Most wells involve digging a vertical shaft downward until it reaches the water table, and then hauling or pumping the water up to the surface. Qanats consist of gently inclined horizontal tunnels dug into sloping terrain. When the horizontal tunnel hits the water table, gravity causes water to simply flow downhill in the channel toward outlets at the base of the slope.

- While the channels that convey the water lay below the surface, the access shafts used for construction and maintenance are visible above ground. The access shafts are often dug near or through large earthen mounds made of material excavated during construction of the vertical shafts and channels.

- From above, these earthen mounds form long chains that appear as relatively continuous lines at Landsat's 30 m/pixel spatial resolution.


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Figure 139: The OLI (Operational Land Imager) of Landsat-8 acquired this image of several qanats leading toward El Jorf on July 2, 2016 (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the USGS)

• October 29, 2016: Kiruna, the largest underground iron ore mine in the world, has been in operation since 1900. But recent years have brought change for the residents of the nearby town. In the coming decade, the 23,000 people and their homes and businesses will move three kilometers away. 112)

- Resource extraction is crucial for the town's existence and economic wellbeing. But the steady development of mine shafts continues to weaken the ground there. In 2004, the mine's operator, the LKAB (Luossavaara-Kiirunavaara Company), announced that development of the mine has threatened the structural integrity of the town's buildings. Some of them, including Kiruna's historic red church, will be taken apart and reassembled at the new location.

- OLI (Operational Land Imager) on the Landsat-8 satellite captured this image (Figure 140) of the Kiruna mine, town, and nearby airport on October 10, 2016. The green vegetation is marbled with yellow, likely the result of birch forests and deciduous shrubs changing color. A dusting of snow whitens some hilltops in the image. The Sun's low angle on the southern horizon casts long shadows on the north sides of the hills.

- The Kiruna orebody is one of the world's largest magnetite-apatite deposits. Sweden, the biggest iron producer in Europe, owes its reserves to volcanic activity many thousands of years ago, according to a paper in Nature. 113)

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Figure 140: Image of the Kiruna Iron Ore Mine and the town of Kiruna, acquired on Oct. 10, 2016 with OLI on Landsat-8 (image credit: NASA Earth observatory, image by Joshua Stevens using Landsat data from the USGS)

• October 6, 2016: A special issue of the journal Remote Sensing of Environment details the improved capabilities and mission role of Landsat 8, the latest satellite in the world's longest, continuous program of Earth observation. 114) 115)

- Now available to the public, the compendium of 23 published papers describes how Landsat 8 is the most capable of the seven operational Landsat missions and highlights how Landsat 8's enhanced performance and new capabilities enable better science and research results. The selected articles cover topics from how the instrument's performance gives higher quality electromagnetic measurements to how its improved geometry allows for the tracking of moving ice sheets.

• October 14, 2016: Glaciers cover 11% of Iceland's landscape, the largest being the Vatnajökull – known as the Vatna Glacier in English – which at 8000 km2 is also the largest glacier in Europe (Figure 141). Up to 1 km thick, the Vatna ice cap has about 30 outlet glaciers – many of which are retreating owing to warming temperatures. 116)

- A number of volcanoes lie underneath this ice cap, including the infamous Grímsvötn, which caused disruption of northern European air traffic in recent years following eruptions and the spread of ash plumes. This volcano is visible as a black arc on the central-left side of the image. In 1996 an eruption of Grímsvötn caused some of the overlying glacial ice to melt. The water then broke out of the ice cap and flooded the nearby outwash plain, causing millions of dollars' worth of damage.

- In the upper-central part of the image, in an area known as the Holuhraun lava field, we can see a bright orange strip of lava through a crack in the surface. This type of elongated volcanic eruption is known as a fissure vent, and usually occurs without any explosive activity.

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Figure 141: Landsat-8 false color image of the Vatnajökull glacier (in blue) and the Holuhraun lava field on Iceland's southeastern coast, acquired on Sept. 6, 2014 (image credit: USGS, ESA)

• September 21, 2016: Today the Landsat project celebrates the 50th anniversary of Secretary of the Interior Stewart Udall's 1966 announcement of "Project EROS (Earth Resources Observation Satellites)". Udall's vision paved the way for what we today know as Landsat, and gave the world the confidence to create satellite systems to monitor our planet with a new perspective. 117)

- Secretary Udall's vision to create "a program aimed at gathering facts about the natural resources of the Earth from earth-orbiting satellites" was an idealistic goal at the time, but on July 23, 1972, the first Earth Resources Technology Satellite (ERTS) was launched from Vandenberg Air Force Base in California. In 1975, it was renamed Landsat 1. Since then, six more Landsat satellites have followed, collectively capturing millions of images of Earth, and creating an impressive archive that has been available at no charge since 2008.

• September 21, 2016: In late July 2016, an illegal campfire gave rise to the Soberanes fire that grew near the California coast between Monterey and Big Sur. The wildfire continued burning in the Los Padres National Forest through August. As of late September, it was still not fully contained. The Landsat-6 satellite acquired the image of the area on September 15, 2016 (Figures 142 and 143, same image with different spectral bands). 118)

- When these images were acquired, the fire had burned 435 km2 and was 55 percent contained. Some of the smoke from the fire hung low in the local valleys, most notably on September 18 after a temperature inversion set in. An air quality report called the air "unhealthy" at sites near the fire including Carmel Valley, Cachagua, and Tassajara.

- Not all of the smoke, however, stayed local. The Ozone Mapper Profiler Suite (OMPS) on Suomi-NPP (Suomi National Polar-orbiting Partnership) satellite observed smoke fanning out to the southwest over the Pacific Ocean and inland to the east and northeast.

- By September 20, the fire was 71 percent contained and had burned 490 km2. New evacuations were in place after winds carried embers across the containment line and started a new "spot" fire measuring less than 1 km2.

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Figure 142: False color image of OLI on Landsat-8 which combines shortwave infrared, near-infrared, and green light to provide a clear view of the charred landscape (dark red). The main area of active fire (bright red), which is nestled amid unburned vegetation (green), is small by comparison (NASA Earth Observatory, image by Jesse Allen using data from USGS)

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Figure 143: OLI image on Landsat-8 in in natural color. The burn scar in this image is brown; the surrounding unburned forest is dark green. The burn scar is subtle in natural color, so the clearest indication of the fire is the rising plume of smoke (NASA Earth Observatory, image by Jesse Allen using data from USGS)

• August 25, 2016: This week marks the 100th anniversary of the National Park Service. We are celebrating this milestone with a gallery of images. On most summer days, a trip to North Carolina's Outer Banks means a peaceful day at the beach soaking up the sun and playing in the waves. But there is evidence all around that this beach is not always so serene. The very existence of these barrier islands is due to the power of wind and water. 119)

- Figures 144 and 145 show a segment of the barrier islands in the vicinity of Cape Hatteras National Seashore. The park's origins date back to the 1930s, when Congress authorized the creation of this first "national seashore park" in the United States. It wasn't until 1953 that the National Park Service acquired enough land to establish the park, and another five years before facilities were in place and the park could formally open.

- Stanley Riggs, a scientist who in the mid 1960s developed the coastal and marine science program at East Carolina University, pointed out some notable features. Skinny parts of the island chain, which appear mostly white without any green vegetation, are "simple" barrier islands. These areas are generally eroding and thinning. The shoreline continues to recede and weak spots form, at which point water from the Atlantic Ocean can break through and form an inlet.

- The year that these images were acquired was a relatively quiet one for storms. In other years, however, hurricanes and nor'easters have opened multiple inlets in a single season. Within a year or two after an inlet opens up, a flood tide delta typically forms behind it and continues the natural cycle of island rebuilding. That cycle is influenced, however, by the human development and maintenance of structures such as highway 12—the road that runs like a spine down the length of North Carolina's barrier islands.

- In contrast, the green vegetated areas along the islands are usually wider and older "complex" barrier islands. The second image shows a detailed view of one such area at Cape Hatteras. In this view, you can see parallel east-west ridges that have built up over time behind the tip of the cape. The relative height of the dunes and distance from the ocean have allowed forests to grow. These are also the more protected and therefore urbanized parts of the island chain.

- Still, the wind and waves take a toll, eroding the east-facing shoreline of the cape and moving sand southward to Diamond Shoals. This huge pile of sand just below the ocean surface extends for about 16 km — and that's small compared to the shoals extending out from other capes in North Carolina, which Riggs calls the "graveyards of the Atlantic" for the hazard they have long posed to ships.

- Areas west of the islands do not escape the forces of nature. Parts of the mainland submerged by rising sea levels have transitioned to sandy shoals, which appear as various shades of white on the west side of Pamlico Sound. These sandy areas have a depth of 3 m or less. The center of Pamlico Sound is darker and deeper, about 6 m. Then, toward the eastern side of the sound the water becomes shallow again as you approach the barrier islands, an area known as Hatteras Flats.

- Storms have even built a mini barrier island on Hatteras Flats—miles out in the sound, but walkable from almost anywhere on the main barrier islands. The flats support rich grass beds, marshes, and nutrient beds that feed the mid-Atlantic fisheries. The park area as a whole is "an incredible habitat for wildlife," Riggs said. Birds overwinter on the islands, and sea turtles nest on its beaches.

- The islands in their natural state are resilient. But storms and coastal change can be hard on infrastructure and the roads that visitors use to access the park. "A little rise in sea level and next series of storms could do a number on that highway out there," Riggs said. "There will always be a national seashore—you just might have to get there by boat."

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Figure 144: These islands have been in flux long before the park was established, and they continue to change today. These images show a moment in time on June 7, 2015, captured with the Operational Land Imager (OLI) on the Landsat-8 satellite. Various stages of island evolution—from build-up to erosion—are all visible along the island chain (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS)

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Figure 145: Landsat-8 detail image of Cape Hatteras (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS)

• July 4, 2016: The Greater Boston area, encompassing the eastern third of Massachusetts, is a playground for the American history enthusiast. Sites important to the American Revolutionary War are interspersed throughout the modern-day metropolitan region; the view from space shows how preserved historic landscapes coexist with the new (Figures 146 and 147). 120)

- In December 1773, American colonists protested British taxation and regulation by dumping hundreds of chests of tea overboard from merchant ships into Boston Harbor. The series of events that followed—including the march of British troops westward to confiscate a cache of weapons—culminated in battles in the towns of Lexington and Concord. The battles marked the start of the Revolutionary War in April 1775.

- The conflicts near Concord and Lexington are memorialized at Minute Man National Historical Park, shown in detail in the second image. By the 1950s, the area grew crowded with roads and suburban growth. Gas stations, restaurants, and an airfield all cropped up in an area that was once farmland and open fields. The park was established in 1959 in part to protect the historic landscape from further development.

- Route 2A cuts through the park and Hanscomb Field still stands as a nearby reminder of 20th Century modernization. In 2003, the National Trust for Historic Preservation listed Minute Man National Historical Park and nearby historic sites as one of the 11 most endangered historical places in the United States.

- Steps have been taken to restore historic structures and to return the landscape to one that more closely resembles the look and feel of the 18th century. For example, many power lines have been removed; stone walls have been rebuilt; and agricultural fields have been opened up. In 2009, the park boundaries grew to include the now-restored Barrett House and its surrounding farm, an important landmark of the war.

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Figure 146: Overview of the Boston region from Boston Harbor to National Historical Park, acquired with OLI of Landsat-8 on October 15, 2015 (image credit: NASA Earth Observatory, image by Jesse Allen using Landsat data from the USGS)

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Figure 147: Detail map of the Minute Man National Historical Park acquired with OLI of Landsat-8 on October 15, 2015 (image credit: NASA Earth Observatory, image by Jesse Allen using Landsat data from the USGS)

• June 15, 2016: Glacial Change in Montana's Blackfoot-Jackson Basin is shown in two Landsat images of 1984 and of 2015. At the current rate of glacier melting, a study arrived at the year 2030, in which the Montana's Glacier National Park will likely be glacier-free. 121)

- Scientists arrived at the year 2030 through a simple geospatial model running on software from the 1990s. The model depicted the change expected to occur to glaciers in the Blackfoot-Jackson basin (shown above), an area that contains the largest concentration of glaciers in Glacier National Park. At the time of the study, glaciers in the basin were also among the park's largest. "It was conjectured that if the largest glaciers disappeared by 2030, most of the smaller ones would probably disappear too," said Daniel Fagre, a research ecologist for the Northern Rocky Mountain Science Center of the U.S. Geological Survey.

- The model took into account the basic parameters, such as warmer summer temperatures and meteorological snowfall. It did not account for more complicated factors such as "snow avalanching" and "snow scouring"—things that can keep a small glacier alive. But despite its simplicity, the model painted an accurate, if broad, picture of the situation: the shrinking of the ice in Glacier National Park is real and happening fast. " People focus too much on the date, but the basic story is still true," Fagre said. "These glaciers will be more or less gone in the next several decades."

- Before these images were acquired, glaciers in the basin had already decreased from 21.6 km2 in area in 1850 to just 7.4km2 in 1979. The Blackfoot and Jackson glaciers once ran together, as a photograph from 1914 shows; by 2009, they had retreated into separate valleys.

- Other phenomena have left their mark on the landscape. In the 2015 image, a burn scar from the Thompson fire is visible southeast of Blackfoot glacier. As global and regional climate continues to warm, the frequency of fire in the park could increase.

- For now, the clearest reflection of climate change is the ice. Year-to-year weather variations matter somewhat, but most of the loss is a response to decadal trends in warming. As we approach 2030, most of these glaciers will be "small insignificant lumps of ice on the landscape," Fagre said. "These tiny remnants could last 10 to 15 years past that time if they are in sheltered places, but the park will no longer really have viable glaciers."

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Figure 148: Landsat-5 TM (Thematic Mapper) image of the Montana's Glacier National Park, acquired on August 17, 1984 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS)

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Figure 149: Landsat-8 OLI (Operational Land Imager) map of the Montana's Glacier National Park, acquired on August 23, 2015 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS)

• May 31, 2016: The Rio Grande is a major North American river, flowing more than 3,000 km from Colorado to the Gulf of Mexico. In 1978, the U.S. Congress designated 315 km of the river along the U.S.-Mexico border as a "wild and scenic river." The designation protects the river's ecosystem and its natural free-flowing state. 122)

- Along the 134 km of the Lower Canyons area, you will find yourself in a truly remote river wilderness. This remoteness is likely part of the reason that a relatively small number of people visit the area compared to other sites managed by the National Park Service. Paddlers visit the Lower Canyons of the Rio Grande take advantage of this free-flowing river, maneuvering water ranging from calm to rapid as they float between canyon walls rising up 150 to 450 m. But it can take at least five days to emerge from a paddling trip through this part of the river.

- Despite its remoteness, the river is not immune from human influence. Dams upstream can affect the river downstream, changing the natural flooding cycles that normally shape the banks and build habitat for plants and animals. Drought can also affect the Rio Grande. In 2003 and 2015, portions of the river near El Paso ran dry.

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Figure 150: The OLI (Operational Land Imager) of Landsat-8 acquired this image of the river on March 21, 2016. It shows a segment of the protected river east of Big Bend National Park. In these "Lower Canyons," layers of rock were laid down about 100 million years ago and then shaped by lifting, folding, and faulting. The river cut through these rocks to form the steep walled canyons visible today (image credit: NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. Caption by Kathryn Hansen)

• May 2016: Preparation for Emergency Conjunction Avoidance Maneuvers: The Landsat FOT (Flight Operations Team) has developed an E-RMM (Emergency -Risk Mitigation Maneuver) procedure, a combination of quick-build spacecraft command buffers and computer scripts, using specifically-defined and human-readable formats, to allow an engineering team the ability to quickly perform complex, critical spacecraft operations. 123)

- So far, Landsat-8 has been collecting nearly 75% more science images per day than originally designed, improving the cost-benefit ratio and expanding science coverage to nearly every day-lit opportunity through most of the year.

- The improved science collection tempo is enabled largely by the use of small, general-purpose command buffers in spacecraft flight software, called ROS (Relative Operations Sequences). ROS files (also called binaries, loads, or buffers), are small, temporary computer files containing a series of commands separated by defined delays, so that a single command can start the buffer and its contents will execute in a set order with predictable timing.

- The ROS loads can be built quickly and easily on the ground for any purpose, and one or more can be uplinked on each spacecraft contact as necessary. The addition of a special ground software script that begins the load process onboard at a specific time also allows the relative timing of the commands to be matched to wall clock times for precise execution of these buffers. Currently, ROS buffers are used for spacecraft science recorder file maintenance, automatically resetting balky equipment, and certain types of troubleshooting and fault recovery.

- The original operations concept at launch was to anticipate the need for a burn at the earliest warning, monitor until a few days before TCA (Time of Closest Approach), and evaluate the need for a burn around two days ahead of the Julian day when it would be executed, though the specific commit time was driven by the conjunction geometry and the TCA relative to the change of Julian day. A general spacecraft command load would be purpose-built to include the burn activities, including suspending science collections for the duration, and when uplinked we would be committed to performing at least part of the burn activities and losing the science collections. In preparing this early, we also committed to using best-guess information about the ΔV requirement; future changes to the ΔV would involve manual commanding and the risk of sending incorrect values.

- As ROS buffers became more widely used in day-to-day operations, a new process was developed to quickly build a special-purpose, propulsive-maneuver command sequence that could be used to avoid orbital debris. The burn concept was termed an Emergency Risk Mitigation Maneuver (E-RMM); it allows the burn to take place as soon as the new orbit can be screened for other conjunctions, instead of waiting for a new spacecraft command load to be built, and therefore provides a more responsive solution in a severely restrictive timeline. The special-purpose buffer includes all the commands the FOT normally inserts into the load for a standard orbit adjust maneuver (e.g., enabling burn software, setting thruster on-time duration, and so on) that can be uplinked, changed, rebuilt, and re-uplinked several times if necessary, and that could be started or stopped with minimal impact to the science imaging schedule. This buffer is built using a special computer script that takes in "knowledge" of when the buffer will start and codes in appropriate delays so that, once the buffer is started at the planned time, key events will happen at the desired wall clock time.

- As a result, FOT can plan and re-plan a burn quickly, uplink and execute the ROS buffer in a single contact, and reduce the time and uncertainty of burn planning from several days to around six hours. The use of a buffer that runs independently of the spacecraft's main command load also offers the ability to work around change-of-day and change-of-year boundaries; a clean break in science data collection from which the FOT can easily recover; and the ability to verify burn parameters quickly, maximizing the abort window.

- As of spring 2016, the Landsat-8 FOT has executed two demonstration burns and a DMU (Drag Make-Up) using E-RMM products. Though we have not executed an actual E-RMM burn on-orbit using this process, our ability to do so has saved team workload and science data collection on at least six occasions through the ability to wait and see how the conjunction event develops. As the low-earth orbit regime will continue to be polluted by space debris for the foreseeable future, the flexibility of burning correctly, and only when necessary, will provide significant benefits to cost, risk, and science for Landsat-8 and its successors.

• May 10, 2016: If a volcano erupts and there is no one there to see it, did it really erupt? Before the advent of satellites and seismic monitoring, volcanic eruptions in distant places would mostly go unnoticed unless they were absolutely extraordinary. Today, scientists can pick up signatures of events occurring far from any human observers.

- That was the case in late April and early May 2016 when satellite sensors detected signs of a volcanic eruption in the far South Atlantic Ocean between South America and Antarctica. Mount Sourabaya, a stratovolcano on Bristol Island, appeared to be erupting for the first time in 60 years. There are no human residents of the island, which is almost always covered in glacial ice and snow. 124)

- OLI (Operational Land Imager) on Landsat-8 acquired the Bristol Island image of Figure 151 using a combination of shortwave-infrared, near-infrared, and red light (Landsat bands 6-5-4) that helps detect the heat signatures of an eruption. The image shows the heat signatures (red-orange) of what is likely hot lava, while white plumes trail away from the crater. The band combination makes the ice cover of the island appear bright blue-green.

- With a roughly rectangular shape of 12 x 14 km, Bristol Island is one of the largest in the South Sandwich Islands chain. The highest peak on the island stands 1100 m above sea level. Due to the remote location and the lack of landing sites amidst its ice cap, the stratovolcano is one of the least studied in the world. The last known eruption on Bristol Island was reported in 1956.

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Figure 151: OLI on Landsat-8 acquired this false-color image on May 1, 2016 (image credit: NASA Earth Observatory, image by Jesse Allen using data from USGS)

• April 30, 2016: A key shipping route through Egypt recently received a major overhaul. The Suez Canal—the first artificial waterway connecting the Mediterranean Sea and the Red Sea—initially opened in November 1869 after 10 years of construction. The "New Suez Canal" opened in 2015 after just one year of construction. 125)

- Since its inception, the canal has been an economically important shortcut between Europe and Asia. The passage through Egypt meant cargo ships no longer had to sail around the southern tip of Africa. Expansion projects over the decades have helped the canal accommodate more traffic and larger ship sizes. The latest effort not only widened and deepened areas along the existing canal, it also added a 35 km new canal that runs parallel to the old one.

- The older single-lane canal, including the north and south access channels, spans 193 km from Port Said on the Mediterranean Sea to the Port of Suez on the Red Sea. Follow the canal south about 76 km from Port Said, and you reach the city of Ismailia, centered in these images. At km 95 you reach Great Bitter Lake, visible at the bottom of these images. The lake is one of the canal's designated holding and passing areas. The time spent waiting in these bypass areas was eased with the addition of the new parallel canal, visible in the right image.

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Figure 152: OLI (Operational Land Imager) on Landsat-8 acquired these images of the canal's mid-section, where the project was focused. The left image shows the area on August 6, 2014, around the start of the expansion; the right image was acquired April 5, 2016, about nine months after the expansion was complete (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS)

• April 12, 2016: Toward the end of April, reprocessing efforts will begin for Landsat-8 OLI/TIRS scenes acquired from January 1 to March 31, 2016 along with data acquired during April, to create nominal Level-1 products containing valid TIRS data. Additionally, all future Landsat-8 scenes will contain valid TIRS data—however, newly processed data will use preliminary estimated position information from the TIRS SSM (Scene Select Mirror). 126)

- To compensate for not having TIRS SSM encoder information to indicate where the TIRS sensor is pointing, a new algorithm has been developed to provide estimates for the TIRS SSM encoder position. Note: SSM is also referred to as "Scene Select Mechanism".

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Figure 153: Diagram of the TIRS telescope and focal plane with the elements contributing to the spectral response labeled (image credit: NASA)

• April 6, 2016: In the early 1600s, the English established their first permanent settlements in North America at Jamestown, Virginia, and then Plymouth, Massachusetts. But those were not the first attempts to colonize America. In the late 16th century, settlers started a settlement on Roanoke Island, North Carolina. The disappearance of that colony remains a mystery today. 127)

- On June 7, 2015, OLI (Operational Land Imager) on Landsat-8 captured this natural-color image of the northern half of Roanoke Island, which is tucked between North Carolina's mainland and barrier islands. Fort Raleigh National Historic Site, which was established 75 years ago on the island's northern shore, spans aquatic habitats, swamp forests, and a rare maritime evergreen forest. Fort Raleigh also preserves relics of England's first attempts to colonize the New World, as well as the history Native Americans, European Americans, and African Americans on Roanoke Island.

- The events that took place within the boundaries of the historic site are subject to debate. Initially, archaeologists thought that the northern part of the island was the main settlement of more than 100 English colonists who arrived in 1587. They based their claim on some European artifacts found within the historic site. But the artifacts were not indicative of habitation, and some experts speculate that the main settlement and fort were located farther south near Shallowbag Bay. Here, ships would be sheltered and settlers could more easily offload supplies.

- In any case, the island's entire settlement was found deserted in 1590. The story of the so-called "Lost Colony," as interpreted by playwright Paul Green, has been performed since 1937 at Fort Raleigh's beachfront theater, visible as a small tan fleck near the shoreline. Researchers have theorized that some of the settlers relocated about 80 km south to Hatteras Island. Other clues uncovered in 2012 from an old map suggest that some colonists might have ventured inland.

- At Fort Raleigh, one can also learn about the culture of the Algonquians, the natives who long inhabited the area, cultivated the land, and fished in the sounds long before Europeans arrived. Or read about a colony established centuries later during the Civil War, when more than 1,000 people—former slaves and families—found refuge on Roanoke.

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Figure 154: OLI image of the northern half of Roanoke Island, along with the Fort Raleigh National Historic Site, acquired on June 7, 2015 (image credit: NASA Earth Observatory, image by Jesse Allen, using Landsat data from the USGS)

• March 30, 2016: Just 25 km northwest of downtown Atlanta, a long parcel of undeveloped forests and hills cuts through the metropolitan suburbs (Figure 155). But the site was not always so peaceful. During the summer of 1864, the 2,965 acres (1,200 hectare) of this Civil War-oriented national park teemed with tens of thousands of men, horses, and cannons. 128)

- The hilly terrain played a role in the battle that commenced on June 27, 1864. Confederate forces had established an arc-shaped line that included Kennesaw Mountain, Little Kennesaw Mountain, Pigeon Hill, and areas to the south. A head-on attack by Union forces failed, and thousands of soldiers were killed. Park visitors can still see historical features, such as trenches that were dug for infantry and cannons. The defeat, however, was not enough to stop Union troops from advancing toward Atlanta, cutting off railroad supply lines, and ultimately reaching the city in early September 1864.

- As this satellite view shows, the mountain ridge is a major geographic feature of the area. Steep, rocky slopes of the range rise on average to about 550 m above sea level. Outcrops and boulders are scattered among a mostly forested landscape. The image was acquired in winter, so vegetation appears less lush and green than it would in summer, when the deciduous trees have foliage. Still, historical surveys note that the landscape during the Civil War battle was even barer, as the summits had been cleared of trees.

- Today, heavy urbanization—roadways and private residential housing—surrounds the park. Construction around the battlefield put additional pressure on the park, which stands as the largest free park in the heavily developed Atlanta metropolitan area. Park managers have had to balance preservation of the memorial landscape with the needs of nearby residents who use the space for recreation and as a commuting route.

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Figure 155: On February 5, 2016, OLI (Operational Land Imager) on Landsat-8 acquired this image of Kennesaw Mountain National Battlefield Park in Georgia, USA. The park protects land associated with a historic battle of the Civil War's Atlanta Campaign (image credit: NASA Earth Observatory,, image by Jesse Allen using Landsat data from the USGS)

• March 20, 2016: It's an archetypal American story: grandeur and legend rising from modest, humble beginnings. Both islands (Figure 156) were once home to vast oyster beds, and one was built up from the spoilings and fill from nearby dredging operations. Then in the late 19th century, the two islands became central to the narrative of the United States of America as "melting pot" for different cultures and a beacon of hope for the "tired, poor, huddled masses" of the world looking to make a new start. 129)

- Liberty Island, once known Bedloe's Island, was an oyster harvesting ground for the Lenape Indians and later for early European settlers. It then saw stints as a quarantine station, a hospital, and a military outpost. Fort Wood, with its walls shaped into an eleven-point star, eventually became the foundation for the Statue of Liberty, which was completed in 1886. The statue was designated a national monument in 1924, and in 1933 responsibility for the statue and island was transferred to the National Park Service. Today Liberty Island is one of the most visited sites in the National Park system, with nearly 4.3 million visitors per year.

- Ellis Island has long had a complicated relationship with the "New Colossus" standing next door. Many people referred to it as the "Island of Hope, Island of Tears." From 1882 to 1954, more than 12 million new immigrants to the United States made their entry to the country through the processing station on Ellis Island. The busiest year was 1907, when 1,004,756 immigrants were processed — 11,747 of them on April 17, the busiest day.

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Figure 156: On Oct. 25, 2015, OLI (Operational Land Imager) of Landsat-8 acquired this image of Ellis Island and the Liberty Island (with the Statue of Liberty National Monument). Those once-modest islands stand like magnificent sentries in New York Harbor, with Jersey City, New Jersey to the west and the lower reaches of Manhattan Island and Brooklyn to the northeast and east (image credit: NASA Earth Observatory, image by Jesse Allen, Landsat data from USGS)

March 15, 2016: ESA has agreed with NASA, NOAA and the USGS to make data available to them from the European Sentinel satellites. With the third Copernicus satellite, Sentinel-3A, recently launched, ESA has signed technical arrangements with these US agencies for accessing Sentinel data. These arrangements coordinate the technical implementation covering the Sentinel data access to the US. 130) 131)

- ESA and its international partners are pursuing Earth observation activities in a number of areas of common interest, and are sharing each other's satellite data. All sides are committed to the principle of full, free and open access to the European Sentinel and the NASA, NOAA and USGS Earth observation satellite data and information.

- The signed arrangement will allow NASA, NOAA and USGS to systematically retrieve the Sentinel data from a dedicated International Data Hub operated by ESA. These agencies will then transfer the data to the US, absorbing them in their existing data access systems, such as EarthExplorer and GloVIS, and disseminating them to their own user communities.

- For over three decades, ESA has been acquiring, processing and disseminating data from a number of US missions such as Landsat to the European user communities as part of its Earthnet Third Party Mission Program.

- While the US agencies' objective is to serve the US user communities with priority, the Sentinel data will continue to be freely accessible for Copernicus Services, as well as to users worldwide, through the ESA operated data hubs.

• March 13, 2016: In February 2016, the United States government established the world's second-largest desert preserve. In designating three new national monuments in the California desert, the U.S. DOI (Department of the Interior) added 1.8 million acres (728, 400 hectare) to an existing 7.6 million acres (3, 075, 600 hectare) of protected land. This image from the Operational Land Imager (OLI) on Landsat 8 shows how they all connect. (The image is a composite of satellite data from Landsat 8 passes on February 8 and February 17, 2016.). 132)

- The western edge of Sand to Snow National Monument is located about 120 km east of downtown Los Angeles. This aptly named monument encompasses 150,000 acres (60,700 hectare) from the floor of the Sonoran Desert to the mountaintops in San Bernardino National Forest. Ecological diversity at the various altitudes makes this monument unique.

- Hikers encounter some of this diversity along 50 km of the Pacific Crest Trail that crosses through the monument, from Whitewater Canyon up 2100 m to Mission Springs.

- Sand to Snow shares a common boundary with Joshua Tree National Park, which in turn connects to Mojave Trails National Monument—the largest new addition at 1.6 million acres. Lava flows and mountains spread across this tract of the Mojave Desert. The focal point is the sand dunes; in particular, the remote and nearly pristine Cadiz Dunes that formed from the sand of dry lake beds.

- Finally, tucked into the northeast corner of the pre-existing Mojave National Preserve is the smallest addition—the 20,920 acres (8,460 hectare) of Castle Mountains National Monument. But this smallest addition is an important one. Inclusion of Castle Mountains connects ecosystems in the New York Mountains and the Piute Mountains. Protection of this area ensures that habitat stays intact for wildlife such as the desert bighorn sheep.

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Figure 157: Landsat-8 OLI composite image of the California desert preserve acquired on Feb. 8 and 16, 2016 (image credit: NASA Earth Observatory, Jesse Owen using Landsat data from USGS)

• Feb. 18, 2016: A partnership has been established between ESA (European Space Agency) and the USGS to allow for USGS storage and redistribution of data acquired by the MSI (Multispectral Instrument) on ESA's Sentinel-2A satellite that was launched in June 2015. The collaborative effort between ESA and USGS will provide for public access and redistribution of global acquisitions of Sentinel-2A data at no cost, allowing users to download the MSI imagery from the USGS. The MSI sensor acquires 13 spectral bands that are highly complementary to data acquired by the USGS Landsat-8 OLI (Operational Land Imager) and Landsat 7 ETM+ (Enhanced Thematic Mapper Plus). 133)

• Feb. 11, 2016: Today the Landsat-8 spacecraft is 3 year on orbit and operational. So far, the satellite has acquired more than 675,000 scenes, adding valuable time series data to the USGS Landsat Archives!

- As of February 10, 2016, many of the scenes acquired from October to December 2015 have been reprocessed into nominal Level-1 products containing valid TIRS (Thermal Infrared Sensor) data and are available for download. The generation of Landsat-8 surface reflectance products from these data will become available within the next week. 134)

• January 26, 2016: Two days after a massive winter storm system dropped snow from Tennessee and Georgia to Massachusetts, millions of Americans are digging out. By some news accounts, more than 30 million people lived in areas that received at least 50 cm of snow, and 3 million more saw at least 75 cm. 135)

- The highest snow total was recorded in Glengarry, West Virginia at 107 cm. Snow totals approached records at airports near Baltimore at 74 cm, Philadelphia at 57 cm, and Newark, New Jersey at 71 cm. The National Zoo in Washington, D.C. counted 57 cm and Central Park in New York picked up 68 cm.

- At least 37 people have died as a result of car accidents, hypothermia, carbon monoxide poisoning, or over-exertion from shoveling snow, according to multiple news reports. At least a quarter-million people have lost electric power, and more than 13,000 airline flights have been canceled.

- Beyond the snowfall, near-hurricane force winds combined with astronomically high tides to produce storm surges on the Delaware and New Jersey coasts. Sea water poured into coastal towns, while extensive beach erosion occurred as far north as Massachusetts.

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Figure 158: OLI on Landsat-8 captured this natural-color image of Virginia, Maryland, and Washington D.C. in the early afternoon on January 24 (image credit: NASA Earth Observatory, Joshua Stevens)

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Figure 159: Close-up of Washington D.C. drawn from the image of Figure 158; note the long shadow cast by the Washington Monument (image credit: NASA Earth Observatory, Joshua Stevens)

• January 13, 2016: The Landsat-8 TIRS (Thermal Infrared Sensor) data continue to be collected with the scene select mirror encoder electronics disabled (mode 0). While in this mode, the TIRS LOS (Line of Sight) model will be regularly updated and modifications are being made to automate revisions to the LOS in the LPGS (Level-1 Product Generation System). 136)

- OLI and TIRS data that have been collected through the 4th quarter of 2015 (October-December); they will be reprocessed into nominal Level-1 products containing valid TIRS data, and will be available in February 2016.

- TIRS data acquired during the 1st quarter of 2016 (January-March) will be reprocessed and made available in April 2016. A strategy is being developed for generating near-realtime products moving forward while operating in mode 0. More details will be posted on the Landsat Missions Web site as they become available.

• Nov. 17, 2015: The Landsat-8 FOT (Flight Operations Team) continues to monitor current levels within TIRS (Thermal Infrared Sensor) SSM (Scene Select Mirror) encoder electronics. The FOT and Calibration Validation team are continuing to investigate the current anomaly and analyze instrument telemetry data in order to accurately measure the position of the SSM and to develop the necessary parameters for the processing TIRS data under an alternative operations concept. 137)

- TIRS data will continue to be routinely collected but will not be processed to Level-1 products until the geometric model parameters are finalized and the algorithms and code in the LPGS (Landsat Level-1 Product Generation System) have been updated, tested, and verified. These activities are expected to be completed no sooner than February 2016, at which time all products will be reprocessed to provide valid TIRS data.

- Following the implementation of an alternate TIRS processing capability, the zero-fill Landsat-8 scenes will be reprocessed and made available from the USGS archive. Mission operations will continually assess potential opportunities for return to normal operations on the B-side encoder electronics. However, at this time, the probability of return to normal operations is unknown.

• Nov. 13, 2015: Free Data Proves Its Worth for Observing Earth. Since late 2008, when Landsat Earth observation images were made available to all users free of charge, nearly 30 million Landsat scenes have been downloaded through the USGS (U.S. Geological Survey) portal – and the rate of downloads is still increasing. That's a lot of free data about the state of the planet. But what is it worth? How valuable can something free possibly be? 138)

- The worth of many things is related to scarcity. If there are too many houses or diamonds, bushels of corn or barrels of oil for sale, the price for these items falls. A free market determines the market value of what we might hope is a $500,000 house or a $5,000 diamond.

- The concept of market value breaks down for goods and services that society has determined should be freely available to everyone. Free data for earth observation fits into this category. It is a public good ­– along with public education, public roads, and public parks. While these services are not actually free (they are, of course, funded with public money), we know that the broad use of such services benefits all of society so the cost to each individual user is largely borne by all.

- The Department of the Interior's policy of releasing the full Landsat archive at no cost allows researchers around the world in government, in the private sector, and at universities and institutions to generate even more data applications that are good for society. These purpose-driven data applications – known on mobile devices as "data apps" – can serve commercial endeavors in agriculture and forestry; they can enable land managers in and out of government to work more efficiently; they can help us define and address critical climate and environmental issues.

- The DOI (Department of the Interior) policy of releasing the full Landsat archive at no cost allows researchers around the world in government, in the private sector, and at universities and institutions to generate even more data applications that are good for society. These purpose-driven data applications – known on mobile devices as "data apps" – can serve commercial endeavors in agriculture and forestry; they can enable land managers in and out of government to work more efficiently; they can help us define and address critical climate and environmental issues.

- In the United States, the federal government invests about $3.5 billion annually in civil earth observations and data (including Landsat and other satellites, weather, GPS, etc.) across multiple agencies, while optimizing related investments that are also made by state, local and tribal governments, academia, and industry. The information derived from earth observations supplies the foundation for scientific advances in many fields and enables multiple federal agencies and partners to carry out their missions. Federal investments in various aspects of earth observation are conservatively estimated to add $30 billion to the U.S. economy each year by providing Americans with critical knowledge about natural resources, climate and weather, disaster events, land-use change, ecosystem health, ocean trends, and many other earth-related phenomena.

- The USGS, a bureau of the DOI, is a major contributor to civilian earth observation through its support of the Landsat mission in partnership with NASA. First launched by NASA in 1972, the Landsat series of satellites has produced the longest, continuous record of Earth's land surface as seen from space.

- Landsat images spanning four decades have been used by scientists and resource managers to monitor water quality, glacier recession, coral reef health, land use change, deforestation rates, and population growth. To give a few examples of Landsat's many commercial applications, Landsat data have been used to track the use of irrigation water, to assist drought-stricken California grape growers, and to contribute to the success of a forestry start-up company. As an indication of widespread public interest in Landsat data, third party avenues to the data and innovative ways to use it are available from Amazon, ESRI (Environmental Systems Research Institute) and Google.

- A recent White House-led assessment determined that Landsat is among the Nation's most critical Earth observing systems, second only to GPS and weather. In 2013, the U.S. National Research Council found, "The economic and scientific benefits to the United States of Landsat imagery far exceed the investment in the system." In 2014, the Landsat Advisory Group of the National Geospatial Advisory Committee was as even more specific in its finding, "The economic value of just one year of Landsat data far exceeds the multi-year total cost of building, launching, and managing Landsat satellites and sensors."

- Other nations recognize the benefits of free and open data. Fundamental knowledge of the land and its resources is a basic need for effective government and a productive economy in any nation. More than 30 countries and geopolitical groups now have earth observing satellites, reflecting a wide range of national priorities around the world for environmental monitoring and economic growth. At the same time, more countries are adopting policies of full, free, and open data for earth observation, whether the observation operations are conducted by their national satellites or whether the data is shared between countries and with the public. — In Rwanda, for example, the government has developed and used open data to support national land use planning via their National Land Use Portal, which provides transparency collaboration and cooperation among many different partners to help shape a more sustainable future. Brazil, a co-leader of the Open Government Partnership in South America, provides its citizens the opportunity to participate in the planning and development of public policies by providing government data on hydrography, transportation, energy and communications, and more, through their Brazilian Portal of Open Data.

- October 19, 2015: The United States and the European Commission signed an agreement on Copernicus Cooperation. The European Copernicus Program has adopted a policy of free and open data from its Sentinel series of satellite missions, helping make Europe a world leader in the implementation of free and open data policies. U.S. Deputy Assistant Secretary of State for Science, Space and Health Jonathan Margolis and European Commission Director for Space Policy, Copernicus and Defence Philippe Brunet signed the arrangement in Washington, D.C., on October 16. The arrangement will allow experts from U.S. agencies, including NASA, NOAA, and the USGS, to pursue cooperative data sharing activities with European counterparts, including the European Commission,ESA (European Space Agency), and EUMETSAT (European Organization for the Exploitation of Meteorological Satellites). This cooperation will enhance data access, validation, and quality control as well as satellite system compatibility, interoperability, and instrument inter-calibration. 139)

• In October 2015, a system of storms caused significant flooding in most of California's Death Valley National Park. Flash floods from the storm destroyed roads and utilities, and damaged several historical structures. In particular, a flash flood of water and mud caused extensive damage to Scotty's Castle, an ornate mansion built in the 1930s and one of the most popular landmarks in Death Valley National Park. The Oct. 18-19 storm dumped ~7 cm of rain, more than the region typically gets in a year. 140)

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Figure 160: A false-color Landsat-8 image highlights hydrogeology in Death Valley after a major flooding event, acquired on Oct. 26, 2015; the areas in green to blue are locations with moisture content. Especially striking is the Badwater Basin, normally a dry lakebed, which became full of water( image credit: USGS, NASA)

• August 12, 2015: Algae are complicated. The little plants can be both good and bad. Single-celled algae called phytoplankton are a main source of food for fish and other aquatic life, and account for half of the photosynthetic activity on Earth—that's good. 141) 142)

- But certain varieties such as some cyanobacteria produce toxins that can harm humans, fish, and other animals. Under certain conditions, algae populations can grow explosively — a spectacle known as an algal bloom, which can cover hundreds of square kilometers. For example, in August 2014, a cyanobacteria outbreak in Lake Erie prompted Toledo, Ohio, officials to ban the use of drinking water supplied to more than 400,000 residents. - In the United States alone, freshwater degradation from "bad" algae costs the economy about $64 million a year.

- NASA, the U.S. EPA (Environmental Protection Agency), NOAA (National Oceanic and Atmospheric Administration), and the USGS (U.S. Geological Survey) are doing something about it. NASA has long used Earth observing satellites to locate algal bloom outbreaks in the ocean. But now, this unique satellite data will be routinely produced in a form that helps US water quality managers monitor the freshwater. Water quality managers will soon, with a peek at their cell phones, have an answer to "how's the water?"

- The four agencies are working on a joint project, sponsored by NASA, to transform satellite data into an indicator of cyanobacteria outbreaks in the freshwater supply. The data will be integrated into an EPA Android smart phone application so environmental officials can see – at a glance – the condition of a specific water body.

- "With our app, you can view water quality on the scale of the US, and zoom in to get near-real-time data for a local lake," explains the EPA's Blake Schaeffer, Principal Investigator for the project. "When we start pushing this data to smartphone apps, we will have achieved something that's never been done – provide water quality satellite data like weather data. People will be able to check the amount of ‘algae bloom' like they would check the temperature."

- Here's how it works: A harmful species of cyanobacteria emits chlorophyll and fluorescent light at various points in their life cycles. Landsat and NASA's MODIS (Moderate Resolution Imaging Spectroradiometer ) can detect these "ocean color" signals, which reveal the location and abundance of cyanobacteria. The project team will collect this data for freshwater bodies and convert it into a form accessible through web portals and the EPA mobile app. In addition to MODIS, they'll draw data from the Sentinel-2 and Sentinel-3 satellites of ESA (European Space Agency).

- With early warning about a developing bloom, officials at water treatment plants will be better able to determine when, where, and how much to treat the water to keep consumers safe. That means unnecessary — and expensive — overtreatment may be avoided. The data will also help park managers alert swimmers, boaters, and other recreational users to hazardous conditions. Says NASA Administrator Charles Bolden: "We're excited to be putting NASA's expertise in space and scientific exploration to work protecting public health and safety."

- The project will also help scientists understand why "bad" algae outbreaks occur. By comparing the color data with landcover change data, they'll learn more about environmental factors that spur algal growth. The result: better forecasts of bloom events. So we'll know when an algae bloom is safe or harmful.

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Figure 161: A vast, seemingly benign bloom of phytoplankton gave the Atlantic Ocean a chalky green color on August 3, 2015. The OLI (Operational Land Imager) on the Landsat-8 satellite observed the scene off the coast of New Jersey and New York, in an area referred to by oceanographers and geologists as the New York Bight (image credit: NASA Earth Observatory)

• July 17, 2015: Located near the western edge of the Sahara Desert, the Eye of the Sahara is a feature that resembles a large eye when viewed from space. Also known as the Richat Structure or Guelb er Richat, the Eye is a symmetrical dome of eroded sedimentary and volcanic rock. The outermost rings measure approximately 40 km across. Persistent northeasterly winds keep much of the dome free from sand, exposing the various layers of rock. The circular feature was initially interpreted to be an asteroid impact structure, but most scientists have now concluded that it was caused by geologic uplift. 143)

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Figure 162: Eye of the Sahara, Mauritania, acquired on June 28 and July 5, 2015 (Lat: 20.983º, Long: -11.459º): This Landsat mosaic of four different scenes shows the geologic feature in false color. By blending visible and infrared wavelengths (bands), scientists can enhance the visibility of the various rock layers in contrast to the surrounding sand (yellow to white), image credit: EROS Data Center, USGS

• June 19, 2015: The Landsat-8 image of the San Francisco Bay Area (Figure 163) was released by ESA in the 'Earth from Space video program'. The city of San Francisco is on a peninsula in the center left section of the image. In the upper-central portion, we can see the delta of the Sacramento and San Joaquin rivers with brown, sediment-filled water flowing down into the larger bay. Starting in the top-left corner of the image and running diagonally to the south is the San Andreas Fault. This is the border between the North American and the Pacific tectonic plates, and is responsible for the high earthquake risk in the area. 144)

Surrounding the Bay one can see densely populated urban areas in white/grey, while forests and park areas appear in shades of green. In the upper-right corner, one can see geometric shapes of large-scale agriculture, with fields in different colors depending on the vegetation type. Distinguishing between different types of land cover is an important task for Earth-observing satellites, helping us to understand the landscape, map how it is used and monitor changes over time.

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Figure 163: The OLI instrument of Landsat-8 captured this image of the San Francisco Bay Area on March 5, 2015 (image credit: USGS, ESA)

• July 7, 2015: The Landsat-8 spacecraft and its subsystems are operating nominally. 145)

TIRS anomaly:

• 19 Dec. 2014 – Mechanical Control Electronics (MCE) reached a yellow over-current limit. Scene Select Mirror (SSM) encoder was switched to ‘Mode-0' which basically disables the encoder

- TIRS bands in products were set to 0 (until we reprocess to handle mirror drift)

• 2 Mar. 2015 – TIRS switched to Side-B ‘Mode-4'. Commission and calibration period followed

- Develop new parameters for CPF, BPF, RLUT

• 30 Apr. 2015 – Reprocessing of TIRS data started

- Mode-0 data (19 Dec. 2014 – 2 Mar. 2015)

- Commissioning data – Side-B ‘Mode-4' data (2 Mar. 2015 – 30 Apr. 2015)

• 14 May 2015 – Reprocessing completed.

TIRS Stray Light:

• Discussion forthcoming (Ron Morfitt)

• Tentatively planned for LPGS 2.6 (~October)

• Plan to reprocess OLI_TIRS data once stray light algorithm is validated

Table 6: Ground System Activities Related to TIRS (Ref. 145)

• May 20, 2015: Since measurements began in 1895, Alaska's Hubbard Glacier has been thickening and steadily advancing into Disenchantment Bay. The advance runs counter to so many thinning and retreating glaciers nearby in Alaska and around the world. The image of Figure164 , acquired by OLI (Operational Land Imager) on Landsat-8, shows Hubbard Glacier on July 22, 2014. The yellow lines indicate the location of the terminus on August 1, 1978, and on July 13, 2002. - The image of Figure 165 shows a close-up of the glacier's terminus on July 13, 2002. 146)

- According to Leigh Stearns, a glaciologist at the University of Kansas, Hubbard's advance is due to its large accumulation area; the glacier's catchment basin extends far into the Saint Elias Mountains. Snow that falls into the basin either melts or flows down to the terminus, causing Hubbard to steadily grow. In addition, Hubbard is building up a large moraine, shoveling sediment, rock, and other debris from Earth's surface onto the glacier's leading edge. The moraine at the front gives the glacier stability and allows it to advance more easily because the ice does not need to be as thick to stay grounded. - If it is thin, it can start floating and will not necessarily advance.

- Twice in the past hundred years — in 1986 and again in 2002 — the moraine has made contact with Gilbert Point and blocked the entrance to Russell Fjord. With nowhere to drain, runoff caused the water level in the fjord to rise rapidly. Water levels to rose 0.24 m per day. However, the closure was temporary, as water pressure overpowered the encroaching ice and debris and burst through the natural dam, returning the fjord to normal levels.

- In 2002, Leigh Stearns was attending a glaciology conference in nearby Yakutat, Alaska, a town that depends on Russell Fjord's marine life. "Understanding Hubbard's behavior is scientifically interesting," Stearns said, "but it also has immediate consequences for the town of Yakutat." — Those consequences provoked her to investigate what controls the terminus position and its advance, and to estimate when the fjord might become permanently blocked. The findings, recently accepted for publication in the Journal of Geophysical Research, explain how the mechanics at the terminus override the influence of other climate fluctuations. 147)

- One estimate suggests that the fjord could permanently close by 2025. But Hubbard's terminus is nearly 14 km wide, and does not advance at the same rate across its entire width. The region adjacent to Gilbert Point, where the closure would occur, advances more slowly, because seawater passing through the gap constantly erodes the ice. Based on the current rate of advance at the gap, Leigh Stearns estimated that closure could occur by 2043. Leigh Stearns cautions, however, that these closure dates are "projections based on our current observations, and should be viewed with skepticism."

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Figure 164: Advancement of Alaska's Hubbard Glacier into the Disenchantment Bay acquired on July 22, 2014 with the OLI instrument on Landsat-8 (image credit: NASA Earth Observatory, USGS, Joshua Stevens)

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Figure 165: Advancement of Alaska's Hubbard Glacier into the Disenchantment Bay acquired on July 13, 2002 with the ETM+ instrument on Landsat-7 (image credit: NASA Earth Observatory, USGS, Joshua Stevens)

• May 8, 2015: On March 6, 2015 the Landsat-8 TIRS (Thermal Infrared Sensor) switched from A side to B side electronics to resolve a problem with the A side encoder electronics. At that time, a plan was outlined for reprocessing data acquired since the problem began. 148)

- Beginning April 30, 2015, Landsat-8 scenes acquired from December 19, 2014 to March 13, 2015 began reprocessing to repopulate the TIRS data in the products. This calibration notice details the data changes during this timeframe. The reprocessing effort is expected to complete by May 18, 2015.

- Some TIRS data for a number of scenes will not be processed due to non-nominal instrument configuration. There were several intervals identified that the data was good for a portion of the interval, but where the SSM (Scene Select Mechanism) was commanded to rotate off nadir making the TIRS data unusable for the other portion of the interval. The reprocessing will process those where TIRS was well outside the field of view of OLI due to an off nadir SSM as OLI only products.

• April 16, 2015: Landsat-8 Thermal Data Reprocessing Update. On March 6, 2015 , USGS reported that the Landsat-8 TIRS (Thermal Infrared Sensor) resumed normal imaging operations, and outlined plans for reprocessing data acquired since December 19, 2014, when problems occurred in the A-side electronics of the sensor. Provisional TIRS data acquired since March 13, 2015 were expected to require reprocessing to refine the absolute calibration; however, based on a small number of vicarious measurements, it has been determined that these data will not need to be reprocessed for now since the radiometry appears to be consistent with the previous A-side data. The calibration will be monitored and updated in the future if needed. 149)

• April 12, 2015: March 2015 marked the 15th year that iceberg B-15 remained afloat around Antarctica... at least what's left of it. The iceberg first made its break from the Ross Ice Shelf in late March 2000. One of the largest icebergs ever observed, it measured about 270 km long and 40 km wide — almost as large as the state of Connecticut. 150)

- Fifteen years later, the U.S. National Ice Center (NIC) reported that eight fragments of the original berg remain (icebergs and fragments must measure at least 19 km long in order to be named and tracked by the center). According to NIC's weekly report from April 3, 2015, the largest surviving fragment was B-15T, which measured 52 km long and 13 km wide.

- The OLI (Operational Land Imager) on Landsat-8 acquired this natural-color image of B-15T on January 14, 2015 (Figure 166). The iceberg was located amid sea ice off the Princess Astrid Coast, just east of its position pictured in an image acquired April 5, 2015, by the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite.

- Many icebergs get caught up in the currents circling Antarctica and then eventually spin off to the north and break up. However, icebergs that stay trapped in cool coastal waters can persist for decades.

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Figure 166: Iceberg B-15T still adrift; the image was acquired by OLI on January 14, 2015 (image credit: NASA Earth Observatory, Joshua Stevens, USGS)

• March 25, 2015: Landsat is a key data input for many products developed and used in water resources, agricultural monitoring, land use and land cover monitoring, forest management, and development planning. Yet, Landsat's contribution goes beyond its use solely as a primary data input. The products and processes developed by the Landsat program provide tools for data accuracy and visual communication improvement of other satellite imagery. These products are provided by the Landsat program at no cost to the users and have proven to be valuable assets to the private tech sector. This case study explores that various correction capabilities that Landsat offers to other satellite operators, acting as a tool in improvement of usability of other imagery. Several satellite companies and satellite imagery users are highlighted as beneficiaries of Landsat products.

- Landsat base layer: A base layer is a data set used as a reference for the display, analysis or correction of other data. Imagery, such as from Landsat and Landsat-like satellites is often used as a base layer. As a base layer, Landsat imagery is particularly helpful for verifying the accuracy of data due to the high quality of geometric correction and orthorectification of Landsat Level 1T data. Frank Warmerdam of Planet Labs, a company that designs, builds and operates a network of small satellites, notes that Landsat's high quality scenes provide a "trusted global basemap" for public and private sector use. Mapbox (Mapbox with HQ in Washington DC is one of the biggest providers of custom online maps for major websites) creates custom maps with open source tools and uses Landsat imagery as a basemap for a wide range of moderate resolution products. DigitalGlobe, a satellite imagery provider, is another user of Landsat imagery. As DigitalGlobe's data archive continues to grow, their use of Landsat imagery will likely be declining. However, the company used Landsat imagery to get started with their "DigitalGlobe Basemap" product series. Landsat data are also used by DigitalGlobe in parts of the world where either no high resolution data or no recent high resolution data is available.

- Processing satellite data using Landsat: A vast amount of processing is required to take the raw imagery collected by satellites and translate it into usable data for analysis. Spatial and spectral corrections are necessary in order to accurately locate the imagery on the earth's surface and convert pixel values to meaningful measures of the surface being captured. The Landsat program offers state of the art technology and methodology for conducting these corrections and as a result provides trusted remotely sensed data set for global coverage at the moderate resolution level. Due to Landsat's high standards and well documented approaches to spatial and spectral corrections, the correction and calibration of other satellite imagery can be achieved through the use of Landsat imagery.

- Spatial correction: Spatial correction, sometimes referred to as geo-rectification, geo-registration or spatial tie-down, involves accurately locating imagery on the earth's surface as well as correcting for distortions in the image through geometric correction and orthorectification. Geometric correction requires assigning known coordinates to points in the image, which geolocates the image to the correct place on the Earth's surface. Additionally, it corrects for large scale distortion or error inherent in image due to earth movement, earth curvature, and/or satellite movement during collection. Correcting small scale distortion is done through orthorectification, a type of geometric correction that utilizes digital elevation data to more accurately correct for distortions due to terrain.

The capability of Landsat to assist in spatial correction of other satellite data is utilized by companies such as DMCii, Planet Labs and BlackBridge. DMCii, a satellite imagery provider, uses Landsat data as a base layer for providing orthorectification for customers who do not have their own reference data, which is most of their customer base. This helps keep the costs down while improving the accuracy of DMCii's products. Planet Labs uses Landsat for the spatial tie down process everywhere around the globe for consistency and convenience. However, when processing difficult areas such as jungles and mountains, Landsat is a particularly critical resource. "Without Landsat it would be essentially impossible to get good GCP (Ground Control Point) locations from other sources," says Frank Warmerdam of Planet Labs. Similarly, BlackBridge, Canada's foremost supplier of satellite imagery products, is using Landsat imagery to perform geometric correction and orthorectification on areas in northern Africa and eastern Asia, where no better GCP's are available. BlackBridge has been using Landsat GCP since 2009 on about 750,000-800,000 out of 1 million products. The company will likely continue to use Landsat GCP's until higher accuracy GCP's become available for the rest of the landmass on Earth.

- Spectral corrections: Another important component of imagery processing is spectral correction. Spectral correction includes spectral characterization and radiometric calibration. Spectral characterization is a process of determining how different portions of the electromagnetic wavelength interact with an object. Radiometric calibration is a broader term for the process of relating values recorded (sensed) by a satellite sensor with radiance values (what was actually reflected/emitted on the ground). Calibration can either be absolute or relative and can employ different methods depending on when in the process the calibration is being performed.

For radiometric calibration, cross-calibration and surface reflectance are the principle processes used to correct satellite imagery. Cross-calibration is a form of relative calibration which compares values collected by one satellite sensor against values collected by a second satellite sensor. If one of the sensors has had corrections applied, the corrected values can be used for relative radiometric calibration of the other sensor. This method can be a cost effective method for radiometric calibration of operational satellites (Liu et al. 2004). DMCii initially used Landsat 7 as a standard reference satellite for cross-calibration over Libya and Antarctica. The company is now working on incorporating Landsat 8 data, which produces a good long term baseline for cross-calibration. In the future, DMCii anticipates incorporating data from the European Union Sentinel-2 mission into their tool kit.

For certain analyses of satellite imagery, it is necessary to calibrate for surface reflectance, which is the ratio of solar energy that is reflected rather than absorbed by an object on the earth's surface. However, the reflected energy must first pass back through the atmosphere before it is detected by the satellite sensor. As a result, corrections must be applied to remove atmospheric effects. Landsat currently uses a set of algorithms known as LEDAPS (Landsat Ecosystem Disturbance Adaptive Processing System ). This type of radiometric calibration uses auxiliary data including ozone, water vapor, geopotential height, and aerosol optical thickness to calculate surface reflectance. Once these corrections are applied, surface reflectance products represent what radiance values would be under ideal conditions (i.e., no atmospheric effects). Many higher-level surface geospatial analyses—including vegetation indexes, albedo, LAI (Leaf Area Index), burned area, land cover, and land cover change – rely on surface reflectance products. The availability of these products in the private sector is highly valued by the users.

Mapbox reports that of all the atmospheric correction methods tested by them, LEDAPS is the one they trust most. "LEDAPS allows types of comparison and analyses that would otherwise require significant single-purpose investments. We estimate that LEDAPS has saved our company approximately $250,000 in technical and opportunity costs over the last 24 months, and that number is steadily increasing," says Charlie Loyd, a member of Mapbox's satellite team. "Other than its accuracy, the key to LEDAPS's value to us is its generality. We can apply LEDAPS to a Landsat scene once and have output that's equally appropriate for true color imagery, classification algorithms, NDVI (Normalized Difference Vegetation Index), and other indexes. We recommend it broadly, knowing that it will meet virtually any user's needs for atmospheric correction. For these reasons, LEDAPS is the only non–in-house component of our Landsat software pipelines that we consider effectively irreplaceable."

DigitalGlobe is another company that has accrued benefits through LEDAPS. The company sees Landsat as a key input in the development process of their own surface reflectance product. In 2013, DigitalGlobe introduced a new product, seamless country-scale orthomosaics at half meter resolution, using Landsat for surface reflectance to bootstrap to a base map. DigitalGlobe reports that having Landsat data available accelerated the introduction of the product by about 9 months. While the company does not break out revenue by product in their public reporting, this particular product represents multiple millions of dollars of revenue annually.

- Additional benefits: In addition to the more specific spatial and spectral correction benefits discussed above, the Landsat program as a whole offers additional benefits to the private satellite imagery community. According to Frank Warmerdam of Planet Labs, the Landsat archive acts as a common reference point among datasets, where the well-published and respected nature of Landsat products provides a reference for product to product relation. Along with Landsat's long continuous data record and exceptional technical integrity, it is made indispensable by its free distribution (Charlie Loyd, Mapbox, written communications, 2014). The free and open access to the Landsat current and archived data enables private companies to improve their products at minimal cost, while developing additional products to push to the market.

Table 7: The impact of the Landsat program data in direct and complementary uses of Landsat imagery in various non-government programs 151)

• March 20, 2015: Ulan Bator, Mongolia, is featured in Figure 167. Sitting in the valley of the Tuul River – running northeast to southwest across the image – the city is flanked by the Bogd Khan Mountain to its south (center of image). This forested mountain is the site of one of the oldest national parks in the world, home to wildlife such as foxes and wolves and endangered species of hare and deer. 152)

- South of the mountain, a light covering of clouds blanket the steppe eco-region. This is part of the greater Eurasian Steppe, stretching from Moldova through Siberia, characterized by grasslands, savannahs and shrublands. The area pictured is also part of the discontinuous permafrost zone, meaning that in some areas the ground is frozen year round, while other areas thaw for weeks or months at a time. This poses a challenge for building, so many suburban residents of Ulan Bator live in traditional dwellings that are built on top of the soil. These circular houses – called yurts – are traditionally made from steam-bent wood and covered in layers of fabric for insulation.

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Figure 167: The Mongolian capital of Ulan Bator is captured in this image from the Landsat-8 satellite, acquired on Feb. 19, 2015 (image credit: USGS, ESA)

• March 6, 2015: The Landsat-8 TIRS (Thermal Infrared Sensor) resumed normal imaging operations on March 4, 2015, and nominal blackbody and deep space calibration data collection will resume on March 7, 2015. 153)

- Since the current anomaly associated with the scene select mirror encoder electronics forced a suspension of TIRS Level-1 data processing on December 19, 2014, an exhaustive study has been conducted to determine the root cause of the anomaly and to develop plans for reconfiguring the instrument for a return to nominal operations. During this time TIRS data continued to be collected and archived, although Level-1 processing was suspended.

- On March 2, 2015, the TIRS mechanism control electronics (MCE) were swapped to the redundant side ("side-B") and TIRS data collection resumed on March 4, 2015. It will still take several weeks of commissioning the instrument with the side-B MCE and obtaining sufficient calibration data to resume Level-1 processing. Likewise, TIRS data collected December 19, 2014 through March 1, 2015 will require updated calibration parameters before these data can be processed to generate Level-1 products.

- On March 13, 2015, processing of Landsat-8 TIRS data resumed. The newly processed data includes the revised Calibration Parameter Files established after the mechanism control electronics (MCE) swap on March 2, 2015. Investigations are continuing to improve the data product, and reprocessing of TIRS data acquired since December 19, 2014 is still planned. 154)

• March 6, 2015: The oceans may be vast, yet they still can grow crowded. Some congested areas have enough ship traffic that the IMO (International Maritime Organization) and other groups maintain traffic separation schemes—the equivalent of highways for ships—to reduce the risk of collisions. - The vessels in Figure 168 are most likely cargo ships, though some may be ferries or fishing boats. The ships appear as small gray and white specks. In the shallow coastal waters, their propellers kick up long, brown sediment plumes. Most of the northbound ships make a turn to the northwest as they round the tip of Shandong. 155)

- According to the IMO, the practice of following predetermined routes for shipping originated in 1898. It was first adopted by shipping companies operating passenger ships across the North Atlantic. Since then, traffic separation schemes have been established in most congested areas, causing the number of ship collisions and groundings to drop dramatically.

- But with upwards of 86,000 merchant ships on the world's oceans, accidents still happen. On May 2, 2010, the Bright Century, a cargo ship loaded with 170,000 tons of iron ore, sank after it collided with a freighter about 37 km east of Shandong Peninsula. In December 2012, a fishing boat collided with a cargo ship near the peninsula and sank with 11 fisherman on board.

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Figure 168: OLI on Landsat-8 captured this view of northbound and southbound shipping lanes off the coast of China's Shandong Peninsula on February 24, 2015. The lanes form one of the main routes from the Yellow Sea into the Bohai Sea and the Chinese ports of Dalian and Tianjin, two of the busiest in the world. As shown by this map, several lanes of traffic intersect northeast of the Shandong Peninsula (image credit: USGS, NASA Earth Observatory, Jesse Allen)

• The image of Figure 169 was released on Feb. 13, 2015 in ESA's 'Earth from Space video program.' Las Vegas with its grid-like urban plan is visible near the center. Sitting in a basin of the Mojave Desert, the city is surrounded by a number of mountain ranges. 156)

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Figure 169: Image of Las Vegas and Lake Mead acquired with OLI of Landsat-8 on Sept. 23, 2014 (image credit: USGS, ESA)

Legend to Figure 169: Zooming in southeast of the city one can see large, dark shapes in one of the desert valleys. These are solar panels of a large-scale plant called Nevada Solar One. The plant harnesses enough energy to power an estimated 14 000 homes a year. - Satellites can assist in the selection of sites of solar power plants by providing sunshine maps that combine information on overall solar irradiance and average cloudiness. Along with other space-derived products such as digital elevation models, this can help sustainable energy companies pinpoint areas best suited for exploiting solar energy.

The large dark area pictured is Lake Mead, the largest reservoir in the country. It primary source is the Colorado River, flowing in from the east and out to the south. This massive reservoir was established in the early 1930s by the construction of the Hoover Dam on the Colorado River. Drought and increased water demand in recent years have resulted in a decline in water levels, hitting record lows last summer. The lake and surrounding area form the Lake Mead National Recreation Area, where visitors can go boating, swimming, fishing, hiking, biking and camping.

• January 27, 2015: Authorities in the Indian states of Jammu and Kashmir are concerned that a landslide blocking the Tsarap River (also called the Phuktal River) may lead to a damaging flood downstream. 157)

- The landslide, which reportedly occurred on December 31, 2014, sent enough fine-grained debris into the river to create an earthen dam. As of January 20, 2015, that dam was about 600 m long, according to an analysis of satellite imagery collected by the ISRO's (Indian Space Research Organization) CartoSat-2. The artificial lake that formed behind the dam was nearly 8 km long and covered about 55 hectares (300 acres). Aerial surveys suggest the mound of debris blocking the river was about 60 m high.

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Figure 170: Landslide in Northern India: OLI acquired this image of landslide debris and the barrier lake on January 18, 2015 (image credit: NASA Earth Observatory, Joshua Stevens, USGS)

Legend to Figure 170: Notice that the river appears wider upstream of the landslide. The river also appears brighter after the landslide because the surface has frozen and a fresh coat of snow coats the ice. After surveying the situation on January 18, a team of civilian and military engineers recommended that people who live downstream move to higher ground. They also discouraged authorities from using explosives to clear the blockage as doing so could trigger additional landslides. While the chance of a catastrophic flood is lower with the lake frozen, the risk will increase when temperatures rise in the spring. As a precautionary measure, authorities have closed the Chadar ice trek, a popular route that involves hiking on frozen river ice downstream of the blockage.

• January 27, 2015: The Landsat-8 spacecraft is operating nominally and acquires OLI and TIRS data. However, the TIRS level-1 processing remains suspended. 158) 159)

- On December 19, 2014, the TIRS instrument on Landsat-8 was reconfigured due to detection of anomalous current levels associated with the scene select mirror encoder electronics. Since that time substantial testing has been conducted to isolate the root cause of the problem and to evaluate options for returning to routine operations. - During this time, TIRS data has been routinely collected with OLI data, but due to the lack of definitive calibration coefficients the processing of TIRS data to level-1 products has been suspended.

- Once a plan to return to normal operations has been defined, the backlog of TIRS data that have been collected will be processed to Level-1 products. Updates to the status of plans to resume normal operations will be provided periodically.

• The Landsat-8 image of Figure 171 was released on Jan. 30, 2015 showing Corsica, the most mountainous island of the Mediterranean Sea. About 40% of the island's surface area is dedicated to nature reserves, and its mountains are a popular destination for hiking. For beachgoers, the island boasts over 1000 km of coastline. 160)

- Near the northeastern coast, one can see the island's largest coastal lagoon, the Etang de Biguglia. This nature reserve has been noted for its support of numerous breeding and wintering waterbirds, as well as the vulnerable Hermann's tortoise and long-fingered bat.

- This lagoon is one of the over 2000 sites worldwide considered to be wetlands of international importance by the Ramsar Convention, an intergovernmental treaty for the sustainable use of wetlands. The World Wetlands Day is observed on 2 February, the anniversary of the signing of the Convention.

- ESA has been assisting the Ramsar Convention for a decade through the GlobWetland project, which provides satellite data to be used to monitor these precious resources. The next phase of the project, called GlobWetland Africa, will collaborate closely with ESA's TIGER initiative, which trains African water authorities and researchers in exploiting satellite data and Earth observation technology for sustainable water resource management.

- The Etang de Biguglia is not the island's only Ramsar site: further inland in the central-north part of the island is an active raised bog, home to a number of protected bat, reptile, bird and amphibian species.

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Figure 171: Image of the island of Corsica, acquired by Landsat-8 on August 29, 2014 (image credit: USGS, ESA)

• The Landsat-8 image of Figure 172 was released by ESA on January 23, 2015 showing parts of the Swiss and Italian Alps as well as the Aletsch Glacier, the largest glacier in the Alps located in the center of the image. The glacier originates in a large, flat area of snow and ice high in the mountains called Concordia, where three smaller glaciers converge. It extends south, and its meltwater creates the Massa River in the valley below. Owing to climate change, the glaciers in this region are showing long-term retreat. The melting ice has given birth to new lakes, which pose risks such as flooding and landslides to communities at lower level. 161)

- Aletsch and the surrounding mountains are part of the Jungfrau-Aletsch protected area, a UNESCO World Heritage site. The area is of major importance to scientific research in geology, geomorphology, climatic change, biology and atmospheric physics. It features a wide diversity of ecosystems, and its landscape has played an important role in European art, literature, mountaineering and alpine tourism.

- One particularly popular tourist destination is the Swiss city of Interlaken, located between lakes Thun and Brienz, seen in the upper part of the image. From the city, locals and visitors alike have easy access to the mountains and water bodies, and can partake in a variety of outdoor activities during all seasons.

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Figure 172: Image of the Aletsch Glacier in the Swiss and Italian Alps, acquired by OLI of Landsat-8 on June 8, 2014 (image credit: USGS, ESA)

• 2014 update: Landsat imagery provides the United States and the world with continuous, consistent inventory and monitoring of critically important global resources. Supplying an unprecedented record of global land cover status and change for over 40 years, Landsat imagery is an essential "national asset" which has made and continues to make critical "contributions to U.S. economic, environmental, and national security interests." Because Landsat imagery is used most often by governmental and other non-commercial entities, the general lack of market forces makes estimating the economic value of Landsat data challenging. However, cost savings from operational efficiency improvements, avoided alternative replacement costs (assuming Landsat data were not available), and opportunity costs related to economic and environmental decision-support can be used to estimate the value of Landsat data. 162)

• Dec. 19, 2014: A small portion of underwater structures of the Great Bahama Bank is pictured in Figure 173. Sitting north of Cuba, the bank is made of limestone – mainly from the skeletal fragments of marine organisms – that has been accumulating for over 100 million years. Currents sculpted these underwater sediments into the wavy pattern we see along the bottom of the image, just a few meters deep. 163)

The shallow waters drop off into the deep, dark water of an area known as the Tongue of the Ocean. With depths of up to about 4000 m, this trench surrounded by islands, reefs and shoals has an opening to the Atlantic Ocean at its northern end. The trench was carved during the last Ice Age when the land was still above sea level and exposed to erosion from draining rainwater. As the Ice Age ended and the massive ice sheets across the globe melted, global sea levels rose and flooded the canyon.

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Figure 173: An image of the Great Bahama Bank acquired with Landsat-8 on Feb. 5, 2014 and released on Dec. 19, 2014 (image credit: USGS, ESA)

The MODIS image of the Great Bahama Bank of Figure 174 provides a much broader view of the area, including the Tongue of the Ocean. 164)

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Figure 174: A MODIS image on Aqua of the Great Bahama Bank captured on Jan. 9, 2014 (image credit: NASA Earth Observatory)

• Nov. 7, 2014: The Landsat-8 image of Figure 175 was released by ESA on Nov. 07, 2014. It shows part of the Middle East, with the Jordan Rift Valley running north to south. The most prominent feature in this image is the Dead Sea: the lowest point on Earth's surface, with 427 m below sea level. The Dead Sea is 50 km long, 15 km wide at its widest point, and 306 m deep. The extremely high salinity (34.2%) means fish cannot live in this water body, although there are bacteria and fungi. 165)

- With the Jordan River as its main source of water, the Dead Sea is an ‘endorheic' basin, meaning that the water has no outflow. Nonetheless, the water level has been dropping, an effect of the diversion of incoming water from the river.

- Note the greenish rectangles just south of the Sea. This is a large complex of mineral evaporation ponds used to produce sodium chloride and other salts for the chemical industry and human and animal consumption. These ponds are separated from the northern part of the Dead Sea by what once was the Lisan Peninsula but lowering water levels have exposed the sea bed, dividing the two sections completely.

- Throughout the rest of the image one can see built-up areas such as Amman, the capital of Jordan, in the upper right and Jerusalem near the green hills west of the Dead Sea. Further west we can see green patches of agriculture on the coastal plain, with Tel Aviv on the Mediterranean coast. - In the lower-left corner of the image, one can clearly see the division between Israel and the Gaza Strip not only by the outline of the border, but in the difference in agricultural practices.

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Figure 175: Landsat-8 image of the Dead Sea, acquired on July 4, 2013 with OLI (image credit: USGS, ESA)

• Oct. 26, 2014: On October 17, 2014, the eye of category 3 Hurricane Gonzalo passed right over Bermuda. The storm knocked out power to most of the island and caused between $200–$400 million in property damage, though it did not cause any deaths. The potent storm also stirred up the sediments in the shallow bays and lagoons around Bermuda, spreading a huge mass of sediment across the North Atlantic Ocean. 166)

OLI ( Operational Land Imager) on the Landsat 8 satellite acquired the two natural-color views of Bermuda in Figures 176 and 177. After the storm, visible plumes of sediment stretch 25 to 30 km from Bermuda. They extend mostly to the south and east of the island, suggesting that the last winds from the storm may have been out of the northwest. The suspended sediments were likely a combination of beach sand and carbonate sediments from around the shallows and reefs.

Coral reef and carbonate island environments—Bermuda is a classic example—produce large amounts of calcium carbonate (CaCO3) mainly in the form of aragonite and magnesian calcite. One island can produce as much CaCO3 as several hundred square kilometers of open ocean. But unlike the calcium carbonate produced in the open ocean by coccolithophores, foraminifera, and pteropods, the sediment produced by reefs stays on the reef flats (where there is coralline algae that also produces carbonate). It builds up over time and forms islands.

These stores of calcium carbonate sediments can get moved from the shallows to the deep ocean by storms or density flows. The strong winds of storms like Gonzalo can move a large amount of sediment off the shallow islands in a single event. Density flows can happen when the shallow water on the reef flat is cooled by a weather system, making it more dense than the surrounding ocean water, and it sinks to the deep ocean, taking sediments with it.

Storm-induced export of carbonate sediments into the deep ocean—where they mostly dissolve—is a significant process in the ocean's carbonate and carbon cycles. It's also important for the eventual neutralization of excess carbon dioxide entering the oceans because of increasing atmospheric CO2 concentrations from fossil fuel combustion. The dissolution of calcium carbonate is an important process in the carbon cycle; it is one of the ways that the oceans naturally balance the addition of carbon dioxide to ocean waters. However, as more CO2 is added to the surface waters due to rising atmospheric concentrations, it is becoming increasingly difficult for coral and coralline algae to make calcium carbonate.

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Figure 176: OLI image of Bermuda acquired on Oct. 2, 2014 (image credit: NASA, Earth Observatory)

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Figure 177: OLI image of Bermuda, acquired on Oct. 18, 2014, a day after Gonzalo passed through (image credit: NASA, Earth Observatory)

• Sept. 29, 2014: The greens and blues of the ocean color from NASA satellite data (Figure 178) have provided new insights into how climate and ecosystem processes affect the growth cycles of phytoplankton—microscopic aquatic plants important for fish populations and Earth's carbon cycle. 167)

Climate change will unquestionably influence global ocean plankton because it directly impacts both the availability of growth-limiting resources and the ecological processes governing biomass distributions and annual cycles. Forecasting this change demands recognition of the vital, yet counterintuitive, attributes of the plankton world. The biomass of photosynthetic phytoplankton, for example, is not proportional to their division rate. Perhaps more surprising, physical processes (such as deep vertical mixing) can actually trigger an accumulation in phytoplankton while simultaneously decreasing their division rates. These behaviors emerge because changes in phytoplankton division rates are paralleled by proportional changes in grazing, viral attack and other loss rates. Here, the trophic dance between predators and prey is discussed, how it dictates when phytoplankton biomass remains constant or achieves massive blooms, and how it can determine even the sign of change in ocean ecosystems under a warming climate. 168)

At the bottom of the ocean's food chain, phytoplankton account for roughly half of the net photosynthesis on Earth. Their photosynthesis consumes carbon dioxide and plays a key role in transferring carbon from the atmosphere to the ocean. Unlike the plant ecosystems on land, the amount of phytoplankton in the ocean is always followed closely by the abundance of organisms that eat phytoplankton, creating a perpetual dance between predators and prey. This new analysis shows how tiny imbalances in this predator-prey relationship, caused by environmental variability, give rise to massive phytoplankton blooms, having huge impacts on ocean productivity, fisheries and carbon cycling.

The continuous year-in and year-out measurements provided by NASA's ocean color satellites have dramatically changed our understanding of phytoplankton dynamics on the Earth.

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Figure 178: Landsat-8 image of a phytoplankton bloom (green and blue swirls) near the Pribilof Islands off the coast of Alaska, in the Bering Sea, acquired on Sept. 22, 2014 (image credit: NASA/GSFC, USGS)

In early September 2014, the SLI (Sustainable Land Imaging) Office at NASA/GSFC announced, that the following companies have been awarded contracts to carry out the SLI 'Reduced Instrument Envelope Study'.

• BATC (Ball Aerospace & Technologies Corporation) of Boulder, CO

• Exelis Inc., Geospatial Systems of Fort Wayne, IN

• Lockheed Martin Space Systems Company of Greenbelt, MD

• Northrop Grumman Systems Corporation, Aerospace Systems of Redondo Beach, CA

• Raytheon Company of El Segundo, CA

• SST-US (Surrey Satellite Technology US LLC) of Englewood, CO.

The study focuses on investigating mid-term capabilities and technologies for instruments that may enable more efficient implementation of the SLI program objectives to continue the Landsat heritage of measurements. The study contract awards are intended to enable contractors to perform a more detailed analysis of techniques and trends that lead to reduction in size and mass of spaceborne Earth-imaging instruments, potentially resulting in cost savings to the U.S. Government while still meeting the SLI program objectives. These studies will be of 6-month duration.

Landsat data provide a consistent and reliable foundation for research on land use change, forest health, and carbon inventories, and changes to our environment, climate, and natural resources. Additionally, the free and open availability of the Landsat data enables the measurements to be used routinely by decision makers both inside and outside the Government, for a wide range of natural resource issues, including water resource management, wildfire response, agricultural productivity, rangeland management, and the effects of climate change.

The U.S. Government has committed to continue the Landsat program and its invaluable data stream. To continue data collection beyond Landsat-8, the Administration proposes to design and implement a spaceborne system to provide global, continuous Landsat-quality multispectral and thermal infrared measurements for at least the next 25 years. The satellite system may be combined with alternative sources for Landsat-quality data, either procured through commercial approaches or through partnership agreements, as they become available. In accordance with Administration objectives, NASA will lead the system design study in close collaboration with the USGS (United States Geological Survey) and be informed by existing knowledge of current and desired capabilities. The aim of the study will be to define a programmatically sustainable system that balances measurement capability, likelihood of data continuity (minimizing risks of gaps to the extent possible), and cost/affordability over the lifetime of the program. Technology infusion over the lifetime of the program will be considered as a feature of the long-term sustainable program.

In FY 2014, NASA will initiate the definition of a sustained, spaceborne, global land imaging capability for the nation, ensuring continuity following LDCM. Near-term activities led by NASA, in cooperation with USGS, will focus on studies to define the scope, measurement approaches, cost, and risk of a viable long-term land imaging system that will achieve national objectives. Evaluations and design activities will include consideration of stand-alone new instruments and satellites, as well as potential international partnerships. It is expected that NASA will support the overall system design, flight system implementation, and launch of future missions, while USGS will continue to fund ground system development, post-launch operations, and data processing, archiving, and distribution.

Table 8: Sustainable Land Imaging Architecture Study 169)

• August 27, 2014: Ethiopia's Danakil Depression (or Afar Depression) exhibits some uncommon wonders: lava that burns blue, bright yellow hot springs, and lakes of bubbling mud. These otherworldly oddities are all manifestations of a tectonic process called continental rifting. In other words, the Earth is pulling apart at the seams here. 170)

In northeastern Africa, the Arabian, Somali, and Nubian (or African) plates are separating, thinning Earth's crust as they pull apart. The Danakil Depression lies between the Danakil Alps (east) and the Ethiopian Plateau (west), which were once joined until the rifting process tore them apart. The land surface is slowly sinking, and Danakil Depression will someday fill with water as a new ocean or great lake is born. But for now, the region is full of other interesting liquids.

The image (Figure 179) shows a few of the diverse and compelling features of the Danakil Depression. Chief among them is Gada Ale, the northernmost volcano in the Erta Ale volcanic range. Gada Ale is a 287 m stratovolcano built of lava and ash, and it has a crater lake full of boiling mud and sulfurous gases. Basalt lava from the volcano paints the surrounding terrain a dark hue, with the youngest flows being the darkest colors in the satellite image.

Just southwest of Gada Ale, a 2 km wide salt dome has pushed ancient lava flows up to heights of 100 m. North of Gada Ale, a salt lake (Lake Karum) lies 116 m below sea level. To the south lies the Catherine Volcano, a 120 m circular shield surrounded by a tuff ring (an amalgamation of volcanic ash). With gently sloping sides of basaltic lava, the volcano has been dated at less than one million years old. In the center of that tuff ring is a small, salty lake fed by thermal springs.

The Afar people have survived in this unforgiving region for at least 2,000 years, mining and selling the plain's abundant salt, which was once used as currency in Ethiopia. The harsh desert also has created an ideal exposure for the tectonic rifting—a process that often occurs on the recesses of the ocean seafloor or elsewhere on land where younger sedimentary rocks obscure the geologic record.

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Figure 179: The image of the Danakil Depression was acquired on June 27, 2014 with OLI on Landsat-8 (image credit: NASA Earth Observatory, Jesse Allen and Robert Simmon)

• August 20, 2014: Retreat of the Yakutat Glacier in Alaska. Natural processes and human-caused warming have combined to bring rapid change to a glacier in southeastern Alaska. The Yakutat Glacier is one of the fastest retreating glaciers in the world. It is the primary outlet for the 810 km2 Yakutat ice field, which drains into Harlequin Lake and, ultimately, the Gulf of Alaska. 171)

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Figure 180: Image of the Yakutat Glacier acquired with the OLI instrument of Landsat-8 on August 13, 2014 (image credit: NASA, USGS Earth Observatory)

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Figure 181: Image of the Yakutat Glacier acquired with the TM instrument on Landsat-5 on August 22, 1987 (image credit: NASA, USGS Earth Observatory)

Legend to Figures 180 and 181: Landsat satellites captured this pair of images showing changes in the glacier and lake. The TM (Thematic Mapper) on Landsat -5 acquired the image of Figure 181 on August 22, 1987; the OLI (Operational Land Imager) on Landsat-8 captured the image of Figure 180 on August 13, 2013. Snow and ice appear white and forests are green. The brown streaks on the glaciers are lateral and medial moraines.

Over the past 26 years, the glacier's terminus has retreated more than 5 km. What is causing the rapid retreat? University of Alaska glaciologist Martin Truffer and colleagues pointed to a number of factors in their 2013 study published in the Journal of Glaciology. The chief cause is the long-term contraction of the Yakutat Ice Field, which has been shrinking since the height of the Little Ice Age. - Once part of a much larger ice field, Yakutat has been contracting for hundreds of years. As other nearby glaciers retreated, Yakutat ice field was cut off from higher-elevation areas that once supplied a steady flow of ice from the north. With that flow cut off, there simply is not enough snow falling over the low-elevation Yakutat ice field to prevent it from retreating.

Beyond this natural change, human-caused global warming has hastened the speed of the retreat. Between 1948–2000, mean annual temperatures in Yakutat increased by 1.38°Celsius . Between 2000 and 2010, they rose by another 0.48°C . The warmer temperatures encourage melting and sublimation at all ice surfaces exposed to the air.

In the past few years, the breakdown of a long, floating ice tongue has triggered especially dramatic changes in the terminus of the Yakutat glacier. For many years, Yakutat's two main tributaries merged and formed a 5 km calving face that extended far into Harlequin Lake. In the past decade, satellites observed a rapid terminus retreat and the breakup of the ice tongue in 2010. As a result, the calving front divided into two sections, with one running east-west and another running north-south.

• July 2, 2014: The Landsat 8 satellite is helping researchers to spot organisms like aquatic algae from space, gathering information that could direct beachgoers away from contaminated bays and beaches. With improved sensors and technology on the latest Landsat satellite, researchers can now distinguish slight variations in the color of coastal water due to algae or sediments to identify potential problem areas. 172)

- The OLI (Operational Land Imager) on Landsat-8 added the "New Deep Blue" band (433-453 nm) to pick up dark blue colors to help studies that are looking at coastal areas, both of lakes and oceans. Pollutants from land impact fresh and salt-water ecosystems including coral reefs.

Beyond the blue of the water, a study of John Schott of RIT (Rochester Institute of Technology) at the University of Rochester, N. Y. is paying attention to three colors to decipher what's in Lake Ontario: green, yellow and grey. Green indicates the presence of chlorophyll, the molecule found not only in land plants but in lake algae. The yellow color is decaying plant matter. The gray color, apparent from a combination of Landsat's bands, comes from particulates like dust and soil, or from dead algae that have lost their chlorophyll.

- After paddling out in boats and testing the waters on the same day Landsat 8 passed overhead, the team compared the water samples to the satellite data. The comparisons are used to create tables and computer programs that can use the satellite data to help determine water quality and composition. This summer, the team plans to sample the harmful algal blooms that start small in Lake Ontario's bays and rivers – which could grow and cause water quality and public health concerns.

- It's not just the algae floating on the surface that Landsat-8 can spy. Scientists with the Michigan Tech Research Institute are tracking the spread of Chladophora, a hair-fine algae that attaches to shallow water rocks, or the shells of dead invasive zebra and quagga mussels. Occasionally, due to storms in the Great Lakes, the algae slough off the rocks, and cover the beach in a green decaying mess.

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Figure 182: Landsat 8's new blue band and improved ability to distinguish subtle color variations help researchers study coastal water quality. John Schott and colleagues at RIT are measuring chlorophyll and more along Lake Ontario's shores. (image credit: RIT, NASA, USGS)

- Sediment swirls and chlorophyll whirls: Researchers in Belgium are looking at the swirls of sediments created by wind turbines in near shore waters. Wind companies are required to monitor the environmental impact of the turbines, explained Quinten Vanhellemont, a scientist with the Royal Belgian Institute for Natural Sciences, and Landsat-8 has the spatial resolution – and the sensitivity – to pick up some of the smaller features. The resolution and sensitivity of the imager on board makes it an ideal sensor for coastal water applications.

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Figure 183: Close-up of the Thames Estuary wind power turbines of the London Array and sediment swirls on the coast of England (image credit: NASA, USGS)

- At NASA/GSFC, scientists in the Ocean Ecology Laboratory are looking to Landsat-8 as well. They have created open-source software that researchers use to analyze satellite data for studies on marine phytoplankton chlorophyll concentration other water constituents. Currently they use satellites that take the big view, but Bryan Franz, a research oceanographer at Goddard, worked with Vanhellemont to see how well Landsat 8 data could be processed to determine chlorophyll patterns in coastal waters. It shows promise, Franz said. He plans to add Landsat 8 data to the software this summer to see how the ocean research community will use it (Ref. 172).

• The image of Figure 184 was released on July 1, 2014 in NASA's Earth Observatory program. Turkmenistan is a desert country that lies east of the Caspian Sea and borders Iran, Afghanistan, Uzbekistan, and Kazakhstan. Annual precipitation across the country ranges from 300 mm in the mountains to 80 mm in the desert northwest. In a country just larger than California, nearly 80% of the land is defined as desert. 173)

Despite the harsh, dry environment, these desert expanses were once part of the ancient east-west trade route between the Roman Republic and Han Dynasty. As part of the Silk Road from Europe to China, Turkmenistan was coveted by the Mongols, Turks, and Russians. Each have taken turns ruling the region over the past two millennia.

In the 18th century, people in the region started to think about taming the great Garagum Desert (also known as the Kara Kum or Karakumsky). The idea was to bring water southward from the Amu-Darya River, which runs through the northern desert. Under Soviet rule in the 1950s, the idea was realized. - In a feat of engineering, water from the Amu-Darya was channeled more than 1,300 km to irrigate the southern lands. Under construction from 1954 to 1988, the Garagum Canal project opened a million hectares of land to farming of cotton, wheat, melons, and animal fodder. Today, agriculture accounts for 7% of Turkmenistan's gross domestic product and employs nearly half of the country's workforce.

In this natural-color Landsat-8 image acquired on April 18, 2014, the Hanhowuz (Khauzkhan) Reservoir jumps out as a splash of turquoise amidst desert browns. The reservoir was constructed in a natural depression to capture winter runoff and overflow from the canal for use later during the driest periods of summer. Phytoplankton thrive in the warm waters, as do many commercial fish—including Aral barbel, asp, and catfish.

In the image of Figure 184, Garagum Canal is the brown ribbon dropping down from the upper right corner and heading south and east from the reservoir. A portion of the canal is diverted, and one can see the brown sediment-laden water entering the reservoir from the east and dropping its load of suspended sediments. The water that leaves is turquoise and travels west to irrigate the Tedjen Oasis. Roughly rectilinear farmlands appear on either side of that section of the canal.

Water is vital to the existence of Turkmenistan, but the canal that started as an engineering wonder for arid lands has also turned out to be an environmental tragedy. The canal has starved the Aral Sea, which has lost about 90% of its water since the canal's creation. Making matters worse, inefficient earthen canals lose nearly half of the canal water between the Aral Sea and Turkmenistan's farms. Smudges of green-grey along their sides of the canal (north of the reservoir) show where water has seeped out.

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Figure 184: Image of the Hanhowuz Reservoir in Turkmenistan, acquired by the OLI instrument of Landsat-8 on April 18, 2014 (image credit: USGS, NASA)

• The image of Figure 185 was released on June 18, 2014 in NASA's Earth Observatory program. The double oxbow — called the loop — is known as an "entrenched meander" by geologists, the Loop's canyon walls are about 150 m high. The lower canyon walls are part of the Hermosa Formation, a group of sedimentary rock layers that formed about 300 million years ago. At the narrowest point, just 150 m of rock separate the channels of the East Loop; the slightly wider neck of the West Loop measures about 520 m. As the Colorado River continues to erode the canyon wall, it will eventually punch through and create a new channel, leaving an oxbow lake and later a rincon. 174)

How the entrenched meanders of the Colorado River (and other rivers that flow through the Colorado Plateau) formed has intrigued western geologists since a team of explorers led by John Wesley Powell passed through the Canyonlands region in 1869. Were meanders established by ancestral rivers that flowed on softer sediments long before tectonic forces uplifted the Colorado Plateau? Or was it something about the rock of the Colorado Plateau that determined the shape and distribution of oxbows and meanders?

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Figure 185: The double oxbow loop of the Colorado river in Canyonlands National Park acquired by OLI of Landsat-8 on May 13, 2014 (image credit: USGS, NASA)

• Figure 186 is a Landsat-8 image of the southwestern coast of Greenland, released by ESA on June 13, 2014. Multiple ice streams, that drain the Greenland ice sheet, are pictured in this satellite image. 175)

- Covering more than 2,000,000 km2, Greenland is the world's largest island and home to the second largest ice sheet after Antarctica. Scientists, using data from Earth-observing satellites, have discovered that the rate of ice sheet melting is increasing. Between 1992 and 2012, Greenland was responsible for adding about 7 mm to the average global sea level. Many areas in Greenland – especially along the coast – are losing up to 1 m of ice thickness per year.

- Melting ice sheets, caused by rising temperatures and the subsequent rising of sea levels, is a devastating consequence of climate change, especially for low-lying coastal areas. In addition, the increased influx of freshwater into oceans affects the salinity, which in turn impacts global ocean currents – a major player in the regulation of our climate.

- Monitoring the effects of climate change on the cryosphere and oceans using Earth-observing satellites is the main topic of an event which took place on June 13, 2014 at the Royal Society in London. The event was jointly organized by ESA and the UK Space Agency (UKSA) with the aim to provide an overview of the outcome and scientific significance of the achievements of the Climate Change Initiative with a focus on new climate data sets from space, the cryosphere and the ocean.

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Figure 186: Image of the southwestern coat of Greenland acquired by OLI (Operational Land Imager) of Landsat-8 on June 12, 2013 (image credit: USGS, ESA)

Legend to Figure 186: In the lower part of the image, one can see icebergs speckling the waters of a fjord, with the mountainous Nuussuaq Peninsula visible along the bottom of the image.

• June 2014: During the early on-orbit period of Landsat-8, ground-based measurements indicated a significant error in the radiance produced from TIRS (Thermal Infrared Sensor), especially in Band 11. 176)
After several months of analysis, the NASA TIRS team suspected a stray light issue with the sensor. Scans of the moon by the TIRS instrument have confirmed this. Users were notified of the issue through the Landsat-8 Calibration Notices (https://landsat.usgs.gov/calibration_notices.php) and the USGS Landsat Updates (http://landsat.usgs.gov/about_Landsat_Updates.php), starting in August 2013.

- During the early on-orbit period of Landsat-8, ground-based measurements indicated a significant error in the radiance produced from the TIRS. After collecting additional ground measurements through the summer of 2013, this error was estimated to be 0.29 W/m2/sr/mm for Band 10 and 0.51 W/m2/sr/mm for Band 11.

- All errors showed that TIRS reported a higher radiance than the ground measurements, as shown in the left graph of Figure 187. The right graph shows the results after accounting for this average radiance error, which is the calibration adjustment that was implemented for reprocessing in February 2014. The adjustment accounts for the apparent bias, but there remains a significant amount of variance, especially within Band 11.

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Figure 187: Thermal band errors (left graph) prior to calibration adjustment and (right graph) after calibration adjustment (image credit: USGS, NASA)

• May 22, 2014: After 14 years of drought, Lake Powell (on the Colorado River) was at 42 % of its capacity as of May 20, 2014. The low water levels are evident in these images of Figures 188 and 189, which were acquired by the Landsat-8 satellite on May 13, 2014. White bleached rock show where Lake Powell's shore is when the reservoir is at capacity. In Figure 188, which shows the northern section of Lake Powell, a muddy Colorado River flows through a largely empty lakebed. The Figure 189 shows a section of the reservoir closer to the Glen Canyon Dam and popular with boaters. Here, Halls Creek Bay is clearly smaller than it is in the National Park Service map of Lake Powell. 177)

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Figure 188: Image of the northern section of Lake Powell acquired by Landsat-8 on May 13, 2014 (image credit: NASA Earth Observatory, USGS)

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Figure 189: Image of the Lake Powell section closer to the Glen Canyon Dam acquired by Landsat-8 on May 13, 2014 (image credit: NASA Earth Observatory, USGS)

Legend to Figures 188 and 189: Water rules the western United States. Not only does it sustain cities, but it also fuels the economy. It's both a primary source of electricity and the foundation for agriculture. For all that, water is often not available in the Southwest and Intermountain West. To ensure a steady supply, the United States built a series of reservoirs throughout the 20th century. The two largest, Lake Mead and Lake Powell, sit behind massive dams on the Colorado River and provide water and electricity to several western states.

It is normal for water levels to fluctuate in the reservoir depending on how much water flows in from snow and rain and how much flows out to meet needs. However, it has been dry in all but three of the past 14 years. At the beginning of 2000, Lake Powell was at 94% of capacity. By October 2013 (the beginning of the 2014 water year), water levels had dropped to a low of 50% capacity, according to the Bureau of Reclamation, the agency that manages the reservoir. The Earth Observatory's World of Change shows this annual fluctuation and overall decline. With slightly above average snowpack in the basin that feeds the lake, water levels are expected to rebound to about 51% of capacity by October 2014, the end of the current water year.

While the drop in water levels are worrying for those who generate electricity or use the water for agriculture, the lower water levels may be a draw for recreation. Boaters coming to Lake Powell in the spring of 2014 will find beaches and rock formations that are usually underwater. Bullfrog Bay is the starting point for many boat rentals. The popularity of the spot is evident in the lower image: boats dot the surface of the water, just tiny white flecks at this scale.

• April 25, 2014: Of the roughly 1,550 volcanoes that have erupted in the recent geologic past, 113 are found on Kamchatka. Forty Kamchatkan volcanoes are "active," either erupting now or capable of erupting on short notice. The Operational Land Imager (OLI) on Landsat-8 captured activity at five of them during a single satellite pass on April 14, 2014. The imagery can be found at the following reference. 178)

• On April 8, 2014, the NASA Earth Observatory series released an image of Landsat-8 which spotted a perfect alluvial fan in Kazakhstan's Almaty province on September 9, 2013 (Figure 190). 179)

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Figure 190: OLI of the Landsat-8 satellite captured this view of an alluvial fan in Kazakhstan's Almaty province on Sept. 9, 2013 (image credit: NASA Earth Observatory, USGS)

Legend to Figure 190: In the lower left of the image, the Tente River flows through a narrow channel in the foothills of the Dzungarian Alatau range. Where the Tente emerges from the hills near Lake Alakol, it spreads out and becomes a braided stream. The movement of the channel over time has left a large fan that's about 20 km across at its widest point.

Mountain streams are usually confined to narrow channels and tend to transport sizable amounts of gravel, sand, clay, and silt—material that geologists call alluvium. The type and quantity of alluvium transported depends on the volume of the water flow and the gradient of the stream. Larger rivers pick up more alluvium than smaller ones; fast-flowing streams on steep slopes transport coarser sediment than slow-moving ones on shallow slopes.

The narrowest point of an alluvial fan—closest to the mountain front—is known as the apex; the broader part is called the apron. Alluvium deposited closer to the apex tends to be coarser than the material that makes up the apron. Alluvial fans are more likely to form in deserts because there is plenty of loose alluvium and not much vegetation to prevent stream channels from shifting.

Alluvial fans in arid areas are often used for agriculture because they are relatively flat and provide groundwater for irrigation. This fan is no exception. The blocky green pattern across the apron are fields or pasture land. A number of towns and villages, including Usharal and Beskol, are visible along the fan's outer edge. The straight feature cutting through Beskol and along the northeastern portion of the fan are railroad tracks.

• In March 2014, the Landsat-8 spacecraft and its payload are operating nominally. 180)

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Figure 191: Landsat-8 spacecraft status (image credit: USGS)

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Figure 192: Landsat-8 and Landsat-7 observation coverage frequency in the fiscal years FY13 and in March FY14 (image credit: NASA) 181)

• Feb. 25, 2014: Large landslide detected in Southeastern Alaska. Using imagery from the Landsat-8 satellite, scientists have confirmed that a large landslide occurred in southeastern Alaska on February 16, 2014. A preliminary estimate suggests the landslide on the flanks of Mount La Perouse involved 68 million metric tons of material, which potentially makes it the largest known natural landslide on Earth since 2010.

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Figure 193: OLI of Landsat-8 acquired this image on February 23, 2014 (image credit: NASA Earth Observatory) 182)

Legend to Figure 193: The avalanche debris appears light brown compared to the snow-covered surroundings. The sediment slid in a southeasterly direction, stretching across 7.4 km and mixing with ice and snow in the process. The slide was triggered by the collapse of a near-vertical mountain face at an elevation of 2,800 m, according to Colin Stark, a geophysicist at the Lamont-Doherty Earth Observatory at Columbia University.

Stark first became aware that a landslide may have occurred when a rapid detection tool that sifts through data collected by a global earthquake monitoring network picked up a signal indicative of a fairly significant event. The earthquake sensors detect seismic waves—vibrations that radiate through Earth's crust because of sudden movements of rock, ice, magma, or debris.

While both earthquakes and landslides produce both high-frequency and low-frequency waves, landslides produce more low-frequency waves on balance than earthquakes. Most earthquake detection tools are focused on high-frequency waves, but the detection tool Stark was using the Global CMT (Centroid-Moment-Tensor) Project, also looks closely at low-frequency waves, meaning it is more likely to detect landslides than other tools.

• Feb. 11, 2014: One year ago, on Feb. 11, 2013, NASA launched the Landsat-8 Earth-observing satellite from Vandenberg Air Force Base in California. The launch went perfectly, and 100 days later NASA transferred operational control to the USGS (U.S. Geological Survey). Landsat-8 then joined its predecessor satellites to provide a continuous record of change across Earth's land surfaces since 1972. 183)

- Landsat-8 is acquiring around 550 images/day – significantly more than the 400-image/day design requirement. Between Landsat-7 (launched in 1999 and still active) and Landsat-8, nearly 1,000 images/day are being collected. This is almost double the imagery collected three years ago, when Landsat-5 and -7 were operating together. The ability of Landsat-8 to image more frequently in persistently cloudy areas (e.g., humid tropics, high latitudes) is improving data collection in areas of critical importance for climate studies.

- Landsat-8's robust data processing system also enables images to be available for public use within five hours of their arrival at the USGS EROS (Earth Resources Observation and Science) Center in Sioux Falls, S.D. Since 2008, all Landsat data is free to all. Enhanced Landsat-8 data have quickly found their way into a wide range of operational applications, including forest health monitoring by the U.S. Forest Service, burn severity mapping by the USGS, NASA and the National Park Service, and cropland mapping by the National Agricultural Statistical Service.

- During the past 12 months, the USGS-EROS Center and NASA/GSFC have worked in close collaboration — putting the new satellite through its paces by steering it into its orbit, calibrating its detectors, collecting test images and certifying the mission for sustained operation.

- As partners in the Landsat program since its inception in the 1960s, USGS and NASA have distinct roles. NASA develops remote-sensing instruments and spacecraft, launches the Landsat satellites and validates their performance. The USGS then assumes ownership and operation of the Landsat satellites, in addition to managing ground-data reception, archiving, product generation and distribution.

• January 2014: The Landsat-8 spacecraft and its payload are operating nominally in 2014 with performance exceeding specifications in many respects. 184)

• January 10, 2014: Figure 194 is an OLI image of Guinea-Bissau and the Bissagos islands. Mangrove swamps are abundant along this coastline, acting as important feeding grounds for fish, birds and animals. Flowing from the east, the Geba River empties into the Atlantic Ocean, with the country's capital city of Bissau located on the river estuary. The city appears as a light brown area in the upper-central portion of the image. 185)

- Off the coast in the lower-left section of the image are the Bissagos (or Bijagós) islands – an archipelago of over 80 islands and islets. In 1996 the archipelago was declared a UNESCO Biosphere Reserve. A diversity of mammals, reptiles, birds and fish can be found on the islands, including protected or rare species such as the Nile crocodile, hippopotamus, African manatee and the common bottlenose dolphin. The archipelago has also been recognized as an important site for green sea turtles to lay their eggs.

- In the lower left corner, the island of Orango looks like a tree, with the waterways like branches and land appears as foliage. This island is the center of a national park, and is known for its matrimonial tradition where marriage is formally proposed by the women – who are also responsible for building the homes.

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Figure 194: The coast of Guinea-Bissau in West Africa is pictured in this image from the Landsat-8 satellite, acquired with OLI on May 3, 2013 (image credit: USGS, ESA)

• Dec. 09. 2013: The coldest spot on Earth was found to be in Antarctica on the East Antarctic Plateau where temperatures in several hollows can dip below minus 92ºC on a clear winter night. Scientists made the discovery while analyzing the most detailed global surface temperature maps to date, developed with data from remote sensing satellites including the new Landsat 8, a joint project of NASA and the U.S. Geological Survey (USGS). 186)

The researchers analyzed 32 years' worth of data from several satellite instruments. They found temperatures plummeted to record lows dozens of times in clusters of pockets near a high ridge between Dome Argus and Dome Fuji, two summits on the ice sheet known as the East Antarctic Plateau. The new record of minus 93.2º C was set Aug. 10, 2010.

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Figure 195: The lowest temperature on Earth at -93.2ºC was measured in Antarctica on Aug. 10, 2010 (image credit: NASA)

• Nov. 2013: The OLI instrument of Landsat-8 acquired imagery of lava flows in northern Chile, highlighting some of the distinctive features of a coulée. Lava domes tend to have steep, cliff-like fronts at their leading edge and wrinkle-like pressure ridges on their surfaces. The Chao is a type of lava dome known as a coulée. These elongated flow structures form when highly viscous lavas flow onto steep surfaces. 187)

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Figure 196: Shapes of lava flows in Chile acquired with OLI on May 13, 2013 and released on Nov. 21, 2013 (image credit: NASA Earth Observatory)

Legend to Figure 196: The Chao dacite sits between two volcanoes in northern Chile: the older and partially-eroded Cerro del Leon and the younger Paniri. The dome itself is a giant tongue of rock that extends southwest from the vent. Curved pressure ridges known as ogives dominate the surface of the 14 km dome.

Volcanologists estimate the Chao dacite dome formed over a period of about 100 to 150 years. A pyroclastic flow during the Chao I phase left light-brown deposits of tephra and pumice at the leading edge of the flow. Pyroclastic flows are avalanche-like events that bring mixtures of hot gas and semi-sold rocks surging down the flanks of volcanoes at speeds as fast as 100 km/hour.

This period was followed by the Chao II phase, when 22.5 km3 of lava erupted. This flow has 400 m tall fronts that stand out with their dark shadows on the southwest end. The final, Chao III phase added another 3.5 km3 of denser lava with a lower viscosity. This type of lava is less likely to form pressure ridges, so surfaces in this part of the flow are comparatively smooth.

• Oct. 22, 2013: Since its launch in February 2013, Landsat-8 has collected about 400 scenes of the Earth's surface/day. Each of these scenes covers an area of about 185 km x 185 km or 34,200 km2 for a total of 13,690,000 km2/day. An area about 40% larger than the United States, every day.

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Figure 197: Lava flows and ash plume from Klyuchevskaya volcano, Kamchatka, acquired by OLI on Oct. 20, 2013 (image credit: NASA)

Legend to Figure 197: Located on Russia's Kamchatka Peninsula, Klyuchevskaya (also spelled Kliuchevskoi) is one of the world's most active volcanoes. More than 100 flank eruptions have occurred at the stratovolcano in the past 3,000 years, according to Smithsonian's Global Volcanism Program. Twelve confirmed eruptions have occurred since 2000.

Klyuchevskaya has been erupting since August 15, 2013, though the intensity of activity surged in October. The Kamchatka Volcanic Eruption Response Team (KVERT) reported a thick plume of ash and steam streaming from the summit on October 11. Subsequent days brought explosive eruptions, lava fountains, and volcanic tremors. At times, the ash plume rose from the summit (elevation 5 km) up to 7.5 to 10 km.

When OLI of Landsat-8 flew over in the afternoon on October 20, multiple lava flows streamed down Klyuchevskaya northern and western flanks. The false-color image of Figure 197 shows heat from the flows in SWIR, and green light. Ash, water clouds, and steam appear gray, while snow and ice are bright blue-green. Bare rock and fresh volcanic deposits are nearly black. 188)

• August 25, 2013: A study of Garden and Hog Islands of Lake Michigan observed by Landsat-8. 189)

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Figure 198: Landsat-8 OLI image (excerpt of Figure 199) of Garden and Hog Islands of Lake Michigan acquired on May 24, 2013 (image credit: USGS)

Legend to Figures 198 and 199: Over thousands of years, retreating glaciers scoured and carved out much of the basin that now holds Lake Michigan. But in some parts of the lake, patches of erosion-resistant rock still protrude above the water. A cluster of small islands in the far northern reaches of the lake—the Beaver Island archipelago—are composed of limestone bedrock covered with a layer of sand and gravel (glacial "till").

Except for Beaver Island, the largest of the group, the islands are unpopulated. About 700 people live on Beaver Island, mainly in a small town on the northern part of the island. A Native American community survived on Garden Island until as recently as the 1900s, but the size of the community dwindled until the last remaining resident died in the 1940s.

The OLI (Operational Land Imager) on Landsat 8 captured the top image (Figure 198) of Garden and Hog islands on May 24, 2013. The lower image, a broader view (Figure 199), shows Beaver Island and the other islands in the context of the great lake. Dense forests, swamps, and sandy beaches dominate the landscape. Offshore, deeper waters appear dark blue, while shallow areas are turquoise.

The shallows around Garden and Hog islands contain numerous parallel rock ridges interspersed by deeper channels. These reef areas offer ideal spawning ground for various species of fish, notably lake trout and perch. Federal and state resource managers have attempted to replenish depleted lake trout populations by stocking northern Lake Michigan waters.

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Figure 199: Landsat-8 OLI image of the upper Lake Michigan acquired on May 24, 2013 (image credit: USGS)

• On August 18, 2013, Mount Sakurajima (Japan) on the island of Kyushu erupted. The eruption lasted for about 50 minutes, sending ash and smoke across the bay into the city of Kagoshima, which is near the southwestern tip of the island of Kyushu in Japan. 190)

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Figure 200: Landsat-8 acquired these images on August 19, 2013 which have been pan-sharpened to more clearly show the remaining smoke continuing to billow from the volcano (image credit: USGS)

Legend to Figure 200: The color image (left) uses Landsat bands 4, 3 and 1 of OLI (Operational Land Imager). The black and white image (right) was acquired with TIRS (Thermal Infrared Sensor) in band 10 and displays the temperature differences. Warmer surfaces appear light gray to white in the thermal image, while cooler areas appear dark gray to black. While there are few clouds near the caldera, the bright land surface indicates the heat on the land near the volcano.

• In June 2013, the Silver Fire of 55850 hectar in size in New Mexico, USA, was observed by Landsat-8 repeatedly to give forest restoration specialists a means to analyze and determine where the burn destroyed vegetation and exposed soil – and where to focus emergency restoration efforts. 191)

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Figure 201: Left: Landsat-8 false color image acquired on May 28, 2013; Right: Landsat-8 image acquired on June 13, 2013, while the New Mexico Silver Fire was still growing, the white puffs with black shadows in the right image are clouds (image credit: USGS, NASA)

Legend to Figure 201: The red color in the right-hand picture means high-severity fire, and the red areas were concentrated in a watershed drainage that fed communities west of Las Cruces, N.M. The BEAR (Burned Area Emergency Response) teams are designed to go in as soon as the flames die down to help protect reservoirs, watersheds and infrastructure from post-fire floods and erosion.

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Figure 202: The Landsat-8 soil burn severity map of the NM Silver Fire shows areas that with high (red), medium (yellow) and low (green) severity burns (imagage credit: USDA Forest Service, Burned Area Emergency Response Team)

Legend to Figure 202: As a wildfire starts to die down, fire managers can contact the Forest Service's Remote Sensing Applications Center in Salt Lake City to request maps that identify the high, moderate and low severity burns. When that call comes in, remote sensing specialist Carl Albury finds satellite imagery of the burned forest both pre- and post-fire.

In Landsat-8 imagery, two of the 11 spectral bands – the near-infrared band (No 5) and a short-wave infrared band (No 6) are used for hot spots. The near infrared reflects well from healthy vegetation, and the short-wave infrared bands reflect well from exposed ground. By comparing the normalized ratio of the near- and shortwave-infrared bands in the pre-fire image to the post-fire image, the burn severity can be estimated (Ref. 191).

Landsat-8 is operational — LDCM was officially renamed to Landsat-8. On May 30, 2013, NASA transferred operational control of the Landsat-8 satellite to the USGS (U.S. Geological Survey ) in Sioux Falls, S.D. This marks the beginning of the operational phase of the Landsat-8. The USGS now manages the satellite flight operations team within the Mission Operations Center, which remains located at NASA's Goddard Space Flight Center in Greenbelt, MD.

The mission carries on a long tradition of Landsat satellites that for more than 40 years have helped to study how Earth works, to understand how humans are affecting it and to make wiser decisions for the future. The USGS will collect at least 400 Landsat-8 scenes every day from around the world to be processed and archived at the USGS/EROS (Earth Resources Observation and Science Center) in Sioux Falls. 192)

• May 22, 2013: One of two new spectral bands identifies high-altitude, wispy cirrus clouds that are not apparent in the images from any of the other spectral bands. The March 24, 2013, natural color image of the Aral Sea, for example, appears to be from a relatively clear day. But when viewed in the cirrus-detecting band, bright white clouds appear. 193)

The SWIR band No 9 (1360-1390 nm) is the cirrus detection band of the OLI (Operational Land Imager) instrument. Cirrus clouds are composed of ice crystals. The radiation in this band bounces off of ice crystals of the high altitude clouds, but in the lower regions, the radiation is absorbed by the water vapor in the air closer to the ground. The information in the cirrus band is to alert scientists and other Landsat users to the presence of cirrus clouds, so they know the data in the pixels under the high-altitude clouds could be slightly askew. Scientists could instead use images taken on a cloud-free day, or correct data from the other spectral bands to account for any cirrus clouds detected in the new band.

Figures 203 and 204 are simultaneous OLI observations of the same area of the Aral Sea region in Central Asia which illustrate the power of interpretation of a scene. The cirrus clouds of Figure 204 are simply not visible in the natural color image of Figure 203. This new analysis feature will give scientists a better handle to study the changing environment.

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Figure 203: Natural color image of the Aral Sea region observed on March 24, 2013 (image credit: NASA)

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Figure 204: Cirrus cloud detection band image of the Aral Sea region observed on March 24, 2013 (image credit: NASA)

• May 9, 2013: Availability of free long-term Landsat imagery to the public. Today, Google released more than a quarter-century of images, provided free to the public, of Earth taken from space and compiled into an interactive time-lapse experience. Working with data from the Landsat Program managed by the USGS (U.S. Geological Survey), the images display a historical perspective on changes to Earth's surface over time. 194) 195) 196) 197)

The long-term archive of Landsat images of every spot on Earth is a treasure trove of scientific information that can form the basis for a myriad of useful applications by commercial enterprises, government scientists and managers, the academic community, and the public at large.

In 2009, Google started working with USGS to make this historic archive of Earth imagery available online. Using Google Earth Engine technology, the Google team sifted through 2,068,467 images—a total of 909 terabytes of data—to find the highest-quality pixels (e.g., those without clouds), for every year since 1984 and for every spot on Earth. The team then compiled these into enormous planetary images, 1.78 terapixels each, one for each year.

• May 6, 2013: As the LDCM satellite flew over Indonesia's Flores Sea on April 29, it captured an image of Paluweh volcano spewing ash into the air. The satellite's OLI instrument detected the white cloud of smoke and ash drifting northwest, over the green forests of the island and the blue waters of the tropical sea. The TIRS (Thermal Infrared Sensor) on LDCM picked up even more. 198) 199)

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Figure 205: An ash plume drifts from Paluweh volcano in Indonesia in this image, taken April 29, 2013 with OLI (image credit: NASA)

By imaging the heat emanating from the 5-mile-wide volcanic island, TIRS revealed a hot spot at the top of the volcano where lava has been oozing in recent months (Figure 206).

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Figure 206: This thermal image was taken by the TIRS instrument on April 29, 2013 (image credit: USGS, NASA)

Legend to Figure 206: A bright white hot spot, surrounded by cooler dark ash clouds, shows the volcanic activity at Paluweh volcano in the Flores Sea, Indonesia. The image of Paluweh also illuminates TIRS' abilities to capture the boundaries between the hot volcanic activity and the cooler volcanic ash without the signal from the hot spot bleeding over into pixels imaging the cooler surrounding areas.

• May 2, 2013: All spacecraft and instrument systems continue to perform normally. LDCM continues to collect more than 400 scenes per day and the U.S. Geological Survey Data Processing and Archive System continues to test its ability to process the data flow while waiting for the validation and delivery of on-orbit calibration, which convert raw data into reliable data products. 200)

• On April 12, 2013, LDCM (Landsat Data Continuity Mission) reached its final altitude of 705 km. One week later, the satellite's natural-color imager (OLI) scanned a swath of land 185 km wide and 9,000 km long. 201) 202)

• Since April 4, 2013, LDCM is on WRS-2 (Worldwide Reference System-2),

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Figure 207: These images show a portion of the Great Salt Lake, Utah as seen by LS-7 (left) and LS-8 (LDCM) satellites (right); both images were acquired on March 29, 2013 (image credit: USGS, Ref. 202)

Legend to Figure 207: On March 29-30, 2013, the LDCM was in position under the Landsat 7 satellite. This provided opportunities for near-coincident data collection from both satellites. The images below show a portion of the Great Salt Lake in Utah, and the Dolan Springs, Arizona area, the latter of which is used in Landsat calibration activities. 203)

• March 21, 2013: Since launch, LDCM has been going through on-orbit testing. The mission operations team has completed its review of all major spacecraft and instrument subsystems, and performed multiple spacecraft attitude maneuvers to verify the ability to accurately point the instruments. 204)

- As planned, LDCM currently is flying in an orbit slightly lower than its operational orbit of 705 km above Earth's surface. As the spacecraft's thrusters raise its orbit, the NASA-USGS team will take the opportunity to collect imagery while LDCM is flying under Landsat 7, also operating in orbit. Measurements collected simultaneously from both satellites will allow the team to cross-calibrate the LDCM sensors with Landsat 7's Enhanced Thematic Mapper-Plus instrument.

- After its checkout and commissioning phase is complete, LDCM will begin its normal operations in May. At that time, NASA will hand over control of the satellite to the USGS, which will operate it throughout its planned five-year mission life. The satellite will be renamed Landsat 8. USGS will process data from OLI and TIRS and add it to the Landsat Data Archive at the USGS Earth Resources Observation and Science Center, where it will be distributed for free via the Internet.

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Figure 208: First image of LDCM released in March 2013 (image credit: NASA) 205)

Legend to Figure 208: The first image shows the meeting of the Great Plains with the Front Ranges of the Rocky Mountains in Wyoming and Colorado. The natural-color image shows the green coniferous forest of the mountains coming down to the dormant brown plains. The cities of Cheyenne, Fort Collins, Loveland, Longmont, Boulder and Denver string out from north to south. Popcorn clouds dot the plains while more complete cloud cover obscures the mountains.
The image was observed on March 18, 2013 using data from OLI (Operational Land Imager) bands 3 (green), 5 (near infrared), and 7 (short wave infrared 2) displayed as blue, green and red, respectively.

• March 18, 2013: First day of simultaneous OLI and TIRS Earth imaging (Ref. 202).

• Feb. 21, 2013: The LDCM mission operations team successfully completed the first phase of spacecraft activation. All spacecraft subsystems have been turned on, including propulsion, and power has been supplied to the OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) instruments. 206)

• LDCM will go through a check-out phase for the next three months. Afterward, operational control will be transferred to NASA's mission partner, the USGS (U.S. Geological Survey), and the satellite will be renamed to Landsat-8. The data will be archived and distributed free over the Internet from the EROS (Earth Resources Observation and Science) center in Sioux Falls, S.D. Distribution of Landsat-8 data from the USGS archive is expected to begin within 100 days of launch.

• The LDCM spacecraft separated from the rocket 79 minutes after launch and the first signal was received 3 minutes later at the ground station in Svalbard, Norway. The solar arrays deployed 86 minutes after launch, and the spacecraft is generating power from them (Ref. 25).

Minimize Sensor Complement

Sensor complement: (OLI, TIRS)

Background: In 2008 the TIRS (Thermal Infrared Sensor) instrument was still regarded an option to the LDCM mission. However, in Dec. 2009, the US government confirmed that TIRS would be developed and would be on board the LDCM spacecraft. In the spring of 2010, TIRS passed the CDR (Critical Design Review). 207) 208)

The OLI and TIRS data are merged into a single data stream. Together the OLI and TIRS instruments on LDCM replace the ETM+ instrument on Landsat-7 with significant enhancements.

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Figure 209: Photo of the EM PIE (Payload Interface Electronics) equipment, image credit: NASA

 

OLI (Operational Land Imager):

Already in July 2007, NASA had awarded a contract to BATC (Ball Aerospace Technology Corporation) of Boulder, CO, to develop the OLI (Operational Land Imager) key instrument for LDCM. The BATC contract terms call for the design, development, fabrication and integration of one OLI flight model. Furthermore, the company is also required to test, deliver and provide post-delivery support and five years of on-orbit support for the instrument.

The multispectral and moderate resolution OLI instrument has similar spectral bands to the ETM+ (Enhanced Thermal Mapper plus) sensor of Landsat-7. It includes new coastal aerosol (443 nm, band 1) and cirrus detection (1375 nm, band 9) bands, though it does not have a thermal infrared band.

The following list provides an overview of the most important observation requirements for the OLI instrument: 209)

• The specifications require delivery of data covering at least 400 Landsat scenes/day (185 km x 180 km) for the US archive. The data are to be acquired in a manner that affords seasonal coverage of the global land mass. Data are required for the heritage reflective Thematic Mapper (TM) spectral bands plus two new bands, a blue band for coastal zone observations and a short wave infrared band for cirrus cloud detection.

• 30 m GSD (Ground Sample Distance) for VIS/NIR/SWIR, 15m GSD for PAN data.

• The specifications do not require thermal data (TIR band), representing a departure from the TM (Thematic Mapper) heritage. The specification also requires data providing a 30 m GSD (Ground Sample Distance) for each of the multispectral bands. Note: The TIR band was deselected due to the extra cost of active cooling.

• An edge response slope is also specified for the image data from each spectral band. The edge response is defined as the normalized response of the image data to a sharp edge as expressed in a Level 1R VDP (Validation Data Product). An edge response slope of 0.027 is required for bands 1 through 7, a slope of 0.054 is required for the panchromatic band, band 8, and a slope of 0.006 for the cirrus band, band 9.

• All instrument source data will be quantized to 12 bit resolution.

Band Nr

Band Name

Spectral range (nm)

Use of data

GSD

Radiance (W/m2 sr μm), typical

SNR
(typical)

1

New Deep Blue

433-453

Aerosol/coastal zone

30 m

40

130

2

Blue

450-515

Pigments/scatter/coastal

 

 

30 m
(TM heritage bands)

40

130

3

Green

525-600

Pigments/coastal

30

100

4

Red

630-680

Pigments/coastal

22

90

5

NIR

845-885

Foliage/coastal

14

90

6

SWIR 2

1560-1660

Foliage

4.0

100

7

SWIR 3

2100-2300

Minerals/litter/no scatter

1.7

100

8

PAN

500-680

Image sharpening

15 m

23

80

9

SWIR

1360-1390

Cirrus cloud detection

30 m

6.0

130

Table 9: NASA/USGS requirements for LDCM imager spectral bands

• The WRS-2 (Worldwide Reference System-2) defines Landsat scenes as 185 km x 180 km rectangular areas on the Earth's surface designated by path and row coordinates. This heritage system is used to catalogue the data acquired by the Landsat 4, 5, and 7 satellites and will also be used for the LDCM.

• Provide "standard", orthorectified data products within 24 hours of observation (products available via the web at no cost)

• Data calibration consistent with previous Landsat missions

• Continue IC (International Cooperator) downlinks

• Support priority imaging and a limited off-nadir collection capability (± 1 path/row).

OLI (LDCM)

ETM+ (Landsat-7)

Band Nr

Wavelength (µm)

GSD (m)

Band No.

Wavelength (µm)

GSD (m)

8 (PAN)

0.500 - 0.680

15

8 (PAN)

0.52 - 0.90

15

1

0.433 - 0.453

30

 

 

 

2

0.450 - 0.515

30

1

0.45 - 0.52

30

3

0.525 - 0.600

30

2

0.53 - 0.61

30

4

0.630 - 0.680

30

3

0.63 - 0.69

30

 

 

 

4

0.78 - 0.90

30

5

0.845 - 0.885

30

 

 

 

9

1.360 - 1.390

30

 

 

 

6

1.560 - 1.660

30

5

1.55 - 1.75

30

7

2.100 - 2.300

30

7

2.09 - 2.35

30

OLI does not include thermal imaging capabilities

6 (TIR)

10.40 - 12.50

60

Figure 210: Spectral parameter comparison of OLI and ETM+ instruments

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Figure 211: OLI and ETM spectral bands (image credit: NASA)

OLI instrument:

The OLI design features a multispectral imager with a pushbroom architecture (Figure 212) of ALI (Advanced Land Imager) heritage, a technology demonstration instrument flown on the EO-1 spacecraft of NASA (launch Nov. 21, 2000). A pushbroom implementation is considered to be more geometrically stable than the whiskbroom scanner of the ETM+ instrument. As a tradeoff of this architecture selection, the imagery must be terrain corrected to ensure accurate band registration.. 210) 211) 212) 213) 214)

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Figure 212: Schematic view of the OLI instrument design (image credit: BATC)

The FPA (Focal Plane Assembly) consists of 14 FPMs (Focal Plane Modules). This is a consequence of the pushbroom architecture selection for OLI leading to a different set of geometric challenges than a cross-track whiskbroom implementation. Instead of using a small focal plane and a scanning mirror, 14 FPMs are required to cover the full Landsat cross-track field of view. Each FPM contains nine spectral bands in along-track (Figure 213). The along-track spectral band separation leads to an approximately 0.96-second time delay between the leading and trailing bands. This time delay creates a small but significant terrain parallax effect between spectral bands, making band registration more challenging.

The along-track dimension of the OLI focal plane (see Figure 214) also makes it desirable to "yaw steer" the spacecraft. This means that the spacecraft flight axis is aligned with the ground (Earth fixed) velocity vector, rather than with the inertial velocity vector, in order to compensate for cross-track image motion due to Earth rotation.

Although the pushbroom architecture requires many more detectors and a correspondingly larger focal plane, it also allows for a much longer detector dwell time (~4 ms for OLI vs. 9.6 µs for ETM+), leading to much higher signal-to-noise ratios. The lack of moving parts in the pushbroom design also allows for a more stable imaging platform and good internal image geometry.

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Figure 213: Schematic view of the FPM layout concept (image credit: BATC, USGS)

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Figure 214: Orientation of the FPMs in the FPA (Focal Plane Assembly) of the OLI instrument (image credit: BATC)

Each FPM contains detectors for each spectral band, silicon for the VNIR bands and HgCdTe for the SWIR bands and a butcher-block filter assembly to provide the spectral bands.

OLI features about 6500 active detectors per multispectral band and 13000 detectors for the panchromatic band. These detectors are organized as blocks ~500 multispectral (1000 panchromatic) detectors wide within 14 focal plane modules (FPMs) that make up the focal plane assembly. Each module has its own butcher-block assembly spectral filter. This provides significantly improved signal to noise performance, but complicates the process of radiometrically matching the detectors responses. Similarly, the lack of a scan mirror removes the need for knowledge of its movement, but requires knowledge of the detectors locations across a much larger focal plane (Ref. 2).

Observation technique

Pushbroom imager

Spectral bands

9 bands in VNIR/SWIR covering a spectral range from 443 nm to 2300 nm

Telescope

- Four-mirror off-axis telescope design with a front aperture stop
- Use of optical bench
- Telecentric design with excellent stray light rejection

FPA (Focal Plane Assembly)

- Consisting of 14 sensor chip assemblies mounted on a single plate
- FPA is passively cooled
- Hybrid silicon / HgCdTe detectors
- Butcher block filter assembly over each SCA (Sensor Chip Assembly)

Swath width (FOV=15º)

185 km

GSD (Ground Sample Distance)

15 m for PAN data; 30 m for VNIR/SWIR multispectral data

Data quantization

12 bit

Calibration

- Solar calibrator (diffuser) used once/week
- Stimulation lamps used to check intra-orbit calibration
- Dark shutter for offset calibration (used twice per orbit)
- Dark detectors on focal plane to monitor offset drift

Instrument, mass, power, size

 

Table 10: Overview of OLI instrument parameters

The OLI will provide global coverage by acquiring ~400 scenes per day in six VNIR and three SWIR bands, all at 12 bit radiometric resolution. In addition to these bands, there will be a tenth band consisting of covered SWIR detectors, referred to as the ‘blind' band, that will be used to estimate variation in detector bias during nominal Earth image acquisitions. The OLI bands are distributed over 14 SCAs (Sensor Chip Assemblies) or FPMs, each with 494 detectors per 30 m band and twice as many for the 15 m panchromatic band - totaling in over 75000 imaging detectors. 215)

OLI calibration:

The OLI calibration subsystem (Figures 215 and 216) consists of two solar diffusers (a working and a pristine), and a shutter. When positioned so that the sun enters the solar lightshade, the diffusers reflect light diffusely into the instruments aperture and provide a full system full aperture calibration. The shutter, when closed, provides a dark reference. In addition, two stim lamp assemblies are located at the front aperture stop. Each lamp assembly contains three lamps (per redundant configuration) that are operated at constant current and monitored by a silicon photodiode. The lamp signal goes through the full telescope system. Additionally, the OLI focal plane will include masked HgCdTe detectors, that is, detectors that will be blocked from seeing the Earth's radiance (Ref. 2). 216) 217)

Solar diffusers:

- Full-aperture full system Spectralon diffuser, designed to be used at different frequencies to aid in tracking the system and diffuser changes. The pristine diffuser will be used to check degradation of main diffuser.

- The primary solar diffuser will nominally be deployed every 8 days to track the calibration of the OLI sensor and perform detector-to-detector normalization.

- The solar diffuser based calibration requires a spacecraft maneuver to point the OLI solar calibration aperture towards the sun. The pristine diffuser will be used on a less frequent basis, about every six months, as a check on the primary diffuser's degradation.

Stimulation lamps:

- Multi—bulbed tungsten lamp assemblies, that illuminate the OLI detectors through the full optical system, similarly designed to be used at different frequencies to separate lamp and system changes. The working lamp will be used daily for intra-orbit calibration/characterization; the reference lamp set approximately monthly, and the pristine lamp set approximately twice a year.

- The lamb assembly can also be compared to solar diffuser measurements to check stability.

Dark shutter:

- Used twice per orbit for offset calibration

• Dark detectors on focal plane to monitor offset drift

• Linearity checked by varying detector integration time.

The LDCM operational concept also calls for the spacecraft to be maneuvered every lunar cycle to view the moon, providing a "known" stable source for tracking stability over the mission. A side-slither maneuver, where the spacecraft is rotated 90º to align the detector rows with the velocity vector, is also planned. These data will provide an additional method to assess the detector-to-detector radiometric normalization.

Pre-launch spectro-radiometric characterization and calibration (Ref. 216):

The spectral characterization of the OLI instrument is being performed at the component, focal plane module and fill instrument levels. The components, which have all completed testing, include detector witness samples, spectral filters prior to dicing into flight filter sticks, the focal plane assembly window witness samples and telescope mirror witness samples.

The FPM (Focal Plane Module) level tests, which are also complete, are specifically designed to characterize the spectral out-of-band response. The FPM level tests measure the spectral response of all the detectors by illuminating the full focal plane at approximately the correct cone angle.

An integrating sphere is used in the pre-launch radiance calibration of the OLI. The traceability of the calibration of this sphere will start with the 11" OLI transfer sphere directly calibrated at the NIST Facility for Spectroradiometric Calibration (FASCAL). While still at NIST, this OLI transfer sphere is checked by independently NIST calibrated University of Arizona (UAR VNIR transfer radiometer), NASA and NIST (Government Transfer Radiometers) radiometers. Also, the Ball Standard Radiometer (BSR), that has filters matching the OLI bands, views the sphere.

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Figure 215: OLI block diagram illustrating the calibration subsystem in front of the telescope (image credit: NASA, BATC)

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Figure 216: Blow-up of the calibration subsystem illustrating the solar diffuser and shutter assemblies (image credit: NASA, BATC)

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Figure 217: Illustration of the OLI instrument (image credit: NASA, BATC)

In Nov. 2008, the OLI instrument passed the ICDR (Instrument Critical Design Review). 218)

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Figure 218: Photo of the completed OLI instrument with electronics (image credit: BATC, NASA, USGS)

Delivery of the OLI instrument in the summer of 2011 (Ref. 3).

 

TIRS (Thermal Infrared Sensor)

The TIRS instrument is providing continuity for two infrared bands not imaged by OLI. NASA/GSFC is building the TIRS instrument inhouse. TIRS is a late addition to the LDCM mission, the requirements call for a GSD (Ground Sample Distance of 120 m for the imagery; however, the actual GSD will be 100 m.

The LDCM ground system will merge the data from both sensors into a single multispectral image product. These data products will be available for free to the general public from the USGS enabling a broad scope of scientific research and land management applications. 219) 220)

TIRS is a QWIP (Quantum Well Infrared Photodetector) based instrument intended to supplement the observations of the OLI instrument. The TIRS instrument is a TIR (Thermal Infrared) imager operating in the pushbroom mode with two IR channels: 10.8 µm and 12 µm. The two spectral bands are achieved through interference filters that cover the FPA (Focal Plane Assembly). The pushbroom implementation increases the system sensitivity by allowing longer integration times than whiskbroom sensors. The two channels allow the use of the "split-window" technique to aid in atmospheric correction.

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Figure 219: Functional block diagram of TIRS (image credit: NASA, Ref. 217)

The focal plane consists of three 640 x 512 QWIP GaAs arrays mounted on a silicon substrate that is mounted on an invar baseplate. The two spectral bands are defined by bandpass filters mounted in close proximity to the detector surfaces. The QWIP arrays are hybridized to ISC9803 readout integrated circuits (ROICs) of Indigo Corporation. The focal plane operating temperature will be maintained at 43 K (nominally). 221) 222) 223)

Instrument type

Pushbroom imager

Two channel thermal imaging instrument

10.8 and 12.0 µm band centers

Bandwidths

10.3-11.3 µm,
11.5-12.5 µm

GSD (Ground Sample Distance)

100 m (nominal), 120 m (requirement)

Swath width

185 km, FOV = 15º

Operating cadence

70 frames/s

Instrument calibration

- Scene select mirror to select between 2 calibration sources
- Two full aperture calibration sources: onboard internal calibration and space view

Detector

- Three SCA (Sub-Chip Assembly) QWIP detectors built in-house at Goddard
- FPA consists of three 640 x 512 detector arrays
- Pixel size of 25 µm producing an IFOV of 142 µrad
- The FPA consists of an invar "spider" which is bonded to the silicon interface board
containing the QWIPs and on which the "daughter boards" are mounted.
- Actively cooled FPA operating at 43 K
- Two-stage cryocooler provided by BATC

Telescope

- The telescope is a 4-element refractive lens system.
- Passively cooled telescope operating at 185 K

Telescope f number

f/1.64

Data quantization

12 bit

Instrument mass, size, power

236 kg, approx: 80 cm x 76 cm x 43 cm, 380 W

Table 11: TIRS instrument parameters

QWIP detector: The development of the QWIP detector technology has made great strides in the first decade of the 21st century. In 2008, NASA/GSFC revised the design of the infrared detector concept of the TIRS (Thermal Infrared Sensor) imager, under development for the LDCM (Landsat Data Continuity Mission). The initially considered HgCdTe-based detector design was changed to a QWIP design due to the emergence of broadband QWIP capabilities in the MWIR and TIR (LWIR) regions of the spectrum. The introduction of QWIP technology for an operational EO mission represents a breakthrough made possible through collaborative efforts of GSFC, the Army Research Lab and industry (Ref. 222).

An important advantage of GaAs QWIP technology is the ability to fabricate arrays in a fashion similar to and compatible with the silicon IC technology. The designer's ability to easily select the spectral response of the material from 3 µm to beyond 15 µm is the result of the success of band-gap engineering. 224)

Advantages of QWIP technology:

- Large lattice-matched substrates

- Mature materials technology

- No unstable mid-gap traps

- Inherently, radiation hard.

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Figure 220: QWIP quantum state diagram (image credit: NASA/JPL)

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Figure 221: TIRS 10-13 µm QWIP spectral response requirement (image credit: NASA)

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Figure 222: Overview of the TIRS focal plane layout (image credit: NASA, Ref. 217)

The three arrays are precisely aligned to each other in the horizontal and vertical directions (to within 2 µm). There is a requirement that the detection region within the QWIP array be within 10 µm of a common focal plane altitude. This specification is challenging since it includes surface non-uniformities of the baseplate, substrate, the QWIP/ROIC hybrid and the epoxy bond lines between these components. Nonetheless, since there are three discreet arrays they must all fall within a single focus position.

The filter bands are further confined to specific regions of the QWIP array. Although each array contains 512 rows, after all the operational requirements are satisfied (frame rate, windowing, co-registration, scene reconstruction, etc.) only 32 rows are available under each filter band separated by 76 rows of occluded pixels (for dark current subtraction). Once all these requirements are incorporated into the focal plane design, eligible rows on any given array are pre-determined. Of these eligible rows, there must be three that can be combined to make two perfect rows, or preferably, at least two perfect rows (that is, rows where all pixels meet every specification).

TRL (Technology Readiness Level) tests: An important and essential process for qualifying new or previously unused technology in a NASA space mission is the technology readiness level demonstration. There are nine levels with level 6 (TRL 6) being the level at which new hardware must be demonstrated. Typically, this means qualification in the environment which the instrument will be subjected through out the mission; radiation effects, vibration, thermal cycling and (in some cases) shock. Both the readout and QWIP hybrids were subjected to gamma, proton and heavy ion radiation equivalent to 35 krad or almost 10 times the expected mission dose. At these levels and at the operating temperature of 43 K minimal effects were observed and none were considered to be a mission risk.

A fully functioning focal plane assembly was subjected to 40 thermal cycles from 300 K to 77 K and back to 300 K. Every tenth cycle went to 43 K to collect the array performance data. After the completion of the 40 cycles there was essentially no change in any of the three QWIP arrays (2 grating QWIP hybrids and one C-QWIP hybrid). - The final environmental test performed was vibration to simulate the effect of the launch. Since this is a qualification test the vibration loads are specified 3db above the expected loads. The focal plane assembly was subjected to a series of vibration input loads including x, y and z-axis random vibration for 2 minutes/axis, a sine sweep and sine burst test (15 g at 20 Hz). No failures occurred and this assembly and the overall design was certified by an independent review panel as having met the requirements for TRL 6.

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Figure 223: Schematic view of the FPA (Focal Plane Assembly), image credit: NASA

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Figure 224: Photos of the FPA (image credit: NASA)

Legend to Figure 224: The left photo of the FPA is without filters showing the 3 QWIPs in the center. The daughter boards are the red and green assemblies to the left and right, respectively. The invar spider is the component with the 4 arms. - The right picture of the FPA comes with the filters attached. Note that there are two filters over each array with a thin dark strip between them.

Optical system: The imaging telescope is a 4-element refractive lens system. A scene select mechanism (SSM) rotates a scene mirror (SM) to change the field of regard from a nadir Earth view to either an on-board blackbody calibrator or a deep space view. The blackbody is a full aperture calibrator whose temperature may be varied from 270 to 330 K.

The optical system, consisting of a lens with three Ge elements and one ZnSe element, produces nearly diffraction-limited images at the focal plane. All but 2 of the surfaces are spherical, which simplifies fabrication. The optics are radiatively cooled to a nominal temperature of 185 K to reduce the contribution of background thermal emission to the measurement noise. Because of the fairly strong thermal dependence of the index of refraction of Ge, the focus position of the lens is a function of the optics temperature. This provides a method of adjusting focus so that, in the unlikely event that launch conditions or some other effect defocus the system, the temperature of the optics may be changed by ±5 K to refocus. That is, thermal control of the lens provides a non-mechanical focus mechanism. A +5 K change does not significantly degrade the noise performance.

A precision scene select mirror is an essential component of the TIRS instrument and it is driven by the scene select mechanism. It rotates around the optical axis on a 45º plane to provide the telescope with a view of Earth through the nadir baffle and two full aperture sources of calibration, onboard variable temperature blackbody (hot calibration target) and space view (cold calibration target). The onboard blackbody will be a NIST (National Institute of Standards and Technology) certified reference source (Figure 225).

TIRS is able to achieve a 185 km ground swath with a 15º FOV (Field of View) functioning in the pushbroom sample collection method. This method will have the benefit of being able to collect and record data without movement artifacts due to its wide instantaneous field of view. Frames will be collected at an operating cadence of 70 per second. The collected data will be stored temporarily stored on board and periodically sent to the USGS EROS facility for further storage. The instrument is designed to have an expected lifetime of at least a three years.

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Figure 225: The TIRS optical sensor unit concept (image credit: NASA)

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Figure 226: Schematic view of the TIRS instrument internal assembly (image credit: NASA, Ref. 217)

Legend to Figure 226: Model of the TIRS instrument showing the major components of the TIRS sensor. The scene select mechanism rotates the field of regard from the Earth view to either the space view or to the on-board calibrator. The right side provides some detail of optical system showing the 4-element lens, a cut-away view of the SM and the thermal strap connecting the FPA to the cryocooler cold tip. The MEB (Main Electronics Box) and the CCE (Cyrocooler and its associated Control Electronics), not shown, are mounted to the spacecraft.

TIRS instrument calibration:

Consistent with previous Landsat missions, LDCM TIRS will be fully calibrated prior to launch. Calibration measurements will be made at GSFC and will be done at the component, subsystem and instrument level. NIST-traceable instrument level calibration will be done using an in-chamber calibration system. 225) 226)

Among other uses, TIRS data will be used to measure evapotranspiration (evaporation from soil and transpiration from plants); to map urban heat fluxes, to monitor lake thermal plumes from power plants; to identify mosquito breeding areas and vector-borne illness potential; and to provide cloud measurements. The evapotranspiration data may be used to estimate consumptive water use on a field-by-field basis.

TIRS instrument calibration makes use of the following elements:

• Precision scene select mirror to select between calibration sources and nadir view

• Two full aperture calibration sources

- Onboard variable temperature blackbody

- Space view

- Calibration every 34 minutes

• NIST Traceable radiometric calibration

Landsat8_AutoA

Figure 227: Schematic of inclusion of NIST standards (image credit: NASA)

TIRS calibration system:

• A 41 cm diameter source is covering full field and aperture of TIRS (Flood Source)

• Target Source Module (GeoRadSource)

- Blackbody point source w/ filter & chopper

- All reflective, off-axis parabola collimator

- Motorized target and filter wheels

- A square steering mirror system (33 cm side length) is permitting coverage of the full aperture and field

• Cooled enclosure over entire system

• External monochromator (spectral source)

• Components are mounted to common base plate.

The TIRS radiometric response is determined via the prelaunch characterization relative to the laboratory blackbody. This approach provides the highest accuracy calibration. The calibration philosophy is then to evaluate (or validate) the calibration parameters once TIRS is on orbit. If the calibration of TIRS is demonstrated to change significantly while on orbit using measurements during the checkout period, then the on-board blackbody (OBB) will be used as the primary pathway to NIST traceability.

Landsat8_Auto9

Figure 228: Illustration of the TIRS calibration system (image credit: USGS)

Landsat8_Auto8

Figure 229: Illustration of TIRS on the LDCM spacecraft (image credit: NASA, Ref. 3)

SSM (Scene Select Mechanism) of TIRS:

The SSM for the TI RS instrument, developed at NASA/GSFC, is a single axis, direct drive mechanism which rotates a 207 mm scene mirror from the nadir science position to the 2 calibration positions twice per orbit. It provides pointing knowledge and stability to ~10 µradians. The SSM can be driven in either direction for unlimited rotations. The rotating mirror is dynamically balanced over the spin axis, and does not require launch locking. 227)

The design of the SSM is straightforward; it is a single axis rotational mechanism. The operational cadence was to hold the scene mirror stationary for ~40 minutes staring at nadir, rotate 120º to the space view aperture and stare for 30 seconds, rotate 120º to the internal blackbody and stare for 30 seconds and then rotate the mirror to the back to nadir. Then the entire process would start again. The mechanism would be operating all of the time, or have a 100% duty cycle. Since LDCM/TI RS was to be in a highly-inclined polar orbit, the general idea was to calibrate twice per orbit while over the poles.

Landsat8_Auto7

Figure 230: Cutaway view of the SSM (image credit: NASA)

Instrument mass, power

15 kg, 6 W average

Pointing knowledge, stability

±9.7 µradians over 34 minutes, ±9.7 µradians over 2.5 seconds

Duty cycle

100%

Thermal operational

0 / +20ºC stable to ±1ºC

Thermal survival range

-50 / +40ºC

Lifetime

3.25 years on orbit

Redundancy

A/B side block redundancy

Operational cadence

Stare nadir for 30-40 minutes
Rotate 120º in < 2 minutes to space view
Stare for ~30 seconds,
Rotate 120º in < 2 minutes to blackbody view
Stare for ~30 seconds
Rotate to 120º in < 2 minutes to nadir view

Table 12: SSM driving requirements

 

Parameter

Landsat ETM+

LDCM OLI

GMES/Sentinel-2 MSI

Spectral bands

Band

µm

Band

µm

Band

µm

 

 

1 (blue)

0.43-0.45

B1 (blue)

0.43-0.45

1 (blue)

0.45–0.52

2 (blue)

0.45–0.52

B2 (blue)

0.46–0.52

2 (green)

0.52–0.60

3 (green)

0.52–0.60

B3 (green)

0.54–0.58

3(red)

0.63–0.69

4 (red)

0.63–0.68

B4 (red)

0.65-0.68

 

 

 

 

B5 (red edge)

0.70-0.71

 

 

 

 

B6 (red edge)

0.73-0.75

 

 

 

 

B7 (red edge)

0.77-0.79

4 (NIR)

0.76–0.90

 

 

B8 (NIR)

0.78-0.90

 

 

5 (NIR)

0.84-0.88

B8a (NIR)

0.86-0.88

 

 

 

 

B9 (water vapor)

0.93-0.95

 

 

9 (cirrus)

1.36-1.39

B10 (cirrus)

1.37-1.39

5 (SWIR1)

1.55–1.75

6 (SWIR1)

1.56-1.66

B11 (SWIR1)

1.57-1.66

7 (SWIR2)

2.08–2.35

7 (SWIR2)

2.10-2.30

B12 (SWRIR2)

2.10-2.28

 

 

LDCM TIRS

 

 

6 (TIR)

10.4–12.5

10 (TIR1)

10.3-11.3

 

 

 

 

11 (TIR2)

11.5-12.5

 

 

GSD at nadir

30 m VNIR
15 m Pan
60 m TIR

30 m VNIR
15 m Pan
100 m TIR

10 m (B2, B3, B4, B8)
20 m (B5, B6, B7, B8a, B11, B12)
60 m (B1, B9, B10)

Quantization

8 bit

12 bit

12 bit

Onboard Calibration

Yes

Yes

Yes

Resivit time

16 days

16 days

5 days (2 satellites)

Off-axis viewing

Up to 7.5º off nadir

Up to 7.5º off nadir

Up to 10.3º off nadir (w/o pointing)

Orbit altitude

705 km

705 km

786 km

Swath width

185 km

185 km

290 km

Architecture

Cross-track scanner (Whiskbroom)

Pushbroom

Pushbroom

Table 13: Comparison of Landsat and GMES/Sentinel-2 imager specifications 228)

 

Collection of imagery onboard LDCM:

The co-aligned instruments are nominally nadir pointed and sweep the ground track land surface in contiguous image data collections, also known as image intervals. Each image interval may contain from a few WRS-2 scenes for an island or coastal area up to 77 contiguous WRS-2 scenes for an extended area of interest. For each image interval, the observatory executes a pre-defined imaging and ancillary data collection sequence as shown in Figure 231. 229)

Prior to the image interval, the spacecraft configures the onboard systems for the mission data collection session. A specific number of intervals are pre-defined on the ground based upon the number of WRS-2 scenes scheduled for collection, and allocated in the SSR (Solid State Recorder). Each instrument will transmit focal plane sensor data and instrument ancillary data (voltages, temperatures, etc.), which the spacecraft will interleave with the spacecraft ancillary data (attitude, ephemeris, etc), and record to files in the SSR.

Landsat8_Auto6

Figure 231: Data collection sequence (image credit: USGS, NASA)

If the observatory is over an IC (International Cooperatoror) or LGN (Landsat Ground Network) station, it will simultaneously transmit data in real time to the ground. In addition, each instrument performs routine on-board calibrations (blackbody, lamps, etc) before and after each image interval, and during less frequent occasions utilizing the sun and moon as external calibration sources. A representation of the global image collection and calibration opportunities within the WRS-2 grid is shown in the 16-day repeating DRC-16 (Design Reference Case-16) in Figure 232.

The DRC-16 was developed to aid the mission architects in identification of all image and calibration activities and to verify that all are consistent with spacecraft power and mission data management capabilities. Instrument solar, lunar, and internal calibrations are required by ground system processing systems for image reconstruction, and to produce finished and distributable image products.

Landsat8_Auto5

Figure 232: Illustration of DRC-16 collections (image credit: USGS, NASA)

End to end mission data flow is represented in Figure233 . Mission data originates as instrument sensor (or "image") data, and are collected and processed by the instrument electronics. The instrument electronics transmits the image data to the spacecraft PIE (Payload Interface Electronics) over a HSSDB (High Speed Serial Data Bus), using a serializer-deserializer integrated circuit pair. OLI image data are compressed using the USES (Universal Source Encoder for Space) ASIC (Application-Specific Integrated Circuit), which implements the Rice algorithm for lossless compression. - TIRS data are not compressed due to the low data rate. Instrument image data are interleaved with spacecraft ancillary data to create a file, which is stored and/or provided to the transmitter for downlink.

Ancillary data are collected at rates up to 50 Hz, and is comprised of GPS (Global Positioning System) data, IMU (Inertial Measurement Unit) data, star tracker data, and select instrument engineering information required by ground system algorithms for image product generation. The ancillary data are multiplexed within the mission data files every second.

Mission data files are intentionally fixed in size at 1GB. A system architecture trade study was performed early in mission definition to establish the optimum file size given the implementation of Class 1 CCSDS (Consultative Committee for Space Data Systems) CFDP (File Delivery Protocol), and a required link BER (Bit Error Rate) of < 10-12. Utilizing the 440 Mbit/s available downlink capacity, each downlinked mission data file requires 22 seconds of continuous transmission for a completed delivery to the ground system. The low BER requirement on the communication link provides the confidence that only one file over several days would require retransmission, well within the available contact time with the ground stations.

Landsat8_Auto4

Figure 233: Overview of the mission data flow (image credit: USGS, NASA)

Simultaneous real-time and playback mission data files are transmitted to the ground through virtual channels within a single physical channel. Five data streams on the transmitter interface board may be multiplexed on to the link via an arbiter, which interleaves the data streams according to a pre-established priority scheme. The data streams priorities are:

1) Real-time for the OLI instrument

2) Real-time for the TIRS instrument

3) SSR playback channel 1

4) SSR playback channel 2

5) A virtual channel for fill frames in case no image data are available for downlink.

The five virtual channels are arbitrated in priority order on a frame-by-frame basis. The OLI instrument has the highest priority followed by the TIRS instrument and, since the combined mission data rates are less than the total downlink bandwidth available, there is always residual bandwidth available for mission data playback. This enables maximum utilization of the downlink bandwidth. SSR playback 1 has priority over SSR playback 2. SSR playback 2 is controlled by an autonomous on-board spacecraft flight software task that queues files for playback by a predefined algorithm (i.e. oldest to newest priority files first, oldest to newest non-priority files next).

SSR playback 1 is specifically for ground system intervention, as required to supersede the onboard autonomous SSR playback 1, to downlink files which are a higher priority than originally categorized. SSR playback 2 will resume automatically upon the completion of SSR playback 1 ground commands, and there is no need to stop and restart the autonomous SSR playback 2 queue. As a frame finishes transmission, the priority arbiter selects the highest priority channel that has a frame buffer ready for transmission for the next frame.

To ensure the bandwidth of the space to ground data link is at least twice the bandwidth of the real-time mission data, the spacecraft compresses OLI image data in near real time using CCSDS compression. During early hardware development, using simulated data derived from the ALI (Advanced Land Imager) sensor aboard the EO-1 (Earth Observing-1) satellite (the precursor to the OLI instrument), data sets were constructed and flowed through the compression chip and achieved a nominal 1.55:1 compression. As compression varies on the OLI real-time virtual channel, the playback capacity also varies to use the bandwidth that is available.

The multiplexed virtual channels of mission data are provided to the RF X-band subsystem, where the transmitter adds CCSDS layers and LDPC (Low Parity Density Check) 7/8-rate forward error correction to the 384 Mbit/s data stream, resulting in a 440 Mbit/s stream from the X-band subsystem. The X-band stream is modulated, amplified and down-linked from the spacecraft antenna to the ground station antenna/receivers.

The ground station antenna system receives the 8200.5 MHz OQPSK (Offset-keyed Quadrature Phase Shift Keying) X-band signal from the observatory and forwards the down converted 1.2 GHz or 720 MHz intermediate frequency (IF) signal to a programmable telemetry receiver. The IF signals are routed through a matrix switch, providing signal distribution or routing to redundant equipment as needed.

Within the programmable telemetry receiver, the IF signal from the switching matrix is subject to low-pass filtering to prevent subsequent aliasing followed by an AGC (Automatic Gain Control) action. The AGC action is the last analog handling of the signal prior to the digitizer. The entire ground processing that remains is accomplished in the digital domain. The signal is immediately digitally demodulated within a specially designed modified Costas loop and the resultant baseband signal, now a softbit stream, is sent to the bit synchronizer. The bit stream has ambiguity resolved and is then frame synchronized. The frame synchronizer parses the data stream into equal length frames; queuing on a predefined frame synchronization pattern. The data are de-randomized using the conventional CCSDS algorithm and then stripped of parity and bit-corrected by the LDPC 7/8-rate FEC (Forward Error Correction) decoder.

The frame synchronization processor routes the framealigned data stream to the VCDU (Virtual Channel Data Unit) processor. The VCDU processor identifies the unique virtual channels within the frames and outputs these VCDU into individual data streams for packet processing.

The mission data stream from the VCDU processor is processed through the CCSDS packet processor to separate APID (Application Process Identifiers). The packet processor outputs the resulting mission stream to the CFDP processor.

 


 

Landsat-8 / LDCM ground system:

The LDCM ground system includes all of the ground-based assets needed to operate the LDCM observatory. The primary components of the ground segment are : 230) 231) 232)

- MOE (Mission Operations Element)

- CAPE (Collection Activity Planning Element)

- GNE (Ground Network Element)

- DPAS (Data Processing and Archive System).

The USGS (United States Geological Survey) -and their associated support and development contractors - will:

- Develop the Ground System (comprised of the Flight Operations and Data Processing and Archive Segments), excluding procurement of the MOE

- Provide ground system functional area expertise across all mission segments

- Lead, fund, and manage the Landsat Science Team

- Acquire the FOT (Flight Operations Team) and produce the FOT products 233)

- Lead the LDCM mission operations, after the completion of the on-orbit checkout period

- Accept and execute all responsibilities associated with the transfer of the LDCM OLI (Operational Land Imager) instrument, TIRS (Thermal Infrared Sensor) instrument, spacecraft bus and Mission Operations Element contracts from NASA following on-orbit acceptance of the LDCM system including assuming contract management"

- Provide system engineering for the USGS-managed segments and elements.

The MOE is being provided by the Hammer Corporation. The MOE contract was awarded in September 2008. The MOE provides capability for command and control, mission planning and scheduling, long-term trending and analysis, and flight dynamics analysis. The overall activity planning for the mission is divided between the MOE and CAPE. The MOE hardware and software systems reside in the LDCM MOC (Mission Operations Center).

The CAPE develops a set of image collection and imaging sensor(s) calibration activities to be performed by the observatory. The CAPE schedules activities on a path-row scene basis. The MOE converts CAPE-generated path-row scenes to observatory activities, schedules these and any other detailed observatory activities, and generates commands necessary to collect the identified scenes and operate the observatory.

The GNE is comprised of two nodes located at Fairbanks, Alaska and Sioux Falls, SD. Each node in the GNE includes a ground station that will be capable of receiving LDCM X-band data. Additionally, each station provides complete S-band uplink and downlink capabilities. The GNE will route mission data and observatory housekeeping telemetry to the DPAS.

The DPAS includes those functions related to ingesting, archiving, calibration, processing, and distribution of LDCM data and data products. It also includes the portal to the user community. The ground system, other than the MOE, is developed by USGS largely through their support service contract. The DAPS will be located at the USGS EROS (Earth Resources Observation and Science) Center in Sioux Falls, SD.

Data access policy: All Landsat data are freely available over the Internet.

Landsat8_Auto3

Figure 234: Illustration of the Landsat-8 mission elements and communication architecture (image credit: NASA) 234) 235)

LGN (LDCM Ground Network) stations: The LGN is a collection of ground stations with state of the art electronics and sophisticated ground software, each providing similar mission services. The configuration of LGN uses the ground stations located at the EROS Center campus in Sioux Falls, South Dakota, the GLC (Gilmore Creek) ground station in Fairbanks, Alaska, and the SvalSat (Svalbard Satellite Station) ground station in Svalbard (Spitsbergen), Norway.

Each LGN ground station consists of a tracking antenna, S-band and X-band communication equipment, mission data storage and a file routing DCRS (Data Collection and Routing Subsystem). The LGN antenna receives X-band mission data files (autonomous playback or commanded) from the observatory, while simultaneously performing file management and subsequent image collection operations over S-band. The S-band and X-band systems of each LGN station interfaces with the MOE and DPAS in a closed loop fashion.

The USGS maintains agreements with several foreign governments referred to as the Landsat ICs (International Cooperators). The ICs are a special user community that has the ability to receive LDCM mission data from the observatory real-time X-band downlink stream. Real-time imaging sensor and ancillary data (including spacecraft and calibration data) required to process the science data are contained within the real-time stream downlink.

The ICs will be capable of receiving real-time X-band imaging sensor data downlinks and sending metadata to the DPAS. The ICs will submit imaging sensor data collection and downlink requests to the CAPE (via the DPAS user portal). ICs participate in a bilateral DV&E (Data Validation & Exchange) program with the DPAS. This program includes exchange of archive data upon request, and validation of IC processed level 1 data products by the USGS.

Landsat8_Auto2

Figure 235: Overview of the LDCM system architecture (image credit: USGS)

Item

Parameter

Total size

System

Daily volume of 400 scenes

390 GByte

Spacecraft

C&DH data rate

260.92 Mbit/s

Space to ground communication

Downlink data rate
LDPC ⅞ rate packet

384 Mbit/s data, 441 Msample/s symbol
8160 bit

Ground station

Minutes per day (14 contacts)

98 minutes

Science archive

5 year archive

~ 400 TB

Table 14: Overview of data volumes for processing and archiving functions

IC (International Cooperator) Ground Stations of the Landsat Program:

• In 41 years, 39 IC stations in 23 countries

• Most still collect and/or distribute Landsat products, reducing the load on U.S. Systems

• More than 215,000 products distributed in 2012

- Represents a nearly 10% off-loading of network bandwidth

- Enhanced regional exploitation of Landsat data

Landsat8_Auto1

Figure 236: Overview of the IC (International Cooperator) network (image credit: USGS, Ref. 180)

 

IAS (Image Assessment System):

Once the LDCM spacecraft is in orbit, the radiometric, geometric and spatial performance of OLI and TIRS sensors will be continually monitored, characterized and calibrated using the IAS (Ref. 215).

Background: The IAS was originally developed to monitor radiometric and geometric performance of the Landsat-7 ETM+ sensor and the quality of the image data in the Landsat-7 archive. The operational performance monitoring is achieved by processing a number of randomly selected Level 0R (raw reformatted) images to Level 1R (radiometrically corrected) and Level 1G (geometrically corrected) products. In that process, image statistics at different processing levels, calibration data, and telemetry data are extracted and stored in the IAS database for automatic and off-line assessment. The IAS also processes and analyzes the pre-selected geometric and radiometric calibration sites and special calibration acquisitions, e.g. solar diffuser or night data needed for radiometric calibration or noise and stability studies. The final and most important product of the IAS trending and processing is the CPF (Calibration Parameter File), the file that contains parameters needed for artifact corrections and radiometric and geometric processing of raw image data. To maintain the accuracy of the dynamic parameters, the CPF is updated at least once every three months.

The purpose of the LDCM IAS is to maintain accurate spectral, radiometric, spatial and geometric characterization and calibration of LDCM data products and sensors, ensuring compliance with the OLI and TIRS data quality requirements. The IAS will trend results of processing standard Earth images and nonstandard products, such as lunar, solar, dark Earth or stellar images, evaluate image statistics and calculate and store image characteristics for further analysis.

Landsat8_Auto0

Figure 237: The LDCM ground system concept (image credit: USGS)

The IAS will automatically generate calibration parameters, which will be evaluated by the calibration analysts. In addition to standard operations within the IAS, the CVT (Calibration and Validation Team) will use a ‘toolkit' module containing instrument vendor developed code and routines developed by the CVT, as a research and development environment for improvements of algorithm functionality and anomaly investigations.

Compared to the previous IAS versions, the LDCM IAS system will have to handle a significantly larger and more complex database that will include characterization data from all normally acquired images (~ 400 scenes per day, with special calibration acquisitions, e.g solar and lunar) processed through the product generation system. OLI's pushbroom design (~ 75000 detectors), as opposed to an ETM+ whiskbroom design, requires characterization and calibration of about 550 times more detectors than in case of ETM+ (136 detectors) and represents a major challenge for the LDCM IAS. An additional challenge is that the LDCM IAS must handle data from two sensors, as the LDCM products will contain both the OLI and TIRS data.

For radiometric and geometric processing, see Ref. 215).

• Processing latency for real-time downlinks

• Average latency is ~ 5 hours from acquisition to product availability

• Closed loop between ground and space for data management

• The system requirement calls for 85% data availability to the user community through EROS Portal within 48 hours. The actual performance for Landsat-8 averages within 5 hours.

Table 15: Landsat 8 operational characteristics (Ref. 180)

Landsat-8 reprocessing (Ref. 180):

• All Landsat 8 data is being reprocessed to make corrections based on first year data analysis.

• Corrections to both OLI (Operational Land Imager) and the TIRS (Thermal Infrared Sensor) data are being made including:

- all calibration parameter file updates since launch

- improved OLI reflectance conversion coefficients for the cirrus band

- improved OLI radiance conversion coefficients for all bands

- refined OLI detector linearization to decrease striping

- a radiometric offset correction for both TIRS bands

- a slight improvement to the geolocation of the TIRS data

• Approximately 90% of reprocessing is completed with estimated completion by March 30, 2014.

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31) Rebecca C. Trinh, Cédric G. Fichot, Michelle M. Gierach, Benjamin Holt, Nabin K. Malakar, Glynn Hulley, Jayme Smith, "Application of Landsat 8 for Monitoring Impacts of Wastewater Discharge on Coastal Water Quality," Frontiers in Marine Science, 26 October 2017, https://doi.org/10.3389/fmars.2017.00329, URL: https://tinyurl.com/yaqnwglr

32) "The Geologic Wonder of the Neuquén Basin," NASA Earth Observatory, Image of the day for 19 October 2018, URL: https://earthobservatory.nasa.gov/images/92908/the-geologic-wonder-of-the-neuquen-basin

33) "Glacier Flour in Greenland Skies," NASA Earth Observatory, Image of the day for 17 October 2018, URL: https://earthobservatory.nasa.gov/images/
92891/glacier-flour-in-greenland-skies

34) "Devastation in Palu After Earthquake, Tsunami," NASA Earth Observatory, Image of the day for 3 October 2018, URL: https://earthobservatory.nasa.gov/images/92836/
devastation-in-palu-after-earthquake-tsunami

35) "Urban Growth of New Delhi," NASA Earth Observatory, image of the day for 27 September 2018, URL: https://earthobservatory.nasa.gov/images/92813/urban-growth-of-new-delhi

36) "Volcanic Hell Makes for Bathing Heaven," NASA Earth Observatory, Image of the day for 26 September 2018, URL: https://earthobservatory.nasa.gov/
images/92802/volcanic-hell-makes-for-bathing-heaven

37) "Between the Ripples of the Namib Sand Sea," NASA Earth Observatory, Image of the day for 4 September 2018, URL: https://earthobservatory.nasa.gov/images/92695
/between-the-ripples-of-the-namib-sand-sea?src=eoa-iotd

38) "Vredefort Crater," NASA Earth Observatory, Image of the day for1 September 2018, URL: https://earthobservatory.nasa.gov/images/92689/vredefort-crater

39) "Meandering Bends of the Lower Padma River," NASA Earth Observatory, Image of the day for 28 August 2018, URL: https://earthobservatory.nasa.gov/images/92672/meandering
-bends-of-the-lower-padma-river

40) "Archaeology from Afar in Uzbekistan," NASA Earth Observatory, Image of the day for 21 August 2018, URL: https://earthobservatory.nasa.gov/
images/92634/archaeology-from-afar-in-uzbekistan

41) "Cape Town's Reservoirs Rebound," NASA Earth Observatory, 17 July 2018, URL: https://earthobservatory.nasa.gov/images/
92428/cape-towns-reservoirs-rebound

42) "One Year Adrift, but Not Far," NASA Earth observatory, 16 July 2018, URL: https://earthobservatory.nasa.gov/images/92420/one-year-adrift-but-not-far?src=eoa-iotd

43) "Satellites Investigate Irrigation in a Stressed Aquifer," NASA Earth Observatory, 9 July 2018, URL: https://earthobservatory.nasa.gov/images/92387?src=eoa-iotd

44) "Volcanic Mood Rings," NASA Earth Observatory, 6 July 2018, URL: https://earthobservatory.nasa.gov/images/92377/volcanic-mood-rings

45) "The Meandering Estuaries of Guinea–Bissau," NASA Earth Observatory, 18 June 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92266

46) "Lava Consumes Vacationland and Kapoho Bay," NASA Earth Observatory, 13 June 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92287

47) "Flower Power in the Netherlands," NASA Earth Observatory, 16 May 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92148

48) "Deforestation in Paraguay," NASA Earth Observatory, 1 May 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92078

49) "Beauty in the Beaufort Ice Pack," NASA Earth Observatory, 30 April 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92067&src=iotdrss

50) "A Ring of Green Around Surgut," NASA Earth Observatory, 25 April 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=92049

51) "Coloring Lake Pontchartrain," NASA Earth Observatory, 11 April 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91977

52) "Decline of Two Glaciers in Northwest Greenland," NASA Earth Observatory, 8 April 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91956&src=iotdrss

53) "Sculpting a Basin," NASA Earth Observatory, 5 April 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91944

54) "Nikumaroro Atoll," NASA Earth Observatory, 26 March 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91889&src=iotdrss

55) "Floodwaters at the Confluence of the Wabash and Ohio Rivers," NASA Earth Observatory, 15 March 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91839

56) "The Sculpting of Ebro Delta," NASA Earth Observatory, 13 March 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91832

57) "Sarawak's Rajang River Delta," NASA Earth Observatory, 6 March 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91787

58) "A New Reservoir in Cambodia," NASA Earth Observatory, 24 Feb. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91761

59) "Greenhouses of Cayambe Valley," NASA Earth Observatory, 15 Feb. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91720&src=iotdrss

60) Patrick Lynch and Laura Rocchio , "Landsat 8 Marks Five Years in Orbit," NASA, 9 Feb. 2018, URL: https://www.nasa.gov/feature/goddard/2018/landsat-8-marks-five-years-in-orbit

61) "The Dizzying Depths of Cotahuasi Canyon," NASA Earth Observatory, 7 Feb. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91686&src=iotdrss

62) "Fuego Erupts," NASA Earth Observatory, 3 Feb. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91671&src=iotdrss

63) "Cape Town's Water is Running Out," NASA Earth Observatory, 30 Jan. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91649&src=iotdrss

64) "Deadly Debris Flows in Montecito," NASA Earth Observatory, 12 Jan. 2018, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91573

65) "Pine Island Iceberg Under the Midnight Sun," NASA Earth Observatory, 26 Dec. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91470

66) "Cape Horn: A Mariner's Nightmare," NASA Earth Observatory, 24 Dec. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91472

67) "The Land Between the Lakes," NASA Earth Observatory, 15 Dec. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91391&src=iotdrss

68) "A Growing City and a Deadly Landslide," NASA Earth Observatory, Dec. 5, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91356&src=iotdrss

69) "Bold Beauty in the Tanezrouft Basin," NASA Earth Observatory, 2 Dec. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91349&src=iotdrss

70) "The Ups and Downs of Lake Chad," NASA Earth Observatory, 25 Nov. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91291&eocn=home&eoci=iotd_image

71) "The Rise and Fall of Africa's Great Lake," NASA Earth Observatory, Nov. 9, 2017, URL: https://earthobservatory.nasa.gov/Features/LakeChad/

72) "A-68 Adrift," NASA Earth Observatory, November, 2017, URL: https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=91052

73) Kathrin Hansen, "The calving of a massive iceberg from the Larsen C ice shelf," Phys.ORG, 16 Nov. 2017, URL: https://phys.org/news/2017-11-calving-massive-iceberg-larsen-ice.html

74) "A Gateway to Antarctica," NASA Earth Observatory, 11 Nov. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91246

75) "Significant Milestone in Improving Usability of Landsat Satellite Data," USGS, 8 November 2017, URL: https://www.usgs.gov/news/significant-milestone-improving-usability-landsat-satellite-data

76) "Lake Balkhash," NASA Earth Observatory, 4 Nov. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91230&src=iotdrss

77) https://en.wikipedia.org/wiki/Lake_Balkhash

78) "A Very Human Landscape in China," NASA Earth Observatory, 29 Oct. 2017: URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91195&src=iotdrss

79) "Check Out These Colors, Maine!," NASA Earth Observatory, 22 Oct. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91154&src=iotdrss

80) "Appalachian Trail," Wikipedia, URL: https://en.wikipedia.org/wiki/Appalachian_Trail

81) "Santa Rosa Scarred by Fire," NASA Earth Observatory, 13 Oct. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=91111&src=iotdrss

82) "Darkness Blooms," NASA Earth Observatory, Sept. 10, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90933

83) "Latest Harmonized Landsat Sentinel-2 (HLS) Version Released," Landsat Science, Sept. 8, 2017, URL: https://landsat.gsfc.nasa.gov/latest-harmonized-landsat-sentinel-2-version-released/

84) "Palm Swamp Fire in Brazil," NASA Earth Observatory, 5 Sept. 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90890

85) https://landsat.gsfc.nasa.gov/landsat-9/

86) "Another Puff of Ash From Klyuchevskoy," NASA Earth Observatory, Aug. 24, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90810

87) "Fire and Ice in Greenland," NASA Earth Observatory, August 12, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90709&src=eoa-iotd

88) Brian L. Markham, Julia A. Barsi, "Landsat-8 Operational Land Imager on-orbit radiometer calibration," Proceedings of IGARSS 2017 (IEEE International Geoscience and Remote Sensing Symposium), Fort Worth, Texas, USA, July 23–28, 2017

89) "July 21, 2017 - Celebrating Forty-Five Years of Landsat," USGS, URL: https://landsat.usgs.gov/july-21-2017-celebrating-45-landsat

90) "Langley Turns 100," NASA Earth Observatory, July 18, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90586&src=eoa-iotd

91) "Island Rises Up off of Cape Hatteras," NASA Earth Observatory, July 12, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90550

92) "Where Tectonic Plates Go for a Swim," NASA Earth Observatory, June 17, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90398

93) "North Patagonian Icefield," NASA Earth Observatory, June 7, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90341

94) "Landslide in Southern Kyrgyzstan," NASA Earth Observatory, May 30, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90255

95) "Landslide Buries Scenic California Highway," NASA Earth Observatory, May 25, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90281&src=iotdrss

96) "Lake Natron, Tanzania," NASA Earth Observatory, Released on May 8, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90191&src=iotdrss

97) "New Rift on Petermann Glacier," NASA Earth Observatory, April 19, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90043

98) "Easter Island," NASA Earth Observatory, April 16, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=90027&src=eoa-iotd

99) "Landsat Images Provided to the Disaster Charter, March 2017," NASA, March 31, 2017, URL: https://landsat.gsfc.nasa.gov/landsat-images-
provided-to-the-disaster-charter-mar-2017/

100) "World of Change: Sprawling Shanghai," NASA Earth Observatory, March 17, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=89853

101) "Contrasting Ridges in Virginia," NASA Earth Observatory, March 15, 2017, URL: https://earthobservatory.nasa.gov/IOTD/view.php?id=89843

102) "Grounded in the Caspian Sea," NASA Earth Observatory, March 1, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89742

103) "Longyangxia Dam Solar Park," NASA Earth Observatory, Feb. 16, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89668

104) "A Clearer View of Silicon Valley," NASA Earth Observatory, Feb. 5, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89554

105) "The Treacherous and Productive Seas of Southern Africa," NASA Earth Observatory, Jan. 27, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89535

106) "Mapping a Tenacious Invader in Lake Thurmond," NASA Earth Observatory, Jan. 4, 2017, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89385

107) "A Shape-Shifting River in Bolivia," NASA Earth Observatory, Dec. 21. 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89266

108) Todd A. Schroeder, Thomas R. Loveland, Michael A. Wulder, James R. Irons, "Landsat Science Team: 2016 Summer Meeting Summary," The Earth Observer, Volume 28, Issue 6, November-December 2016, pp: 45-50, URL: https://eospso.nasa.gov/sites/default
/files/eo_pdfs/Nov-Dec%202016%20color%20508.pdf

109) Kate Ramsayer, Mike Carlowicz, "Mapping the Speed of Ice," NASA Earth Observatory, Dec. 14, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89261

110) Mark Fahnestock, Ted Scambos, Twila Moon, , Alex Gardner, Terry Haran, Marin Klinger, "Rapid large-area mapping of ice flow using Landsat 8," Remote Sensing of Environment,Volume 185, November 2016, pp: 84–94, URL: http://ac.els-cdn.com/S003442571530211X/1-s2.0-
S003442571530211X-main.pdf?_tid=216406f2-c1d2-11e
6-aa7b-00000aab0f01&acdnat=1481
702072_1a58f683c99cb97d6ceeadb3da320cd2

111) "Ancient Waterways in Morocco," NASA Earth Observatory, Nov. 19, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89133

112) "Kiruna Iron Mine," NASA Earth Observatory, Oct. 29, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=89010&src=eoa-iotd

113) Erik Jonsson, Valentin R. Troll, Karin Högdahl, Chris Harris, Franz Weis, Katarina P. Nilsson, Alasdair Skelton, "Magmatic origin of giant ‘Kiruna-type' apatite-iron-oxide ores in Central Sweden," Nature, Scientific Reports 3, Article number: 1644 (2013), doi:10.1038/srep01644, URL: http://www.nature.com/articles/srep01644

114) "Landsat 8 Enhancements Detailed in Journal Special Issue," >NASA, Landsat Science, Oct. 6, 2016, URL: http://landsat.gsfc.nasa.gov/?p=13119

115) Remote Sensing of Environment, "Landsat 8 Science Results," Edited by Thomas R. Loveland and James R. Irons, Volume 185, Pages 1-284 (November 2016)

116) "Vatnajökull," ESA, Earth observation image of the week, Oct. 14, 2016, URL: http://m.esa.int/spaceinimages/Images/2016/10/Vatnajoekull

117) "Celebrating 50 years of Landsat Vision," USGS, Sept. 21, 1966, URL: http://landsat.usgs.gov/project-eros-idea-worked.php

118) "Soberanes Still Burns," NASA Earth Observatory, Sept. 21, 2016: URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88781

119) "Cape Hatteras National Seashore," NASA Earth Observatory, Aug. 25, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88619

120) "Minute Man National Historical Park," NASA Earth Observatory, July 4, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88300&src=eoa-iotd

121) "Glacial Change in Montana's Blackfoot-Jackson Basin," NASA Earth Observatory, June 15, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88190

122) "Lower Canyons of the Rio Grande," NASA Earth Observatory, May 31, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=88178

123) Robert J. Scheid, "Applications for General Purpose Command Buffers: The Emergency Conjunction Avoidance Maneuver," Proceedings of the 14th International Conference on Space Operations (SpaceOps 2016), Daejeon, Korea, May 16-20, 2016, paper: AIAA 2016 2416, URL: http://arc.aiaa.org/doi/pdf/10.2514/6.2016-2416

124) "Signs of an Eruption on Bristol Island," NASA Earth Observatory, May 10, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87995

125) "The New Suez Canal," NASA Earth Observatory, April 30, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87948&src=eoa-iotd

126) "USGS TIRS Update," NASA, April 12, 2016, URL: http://landsat.gsfc.nasa.gov/?p=12294

127) Kathryn Hansen, "Fort Raleigh National Historic Site," NASA Earth Observatory, April, 6, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87804

128) Kathryn Hansen, "Kennesaw Mountain National Battlefield Park," NASA Earth Observatory, March 30, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87778

129) "Statue of Liberty and Ellis Island," NASA Earth Observatory, March 20, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87710

130) "Sentinel data wanted," ESA, March 15, 2016, URL: http://www.esa.int/Our_Activities/Observing_the_Earth/Sentinel_data_wanted

131) Jon Campbell, "USGS Partners with European Space Agency to Deliver Copernicus Earth Data," March 15, 2016, URL: http://landsat.gsfc.nasa.gov/?p=12194

132) "A Monumental Addition in California," NASA Earth Observatory, March 13, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87668&src=eoa-iotd

133) "Sentinel-2 Multispectral Instrument (MSI)," USGS, Feb. 18, 2016, URL: https://eros.usgs.gov/sentinel-2

134) "Landsat Headlines 2016," USGS, URL: http://landsat.usgs.gov/mission_headlines2016.php

135) "A Snow Blanket for the East Coast," NASA Earth Observatory, Jan. 26, 2016, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=87395&src=ve

136) "Landsat 8 Thermal Data Update," USGS, Jan. 13, 2016, URL: http://landsat.usgs.gov/mission_headlines2016.php

137) "Landsat 8 TIRS Anomaly Update," USGS, Nov. 17, 2015, URL: http://landsat.usgs.gov/mission_headlines2015.php

138) Jon Campbell, "Free Data Proves Its Worth for Observing Earth," USGS, Nov. 13, 2015, URL: http://www.usgs.gov/blogs/features/usgs_
top_story/free-data-proves-its-worth-for-observing-earth/

139) "United States and European Union Sign Cooperation Arrangement on Copernicus Earth Observation Data," U.S. Department of State, Oct. 19, 2015, URL: http://www.state.gov/r/pa/prs/ps/2015/10/248336.htm

140) "Death Valley 1,000-year Flood Event," USGS, October 29, 2015, URL: http://eros.usgs.gov/views-news

141) "The Good, the Bad, and the Algae," NASA Landsat Science, August 12, 2015, URL: http://landsat.gsfc.nasa.gov/?p=10861

142) "The Good, the Bad, and the Algae," NASA Science News, June 26, 2015, URL: http://science.nasa.gov/science-news/science-at-nasa/2015/26jun_algae/

143) Jon Campbell, "Landsat Sees Eye of the Sahara," USGS, July 17, 2015, URL: http://www.usgs.gov/blogs/features/usgs_top_story/landsat-sees-eye-of-the-sahara/

144) "Earth from Space: San Francisco Bay Area, USA," ESA, June 19, 2015, URL: http://www.esa.int/spaceinvideos/Videos/201
5/06/Earth_from_Space_San_Francisco_Bay_Area_USA

145) Brian Sauer, "Landsat Operations Report," USGS, Landsat Team Meeting, July 7, 2015, URL: http://landsat.usgs.gov/documents/science_LST
_july2015/Landsat%207%20and%208%20Operations%20an
d%20Mission%20Status%20-%20Sauer.pdf

146) "The Advance of Hubbard Glacier," NASA Earth Observatory, USGS, May 20, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=85900

147) L. A. Stearns, G. S. Hamilton, C. J. van der Veen, D. C. Finnegan, S. O'Neel, J. B. Scheick, D. E. Lawson, "Glaciological and marine geological controls on terminus dynamics of Hubbard Glacier, southeast Alaska," Journal of Geophysical Research, Vol. 120, 2015, DOI 10.1002/2014JF003341

148) TIRS Scene Select Mechanism (SSM) Anomaly," USGS, May 8, 2015: URL: http://landsat.usgs.gov/calibration_notices.php

149) Tim Newman, Tom Cecere, "USGS Land Remote Sensing Program Update," JACIE (Joint Agency Commercial Imagery Evaluation) Workshop, Tampa, FL, USA, May 5-7, 2015, URL: https://calval.cr.usgs.gov/wordpress/wp-content/uploads/JACIE_brief_05.05.15_Cecere.pptx

150) "Iceberg B-15T Still Adrift," NASA Earth Observatory, April 12, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=85682&src=eoa-iotd

151) Larisa Serbina, Colin Leslie, "Landsat and the Private Tech Sector: Direct and Complementary Uses of Imagery," NASA, Landsat Science, March 25, 2015, URL: http://landsat.gsfc.nasa.gov/?p=10208

152) "Ulan Bator, Mongolia," ESA, March 20, 2015, the image is featured on the 'Earth from Space video program,' URL: http://www.esa.int/spaceinimages/Images/2015/03/Ulan_Bator_Mongolia

153) "TIRS Resumes Nominal Operations," NASA, Landsat Science, March 6, 2015, URL: http://landsat.gsfc.nasa.gov/?p=9837

154) "Landsat Headlines 2015 - Landsat-8 Thermal Data Processing Resumed," USGS, March 16, 2015, URL: http://landsat.usgs.gov/mission_headlines2015.php

155) "Shipping Superhighways," NASA Earth Observatory, March 6, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.
php?id=85437&eocn=home&eoci=iotd_readmore

156) "Las Vegas and Lake Mead," ESA, Feb. 13, 2015, URL: http://www.esa.int/spaceinimages/Images/
2015/02/Las_Vegas_and_Lake_Mead

157) "Landslide in Northern India," NASA Earth Observatory, Jan. 27, 2015, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=85149&src=eoa-iotd

158) "USGS Landsat 8 TIRS Update," NASA, Jan. 27, 2015, URL: http://landsat.gsfc.nasa.gov/?p=9679

159) "Landsat-8 TIRS update," USGS, January 27, 2015, URL: http://landsat.usgs.gov/mission_headlines2015.php

160) "Corsica," ESA, Earth observation image of the week, Jan. 30, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/01/Corsica

161) "Aletsch Glacier," ESA, image featured in the Earth from Space video program, Jan. 23, 2015, URL: http://www.esa.int/spaceinimages/Images/2015/01/Aletsch_Glacier

162) "National Geospatial Advisory Committee – Landsat Advisory Group - The Value Proposition for Landsat Applications – 2014 Update," URL: https://www.fgdc.gov/ngac/meetings/december-2014/ngac-
landsat-economic-value-paper-2014-update.pdf

163) "Great Bahama Bank," ESA, image featured in the Earth from Space video program, Dec. 19, 2014, URL: http://www.esa.int/spaceinimages/Images/2014/12/Great_Bahamas_Bank

164) Adam Voiland , "Best of the Archives: Dunes of the Great Bahama Bank," Jan. 16, 2014, URL: http://earthobservatory.nasa.gov/blogs/earthma
tters/2014/01/16/best-of-the-archives-dunes-of-the-great-bahama-bank/

165) "Dead Sea, Middle East," ESA, image featured in the Earth from Space video program, Nov. 7, 2014, URL: http://www.esa.int/spaceinimages/Images/
2014/11/Dead_Sea_Middle_East

166) Jesse Allen, James Acker, Mike Carlowicz, "Gonzalo Stirs Up Sediment and the Carbon Cycle," NASA Earth Observatory, USGS, Oct. 26, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84595

167) Kasha Patel, "NASA Ocean Data Shows ‘Climate Dance' of Plankton," NASA, Sept. 29, 2014, URL: http://www.nasa.gov/content/goddard/nasa
-ocean-data-shows-climate-dance-of-plankton/

168) Michael J. Behrenfeld, "Climate-mediated dance of the plankton," Journal of Nature Climate Change, Vol. 4, 2014, pp. 880–887, Published online, 25 September 2014, doi:10.1038/nclimate2349

169) "Sustainable Land Imaging Architecture Study," NASA/GSFC, Sept. 5, 2014, URL: http://sustainablelandimaging.gsfc.nasa.gov/

170) Laura Rocchio, "Curiosities of the Danakil Depression," NASA Earth Observatory, August 27, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84239

171) Adam Voiland, Robert Simmon, "Retreat of Yakutat Glacier," NASA, Earth Observatory, August 20, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=84180

172) Kate Ramsayer, "Taking NASA-USGS's Landsat 8 to the Beach," NASA, July 2, 2014, URL: http://www.nasa.gov/content/goddard/
taking-nasa-usgs-s-landsat-8-to-the-beach/

173) Laura Rocchio, "Hanhowuz Reservoir, Turkmenistan," NASA Earth Observatory, released on July 1, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83940

174) "The Loop," NASA Earth Observatory, released on June 18, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83875

175) "Earth observation image of the week: multiple ice streams on the southwestern coast of Greenland," ESA, June 13, 2014, URL: http://www.esa.int/spaceinimages/Images/
2014/06/Southwestern_coast_of_Greenland

176) "Landsat 8 Thermal Infrared Sensor (TIRS) Update," USGS, June 6, 2014, in 'Landsat Update - Volume 8 Issue 2 2014,' URL: http://landsat.usgs.gov/about_LU_Vol_8_Issue_2.php#2a

177) "Lake Powell Half Empty," NASA Earth Observatory, May 22, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83716

178) "Five Volcanoes Erupting at Once," NASA Earth Observatory, April 16, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83502

179) "Alluvial Fan in Kazakhstan," NASA Earth Observatory, Jesse Allen and Robert Simmon, April 8, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83455

180) Jenn Sabers Lacey, "USGS EROS Center - 40 Years of Service to our Plnat," Proceedings of JACIE 2014 (Joint Agency Commercial Imagery Evaluation) Workshop, Louisville, Kentucky, USA, March 26-28, 2014, URL: https://calval.cr.usgs.gov/wordpress/wp-content/uploads/
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181) Steven Volz, "NASA Earth Science Flight Program Overview," Proceedings of JACIE 2014 (Joint Agency Commercial Imagery Evaluation) Workshop, Louisville, Kentucky, March 26-28, 2014, URL: https://calval.cr.usgs.gov/wordpress/wp-content/uploads/Volz_JACIE-Presentation.pdf

182) "Large Landslide Detected in Southeastern Alaska," NASA Earth Observatory, Feb. 25, 2014, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83195

183) Kate Ramsayer, Jon Campbell, "NASA-USGS Landsat 8 Satellite Celebrates First Year of Success," NASA News, February 11, 2014, URL: http://www.nasa.gov/content/goddard/
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184) Information provided by Jim R. Irons of NASA/GSFC and by James M. Lacasse of USGS Climate and Land Use Change, Sioux Falls, S.D.

185) "Guinea-Bissau and the Bissagos islands," ESA Earth from Space video program, released on Jan. 10, 2014, URL: http://spaceinimages.esa.int/Images/
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186) Steve Cole, Kate Ramsayer, " NASA release 13-364, Dec. 09.2013, URL: http://www.nasa.gov/press/2013/december
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187) "The Shapes that Lavas Take," NASA Earth Observatory, Nov. 21, 2013, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=82424

188) "Klyuchevskaya Erupts," NASA Earth Observatory, Oct. 25, 2013, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=82227

189) "Garden and Hog Islands, Michigan," NASA Earth Observatory, August 25, 2013, URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=81913

190) "Mount Sakurajima Volcano Erupts," USGS, Aug. 22, 2013, URL: http://landsat.usgs.gov/images/gallery/305_L.jpg

191) Kate Ramsayer, "After a Fire, Before a Flood: NASA's Landsat Directs Restoration to At-Risk Areas," NASA/GSFC, August 21, 2013, URL: http://www.nasa.gov/content/goddard/after-a-fire-before
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192) Steve Cole, Kate Ramsayer, Jon Campbell, "Landsat 8 Satellite Begins Watch," NASA Release 13-160, May 30, 2013, URL: http://www.nasa.gov/home/hqnews
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193) Kate Ramsayer, "NASA's Landsat Satellite Looks for a Cloud-Free View," NASA, May 22, 2013, URL: http://www.nasa.gov/mission
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194) Jon Campbell, "Landsat Images Provide the Gold Standard for New Earth Applications," USGS News rooms, May 9, 2013, URL: http://www.usgs.gov/newsroom/article.asp?ID=3586&from=rss_home

195) Rebecca Moore, "A picture of Earth through time," Google Official Blog, May 9, 2013, URL: http://googleblog.blogspot.de/

196) Steve Cole, "New Public Application of Landsat Images Released," NASA, May 9, 2013, URL: http://www.nasa.gov/mission_pages/landsat/news/google-engine.html

197) "LDCM Mission Updates," NASA, URL: http://www.nasa.gov/mission_pages/landsat/main/mission-updates.html

198) "Landsat Thermal Sensor Lights Up from Volcano's Heat," NASA, May 6, 2013, URL: http://www.nasa.gov/mission_pages/landsat/news/indonesia-volcano.html

199) "Landsat Data Continuity Mission," NASA, News and Features, URL: http://www.nasa.gov/mission_pages/landsat/news/index.html

200) "LDCM Status Update for May 2, 2013," NASA, May 15, 2013, URL: http://www.nasa.gov/mission_pages/landsat/main/mission-updates.html

201) Matt Radcliff, Rob Simmon, Jesse Allen, Holli Riebeek, Paul Przyborski, "Come Fly With the Newest Landsat," NASA Earth Observatory, URL: http://earthobservatory.nasa.gov/
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202) Tom Holm, "Landsat: Building a Future on 40 Years of Success - April 14, 2013, 705 km Orbit," 12th Annual JACIE (Joint Agency Commercial Imagery Evaluation) Workshop , St. Louis, MO, USA, April 16-18, 2013, URL: http://calval.cr.usgs.gov/wordpress/wp-content/
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203) "LDCM Underfly with Landsat 7," USGS, March 29, 2013, URL: http://landsat.usgs.gov/LDCM_Underfly_with_Landsat_7.php

204) Steve Cole, Jon Campbell, "First Images Released From Newest Earth Observation Satellite," NASA, USGS, March 21, 2013, URL: http://www.nasa.gov/home/
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205) "A Closer Look at LDCM's First Scene," NASA, March 21, 2013, URL: http://www.nasa.gov/mission_pages/landsat/news/first-images-feature.html

206) "LDCM Status Update for Feb. 21," NASA, Feb. 21, 2013, URL: http://www.nasa.gov/mission_pages/landsat/main/index.html

207) "NASA Completes Critical Design Review Of One Landsat Instrument," Space Daily, May 28, 2010, URL: http://www.spacedaily.com/reports/NASA_Completes_Critical
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208) Bryant Cramer, "USGS Perspectives on LDCM and Landsat," Landsat Science Team Meeting," Jan. 19-21, 2010, Mountain View, CA, USA, URL: http://landsat.usgs.gov/documents/Jan_2010_Cramer
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209) Tom Loveland, "Landsat and LDCM Status," 2008 NASA Carbon Cycle & Ecosystems Joint Science Workshop, April 28-May 2, 2008, University of Maryland, Adelphi, MD, USA

210) James Storey, Michael Choate, Kenton Lee, "Geometric performance comparison between the OLI and ETM+," Proceedings of the Pecora 17 Memorial Remote Sensing Symposium, Denver, Co, USA, Nov. 16-20, 2008

211) Jeanine Murphy-Morris, "Operational Land Imager ," Landsat Science Team Meeting, Sioux Falls, SD, Jan. 8, 2008, URL: http://landsat.usgs.gov/documents
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212) Edward J. Knight, "OLI Overview and Status," Landsat Science Team Meeting, July 15, 2008, Reston, VA, URL: http://landsat.usgs.gov/documents/Knight_OLI.pdf

213) Bill Ochs, "Status of the Landsat Data Continuity Mission," Landsat Science Team Meeting, July 15, 2008, Reston, VA, URL: http://landsat.usgs.gov/documents/Ochs_LDCM_Status.pdf

214) Edward J. Knight, Brent Canova, Eric Donley, Geir Kvaran, Kenton Lee, "The Operational Land Imager:Overview and Performance," 10th Annual JACIE ( Joint Agency Commercial Imagery Evaluation) Workshop, March 29-31, 2011, Boulder CO, USA, URL: http://calval.cr.usgs.gov/JACIE_files/
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215) Esad Micijevic, Ron Morfitt, "Operational Calibration and Validation of Landsat Data Continuity Mission (LDCM) Sensors using the Image Assembly System (IAS)," Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium) 2010, Honolulu, HI, USA, July 25-30, 2010

216) Brian L. Markham, Philip W. Dabney, Edward J. Knight, Geir Kvaran, Julia A. Barsi, Jeanine E. Murphy-Morris, Jeffrey A. Pedelty, "The Landsat Data Continuity Mission Operational Land Imager (OLI) Radiometric Calibration," Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium) 2010, Honolulu, HI, USA, July 25-30, 2010, URL: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa
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217) Brian Markham, "LDCM On-Orbit Cal/Val Considerations," Proceedings of the Landsat Science Team Meeting, Mesa, AZ, USA, March 1-3, 2011, URL: http://landsat.usgs.gov/documents/LDCM_Cal_Val_Considerations.pdf

218) "Ball Aerospace Completes CDR For Landsat's Operational Land Imager," Nov. 26, 2008, Spacemart, URL: http://www.spacemart.com/reports/Ball_Aerospace_
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219) "NASA Completes Critical Design Review of Landsat Data Continuity Mission," Science Daily, June 1, 2010, URL: http://www.sciencedaily.com/releases/2010/06/100601171850.htm

220) Dennis Reuter, Cathy Richardson, James Irons, Rick Allen, Martha Anderson, Jason Budinoff, Gordon Casto, Craig Coltharp, Paul Finneran, Betsy Forsbacka, Taylor Hale, Tom Jennings, Murzy Jhabvala, Allen Lunsford, Greg Magnuson, Rick Mills, Tony Morse, Veronica Otero, Scott Rohrbach, Ramsey Smith, Terry Sullivan, Zelalem Tesfaye, Kurtis Thome, Glenn Unger, Paul Whitehouse, "The Thermal Infrared Sensor on the Landsat Data Continuity Mission," Proceedings of IGARSS (International Geoscience and Remote Sensing Symposium), Honolulu, Hawaii, USA, July 25-30, 2010, URL: http://landsat.gsfc.nasa.gov/pdf_archive/Reuter_etal-IGARSS2010.pdf

221) Ramsey L. Smith, Kurtis Thome, Cathleen Richardson, James Irons, Dennis Reuter, "Terrestrial Applications of the Thermal Infrared Sensor, TIRS," URL: http://ntrs.nasa.gov/archive/nasa/casi.ntrs
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222) M. Jhabvala, D. Reuter, K. Choi, C. Jhabvala, M. Sundaram, "QWIP-Based Thermal Infrared Sensor for the Landsat Data Continuity Mission," Proceedings of the QSIP (Quantum Structure Infrared Photodetector) 2009 International Conference, January 18-23, 2009, Yosemite, CA

223) M. Jhabvala, D. Reuter, K. Choi, M. Sundaram, C. Jhabvala, A. La, A. Waczynski, J. Bundas, "The QWIP focal plane assembly for NASA's Landsat Data Continuity Mission," Proceedings of the SPIE, 'Infrared Technology and Applications XXXVI,' edited by Bjørn F. Andresen, Gabor F. Fulop, Paul R. Norton, Volume 7660, April 5-9, 2010, Orlando, FLA, USA, pp. 76603J-76603J-13, doi:10.1117/12.862277

224) M. Jhabvala, K. K. Choi, C. Monroy, A. La, "Development of a 1 k × 1 k, 8–12 µm QWIP array," Infrared Physics & Technology, Volume 50, Issues 2-3, April 2007, pp. 234-239

225) K. Thome, D. Reuter, A. Lunsford, M. Montanaro, R. Smith, Z. Tesfaye, B. Wenny, "Calibration overview for the Thermal Infrared Sensor (TIRS) on the LandsatData Continuity Mission," 10th Annual JACIE ( Joint Agency Commercial Imagery Evaluation) Workshop, March 29-31, 2011, Boulder CO, USA, URL: http://calval.cr.usgs.gov/JACIE_files/JACIE11/
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226) K. Thome, D. Reuter, A. Lunsford, M. Montanaro, R. Smith, Z. Tesfaye, B. Wenny, "Calibration of ther Thermal Infrared Sensor on the Landsat Data Continuity Mission," Proceedings of IGARSS (International Geoscience and Remote Sensing Symposium), Vancouver, Canada, July 24-29, 2011

227) Jason Budinoff, Konrad Bergandy, Joseph Schepis, Adam Matuszeski, Richard Barclay, "Development of the Scene Select Mechanism for the Thermal Infrared Sensor Instrument," Proceedings of the 14th European Space Mechanisms & Tribology Symposium – ESMATS 2011, Constance, Germany, Sept. 28–30 2011 (ESA SP-698)

228) Mary Pagnutti, Robert E. Ryan, Kara Holekamp, "Landsat Data Continuity Mission and Sentinel-2 Multi-Spectral Instrument Image Product Simulations for Sensor Comparisons and Data Fusion Research," Proceedings of the 11th Annual JACIE (Joint Agency Commercial Imagery Evaluation ) Workshop, Fairfax, VA, USA, April 17-19, 2012, URL: http://calval.cr.usgs.gov/wordpress/wp-
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229) James Nelson, Robert Patschke, Howard Garon, Alan Ames, Claire Mott, Grant Mah, Jason Williams, James Joseph, "Landsat Data Continuity Mission (LDCM) Space to Ground Mission Data Architecture," Proceedings of the 2012 IEEE Aerospace Conference, Big Sky, Montana, USA, March 3-10, 2012

230) Landsat Data Continuity Mission (LDCM), Ground System (GS) Integration and Test Plan," USGS, LDCM-I&T-001, Version 1.1, September 2009, URL: http://www.usgs.gov/contracts/acq_opp/EROS
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231) Jonathan Gal-Edd, "LDCM Ground System - Network Lessons Learned," SOSTC GSFC May 24-25, 2010, URL: https://info.aiaa.org/tac/SMG/SOSTC/Workshop%20
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232) Dave Hair , Doug Daniels, "Landsat Data Continuity Mission (LDCM) USGS Project Status Report," Proceedings of the Landsat Science Team Meeting, Mesa, AZ, USA, March 1-3, 2011, , URL: http://landsat.usgs.gov/documents/Landsat
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233) Susan M. Good, Ann M. Nicholson, Mark A. Woodard, "Landsat Data Continuity Mission (LDCM) Flight Dynamics System (FDS)," Proceedings of SpaceOps 2012, The 12th International Conference on Space Operations, Stockholm, Sweden, June 11-15, 2012

234) G. R. Mah, H. Garon, C. Mott, M. O'Brien, "Ground System Architectures Workshop 2014, Landsat 8 Test as You Fly, Fly as You Test," Proceedings of GSAW 2014 (Ground System Architectures Workshop), Los Angeles, CA, USA, Feb. 24-27, 2014, URL: http://gsaw.org/wp-content/uploads/2014/03/2014s04mah.pdf

235) Del Jenstrom, "Status of the Landsat Data Continuity Mission," Proceedings of the Landsat Science Team Meeting, Mesa, AZ, USA, March 1-3, 2011
 


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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