Landsat-8 / LDCM (Landsat Data Continuity Mission)
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.
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)
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)
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).
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).
Figure 3: Photo of the EM SSR (Solid State Recorder), image credit: NASA
Figure 4: Block diagram of the C&DH subsystem (image credit: NASA, USGS, Ref. 117)
- 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.
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.
- 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. 117).
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.
Table 1: Overview of spacecraft parameters
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. 117).
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).
Figure 8: Photo of the EM X-band transponder (left) and AMT S-band transponder (right), image credit: NASA
Figure 9: Alternate view of the deployed LDCM spacecraft showing the calibration ports of the instruments TIRS and OLI (image credit: NASA/GSFC)
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)
Figure 11: Anatomy of Landsat 8. Have you ever wondered what all the parts of a satellite do? This video identifies a few of the main components onboard Landsat 8 and tells you about their role in flying the satellite and capturing images of the Earth's surface below (video credit: USGS, NASA) 28)
Figure 12: The Landsat Data Continuity Mission (LDCM), a collaboration between NASA and the USGS (U.S. Geological Survey), will provide moderate-resolution measurements of Earth's terrestrial and polar regions in the visible, near-infrared, short wave infrared, and thermal infrared. There are two instruments on the spacecraft, the Thermal InfraRed Sensor (TIRS) and the Operational Land Imager (OLI). LDCM will provide continuity with the nearly 40-year long Landsat land imaging data set, enabling people to study many aspects of our planet and to evaluate the dynamic changes caused by both natural processes and human practices (video credit: NASA, USGS) 29)
Note: As of February 2020, the previously single large Landsat-8 file has been split into four files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Landsat-8 mission and its imagery in the period 2020, in addition to some of the mission milestones.
Mission status and some imagery of 2020
• September 16, 2020: Today’s Image of the Day concludes a three-part series exploring the changing landscape in Glacier Bay National Park, Alaska. Read about glaciers west of the bay here, and about the glaciers around the bay’s East Arm here. 30)
- In Glacier Bay National Park, the rugged landscape of water, ice, and life is in flux. Icebergs tumble from the fronts of glaciers, and plants are filling in where ice once covered the ground. Scientists and park staff have had a front row seat to all of the dynamic changes through the seasons and years.
Figure 13: Landsat-5 image of the west arm of Glacier Bay acquired with TM (Thematic Mapper) on 5 September 1986 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, topographic data from the Shuttle Radar Topography Mission (SRTM), and land cover data from the Multi-Resolution Land Characteristics (MRLC) Consortium. Story by Kathryn Hansen, inspired by Landsat images prepared by Christopher Shuman (UMBC) for the Earth to Sky partnership between NASA and the National Park Service)
- “Seeing glaciers like Margerie, Lamplugh, Reid, and Grand Pacific is like seeing old friends,” said Emma Johnson, an education specialist at the park in southeastern Alaska. “I can recognize them immediately and tell how they have changed from week to week.”
- “Seeing glaciers like Margerie, Lamplugh, Reid, and Grand Pacific is like seeing old friends,” said Emma Johnson, an education specialist at the park in southeastern Alaska. “I can recognize them immediately and tell how they have changed from week to week.”
Figure 15: The glaciers are all located in the West Arm of Glacier Bay, part of the Y-shaped inlet that is home to the majority of the park’s tidewater glaciers. Until the late 1980s, the park’s daily tour boat cruised up the bay’s East Arm for close-up views of tidewater glaciers—so-called because they flow directly into seawater. But the retreat of the East Arm glaciers onto land has sent tour boat operators into the West Arm instead, where a handful of impressive glaciers still touch the sea (image credit: NASA Earth Observatory)
- “The terminus of the tidewater glaciers is what most people see, but their stories are so much bigger,” Johnson said. “Satellite imagery was critical for helping me and other park rangers see the magnitude of change that has already happened in Glacier Bay.”
- Several decades of change around the West Arm are visible in the images of Figures 13 and 14, acquired in September 1986 with Landsat-5 and September 2019 with Landsat-8. Snow and ice are blue in these false-color images, which blend infrared and visible wavelengths to better differentiate areas of ice, rock, and vegetation.
- Johnson pointed out that the glaciers have changed in different ways over the years. Grand Pacific, for example, advanced into Tarr Inlet for several decades and even joined Margerie Glacier for a bit in the early 1990s before retreating again. Today the glacier is separated from Margerie and its front is completely covered in rocky debris. “More ice used to be visible on the face of Grand Pacific,” Johnson said. “Now I really have to tell people that it’s a glacier or they won’t recognize it.”
- Margerie is the tidewater glacier that visitors see up close, floating within a quarter mile of its face to watch icebergs calve from the front. Other than the calving—a natural part of a tidewater glacier’s life cycle—the front of Margerie remained generally unchanged from the time Johnson arrived at the park in 2009 until about 2017.
- “Margerie was the glacier we highlighted to tell our story as a park with stable or advancing glaciers in a world with overwhelming glacial melt,” Johnson said. In recent years, however, the glacier has pulled away from a small beach on the southern side, and bedrock is now exposed on its northern side.
- Farther south in the bay, Johns Hopkins Glacier is the only tidewater glacier in the park that has been advancing in recent years. The park’s tour boat lets visitors view it from afar—about six miles away, at the entrance to the inlet. But Jason Amundson, a glaciologist at University of Alaska Southeast, has been getting a close-up view.
Figure 16: In summer 2019, Amundson and colleagues deployed cameras near the glacier front as part of a multi-year project to track iceberg motion. Icebergs in Johns Hopkins Inlet serve as important habitat for harbor seals, and scientists want to know how this constantly changing habitat is affected by processes such as iceberg calving, glacier runoff, and fjord circulation (image credit: NASA Earth Observatory)
- In a preliminary analysis of the photos, Amundson was surprised by the lack of icebergs calving in the fjord in 2019, likely due to the buildup of a moraine at the glacier’s end. Fewer icebergs would negatively affect seals that depend on the floating ice for habitat.
- “The interesting story to me at Glacier Bay is how the shifting glacier landscape affects the rich marine ecosystem,” Amundson said. “Research into glacier-ecosystem interactions is pretty new, and so glaciologists and biologists are still learning how to talk the same language. The long history of research in Glacier Bay makes it an excellent place to study these interactions.”
• September 8, 2020: For thousands of years, rivers have shaped the world’s political boundaries. A new study and research database by geographers Laurence Smith and Sarah Popelka details the many ways that rivers shape modern borders. 31) 32)
Figure 17: The researchers merged a global database of large rivers (30 meters or wider)—derived from 7,300 Landsat scenes (Landsat-5, Landsat-7 and Landsat-8) — with maps of international, state, and local boundaries. In the process, they created a new database of river borders that has interesting historical elements, but also relevance for modern management of water, land, and pollution (NASA Earth Observatory, images by Lauren Dauphin, using data from Popelka, S., et al. (2020). Story by Adam Voiland)
- According to the analysis by Smith and Popelka, rivers make up 23 percent of international borders, 17 percent of the world’s state and provincial borders, and 12 percent of all county-level local borders. The map at the top of this page, based on their database, shows all of the U.S. states with borders defined by rivers (in blue). Generally eastern, more densely populated states have more river borders. While no state is entirely bounded by rivers, a few come close, notably Vermont, Iowa, Texas, Minnesota, and Illinois. The very short borders that look more like dots than lines, such as the one along the Oklahoma-Arkansas border, are places where large rivers cross a state border but only follow the border for a short distance.
- In the United States, rivers and their watersheds have a long history of defining both national and state borders. The Royal Proclamation of 1763 used the topographic divide between the Mississippi River basin and east-flowing Appalachian headwaters to help define the original U.S. colonies, an approach that left its legacy on the shape of several eastern seaboard states, including Virginia, North Carolina, and South Carolina.
- After the Revolutionary War, the Treaty of Paris extended U.S. territory to the Mississippi River, eventually helping create several irregularly shaped states in the Midwest. The river now forms borders in parts of ten states: Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Louisiana, and Mississippi.
Figure 18: The MODIS instrument on NASA’s Terra satellite acquired an image of the confluence of the Mississippi and Ohio rivers, a place where Kentucky, Illinois, and Missouri come together in a tripoint. A few hundred kilometers upstream there is another tripoint where the Wabash River joins the Ohio River and Kentucky, Illinois, and Indiana come together (image credit: NASA Earth Observatory)
- There are echoes of European colonialism in the world’s state and local borders. Former colonial territories like the eastern United States, Canada, and Australia have large numbers of state and local borders defined by rivers. “European explorers, cartographers, politicians, and diplomats found rivers to be a convenient way of dividing up territorial claims,” explained Smith, who is now a professor at Brown University but was at the University of California, Los Angeles, when he started the project. “Straight line borders of longitude and latitude were more commonly used in uncharted areas, like the western part of the United States and Australia.”
- While using rivers to divide states may seem conceptually simple, the natural tendency of river courses to change over time has caused complications. If you look carefully at maps and legal history, there are numerous territorial oddities and disputes that have arisen over the years.
- For instance, a series of earthquakes in 1811-12 shifted the course of the Mississippi River in a way that stranded two Tennessee towns — Corona and Reverie — west of the river in what seems like it should be Arkansas. Upstream, the same earthquake, and a lack of precision by early surveyors, left a bit of land known as the Kentucky Bend completely surrounded by parts of Missouri and Tennessee. Meanwhile, Kentucky and Indiana have engaged in a protracted debate about which state owned a piece of land near Evansville that connects to Indiana if the river is low but becomes an island if water is high.
- While the new river border data sheds light on some interesting aspects of history, Smith and Popelka hope it will help address some modern concerns. Since rivers often sit between states, cities, and counties, they are often at the center of complex political controversies involving dams, irrigation, hydropower, flood management, and water pollution. “Given the multitude of stakeholders in river basin management, there is a clear and pressing need to identify them at multiple geographic scales, so that all stakeholders may be considered in riparian water policy decisions,” they wrote.
- While many other researchers and organizations have studied the role rivers play when they serve as international borders, there has been much less attention on rivers as state and local borders. “To my knowledge, this is the first time anybody has quantified the influence of rivers on state and local borders on a global scale,” said Smith in reference to recently released Global Subnational River-Borders (GSRB) data.
• September 2, 2020: Over the past six decades, the Valsequillo reservoir has fallen victim to one of the world’s most invasive aquatic plants. The reservoir located south of the Puebla municipality in central Mexico was once filled with clear water; now nearly half of its surface is covered with clumps of water hyacinths. And Valsequillo reservoir is not unique. The growth is part of a global trend of water bodies being overrun by the unruly floating plants. 33)
Figure 19: The false-color images show the spread of water hyacinths across Mexico’s Valsequillo reservoir from January 10, 2000 (Figures 19), to January 9, 2020 (Figure 20). The images combine infrared, red, and green wavelengths to help differentiate between water and land. Clear water is blue and vegetation is red (the brighter the red, the more robust the vegetation). The images were acquired by the Enhanced Thematic Mapper Plus on Landsat-7 (bands 4-7-1) and the Operational Land Imager (OLI) on Landsat-8 (bands 5-7-1), respectively (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and using data from Kleinschroth, Fritz, et al. (2020). Story by Kasha Patel)
- Loved by many people around the world for their beautiful flowers, the native Amazonian plants are now seen by water managers as pests. The invasive plants, which grow at exponential rates, obstruct waterways, clog hydropower plants, and block sunlight from penetrating much below the water’s surface. A recent study by scientists at the Swiss Federal Institute of Technology (ETH Zürich) showed water hyacinth invasions have increased in reservoirs worldwide in recent decades, despite costly efforts to control the plants.
- “There’s some irony to the situation. Water hyacinths are brought in for their beauty, but then can quickly grow into a monster,” said Scott Winton, study author at ETH Zürich. “You can look at reservoirs throughout the world and see a similar pattern.”
- Winton and his co-authors analyzed 20 reservoirs in the tropics and subtropics with known water hyacinth invasions. Reviewing three decades of Landsat data, the researchers found a significant increase in water hyacinth coverage, especially in the past ten years. Analyzing the areas around each reservoir with land cover data from the European Space Agency, the team then discovered that increasing urban land cover explained 61 percent of changes in water hyacinth coverage.
Figure 21: The natural-color image of OLI shows the same scene in 2020; the water hyacinths are dark green (image credit: NASA Earth Observatory)
Figure 22: This graph shows the peak level of floating vegetation coverage for the basin for each year since 1993, as determined from Landsat data (image credit: NASA Earth Observatory)
- “Rapid urbanization often comes along with untreated sewage water that gets into service waters, which provides nutrients that allow the plants to thrive,” said Fritz Kleinschroth, a co-author and landscape ecologist at ETH Zürich. “We interpret the floating vegetation invasions as an issue of an underlying water pollution problem.”
- Out of the twenty reservoirs analyzed for the study, Valsequillo showed one of the most extensive and sharpest increases in water hyacinth coverage over the past decade. Winton says the surrounding area also gained an extra 200 square kilometers (70 square miles) of urban development from 1992 to 2015. The basin, which was created to provide water for irrigation to the surrounding villages, receives organic waste and heavy metal runoff from the nearby Puebla and Tlaxcala municipalities.
- But the news is not all bad. The team noted that water hyacinths can also play an important role in cleaning polluted water. Calculating the amount of nutrients absorbed by the plants in twelve reservoirs, researchers found that the plants soaked up much of the excess nutrients that had polluted the water. For example, water hyacinths in South Africa’s Hartbeespoort reservoir and Brazil’s Tapacurá reservoir absorbed around 60 and 80 percent of the annual nutrient load, respectively. Valsequillo, however, had so much nutrient pollution that the absorption by water hyacinths did not make much difference.
- “Water hyacinths are vilified because of the problems they cause, but you would have a suite of different problems if those rivers did not contain those plants,” said Winton. “If water hyacinths were not absorbing the excess nutrients, they would most likely be picked up by some other micro-organism or algae that could potentially cause much worse problems.”
- Some reservoirs use water hyacinths in constructed wetlands for wastewater treatment. The idea is to create a small pond near a pollution source and fill it with water hyacinths. The plants will subsequently absorb a lot of the nutrients before the pollution reaches the larger reservoir. Some resource managers have also converted the plants into biogas fuel for energy production, a tactic that was introduced in Disneyland in the 1980s.
- “We have been dealing with severe water hyacinth invasions for more than 50 years in some areas, so we need more integrated approaches to address this problem,” said Kleinschroth. “The ideal is to tackle the underlying nutrient pollution, but there are additional ways that we can co-exist with these plants.”
• August 25, 2020: Using data from Landsat, researchers have created a new map depicting the causes of change in global mangrove habitats between 2000 and 2016. The map will benefit researchers investigating the impacts of mangrove gain and loss on the global carbon cycle, while also helping conservation organizations identify where to protect or restore these vital coastal habitats. 34)
- Mangroves are hardy trees and shrubs that grow in the salty, wet, muddy soils of Earth’s tropical and subtropical coastlines. They protect the coastlines from erosion and storm damage; store carbon within their roots, trunks, and in the soil; and provide habitats for commercially important marine species.
Figure 23: The map shows the location and relative intensity of mangrove losses from 2000 to 2016. Countries colored orange and black had more losses of mangroves from human causes, while those in purple had more losses due to natural causes. The darker the color, the greater the area lost. The bar chart below shows those losses broken down by regions and by 5- and 6-year increments. The lead author of the study was Liza Goldberg, an intern at NASA’s Goddard Space Flight Center and a rising freshman at Stanford University (image credit: NASA Earth Observatory images by Joshua Stevens, using data courtesy of Goldberg, L., et al. (2020). Story by Jessica Merzdorf, NASA Goddard Space Flight Center, with Mike Carlowicz)
- In a study released in 2010, mangroves were found to cover about 138,000 square kilometers (53,000 square miles) of Earth’s coastlines. The majority of these ecosystems were found in Southeast Asia, but they existed throughout the tropical and subtropical latitudes around the globe.
- In the new study, researchers from NASA’s Goddard Space Flight Center used machine learning algorithms to analyze nearly one million images from the Landsat 5, 7, and 8 satellites. They first looked for changes is forest and land cover, then reviewed images for the type of land use. The team found that nearly 3400 square kilometers (1,300 square miles) of mangrove forests were lost between 2000 and 2016, or about 2 percent of global mangrove area. Roughly 62 percent of the losses were due to direct human causes, such as farming and aquaculture.
- Overall, the rate of mangrove habitat losses fell during the period, for both human-caused and natural (environmental) losses such as erosion and extreme weather. However, losses from natural causes now make up more of the overall total than in 2000. For conservation and resource managers trying to prevent loss or re-establish new habitats, this finding suggests the need to better account for natural causes.
Figure 24: Decline in mangrove loss in their natural habitats in the period 2000-2016 (map credit: NASA Earth Observatory)
- Hardy mangrove trees and shrubs provide an array of environmental benefits, noted Lola Fatoyinbo Agueh, a forest ecologist at NASA Goddard and mentor to Goldberg. Adapted to withstand salty water, strong tides, low-oxygen soils, and warm tropical temperatures, mangroves protect coastlines from erosion and storm surges. Their long, stilt-like root systems to hold tight to muddy soil and provide nurseries for marine creatures.
- Mangroves are also uniquely efficient carbon sinks—locations where carbon is removed from the atmosphere and stored in the Earth. Their leaves fall to the waterlogged soil and decompose very slowly, creating peat instead of releasing carbon back into the atmosphere. When these trees and shrubs are cut down or destroyed by storms or floods, that carbon instead escapes into the atmosphere, where it contributes to climate change as a greenhouse gas. Though they make up only 3 percent of Earth’s forest cover, mangroves could contribute as much as 10 percent of global carbon emissions if they were all cut down.
- “Mangroves provide shoreline protection from extreme storms and waves,” said Fatoyinbo. “Because they are amphibious trees, their root structure protects inland areas from the coast. They also protect the coast from the inland areas, because they are able to accumulate a lot of the soil that comes in from upstream or from the coast. They hold that sediment in their roots and essentially grow new land. If you have areas where you have increased erosion due to sea level rise, mangroves might counter that.”
- Mangroves have been threatened by deforestation for at least the past 50 years, as agriculture, aquaculture, wood harvesting, and urban development have caused the loss of more than a quarter of known mangrove forests. Mangroves in Southeast Asia have been especially hard-hit, as people have cleared mangroves to make room for shrimp and rice farming.
Figure 25: In 2002, the Río Cauto Delta in Cuba, pictured here in a January 2020 Landsat-8 image, was named a Ramsar site – an internationally recognized wetland of importance. The delta is home to numerous species of mangroves (image credit: NASA Earth Observatory/Lauren Dauphin)
• August 24, 2020: Nearly every summer, colorful blooms of phytoplankton flourish in the Baltic Sea. And nearly every summer, satellite images detect art-like patterns as the phytoplankton trace the sea’s currents, eddies, and flows. But like the whorls of fingerprints, no two phytoplankton blooms are exactly alike. 35)
Figure 26: These natural-color images, acquired on August 15, 2020, with the Operational Land Imager (OLI) on Landsat 8, show a late-summer phytoplankton bloom swirling in the Baltic Sea. The images feature part of a bloom located between Öland and Gotland, two islands off the coast of southeast Sweden. Note the dark, straight lines crossing the detailed image: these are the wakes of ships cutting through the bloom (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen, with image interpretation by Norman Kuring/NASA GSFC, Ajit Subramaniam/LDEO/Columbia University, and Maren Voss/Leibniz Institute for Baltic Sea Research Warnemuende)
- Confirmation of the type of phytoplankton within this bloom would require the analysis of water samples. But experts familiar with blooms in this region say it is likely to be cyanobacteria—an ancient type of marine bacteria that captures and stores solar energy through photosynthesis. Large, late-summer blooms of cyanobacteria occur almost every year in the Baltic Sea.
- Sediment cores extracted from the seafloor indicate that blooms of cyanobacteria have occurred in the Baltic Sea for thousands of years and they have played an important role in this aquatic ecosystem. Cyanobacteria are “nitrogen fixers” that can convert molecular nitrogen into ammonia—a more biologically useful form of nitrogen that all phytoplankton can use as a nutrient to fuel growth. Cyanobacteria do especially well in the Baltic Sea, where there is ample phosphate—another nutrient important for the organism to grow.
Figure 27: Larger view of the phytoplankton bloom in the Baltic Sea (image credit: NASA Earth Observatory)
- In the past, blooms in the Baltic Sea have intensified as a result of nutrient runoff from lands around the sea (particularly agricultural fertilizer and sewage). This source of excess nutrients has declined in recent decades, but blooms still thrive due to the abundance of phosphate in deeper waters. Excessive phytoplankton and algae growth can deplete the amount of oxygen in the water and cause dead zones.
- In some years, such as 2019, cyanobacteria blooms have covered as much as 200,000 km2 of the sea surface—slightly less than half the size of Sweden.
• August 18, 2020: An island with an unusual shape has been growing in shallow coastal waters near China’s Hainan Island. 36)
- In 2001, Dubai started construction on three large artificial islands in the Persian Gulf shaped like palm trees. A few years later, Doha began dredging for an island that resembled a string of pearls, and the United Arab Emirates went to work building an archipelago of 300 small islands strategically placed to look like a map of Earth.
- Now another island with an unusual shape has been growing in shallow coastal waters near Hainan, China’s southernmost province. Ocean Flower Island, built in Yangpu Bay, spans roughly 8 square kilometers (3 square miles), putting it among the world’s largest artificial islands.
Figure 28: The Operational Land Imager (OLI) on Landsat 8 captured this natural-color image of the new island on May 6, 2020, as construction was wrapping up and the island neared its full opening in late 2020 (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
Figure 29: Early signs of construction of the main island became visible to Landsat in 2012; by 2014, the main flower-shaped island had started to take shape. By 2020, it was flanked by two connected islands shaped like leaves. A mixture of parks, residential towers, museums, and other infrastructure had sprung up on the new land (image credit: NASA Earth Observatory)
- While planners expect the project will attract millions of tourists and boost Hainan’s economy, the project’s environmental impacts have attracted scrutiny. In 2018, China’s central government temporarily suspended construction at Ocean Flower Island—and several others—due to concerns about damage to coral reefs, oysters, and marine ecosystems. The same year, one of China’s regulatory agencies announced a temporary hold on approvals for many commercial land reclamation projects managed by local authorities.
• August 15, 2020: Tourists know Turkey’s Antalya province for its beautiful Mediterranean resorts, but coastal tourism isn’t the only major contributor to the region’s economy. Further inland, farming takes over as the dominant source of revenue and serves as the backbone for rural Turkey. 37)
Figure 30: The images show two important agricultural districts of the Antalya province as they appeared on June 8, 2020, to the OLI on Landsat-8. Crop production in Antalya is valued around $270 million. This map shows farms in the district of Elmalı, where the town of the same name sits at the top of a long upland valley. Elmalı, which means “apple,” produces around 12 percent of Turkey’s apples, as well as the local chickpea snack leblebi (NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- Turkey is home to nearly three million farms, the majority of which are family operated. Turkey is the world’s seventh largest agricultural producer overall, and a top exporter of hazelnuts, chestnuts, apricots, cherries, figs, and olives. Nearly one quarter of the country’s workforce participate in the agricultural sector.
Figure 31: This image shows a portion of the district Korkuteli, where farmers plant grains and oil seeds (image credit: NASA Earth Observatory)
- The arrangement of the farms conforms to the terrain of the Antalya province, which is largely mountainous. Drawing the northern border of Antalya, the Taurus Mountains cut across the province in the east to west direction in an arc. Elmalı and Korkuteli are located in the Bey Dağları mountains, the western range of the Taurus Mountains.
- More than two million people live in villages located within the Taurus Mountains and rely on farming as their major source of income. Because of the terrain, farms are typically small (about 4 hectares or 10 acres).
• August 13, 2020: Glacier Bay National Park in southeast Alaska is famous for its glaciers that flow into the sea. A handful of these tidewater glaciers are accessible via boat, giving visitors a close-up view of towering ice fronts and dramatic calving events. But most of the park’s glaciers are inland, deep in the Alaskan wilderness, where the changes are more difficult to observe with human eyes. 38)
Figure 32: This image of the remote Grand Plateau Glacier, located about 50 km west of Glacier Bay across the Fairweather Range, was acquired on September 7, 1984, with Landsat-5 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, topographic data from the Shuttle Radar Topography Mission (SRTM), and land cover data from the Multi-Resolution Land Characteristics (MRLC) Consortium. Story by Kathryn Hansen)
Figure 33: This image of the remote Grand Plateau Glacier, located about 50 km west of Glacier Bay across the Fairweather Range, was acquired on September 17, 2019, with Landsat-8 (image credit: NASA Earth Observatory)
- “Glacier Bay National Park is a well-known and visited area that is showing significant ice loss,” said Christopher Shuman, a University of Maryland, Baltimore County glaciologist based at NASA’s Goddard Space Flight Center. “But all the glacier thinning and retreat, as well as increased debris-cover and dramatic landslides, haven’t been fully documented yet.”
Figure 34: Overview map of the Glacier National Park (image credit: NASA Earth Observatory)
- Ice was already retreating before satellites were there to observe it. At its maximum extent during the Little Ice Age, Grand Plateau Glacier reached all the way to the Pacific Ocean coastline. Since then, it has progressively retreated from a series of end moraines--debris shoveled into a heap at the front edge of the glacier when it was advancing.
- In the images, a moraine near the coastline acts like a dam, trapping meltwater and forming a proglacial lake. Also note the end moraine visible poking above the surface of the lake in the 2019 image. This mound was left behind by a lobe of the glacier front that appears in the 1984 image.
- Over the past 35 years, the entire flow of the glacier system changed. In the 1984 image, many of the glacier’s branches flow toward the lake to the southwest; by 2019, retreat caused some branches to change course and flow toward the northwest. Notice the change in direction of the thin brown lines tracing the flow of the glacier’s branches. These are medial moraines: rocky debris from the sides of glaciers (lateral moraines) that have merged, causing the debris to be carried down the center of the combined glacier.
- Retreat is not the only change; Grand Plateau is also visibly narrowing and thinning. The island in the center of the 2019 image appears larger as ice has pulled away from its sides leaving more land exposed. The same phenomenon is apparent along the sides of the glacier, as wasting ice has exposed more of the valley walls.
- Another key indicator of change is the appearance of “ogives”—the arc-shaped brown marks on the lower-right part of the glacier in 2019. Rocks that come crashing down onto the glacier are initially spread out. Over time, seasonal accelerations of the glacier compress the debris into arc-shaped bands. There is a stark absence of ogives in the 1984 image. This could be due in part to more snow cover at the time or fewer rockfalls decades ago.
- “The frequency of them is concerning,” Shuman said. “There’s a chance of even more of these rockfalls as the climate continues to warm, melting mountain slopes and causing steep slopes to lose their grip.”
• August 4, 2020: Early detection of harmful algal blooms via satellite can result in significant savings on health care, lost work hours, and other economic costs. That is the finding of a NASA-funded case study published in June 2020 in the journal GeoHealth. 39)
Figure 35: This image, acquired by the Operational Land Imager on Landsat 8, shows Utah Lake as it appeared in natural color on June 20, 2017 (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and data courtesy of Blake Schaeffer/EPA from Stroming, Signe, et al. (2020). Story by Aries Keck, NASA Earth Science Applied Sciences, with Mike Carlowicz)
- Some species of algae and phytoplankton can be harmful to human health when they are present in high numbers. Such blooms can change the color of lake water in ways that are detectable by Earth-observing satellites. Using a 2017 bloom in Utah Lake as a case study, researchers found that early warnings from a satellite-based monitoring project—warnings that came days earlier than other detection methods—provided a measurable benefit for communities around Provo, Utah.
- “Using satellite data to detect this harmful algal bloom potentially saved hundreds of thousands of dollars in social costs by preventing hundreds of cases of cyanobacteria-induced illness,” said study co-author Molly Robertson, a research assistant at the non-profit research group Resources for the Future (RFF).
- The chlorophyll map (Figure 36) is a product of the Cyanobacteria Assessment Network (CyAN), a mulit-agency project that aggregates and analyzes satellite data to detect the presence of certain types of harmful algae in the freshwater lakes and rivers of the United States. The data for the Utah Lake map came from the European Space Agency's Sentinel-3 satellite. CyAN is led by the Environmental Protection Agency and includes NASA, the National Oceanic and Atmospheric Administration, and the U.S. Geological Survey.
- For their analysis, economists compared two scenarios of the June 2017 bloom: the real-world event, in which satellites detected algae in mid-June, and a second scenario in which the bloom was detected in more traditional ways.
- In June 2017, satellite data showed color changes, and thus the presence of algae, on Utah Lake. Remote sensing scientists informed the Utah Department of Environmental Quality, which then tested the waters for toxic algae earlier than observations on the ground alone would have enabled. This advanced warning allowed Utah public health and environmental officials to post warnings to boaters, swimmers, and fishers on June 29, 2017.
- In the second scenario, the Utah Lake bloom was reported by human observers and followed by on-site testing. Water managers then waited for test results and officials deliberated over the need to post warnings. Warnings were finally posted around the lake seven days later (July 6). That delay would have kept the toxic-algae coated lake open to humans and their pets. The study authors then used various health economics models and studies to estimate the costs of that extra exposure to the local community. The advance warning saved an estimated $370,000 for the region.
- The case study was part of a larger effort to develop a framework to measure the economic benefits of detecting harmful algal blooms. “Incorporating satellite data into the harmful algal blooms detection strategy for other large U.S. lakes could yield similar benefits,” Robertson said.
- The Utah Lake analysis and similar studies are projects of the Consortium for the Valuation of Applications Benefits Linked to Earth Science (VALUABLES), a collaboration between RFF and NASA’s Earth Science Applied Sciences program. It focuses on advancing innovative uses of existing techniques and developing new techniques for valuing the information provided by Earth-observing satellites.
Figure 36: The Sentinel-3 map shows the abundance of chlorophyll-a, the sunlight-harvesting pigment in plants and phytoplankton (including algae), on June 21, 2017. Chlorophyll-a measurements increase sharply (green shading in the image) with large blooms of algae and other plant-like organisms in the water.
• July 30, 2020: You may not be able to travel to Jezero Crater on Mars, but you can visit the next best thing: Lake Salda, Turkey. Though it is located a world away, Lake Salda shares similar mineralogy and geology as the dry Martian lakebed. 40)
- Researchers are using their understanding of Lake Salda to help guide the Mars 2020 mission, which will drop the Perseverance rover into the crater to search for signs of ancient life. “One of the great things about visiting Lake Salda is it really gives you a sense of what it would have been like to stand on the shores of ancient Lake Jezero,” said Briony Horgan, a planetary scientist at Purdue University and member of the Perseverance science team.
- Jezero is a 45 km (28 mile) wide ancient impact crater located in the northwest corner of a larger impact basin on Mars—essentially an impact crater within an impact crater. It is noteworthy because it once contained a lake, as evidenced by delta deposits. Previously, scientists discovered carbonate minerals throughout the crater. Using data taken by NASA’s Mars Reconnaissance Orbiter (MRO), Horgan and her team recently discovered evidence that some of these carbonate minerals may have formed in the lake.
- “Carbonates are important because they are really good at trapping anything that existed within that environment, such as microbes, organics, or certain textures that provide evidence of past microbial life,” said Brad Garczynski, a graduate student at Purdue who works with Horgan. “But before we go to Jezero, it is really important to gain context on how these carbonates form on Earth in order to focus our search for signs for life.”
- It just so happens that Lake Salda is the only known lake on Earth that contains the carbonates and depositional features (deltas) similar to those found at Jezero Crater. The first image above shows Jezero Crater as observed by MRO’s Context Camera. Spectral data showed signatures of carbonates on the western edge of the crater, which scientists believe to be the shoreline and beaches of an ancient lake. The carbonates are also present in the delta, which is the planned site of the Perseverance landing.
Figure 37: This image shows Jezero Crater as observed by MRO’s Context Camera. Spectral data showed signatures of carbonates on the western edge of the crater, which scientists believe to be the shoreline and beaches of an ancient lake. The carbonates are also present in the delta, which is the planned site of the Perseverance landing (image credit: Jezero Crater image courtesy of NASA / JPL-Caltech / MSSS / Tanya Harrison)
Figure 38: Though located a world away, Lake Salda, Turkey, shares similar mineralogy as Jezero Crater on Mars. The image shows Lake Salda on June 8, 2020, as observed by the Operational Land Imager (OLI) on Landsat-8. The lake contains alluvial fans full of rock deposits eroded and washed down from the surrounding bedrock (similar to the delta in Jezero). By studying how material is deposited in Lake Salda, the team can learn more about the various depositional processes at Lake Jezero (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- The white shoreline around Lake Salda is comprised of sands and gravels that are dominated by hydromagnesite, which is similar to the carbonate minerals detected at Jezero. Horgan explained that the hydomagnesite sediments along Lake Salda’s shoreline are thought to have eroded from large mounds called “microbialites”—rocks formed with the help of microbes. In Lake Salda, they formed from microbial mats that lived just beneath the surface of the water near the shoreline. As the microbialities grew, they incorporated carbonate materials and created large terrace islands.
Figure 39: In August 2019, Garczynski took this photo of an exposed microbialite island on Lake Salda. Collaborating with colleagues at the Istanbul Technical University, the Purdue research team spent almost a week surveying the lake’s perimeter and surrounding area. Garczynski said these islands are expected to erode over time and will eventually be transported, reworked, and deposited as beach sediments along the shoreline (photo credit: Garczynski, B. J, et al. (2020))
- “The structures themselves are good indicators that microbial activity was involved,” said Horgan. “The best case scenario is to find something like the microbialites we see in Lake Salda also preserved in the rock in Jezero Crater.”
- Horgan is a co-investigator for the Mastcam-Z imaging instrument, which will serve as the main scientific eyes for the Perseverance rover. The instrument will create mosaics of Jezero, perform simple mineral identification, and map the terrain.
- “A lot of our work at Lake Salda is already helping to determine which deposits are most promising to go visit on Mars,” said Horgan. “We’re excited to do the same kind of work that we were doing at Lake Salda, but now with our instruments on the ground at Jezero.”
• July 24, 2020: Since the start of Asia’s summer monsoon season on June 1, 2020, excessive rainfall has pushed lakes and rivers to record high levels in China. Flooding within the Yangtze River Basin, in particular, has displaced millions of people. 41)
- The Yangtze River is Asia’s longest, winding 6300 kilometers (3,900 miles) through China. Together with its network of tributaries and lakes, the river system has undergone significant development as a means to generate power, store water for drinking and irrigation, and control flooding. Today the watershed is dotted with tens of thousands of reservoirs, and its rivers are spanned by numerous dams.
Figure 40: This image shows water moving through the gates of Three Gorges Dam. Spanning a segment of the Yangtze River in central China’s Hubei Province, the dam is 2300 meters long and stands 185 meters high (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
- During the 2020 summer monsoon, floodwater was being held, or “absorbed,” by 2,297 reservoirs in the region, including the one behind Three Gorges Dam. In an attempt to regulate the flow of floodwater, dam operators can discharge water through spillway gates.
- Those gates were open when these images were acquired on June 30, 2020, with the Operational Land Imager (OLI) on Landsat-8. The images are composites of natural color and shortwave infrared to better distinguish the water. Note how the torrent flowing through the spillways changes how the water downstream reflects light, making it appear whiter.
- When these images were acquired in June, the waterways were trying to handle the first major flooding of the monsoon season. A second wave of severe flooding, referred to by local media as the “No. 2 flood,” hit the region in July. Between and during these flood events, continuous adjustments are made to the amount of reservoir outflow flowing through the gates.
- According to the Three Gorges Corporation, the water level in the reservoir reached a record high flood season level of 164.18 meters on July 19. The previous high level reached during the flood season since the dam became fully operational in 2012 was 163.11 meters. The reservoir is designed to hold a maximum water level of 175 meters.
Figure 41: The image shows the smaller Gezhouba Dam, located about 26 km (16 miles) southeast from Three Gorges. This dam also appeared to have its spillway gates open (image credit: NASA Earth Observatory)
• July 22, 2020: The Salmon River is among the longest free-flowing rivers in the United States. On its 425 mile (684 km) course from the Sawtooth Mountains through central Idaho, not one functioning dam impedes its flow. 42)
- The river begins on the north slope of Norton Peak as a trickle, but soon swells into a roaring torrent as it absorbs runoff from multiple ranges. Over hundreds of millions of years, the river has carved some of the deepest gorges in the United States, some of which have more vertical relief than the Grand Canyon. The only deeper gorge in North America is nearby Hells Canyon.
Figure 42: On July 24, 2019, the Operational Land Imager (OLI) on Landsat-8 acquired this natural-color image of a rugged section of a canyon near the confluence of the South Fork and the Salmon River. Notice how it lacks the straight, sheer walls of the Grand Canyon. Instead, the water slowly carved a geologic wonderland of wooded granite ridges, eroded bluffs, and scattered stone towers and crags (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat and topographic data from the U.S. Geological Survey. Story by Adam Voiland)
- The river proved a daunting obstacle for early explorers and pioneers. On August 23, 1805, Lewis and Clark’s dream of finding a water route across North America ended in failure when a scouting party led by the Shoshone guide Swooping Eagle and William Clark turned back after observing a tumultuous scene with the river “roiling, foaming, and beating against the innumerable rocks which crowded its channel.”
- When gold miners and lumberjacks flocked to the area in the 1860s, they had so much trouble getting boats up the river that it simply became known as “the river of no return”—a name that stuck. After Congress set aside land along the riverbanks for conservation in 1980, they called it the Frank Church - River of No Return Wilderness. Protecting 2,366,757 acres, it is the largest contiguous wilderness area in the Lower 48 United States.
Figure 43: Ancient artifacts found along the Salmon River at Cooper’s Ferry add yet another dimension to this remarkable river valley. In 2019, archaeologists from the University of Oregon announced they had discovered bones, charcoal, and spears that radiocarbon dating indicated to be more than 16,000 years old—one of the oldest archaeological sites in the U.S. (image credit: NASA Earth Observatory)
- The discovery added to a growing body of evidence that the first people to reach North America may have arrived by boat rather than over a land bridge connecting to Siberia. At that time, ice sheets would have still covered Beringia and key corridors that people would have had to follow to reach Alaska and Canada, but the Salmon River valley would have been free of ice, making it what archaeologists have described as a logical “off-ramp” for groups from Asia traveling to North America by boat.
• July 8, 2020: In the 1950s, Egyptian President Gamal Abdel Nasser set out to alleviate the cyclic flooding and drought periods in the Nile River region, build the agricultural economy and food supplies, and provide hydroelectric power to towns. Nasser’s government then designed a large dam to tame the mighty Nile River. The Aswan High Dam took a decade to build. The rockfill dam used around 44 million cubic meters (57 million cubic yards) of Earth and rock for its construction—a mass sixteen times greater than Great Pyramid of Giza. It offered better control of the flood cycles and more water storage than its predecessor, the Aswan Low Dam, to the north. 43)
Figure 44: The Operational Land Imager (OLI) on Landsat 8 acquired the data for this natural-color image of Lake Nasser (the Sudanese call their portion Lake Nubia). This composite scene was compiled from cloud-free images from 2013 to 2020. Located in a hot, dry climate with sporadic rain events, the lake loses a lot of water through evaporation and consequently shrinks seasonally in surface area. Water levels are typically highest in November during the flood season and lowest in July during the dry season (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- The new 111-meter (360-foot) tall dam created one of the largest man-made lakes in the world. Named for the Egyptian President, Lake Nasser stretches 480 kilometers (300 miles) long and 16 kilometers (10 miles) wide. Storing more than 100 cubic kilometers (24 cubic miles) of water, the lake took approximately six years to fill.
- Lake Nasser plays an important role in Egypt’s economy. Approximately one quarter of the nation’s population works in agriculture, which depends heavily on irrigation. With a reliable source of water from Lake Nasser, farmers have been able to plant more crops and to do so multiple times per year with the aid of fertilizers. After the reservoir was filled, the country was able to increase its arable land by 30 percent in the first few years, particularly to the west of the lake. Lake Nasser has also created a fishing industry and is a popular tourist attraction due to its crocodiles.
- Researchers, however, are worried about the lake’s future. The Grand Ethiopian Renaissance Dam, which will be Africa’s largest dam for hydroelectric power, is expected to greatly reduce water levels in Lake Nasser and the amount of power generated at Aswan High Dam. Research shows the project, which was 70 percent complete in October 2019, could lead to an irrigation deficit for Egypt in dry years and a decline in fisheries. One study found the lake shrunk 14 percent in surface area from 2015 to 2016, which may have been due to the new dam and the partial filling of its reservoir.
• July 2, 2020: Making a living in the Ferlo region of northern Senegal is a constant challenge. With a long dry season and little land suitable for crops, many of its people migrate with seasonal rains as they tend small herds of cattle, donkeys, and goats. 44)
- Keeping livestock healthy during the long “lean season”—which typically reaches its height between May and July when rains slow and most watering holes dry up—is particularly difficult. Many herding families move frequently, often every few weeks, to find water.
- “Inadequate rainfall puts nomadic herders in a particularly perilous position,” said Rebekke Muench, a scientist at the NASA SERVIR Science Coordination Office. SERVIR is a joint initiative of NASA and the U.S. Agency for International Development (USAID).
Figure 45: This Landsat-8 image shows how difficult it can be to distinguish between watering holes and bare ground in natural-color satellite imagery. Researchers use an image-analysis technique that makes use of near-infrared observations, which are particularly useful for distinguishing between dry and wet surfaces because water strongly absorbs near-infrared light (image credit: NASA Earth Observatory, images by Joshua Stevens, using data courtesy of Vikalp Mishra/NASA Marshall Space Flight Center and Planet Labs, and Landsat data from the U.S. Geological Survey. The SERVIR Global team working on this project includes people from NASA, Agro-Meteorology, Hydrology, and Meteorology (AGRHYMET), Veterinarians without Borders, and the Centre de Suivi Ecologique (CSE). Story by Adam Voiland)
- When rains are inadequate, the consequences can be grave. Lack of suitable forage forces herding families to buy expensive feed to prevent their livestock from starving. Animals end up crowded around just a few popular watering holes, which can easily become hotspots for the spread of viral and bacterial diseases, including foot-and-mouth. The constant walking and the lack of food can easily drive animals and people to exhaustion.
- “There is nothing more heartbreaking than hearing stories of people who spend days traveling through treacherous terrain to reach a trusted watering hole only to find that it has dried up," said Muench. “But this happens all the time.”
Figure 46: This data visualization shows how Landsat-8 (left) and PlanetScope (right) infrared observations allow researchers to find water that is otherwise hard to spot (image credit: NASA Earth Observatory)
- NASA and USAID researchers have developed a web-based tool to help Senegalese pastoralists get through the lean season. The dashboard features a near-real-time water monitoring system based on satellite observations. The system, now being tested and scheduled for release in August 2020, will make it possible for herders to quickly check how much water remains in hundreds of different watering holes in the Ferlo region before venturing to them.
- If people have access to the internet, they will be able to log in to the system directly. For those without internet access, aid organizations in the area plan to send updates about the status of key watering holes via text messages and community radio announcements.
- The SERVIR team began working on the project in 2017 using freely available data from Landsat-8 and ESA's Sentinel-2. More recently, they have assessed more detailed PlanetScope data from Planet Labs, a commercial satellite company. After analyzing images of hundreds of watering holes throughout 2018, it became clear that Planet Labs observations improved the accuracy of the tool, explained SERVIR scientist Vikalp Mishra.
Figure 47: This photograph shows cattle drinking from a watering hole in the Ferlo Valley near the town of Linguère (image credit: NASA Earth Observatory)
- “There were even some very small watering holes that we could only monitor with high-resolution imagery. Planet Labs has so many operating satellites in its fleet, we were able to get new images of northern Senegal on a near-daily basis.” he said. “Landsat, due to its long history and superior radiometric quality, still offers a critically important perspective because it has observations that show how key watering holes have fared over decades, a perspective you cannot get from any other satellite.”
- The use of high-resolution imagery is part of a pilot program to evaluate whether commercial small-satellite constellations could supplement Earth observations from NASA’s fleet of satellites. “Our study shows that the commercial data would complement the Landsat-based system and has potential to improve our water-monitoring tool and help pastoralists in Senegal,” said Mishra. “But commercial data is not free in the long-term, so we are exploring ways in which we can use it on a sustained basis.”
- The new tool will arrive in a period that has been particularly challenging for herding communities in Senegal. Following a year of sparse and erratic rains in 2019, people then had to cope with public health restrictions related to the spread of COVID-19 in 2020. In some parts of the country, the pandemic has even prevented some herding families from moving as they normally would, making it difficult to get their animals to market.
• June 25, 2020: Stretching across 800,000 km2 (300,000 square miles), Namibia contains an array of extreme landscapes: mighty sand dunes, gravel plains, rolling hills, and diamond-rich coastal deserts. 45)
- The Kalahari Desert and Central Plateau are two of the main topographic regions across the country. The Kalahari Desert is a large plain that covers the eastern third of Namibia as well as northern parts of South Africa and nearly all of Botswana. The area is covered by sand that generally appears red due to a thin coating of iron oxide.
Figure 48: Detail map of Namibia. This image shows the convergence of two contrasting geologic regions near the town of Mariental in south-central Namibia. The semi-arid sandy savannah of the Kalahari Desert lies to the east of the town, while the rocky plains of the Central Plateau are located to the west. The image was acquired on May 9, 2020, by the Operational Land Imager (OLI) on Landsat-8 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- Covering the middle stretch of the country from north to south, the Central Plateau is divided between rugged mountains and sandy valleys. It holds much of the country’s population, the nation’s capital, and the Etosha Pan. With many large farms and ranches located in its rolling hills, it contains much of Namibia’s arable land.
Figure 49: Originally founded as a railway stop in 1912, Mariental lies in between the two zones in a hot, arid region that receives little precipitation. Its main economic activities are game farming rather than traditional farming. Specifically, Mariental is a hub for farming sheep and processing sheep skins. It is also known for farming ostrich, which can survive well under the arid conditions (image credit: NASA Earth Observatory)
- Since the town sees so little rain, people get much of their water from the Hardap Dam located 22 kilometers (14 miles) to the northwest. The country’s largest dam controls the flow of the Fish River and provides water for irrigation to grow animal feed. The lake is also important for fish farms and provides a breeding area for the great white pelicans. The image above shows the Hardap Dam.
- The region around the dam is also a popular tourist destination. A resort in the area holds annual competitions for anglers, and visitors can also participate in water sports like canoeing and boating. The area is also home to a game reserve for black rhinos, jackals, and giraffes.
• June 18, 2020: When conservationist Aldo Leopold first paddled the Colorado River Delta in 1922, he was awed by the delta’s seemingly endless maze of green lagoons. “On the map, the Delta was bisected by the river, but in fact the river was nowhere and everywhere,” he wrote in A Sand County Almanac. 46)
- The wildlife, especially, entranced him. “A verdant wall of mesquite and willow separated the channel from the thorny desert beyond,” he continued. “At each bend we saw egrets standing in the pools ahead, each white statue mashed by its white reflection. Fleets of cormorants drove their black prows in quest of skittering mullets; avocets, willets, and yellow-legs dozed one-legged on the bars; mallards, widgeons, and teal sprang skyward in alarm.”
Figure 50: With so much of its water diverted, the Colorado River Delta has dried out and lost much of its vegetation and wildlife. In this natural-color satellite image, the dendritic tidal creeks that flow into the gulf and tidal mudflats look like spindly fingers reaching into the sea. White salt flats and brown, shifting dune fields of the Sonoran Desert flank the delta and Montague Island. The Operational Land Imager (OLI) on Landsat-8 acquired the image on March 20, 2020 (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
Figure 51: Detail image of Colorado River Delta emptying into the Gulf of California, also known as the Sea of Cortez (image credit: NASA Earth Observatory)
- If he were to return and see today’s Colorado River Delta, Leopold would likely be amazed by how much it has changed. With most of the river’s water diverted into an irrigation canal near the U.S. - Mexico border, about 90 percent of the wetlands are gone. The mesquite and willow have largely been replaced by invasive salt cedar. And most of those verdant lagoons have turned into salt flats. Without an influx of nutrients from the river, far fewer species live in the estuary and Gulf of California.
- There are still a few pockets of green that Leopold might find familiar. One of the largest, the Ciénega de Santa Clara wetland, formed by accident in the 1970s when the United States built a canal that drained salty irrigation runoff from farmland in Arizona. As the new source of moisture poured into the desert, an oasis of reeds, cattails, waterfowl, and other types of wildlife grew up around it, turning it into one of the largest wetlands in the area. Today, 280 species of birds spend their winters there.
• June 17, 2020: On the afternoon of June 13, 2020, a vehicle fire near the interaction of Bush Highway and State Route 87 ignited the brush and grass nearby. By June 16, nearly 65,000 acres (100 square miles or 260 km2) northeast of Phoenix, Arizona, had burned, making the Bush Fire the largest in the state this year and the largest in the United States right now. 47)
- According to firefighting and forest management agencies in the region, the fire was burning through tall grass and brush in and around the Tonto National Forest. As of midday on June 16, more than 400 firefighters were battling the flames with helicopters, fire engines, bulldozers, and airplanes. The fire was completely uncontained amid hot, dry, and windy conditions. More than 1,500 people had been evacuated from the Tonto Basin and Sunflower communities.
Figure 52: The satellite images (Figures 52 and 53) show the Bush Fire burn scar and some active fire fronts as they appeared on June 14, 2020. The images were acquired by the Operational Land Imager (OLI) on Landsat 8. The images blend natural-color (OLI bands 4-3-2) with the thermal infrared signature of actively burning fires (bands 6 and 5). This combination makes it easier to see still-active fire lines through the smoke. Scientists from the University of Wisconsin assembled this short animation of the fire spreading at night as observed by the NOAA-NASA Suomi NPP satellite (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat-8 data from the U.S. Geological Survey. Story by Michael Carlowicz)
- The red lines across the detailed image (Figure 52) are fire retardant that was dropped to keep the fire from advancing toward settled areas. This video shows one of the airborne retardant drops, while this closeup demonstration shows the impact and spread of the fluid slurry as it reaches the ground.
- Across the state, the Bighorn Fire has burned nearly 16,000 acres in the Santa Catalina Mountains near Tucson; it was 30 percent contained as of June 16. Near the North Rim of the Grand Canyon, the Magnum Fire charred more than 30,000 acres in Kaibab National Forest; it was 3 percent contained.
- Fire season typically peaks in the U.S. Southwest in June and July. In a seasonal forecast issued on June 1, the National Interagency Fire Center predicted “above normal significant large fire potential” in the region, especially Arizona. Temperatures have been 1 to 6 degrees Fahrenheit above normal for much of the past two months, and rainfall has been below normal.
• June 11, 2020: Through episodic and regional studies, scientists have observed that phytoplankton blooms have been occurring more often in lakes around the world in recent decades. But until recently, no one had assembled a global, holistic view of the phenomenon. Scientists from Stanford University and NASA recently decided to measure the blooming trends globally. What they found was discouraging. 48)
Figure 54: Siling Lake (or Sèlin Cuò) in Tibet is one lake that has had a steady increase in blooming intensity since 1995. This natural-color image was acquired by the Operational Land Imager on Landsat-8 on September 12, 2017 (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Andi Brinn Thomas)
- Working with the long satellite record from Landsat, Stanford environmental scientist Jeff Ho and colleagues examined 71 lakes in 33 countries on six continents. They focused on summertime conditions in large lakes (greater than 100 square kilometers/40 square miles) with different physical settings, latitudes, and levels of human impact.
- They used computers to analyze nearly 32,000 images spread across 28 years, training the computer to detect strong near-infrared signals. Phytoplankton blooms have high concentrations of chlorophyll, the same pigment that helps land-based plants absorb sunlight to make energy. Chlorophyll tends to reflect near-infrared light and absorb blue and green light, so intense blooms produce strong near-infrared signals in infrared imagery.
- The researchers found that phytoplankton blooms over the years typically followed one of four trends: sustained improvement (blooms decreasing), deterioration (blooms increasing), improvement then deterioration, or no significant trend. Across the study period (1984 to 2012), peak summertime bloom intensity rose considerably in 48 out of the 71 lakes (68 percent). Most of the deterioration increased in the latter years of the study period. 49)
- “Toxic algal blooms affect drinking water supplies, agriculture, fishing, recreation, and tourism,” explained lead author Ho. “Studies indicate that just in the United States, freshwater blooms result in the loss of $4 billion each year.”
- One of the common reasons for lake deterioration is nutrient overloading—the accumulation of excess dissolved nutrients in the water from runoff and fertilizer. Excess nutrients such as phosphorous and nitrogen can promote the growth of massive colonies of algae. Sometimes those blooms are directly toxic to other marine species and humans who consume them. Other times, large blooms can suffocate marine life by depleting the oxygen in the water (hypoxia). Lakes are at a higher risk for these sorts of blooms when they have less circulation from rivers flowing in and out; sustained warmer water temperatures; or variability in lake composition, where no one section of the lake has the same physical and chemical makeup.
- Siling Lake (or Sèlin Cuò) in Tibet is one lake that has had a steady increase in blooming intensity since 1995. The lake includes protected wetlands (a Ramsar site) and is major stopover for birds migrating through the region. Most of the land around the lake is used for grazing yaks, sheep, and other livestock, a factor that could contribute to blooms.
- “Algal blooms really are getting more widespread and more intense, and it’s not just that we are paying more attention to them now than we were decades ago,” said Anna Michalak, a co-author on the paper.
- Ho and colleagues found that lakes showing sustained improvement were rare—only six out of the 71 studied. Lake Balaton (pictured above) is one of those six. Sitting in southwest Hungary, Lake Balaton is the largest lake in Central Europe. It is a major tourist destination and key economic resource, so the local government has focused a lot of energy on a water management plan to reduce nutrient pollution. Those efforts could help explains the lake’s improvement across the study period.
- Temperature, precipitation, and fertilizer-use trends across the lakes in the study were not consistent. The few lakes that showed sustained improvement tended to have little to no warming over time. The study authors suggested that lake warming might promote blooms in ways that could counteract efforts to decrease blooming through water quality management.
Figure 55: The natural-color image of Lake Balaton was acquired by OLI on Landsat-8 on 31 August 2019 (image credit: NASA Earth Observatory)
• June 7, 2020: Located within the Arctic Circle, northern Finland experiences some the world’s harshest and snowiest winters. But even the 2020 winter season was exceptional by Finnish standards. 50)
- Lapland, the northernmost region of Finland, just endured its snowiest winter in 60 years. Meteorologists reported that the winter snow arrived in October, and persistent cold temperatures hindered the snow from slowly melting over the months. By January 2020, some towns recorded almost triple the amount of snow on the ground than normal for the season.
- In late May, unusually warm temperatures began to rapidly melt the high volume of snow and caused significant flooding to nearby homes and farms. Several rivers have swelled, causing the closure of a bridge and prompting flood warnings for several towns.
Figure 56: This natural-color image shows the area around Ivalo, Finland, on May 25, 2020. While some land remains frozen, other portions have become muddy with melt water. The image was acquired by the Operational Land Imager (OLI) on Landsat-8. The extent of the flooding also appears in images by satellites using synthetic-aperture radar (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
• June 4, 2020: Birds are pretty sensitive when it comes to temperature. Some species struggle to keep warm during cold winters. Other birds have expanded their range northward as global climate has warmed. It turns out scientists can use this close relationship between temperatures and bird behavior to predict bird biodiversity. 51)
- One way that ecologists assess biodiversity is by measuring the number of different species present in a given location—a measure that scientists call “species richness.” Information on species richness is useful for guiding conservation efforts, such as how to manage a landscape. But wildlife data can be relatively sparse and often reliant upon people in the field conducting surveys.
- “To get around that issue, we try to think of variables that accurately represent where birds occur and can be more readily measured over large scales,” said Paul Elsen, a postdoctoral researcher at University of Wisconsin-Madison when the study was conducted. “Things like elevation and habitat have been used a lot for this, but we also know that temperature is a very important factor for birds.”
- To map temperature patterns across the continental United States, Elsen and colleagues compiled data acquired from 2013 to 2018 by the Thermal Infrared Sensor (TIRS) on Landsat-8. They focused on data from December through February, the cold winter months when birds are most affected by temperature. Then the researchers compared their temperature maps with existing ground-based surveys for large and small resident (non-migratory) birds.
Figure 57: This map shows relative temperatures during the winter across the United States in the period 2013-2018. Note that the temperatures are not quite the same as you would measure from the ground; rather, they show where temperatures are warmer (red) or cooler (blue) than the median temperature detected. The most obvious pattern that emerges is an intuitive one—the country is generally warmer in the south and colder in the north (image credit: NASA Earth Observatory ,images by Joshua Stevens, using Landsat data courtesy of Elsen, P., et al. (2020). Story by Kathryn Hansen)
Figure 58: This map, also derived from TIRS data, shows the magnitude of these temperature differences, or “thermal heterogeneity”—that is, how much temperatures differ across small distances in the landscape. Higher values (red) indicate a greater temperature difference and lower values (yellow) indicate temperatures that are relatively similar. The map shows that the largest differences tend to occur around mountains. Again, the pattern is intuitive: when you are hiking a mountain, the temperature can change drastically as you gain or lose elevation (image credit: NASA Earth Observatory)
- Ground-based survey data indicated that both small and large birds tend to prefer locations with higher overall winter temperatures. Detailed maps show, however, that there can be quite a bit of variation on local scales. Places that are generally cold in winter can still have areas of relative warmth and potential bird habitat.
Figure 59: This detailed map pair shows relative temperature (left) and thermal heterogeneity (right) in the southern Rocky Mountains in the period 2013-2018. Note the large temperature variations. This is common in mountain environments, where temperatures can change over very short distances due to factors such as elevation (image credit: NASA Earth Observatory)
Figure 60: This image pair shows relative temperature (left) and thermal heterogeneity (right) in California’s Central Valley in the period 2013-2018. They show that differences in temperature are not just driven by differences in elevation; they can also be influenced by the region’s farms and orchards (image credit: NASA Earth Observatory)
- “Land cover also influences the thermal environment, and we can really see that in the agriculture map,” Elsen said. “This is a very flat landscape, but there are a lot of different temperatures because there are different kinds of crops creating different local temperature conditions.”
- Small birds do not regulate their body temperature as well as large birds, and they generally do not move as far in search of warmer environments. Ground-based survey data confirm that small birds prefer landscapes with larger thermal differences, likely because they offer more opportunities to find refuge from the cold.
Figure 61: Photo by Amanda Frank via Unsplash (image credit: NASA Earth Observatory)
- In their paper, Elsen and colleagues go on to show that the relationship between temperatures and bird behavior can be used in models to accurately predict bird species richness during the winter. “That means we can make some fairly good predictions about how species might respond to future temperature changes,” Elsen said. 52)
- He cautions, however, that the predictions are limited to the winter season. “We know through subsequent work that the relative temperature and thermal heterogeneity patterns we observed during winter are actually fairly different in summer,” Elsen said. “This means we would have to be careful to make predictions about other time periods.”
• May 30, 2020: Along the Australian coast near Brisbane, the Moreton Bay area is known for its clear blue waters, vast sand banks, and diverse wildlife (Figure 62). But eight decades ago, it had a less placid existence as a major coastal defense port during World War II (WWII). 53)
- In the 1940s, Moreton Bay provided a direct Pacific passage for allies and enemies to approach Brisbane. The Queensland government thus strategically placed defense stations around Moreton Bay, and ships could not enter without undergoing an inspection by the Australian navy. Enemies and unidentified vessels were gunned or bombed.
- Queensland served as a training and support base for Allied Forces in the Pacific theater of World War II. In fact, Brisbane served for a time as headquarters for American General Douglas MacArthur. The city’s population doubled as thousands of soldiers were stationed there. Today, Brisbane is the capital of Queensland and the third most populous city in Australia (more than 2 million residents).
- The natural coastal features stand in contrast to the city’s urban landscape. The underwater blue and green curves transecting the North West Channel reveal sand banks and part of Moreton Bay’s complex delta system. The sand banks were formed after sea levels rose about 6,500 years ago. About 30 meters deep, the offshore tidal delta is constantly shaped by currents that tend to be stronger in the northern half of the bay. The southern half is sheltered from those South Pacific currents by Moreton Island. Water near the Brisbane metropolitan area is typically muddy with sediments carried out by rivers.
- The bay sits at the convergence of tropical and temperate climates, and thus is home to a diverse array of animals. It contains one of the highest densities of dugongs, a relative of the manatee, along the Australian coast. Some evidence suggests that dugongs were once located throughout the bay, but their habitat became restricted as shorelines became urbanized. Moreton Bay is also home to the endangered loggerhead turtle and many species of whales. It supports up to 25 percent of Australia’s bird species, depending on the season.
- Today, the Moreton Bay area is a popular tourist attraction for its history and beauty. Some World War II relics are partially buried on the sand shores. Tourists (particularly newlyweds) visit Honeymoon Bay on Moreton Island to swim in clear waters on isolated beaches. The rocky reefs and deeper channels also provide excellent fishing opportunities for anglers to catch tuna, jewfish, snapper, and sailfish.
Figure 62: This natural-color image shows the northern entry into Moreton Bay as observed on November 6, 2019, by the Operational Land Imager (OLI) on Landsat-8. The bay spans about 1,500 km2 (600 square miles). During WWII, the North West Channel served as a main shipping passageway and was guarded by Fort Bribie and Fort Cowan (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
• May 14, 2020: When oceanographer Serge Andréfouet first saw a satellite image of the Great Bahama Bank, he knew the colors and contours were special. He passed the unique image to a colleague, who submitted it to NASA’s Earth Observatory (EO) for an Image of the Day in 2002 (Figure 63). Nearly eighteen years later, the image is still much appreciated. In fact, it knocked off more recent satellite imagery to win EO’s Tournament Earth 2020. 54)
Figure 63: Andréfouet’s image shows a small section of the Great Bahama Bank as it appeared on 17 January 2001, and was acquired by the Enhanced Thematic Mapper Plus (ETM+) on the Landsat-7 satellite (using bands 1-2-3). At that time the instrument’s blue channel (band 1) helped distinguish shallow water features better than previous satellite mission (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, and GIBS/Worldview.2002 imagery courtesy Serge Andrefouet, University of South Florida. Story by Kasha Patel)
- “There are many nice seagrass and sand patterns worldwide, but none like this anywhere on Earth," said Andréfouet, who is now studying reefs at the Institute for Marine Research & Observation in Indonesia. “I am not surprised it is still a favorite, especially for people who see it for the first time.” He said the image has been featured over the years on numerous websites, in books, and even at rave parties.
- The varying colors and curves remind us of graceful strokes on a painting, but the features were sculpted by geologic processes and ocean creatures. The Great Bahama Bank was dry land during past ice ages, but it slowly submerged as sea levels rose. Today, the bank is covered by water, though it can be as shallow as two meters deep in places. The bank itself is composed of white carbonate sand and limestone, mainly from the skeletal fragments of corals. The Florida peninsula was built from similar deposits.
- The wave-shaped ripples in the images are sand on the seafloor. The curves follow the slopes of underwater dunes, which were probably shaped by a fairly strong current near the sea bottom. Sand and seagrass are present in different quantities and at different depths, which gives the image a range of blues and greens.
Figure 64: The area appeared largely the same when Landsat-8 passed over on February 15, 2020 (image credit: NASA Earth Observatory)
- The shallow bank quickly drops off into a deep, dark region known as the “Tongue of the Ocean.” Diving about 2,000 meters (6,500 feet) deep, the Tongue of the Ocean is home to more than 160 fish and coral species. It lies adjacent to the Andros Island, the largest in the Bahamas and one of the largest fringing reefs in the world.
Figure 65: This image was acquired on 4 April 2020, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, providing an overview of the region (image credit: NASA Earth Observatory, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, Story by Kasha Patel)
- At the time of the 2001 image, researchers did not have a good understanding of the location and distribution of reef systems across the world. Global maps of coral reefs had not changed much since the 19th Century. So researchers turned to satellites for a better view. Andréfouet’s image was collected as part of the NASA-funded Millennium Coral Reef Mapping Project, which aimed to image and map coral reefs worldwide. The project gathered more than 1,700 images with Landsat-7, the first Landsat to take images over coastal waters and the open ocean.
- Today, many satellites and research programs continue to map and monitor coral reef systems, and marine scientists have a better idea of where the reefs are and how they are faring. Researchers now use reef images and maps in tandem with sea surface temperature data to identify areas vulnerable to coral bleaching.
• May 13, 2020: Using a combination of satellite sensors, scientists recently found that Denman Glacier has been retreating both above and below the water line. That one glacier in East Antarctica holds as much ice as half of West Antarctica, so scientists are concerned about its stability. 55)
Figure 66: This natural-color image is a mosaic of cloud-free images acquired by Landsat-8 on February 26-28, 2020 (image credit: NASA Earth Observatory, images by Joshua Stevens, using data courtesy of Brancato, V., et al. (2020), and Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz, NASA Earth Observatory, with Jane Lee and Ian O’Neill, Jet Propulsion Laboratory, and Brian Bell, University of California, Irvine)
- From 1996 to 2018, the grounding line along the western flank of Denman Glacier retreated 5.4 kilometers (3.4 miles), according to a new study by scientists from NASA’s Jet Propulsion Laboratory and the University of California, Irvine (UCI). The grounding line is the point at which a glacier last touches the seafloor before it begins to float.
- Behind the grounding line, the ice is attached to the bedrock; beyond it, glacial ice floats on the ocean as an ice tongue or shelf. The retreat of the grounding line at Denman means more of the glacier’s underside is now in contact with water that could warm and melt it from below. If the grounding line continues to retreat, warmer seawater could eventually penetrate farther upstream beneath the glacier.
Figure 67: This map provides a three-dimensional view of the bed topography—the shape of the land surface and seafloor under the ice—around Denman Glacier, as derived from measurements made by radar and gravity-sensing instruments. The pink line delineates the grounding line as measured in 1996, while yellow indicates the line observed during the new study. (Ice flows from left to right on the map.) The darker the blues, the deeper the seafloor. Note the depth around and behind (left) the grounding line (image credit: NASA Earth Observatory)
- “Because of the shape of the ground beneath Denman’s western side, there is potential for the intrusion of warm water, which would cause rapid and irreversible retreat and contribute to global sea level rise,” said lead author Virginia Brancato, a scientist at JPL, formerly at UCI.
- On its eastern flank, Denman Glacier runs into a 10 km wide underwater ridge. On its western flank, however, the glacier sits over an 1800-meter deep trough that stretches well inland. If the grounding line keeps retreating, seawater could get funneled into that trough—which is smooth and slopes inland—and penetrate far into the continent. (The trough eventually dives to 3500 meters below sea level, the deepest land canyon on Earth. Click here to learn more about the Antarctic landscape beneath the ice.)
- The scientists are concerned by the changes at Denman’ grounding line because there is potential for the glacier to undergo a rapid and irreversible retreat. As global temperatures rise and atmospheric and ocean circulation changes, warm water is increasingly being pushed against the shores of Antarctica by westerly winds.
Figure 68: This map depicts the velocity of the ice surfaces on and around Denman Glacier, as measured by the JPL/UCI team. Ice flows from left (grounded ice) to right (floating ice) in the image. About 24,000 km2 (9,000 square miles) of Denman floats on the ocean, mostly on the Shackleton Ice Shelf and Denman Ice Tongue. That floating ice has been melting from the bottom up at a rate of about 3 meters annually. These measurements, as well as the grounding line and seafloor measurements above, were made through the use of synthetic aperture radar data from the German Aerospace Center’s TanDEM-X satellite and the Italian COSMO-SkyMed satellites, as well laser altimetry data from NASA’s Operation IceBridge (image credit: NASA Earth Observatory)
- “East Antarctica has long been thought to be less threatened, but as glaciers such as Denman have come under closer scrutiny, we are beginning to see evidence of potential marine ice sheet instability in this region,” said Eric Rignot, a cryospheric scientist at JPL and UCI and one of the study authors. “The ice in West Antarctica has been melting faster in recent years, but the sheer size of Denman Glacier means that its potential impact on long-term sea level rise is just as significant.”
- Recent research found that Denman Glacier lost roughly 268 gigatons (1012 tons) of ice, or 7.0 gigatons per year, between 1979 and 2017. Until recently, researchers believed that East Antarctica was more stable than West Antarctica because eastern glaciers and ice sheets were not losing as much ice as those in the western part of the continent. If all of Denman melted, it would result in about 1.5 meters (5 feet) of sea level rise worldwide.
• May 6, 2020: Forest buffers help protect grazing land and animals from the Japanese island's cold, windy winters. 56)
Figure 69: From above, the Konsen Plateau in eastern Hokkaido offers a remarkable sight: a massive grid that spreads across the rural landscape like a checkerboard. As seen in this pair of natural-color images, the pattern is clear year-round—even under a blanket of snow. Both images were acquired by the Operational Land Imager (OLI) on Landsat-8. This image was acquired on 27 September 2019 (NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
- The strips are forested windbreaks—180-meter (590-foot) wide rows of coniferous trees that help shelter grasslands and animals from Hokkaido’s sometimes harsh weather. In addition to blocking winds and blowing snow during frigid, foggy winters, they help prevent winds from scattering soil and manure during the warmer months in this major dairy farming region of Japan. The thinner, less regular strips are forested areas along streams.
Figure 70: Wintery detail image of the windbreaker pattern acquired with OLI on 27 February 2020 (image credit: NASA Earth Observatory)
- The Japanese government began creating the windbreaks in the 1890s as part of an effort to colonize the area. Rather than planting forested strips, they simply cleared squares into the broadleaf forests that were already there at the time, leaving the windbreaks behind. Planners used a grid pattern inspired by land development and farming practices popular at the time in pioneer areas of the midwestern and central United States.
- Over time, as bits of windbreaks were cleared for timber or by wildfires, the broadleaf forests were replaced by plantings of larch and spruce that make up most of the windbreaks today.
• May 4, 2020: Mines across the United States churn out all kinds of minerals, from potash to iron to gold. But the ground around a mine in southern Montana contains a mineral that is a bit more valuable—at least to the scientists who use it to study the Moon. 57)
- The site gained attention from NASA and U.S. Geological Survey scientists for a different type of rock. “Anorthosite is probably the most common single mineral on the surface of the Moon,” said Doug Rickman, an economic geologist and lunar geoscientist (retired, and current part-time contractor) at NASA’s Marshall Space Flight Center.
Figure 71: On August 10, 2018, Operational Land Imager (OLI) on Landsat-8 acquired this image showing part of the Stillwater Complex south of Nye, Montana. The group of rocks spans about 30 miles (50 km) of the Beartooth Mountain Range, and is mined primarily for its chromium and platinum-group metals (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey and topographic data from the Shuttle Radar Topography Mission (SRTM). Story by Kathryn Hansen)
- From Earth, lunar anorthosite is visible as the light-colored, highly reflective parts of the Moon’s surface known as the lunar highlands. These are the Moon’s oldest rocks—more than 4 billion years old—and covered the young Moon’s entire surface before its crust was pummeled and broken up by asteroids and comets. Anorthosite rocks brought back to Earth by Apollo astronauts have helped researchers learn about the Moon’s geologic history.
- But the supply of anorthosite samples from the Moon is limited. Fortunately, the mineral can also be found on Earth. Researchers have demonstrated that terrestrial anorthosite can be a useful analog for studying the history of the lunar crust and the formation of anorthosites on the Moon. Not all anorthosite found around our planet, however, measures up.
- “Anorthosite is not rare on Earth,” Rickman said. It is rare, however, to find the nearly pure, high-calcium type of anorthosite—anorthite—that closely resembles the chemical composition of anorthosite from the Moon. Rocks found within the Stillwater Complex come very close.
- “The Stillwater Complex can teach us about the formation of anorthosite itself, as well as what the surface of the Moon is like in the lunar highlands regions,” said Sarah Deitrick, a lunar geoscientist at NASA’s Johnson Space Center.
- Scientists have also collected anorthosite rocks from mines within the Stillwater Complex—debris from road cuts and mining tailings—to manufacture synthetic moon dust. The term scientists use for this moon dust substitute is “simulated lunar regolith,” or simply “simulants.”
- “These simulants are extremely helpful when it comes to testing equipment, space suits, or anything else that will come in contact with the lunar surface when humans go back to the Moon,” Deitrick said. “The Stillwater Complex has been used to create some of the most accurate simulants that replicate the lunar highlands.”
- But even the high quality anorthsite from the Stillwater Complex is not perfect. Terrestrial influences like temperature and pressure, or exposure to water, can alter the mineral. Scientists have long studied the best way to mill, mix, and handle the materials to arrive at the most Moon-like dust possible.
- There is plenty of detailed geology and chemistry involved with the research, but simulant specialists like Deitrick and Rickman still manage to keep the big picture in mind. “The reason I got interested in simulants was quite simple,” Rickman said. “If you are going to send a billion-dollar system to the Moon you have to test it. If you mess it up on the Moon, it is a long walk back to the nearest hardware store to get parts.”
• May 2, 2020: Most of the 109 fjords of Iceland are clustered in a small area in the east or around the large peninsula in the northwestern part of the island. There are just a handful of fjords along the northern coast. Among them is Eyjafjörður, Iceland’s longest fjord. 58)
- Eyjafjörður has become a prime destination for whales, scientists, and tourists. Humpback, bottlenose, blue, and mink whales frequent the sheltered, nutrient-rich waters to feed on plankton. Scientists are drawn to study the unusual hydrothermal vents found in its shallow waters. And with an ice-free port and a surprisingly mild climate, Akureyri is typically visited by more than 100 cruise ships per year.
- The fjord was created by many thousands of years of glacial activity. When this part of Iceland was cooler and icier, glaciers carved the long, narrow valley by grinding against the land surface as they slid toward the sea. Over time, rising sea levels filled the valley to create the fjord.
- South of the fjord, pastures and farms are concentrated in the valley. It is one of the few areas in the rugged, rocky terrain of Northern Iceland with a significant amount of farmland.
Figure 72: Eyjafjörður spans more than 60 km (40 miles) from its mouth to Akureyri, a city known as Iceland’s “northern capital.” The Operational Land Imager (OLI) on Landsat-8 acquired this image of the fjord on July 8, 2017 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
Figure 73: After a wet March and April 2020, poppy fields bloomed in Southern California. On April 14, 2020, the Operational Land Imager (OLI) on the Landsat 8 satellite acquired these images of vast blooms in the Antelope Valley California Poppy Reserve. These images were acquired when poppy flowers in the valley were thought to be at or near their peak (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
Figure 74: Larger OLI image of Southern California containing the poppy field detail in Antelope Valley (image credit: NASA Earth Observatory)
- The flowers bloomed after Southern California received significant rainfall in March and April 2020. This spring, Lancaster received around 10.5 inches (27 cm) of rain—almost 4 inches (10 cm) above normal. The extra rain may cause the poppies to stick around longer than usual and result in an above-average wildflower year. Park officials called this bloom an “unexpected” surprise due to the late season rains.
- While many parks have restricted visitor access to the park during the COVID-19 quarantine, people can view the flowers through online livestreams. Depending on the day or even hour, the orange patches may change in appearance. The poppies open their petals during sunny periods, appearing like a large blanket over the landscape. The flowers tend close during windy, cold periods. While the orange poppies are easy to spot in satellite imagery, the fields also contain cream cups, forget-me-nots, purple bush lupines, and yellow goldfields (a relative of the sunflower).
• April 25, 2018: Some of the largest natural lakes in Australia are waterless throughout much of the year. Scattered across the country, these ephemeral lakes usually only fill after heavy seasonal rains or passing tropical cyclones drench the landscape. After a tropical storm in early 2020, water levels rose in one such lake. 60)
Figure 75: Detail image of Lake Carnegie. Located in the Shire of Wiluna in Western Australia, Lake Carnegie is one the country’s largest lakes. When full, it is covers about 5,700 square kilometers (2,200 square miles). In dry years, the lake is mostly a muddy marsh. The images show the lake on March 26, 2020, when it was still partially filled. The images were acquired by the Operational Land Imager (OLI) on Landsat 8 (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- While the 2019-2020 austral summer brought record high temperatures to Western Australia, it was also an unusually wet season. In early 2020, numerous tropical storms dumped significant amounts of rain across the region. Overall, rainfall amounts in Western Australia were 9 percent above the average summer.
- Tropical cyclone Blake, in particular, set a number of daily rainfall records in January. Ground stations in Carnegie recorded 27.5 centimeters (around 11 inches) of rain in 24 hours, which was the area’s wettest 24-hour period since records began in 1942. While only a dozen or so people are reported to live around Lake Carnegie, the water can provide important habitat and breeding areas for great flocks of birds.
Figure 76: Thanks to a wet summer, water levels rose in this ephemeral lake in Western Australia. OLI image of Lake Carnegie acquired on 26 March 2020 (image credit: NASA Earth Observatory)
Figure 77: A bounty of marine life thrives within the shoals and seagrass beds of the park. So it was on December 28, 2019, when the Operational Land Imager (OLI) on Landsat 8 captured this natural-color image of the park’s shallow coastal waters. The mostly barren dunes on the shore drew a contrast with the maze of coastal mudflats (dark brown) and shallow seagrass beds (green) that grow beneath a few meters of water. Deeper channels (dark blue) meander and flow among the sea grass and sandy shoals (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland)
- While signs of life are rare on this mostly arid land, the upwelling of cool, nutrient-rich water offshore causes the park’s coastal areas to burst with marine life. Whales, dolphins, and seals all make appearances. Thriving finfish and shellfish populations attract migratory birds to breeding sites here. Expansive tidal mudflats support upwards of 2 million shorebirds, making Banc d'Arguin one of the largest meeting places for Palaearctic birds in the world. Several endangered marine mammals occasionally turn up, notably monk seals and humpback dolphins.
- But Landsat does more than deliver an occasional pretty picture. Scientists have analyzed 20 years of satellite observations and found that the park’s extensive seagrass beds have remained remarkably healthy and resilient, despite weathering occasional damage from storms and dust that temporarily killed grasses in certain areas.
• April 15, 2020: Anak Krakatau maintains a mighty and sometimes menacing presence in the Sunda Strait between Java and Sumatra, with more than 50 known periods of eruptions in almost 2,000 years. The Indonesian volcano’s latest burst of activity has produced numerous plumes and lava flows in 2020, including some relatively small but notable events in April. 62)
Figure 78: On April 13, 2020, the Operational Land Imager (OLI) on Landsat 8 acquired this natural-color image (OLI bands 4-3-2) of the volcano as a plume towered over the peak. The natural-color image is overlaid with the infrared signature detected by OLI of what is possibly molten rock (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
- The location of the plume suggests that it is volcanic in origin,” said Verity Flower, a USRA volcanologist based at NASA’s Goddard Space Flight Center. Flower and colleagues use the Multi-angle Imaging Spectroradiometer (MISR) sensor on NASA’s Terra satellite to measure the height of volcanic plumes and to observe the shape, size, and light-absorbing properties of the particles within plumes. “On April 12, I saw a similar feature in one of the angular MISR images with a plume-like feature above the volcano summit.”
- Based on the color of the plume in the image above, Flower thinks it is likely composed of mostly water vapor and gas. These small, reflective particles make a plume appear white. Conversely, larger and darker ash particles tend to look gray or brown in natural-color images.
- Note the darker part of the plume extending toward the north: it appears lower in altitude than the bright, billowy part of the plume directly over the peak. “It is possible the heavier ash particles emitted are staying lower in the atmosphere and are being transported to the north by near-surface winds,” Flower said. “In contrast, any water and gases within the plume, which are lighter, would be transported higher and would condense rapidly in the atmosphere.”
- Indonesia’s Center of Volcanology and Geological Hazard Mitigation (PVMBG) reported that incandescent rock had erupted onto the volcano’s surface with “insignificant intensity” in the days prior to this image.
- “Anak Krakatau volcano has displayed these small eruptive bursts periodically through the last few years,” Flower said. “However, it can also display more destructive activity such as tsunami-triggering eruptions.”
- According to the April 11 statement from PVMBG, the hazards from the volcano’s recent activity included fountains of lava, lava flows, and ash rain within a radius of 2 kilometers around the crater. Thinner ash rain could extend even farther from the depending on the strength of winds. Still, the alert level remained at two on a scale of one (low) to four (high).
• April 14, 2020: Intense droughts lasting a year or two are common in Chile and other countries with Mediterranean climates. But the drought currently gripping central Chile—which has dragged on for more than a decade—is something quite different. 63)
- Since 2010, precipitation in central Chile has been below normal each year by an average of 20 to 45 percent. Around Santiago, home to more than 7 million people, the lack of rain has been particularly extreme, with just 10 to 20 percent of normal rain falling during the past few years.
- No drought in Chile’s modern meteorological record (since 1915) has lasted longer, Paleoclimatologists who look for clues of past climate conditions in tree rings estimate that the last “megadrought” of this scale probably occurred in this region more than 1000 years ago, explained René D. Garreaud, a scientist at the University of Chile.
- The dwindling rains have had far-reaching consequences, particularly for farmers. In August 2019, Chile’s Ministry of Agriculture declared agricultural emergencies for more than 50 municipalities. Tens of thousands of farm animals have died, and tens of thousands more are at risk. Water supply systems are strained, and reservoirs are low. Many people in rural areas are getting their drinking water from tanker truck deliveries.
- This pair of natural-color images shows El Yeso, one of the main reservoirs that supplies Santiago. By March 2020, the volume had dropped to 99 million cubic meters, about 40 percent of capacity.
Figure 79: Image of the El Yeso reservoir as acquired by OLI on Landsat-8 on 19 March 2016 (image credit: NASA Earth Observatory)
Figure 80: As a persistent drought drags on, water levels are dropping at a key reservoir that supplies Santiago. OLI image on Landsat-8 of the El Yeso reservoir acquired on 14 March 2020 (image credit: NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
• April 9, 2020: The rich mosaic of reeds, ponds, and meadows of the Ili River Delta offer habitat for hundreds of species. Seen from space, the Ili River Delta contrasts sharply with the beige deserts of southeastern Kazakhstan. 64)
Figure 81: When OLI on Landsat-8 acquired this natural-color image on March 7, 2020, the delta was just starting to shake off the chill of winter. While many of the delta’s lakes and ponds were still frozen, the ice on Lake Balkhash was breaking up, revealing swirls of sediment and the shallow, sandy bed of the western part of the lake. Over the deeper eastern part of the lake, ice persisted until the last week of March (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
- Most of the water in Lake Balkhash comes from the Ili River, which pours in through the southeastern shore. The expansive delta and estuary—still dark brown in this image thanks to Central Asia’s harsh winters—is nevertheless an oasis for life year round. Hundreds of plant and animal species make a home here, including dozens that are threatened or endangered.
Figure 82: OLI image of Lake Balkhash with the insert of the Ili River Delta acquired ion 7 March 2020 (image credit: NASA Earth Observatory)
- Wild boars, gazelles, marbled polecats, and several other mammals roam the reed beds, meadows, and occasional forests. Dozens of fish species live or spawn in the lake and in the delta’s mosaic of streams and ponds, including ship sturgeon and wels catfish. Several species of jumping rodents—such as jerboas, voles, and gerbils—scurry amidst the underbrush. Millions of birds, including massive Dalmatian pelicans and endangered white-headed ducks, make use of these wetlands.
- In 2012, Kazakhstan declared the delta a wetland of international importance under the Ramsar Convention, a treaty that encourages the conservation and sustainable use of wetlands throughout the world. But with significant amounts of the Ili River’s water being diverted for dams and irrigation, some observers say that the delta could become vulnerable to the same sort of environmental problems faced by wetlands near the Aral Sea, which has shrunk rapidly in recent decades.
Landsat 8 continued
• April 1, 2020: With the arrival of the spring flood season, millions of Americans living near rivers in the Midwest and Great Plains will be warily watching the weather. In parts of South Dakota, however, last year’s flood season never really ended. 65)
- While federal forecasters do not expect flooding in 2020 to be as severe or prolonged as during record-breaking 2019 floods, they do predict major to moderate floods in 23 states, especially North Dakota, South Dakota, and Minnesota.
Figure 83: On 23 March 2020, the OLI instrument on Landsat-8 captured an image showing high water levels on the James River, a tributary of the Missouri River in eastern South Dakota. For comparison, the second Landsat image (left) shows the same area during a more typical spring in March 2015. In this false-color view (bands 6-5-4), ice appears light blue. Open water is dark blue (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, Story by Adam Voiland)
- With many parts of these states coming off their wettest years on record, soils are already saturated. In South Dakota in 2019, many areas received about twice the average amount of precipitation. Rain and snowfall have been so relentless that at least one river has been stuck at flood stage for more than a year.
- At streamflow gages at Columbia and Stratford, water levels have been at or above flood stage since April 2019, according to data from the U.S. Geological Survey (Figure 84). Prolonged flooding has occurred at four other stations on the James River as well, according to the Missouri Basin River Forecast Center.
Figure 84: High water on the James River in South Dakota has persisted for more than a year. This map shows water level data from the National Water Information System during the period January 1, 2019 - March 30, 2020 (image credit: NASA Earth Observatory)
- “The river levels never fell in the winter because the ground was fully saturated when it froze last fall,” explained Amy Parkin, a meteorologist at the National Weather Service office in Aberdeen, South Dakota. “As the snow and river ice melted over the past few weeks, the water had nowhere to go.”
- The unusually flat terrain in the area has also contributed to the length of the flood. The elevation along the James River only drops 100 feet (30 meters) from the North Dakota border to the Nebraska border, noted Parkin. “The riverbanks are fairly low, and the water does not flow quickly. When there is a strong south wind, we have actually seen the river flow north.”
- NASA’s Earth Applied Sciences Disasters Program plays a role in improving the predictions of and responses to disasters and natural hazards. While NASA is a research organization and not an official first responder to natural disasters like NOAA, USGS, or FEMA, it does have specialized satellites, airplanes, and researchers that can provide unique observations to assess flood impacts. Click here to learn more about some of the unique tools and datasets that NASA provides to aid with flood response.
• March 18, 2020: On January 12, 2020, the Taal Volcano in the Philippines awoke from 43 years of quiet and began to spew gases, ash, and lava into the air. In the days and weeks that followed, the eruption dropped a layer of unusually wet, heavy ash on the surrounding landscape, withering vegetation and turning the lush fields and forests of Volcano Island a ghostly gray. 66)
Figure 85: OLI on Landsat-8 acquired this image of Volcano Island in the Philippines on 6 December 2019 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
Figure 86: Two months later, the ash-damaged landscape still looks more like the Moon than the tropics. On March 11, 2020, the Operational Land Imager (OLI) on Landsat-8 acquired an image of Taal that underscores the consequences of the ashfall (image credit: NASA Earth Observatory)
- Aside from a few green promontories on the north side of the island, ash has altered much of the landscape, including several villages along the coasts. “Most of the ash has likely washed away by now, but signs of it will persist for millennia in the rock record,” explained Erik Klemetti, a volcanologist at Denison University. “Most of the ash that fell within the caldera is in the process of getting concentrated into gullies and streams or deposited into the lake.”
- Volcanic ash is nothing like the soft fluffy material that forms when wood, leaves, or paper burn. Rather, it is made up of small jagged pieces of rock and glass that are hard, abrasive, mildly corrosive, and do not dissolve in water. Thick blankets of volcanic ash can have big consequences for plants, animals, and people. As shown in the Landsat images, most of the vegetation was killed or stripped of leaves. In Taal’s case, the ash was particularly problematic because it grew wet enough to achieve the texture of mud, before drying and hardening into something like cement.
- Coffee, rice, corn, cacao, and banana crops were damaged, according to news reports. In one estimate, damages to plants and animals totaled 577 million Philippine pesos, or $11 million. Despite the widespread effects, plants will eventually recover or re-colonize the island—and the layer of new ash will help keep the soil fertile.
- The damage extended beyond plant life. Dozens of people perished during the eruption. Large numbers of livestock and pets were also left behind when tens of thousands of people evacuated. Ash even affected the fish—mainly tilapia and milkfish—being raised in thousands of aquaculture pens in Taal Lake. According to the Taal Lake Aquaculture Alliance, Inc., about 30 percent of the fish cages in the lake were destroyed during the eruption. To keep the remaining fish alive, farmers appealed to authorities to allow them to feed and harvest the fish despite lockdowns that prevent people from getting near the still-active volcano.
- Water has returned to Taal’s main crater lake, which mostly evaporated or drained during the eruption.
• March 17, 2020: One of the oldest continuously inhabited settlements in the world, Hasankeyf, has been home to more than 20 cultures over the past 12,000 years. Assyrians carved caves into the surrounding limestone cliffs. Romans built a fortress to monitor crop and livestock transportation. Travelers on the Silk Road often stopped in the area to trade during the Middle Ages. 67)
- Remnants of past cultures have been preserved for thousands of years in Hasankeyf, which was absorbed by the Ottoman Empire in the 1500s and has remained part of Turkey ever since. But those artifacts—thousands of human-made caves and hundreds of well-preserved medieval monuments—may soon be underwater. A new dam and reservoir threatens to drown the city.
Figure 87: The 12,000-year old town of Hasankeyf could soon be underwater due to the construction of a new dam. This natural-color image of OLI on Landsat-8 shows Hasankeyf on February 22, 2019. The reservoir began filling in July 2019 (NASA Earth Observatory, images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey)
- Located about 56 kilometers (35 miles) downstream of Hasankeyf, the 138-meter tall Ilisu Dam is expected to provide 1,200 megawatts of electricity (around 1.5 percent of Turkey’s total power-generating capacity). The dam is part of Turkey’s Southeastern Anatolia Project, which consists of 19 hydroelectric plants and 22 dams on the Tigris and Euphrates Rivers. The effort is designed to help promote economic growth and energy independence for the country. But there will also be a cost.
Figure 88: This natural-color image of OLI on Landsat-8 shows Hasankeyf on 12 March 2020 (image credit: NASA Earth Observatory and data from the USGS)
- As of February 2020, water levels behind the dam were rising at a rate of about 15 cm/day. The reservoir is only about one quarter full and is expected to rise another 50 meters in upcoming months—enough to submerge thousands of nearby caves and nearly all of the Hasankeyf fortress previously occupied by the Romans, Mongols, and Seljuk Turks.
- Some historical structures (including a tomb, mosque, and ancient bath) and all residents have been relocated to a new town on a nearby hill called New Hasankeyf (or Yeni Hasankeyf). Once the reservoir is full, a ferry system will shuttle people between the new town and what remains above water in Hasankeyf.
• March 16, 2020: When NASA engineers need to communicate with distant spacecraft, the signal goes out through one of three NASA communication complexes spread around the world. Without the Deep Space Network (DSN), it would not be possible to stay in touch with missions such as Voyager 1—which launched in 1977 and is still sending back signals from interstellar space, some 22 billion kilometers (14 billion miles) away—or the Deep Space Climate Observatory (DSCOVR)—a satellite that takes full-disc images of Earth from 1.5 million kilometers (1 million miles) away. 68)
Figure 89: On February 24, 2020, the Operational Land Imager (OLI) on Landsat-8 acquired a natural-color image of the communications site in Canberra, Australia (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
- Each of the three DSN complexes has large antennas that are designed to enable daily radio communication between NASA spacecraft and engineers on Earth. Canberra, like the other two facilities, has at least four antennas, each with large, parabolic dishes and sensitive receiving stations. In the Landsat image of Figure 89, the dishes appear as white circles.
- The most powerful antenna at the Canberra station is Deep Space Station 43. With a diameter of 70 meters, it is the largest steerable parabolic antenna in the Southern Hemisphere. In March 2020, engineers began working on critical upgrades that will reduce the risk of unplanned outages and make the antenna more compatible with future missions, such as the Mars 2020 rover and other Moon and Mars missions.
Figure 90: Photo of the Canberra DSN site (image credit: DSN. DSN is a service of NASA’s Space Communications and Navigation Program (SCaN) within the agency’s Human Exploration and Operations Mission Directorate)
- The other two DSN sites are in Goldstone, California, and near Madrid, Spain, putting the three stations about 120 degrees apart. The strategic placement allows for continuous communication with spacecraft even as Earth rotates. Together, the three stations make the Deep Space Network the largest and most sensitive scientific telecommunications system in the world.
- NASA’s first station was established in Goldstone, California, in 1958. When it came time to build the second station, the agency chose the Tidbinbilla Valley, 35 kilometers southwest of Canberra, due to its proximity to the city and the fact that the surrounding ridges help shield the site from unwanted radio interference. Construction of the complex began in June 1963, with communication operations beginning in December 1964, in time to support the Mariner 4 encounter with Mars.
• March 7, 2020: In late 2019, the Spanish electrical company Iberdrola completed the largest photovoltaic plant in Europe. Comprised of more than 1.4 million solar panels, the Núñez de Balboa plant has an installed capacity of 500 megawatts and is expected to supply energy to 250,000 people per year. The plant, which took less than a year to complete, is scheduled to start operating in early 2020. 69)
Figure 91: This image shows the Núñez de Balboa photovoltaic plant, located in the town of Usagre in the western Spanish region of Extremadura. The image was acquired with OLI on Landsat-8 on 2 February 2020. The solar panels cover an area of nearly 10 km2 with a mass of than 12,000 tons (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- In addition to residential users, the plant will supply energy to local businesses from a Spanish bank to a supermarket distributor. The company projects that Núñez de Balboa can eliminate 215,000 tons of carbon dioxide emissions per year.
- The photovoltaic plant is part of Iberdrola’s plan to increase clean energy in Spain. The company is planning several projects that could provide 2,000 MW of solar and wind power in Extremadura by 2022. One of the plants—the 590 MW Francisco Pizarro project—is expected to surpass the Núñez de Balboa plant as Europe’s largest solar plant. By 2030, the company plans to commission up to 10,000 MW of solar and wind energy.
• February 27, 2020: During the last Ice Age, advancing and retreating glaciers in northeastern Canada scraped the surface clean of debris to help make visible some stunning fold patterns in the basaltic rock. Those folds are still visible today and appear in these images, which show part of a geologic belt called the New Quebec Orogen (also known as the Labrador Trough). 70)
Figure 92: The orogen stretches southeast from Ungava Bay through Quebec and Labrador, with striking geologic features throughout. These images highlight the deformation in Earth’s crust just east of the Caniapiscau River. The images were acquired on February 13, 2020, by the Operational Land Imager (OLI) on Landsat-8, and were overlaid on a digital elevation model from the Shuttle Radar Topography Mission (SRTM) to give a sense of the topography. Wintertime snow and ice blanket some of the landscape (image credit: NASA Earth Observatory images by Joshua Stevens. using topographic data from the Shuttle Radar Topography Mission (SRTM) and Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
Figure 93: Detail 1 image of Figure 92. The striking patterns in northeastern Canada’s flood basalts tell a story of continental collisions that played out almost two billion years ago.
Figure 94: Detail 2 image of Figure 92
- ”The patterns shown in the images have quite a long history—from rifting to cooling to folding—during continental collision,” said Deanne van Rooyen, a geologist at Cape Breton University who has studied the region. About 2.17 billion years ago, she explained, molten rock erupted from rifts in Earth’s crust and flooded the landscape with basalt. Successive flows of this so-called “flood basalt” were laid down in nearly horizonal layers, producing the step-like pattern visible in these images. When viewed up close, most flows show spectacular columnar jointing structures.
- David Corrigan of the Geological Survey of Canada notes that the cliff face of each flow (or series of flows) represents a step, each standing about 50 to 70 meters tall. Geologists often refer to geometry like this as “traps”—the Dutch word for “step”—which can be found around the planet in places like the Deccan Traps in India or the Siberian Traps in Russia. “I affectionately name our example the ‘Labrador Traps,’” said Corrigan, who previously led a geological mapping project in the general area.
- The gentle folding of the traps came later with the collisions of cratons—ancient, stable parts of Earth’s crust—with a microcontinent known as the “Core Zone” sandwiched in between, Van Rooyen explained. The Core Zone collided first with the North Atlantic Craton around 1.87 billion years ago, and then collided (with the North Atlantic Craton attached) with the Superior Craton between about 1.80 billion years ago. This more recent collision initially occurred head on, but became oblique as the North Atlantic Craton rotated. The rotation caused Core Zone rocks to move down the side of the Superior Craton, and the dragging of layered rock alongside the solid craton gave rise to the folded patterns.
- “These types of folds are not rare,” Corrigan said. “But in this case, they are made spectacular by the nature of the rocks they fold. With a bit of erosion, they become stair-shaped. If they are folded a bit, the stairs, or steps, stand out.”
- But the story does not end there. Sometime after the folds formed, the rock became brittle and the continued motion began to produce linear breaks. The offsets on either side of the cracks indicate movement along the faults. In some places you can see where layers were dragged along the plane of the fault, with the friction causing the folds to curve back toward the fault—an effect called “drag folding.”
- Satellite images and field work have given scientists a good sense of the region’s geology, but there are still plenty of questions to be investigated. “The basic geology is well-mapped,” Van Rooyen said, “but there has been a lot of new work in the area in the past decade by the Geological Survey of Canada as part of their Geomapping for Energy and Minerals (GEM) program, the Newfoundland and Labrador Geological Survey, the Quebec Ministry of Energy and Natural Resources, and many university geologists like me.”
- For example, the flood basalts provide a hint of what the chemical composition of the underlying mantle may have been 2.17 billion years ago, providing key information on Earth’s evolution. Scientists also want to know more about the timing of the evolution of the New Quebec Orogen, such as when the different phases of collision happened. There are also questions about the pressures and temperatures when the rocks formed, as well as questions about the economic potential for the rocks to host gold, platinum, or other important metals.
• February 21, 2020: On February 6, 2020, weather stations recorded the hottest temperature on record for Antarctica. Thermometers at the Esperanza Base on the northern tip of the Antarctic Peninsula reached 18.3°C (64.9°F)—around the same temperature as Los Angeles that day. The warm spell caused widespread melting on nearby glaciers. 71)
Figure 95: The warm temperatures arrived on February 5 and continued until February 13, 2020. The images above show melting on the ice cap of Eagle Island and were acquired by the Operational Land Imager (OLI) on Landsat-8 on February 4 and February 13, 2020 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, Story by Kasha Patel)
- Mauri Pelto, a glaciologist at Nichols College observed that during the warming event, around 1.5 square kilometers (0.9 square miles) of snowpack became saturated with meltwater (shown in blue above). According to climate models, Eagle Island experienced peak melt—30 millimeters (1 inch)—on February 6. In total, snowpack on Eagle Island melted 106 millimeters (4 inches) from February 6- February 11. About 20 percent of seasonal snow accumulation in the region melted in this one event on Eagle Island.
- “I haven’t seen melt ponds develop this quickly in Antarctica,” said Pelto. “You see these kinds of melt events in Alaska and Greenland, but not usually in Antarctica.” He also used satellite images to detect widespread surface melting nearby on Boydell Glacier.
Figure 96: The heat is apparent on this map, which shows temperatures across the Antarctic Peninsula on February 9, 2020. The map was derived from the Goddard Earth Observing System (GEOS) model, and represents air temperatures at 2 meters above the ground. The darkest red areas are where the model shows temperatures surpassing 10ºC (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Kasha Patel)
- Pelto noted that such rapid melting is caused by sustained high temperatures significantly above freezing. Such persistent warmth was not typical in Antarctica until the 21st century, but it has become more common in recent years.
- The warm temperatures of February 2020 were caused by a combination of meteorological elements. A ridge of high pressure was centered over Cape Horn at the beginning of the month, and it allowed warm temperatures to build. Typically, the peninsula is shielded from warm air masses by the Southern Hemisphere westerlies, a band of strong winds that circle the continent. However, the westerlies were in a weakened state, which allowed the extra-tropical warm air to cross the Southern Ocean and reach the ice sheet. Sea surface temperatures in the area were also higher than average by about 2-3°C.
- Dry, warm foehn winds also could have played a part. Foehn winds are strong, gusty winds that cause downslope windstorms on mountains, often bringing warm air with them. In February 2020, westerly winds ran into the Antarctic Peninsula Cordillera. As such winds travel up the mountains, the air typically cools and condenses to form rain or snow clouds. As that water vapor condenses into liquid water or ice, heat is released into the surrounding air. This warm, dry air travels downslope on the other side of the mountains, bringing blasts of heat to parts of the peninsula. The drier air also means fewer clouds and more direct sunlight.
- “Two things that can make a foehn-induced melt event stronger are stronger winds and higher temperatures,” said Rajashree Tri Datta, an atmospheric researcher at NASA’s Goddard Space Flight Center. With warmer air in the surrounding atmosphere and ocean, the conditions were conducive this month for a foehn wind event.
- This February heatwave was the third major melt event of the 2019-2020 summer, following warm spells in November 2019 and January 2020. “If you think about this one event in February, it isn’t that significant,” said Pelto. “It’s more significant that these events are coming more frequently.“
• February 17, 2020: About 7,000 years ago, a vast lake spread hundreds of km2 across north-central Africa. Known to scientists as Lake Mega Chad, it covered more than 400,000 km2 (150,000 square miles) at its peak, making it slightly larger than the Caspian Sea, the biggest lake on Earth today. 72)
- Modern Lake Chad has shrunk to just a fraction of its former size, but evidence of the lake’s ancient shorelines is still etched into desert landscapes — hundreds of kilometers from the shores of the modern lake.
Figure 97: Detail image of the Space Shuttle SRTM mission in February 2000 showing the ancient short line of Lake Chad. The spits etched into a desert in Chad were actually formed thousands of years ago along the shores of a vast lake (image credit: NASA Earth Observatory, image by Joshua Stevens, using topographic data from the Shuttle Radar Topography Mission (SRTM))
- Sand spits generally form along coves and estuaries as prevailing winds drive currents that transport sand and other sediments along the shore. In the era of Lake Mega Chad (and today), winds blew from the northeast, which caused the spit to grow toward the southwest.
Figure 98: Superimposed images of SRTM (2000) and Landsat-8 data (2020). Elevation data from the Shuttle Radar Topography Mission (SRTM) reveals the former shorelines of the lake. In the map above, lower-elevation areas appear darker. An image from the Operational Land Imager (OLI) on Landsat-8 marks the location of the present-day lake. The elevation data highlights sand spits and beach ridges that formed along Lake Mega Chad’s northeastern shores [image credit: NASA Earth Observatory images by Joshua Stevens. using topographic data from the Shuttle Radar Topography Mission (SRTM) and Landsat data from the U.S. Geological Survey. Story by Adam Voiland]
• February 14, 2020: In a waiting game that spanned several months of 2019 and 2020, scientists watched cracks grow across the tongue of Antarctica’s Pine Island Glacier. It was always a matter of when, not if, the glacier would spawn a new iceberg. In this case, it spawned many. 73)
- The waiting ended on February 9, 2020, when radar images from the Sentinel-1 satellites showed numerous icebergs detaching from the glacier and floating in Pine Island Bay. The largest piece, Iceberg B-49, is about twice the size of Washington D.C. It is the only piece large enough to be named and tracked by the U.S. National Ice Center.
Figure 99: Through patchy cloud cover satellites captured natural-color imagery, including the detailed view, which was acquired on February 11, 2020, with the Operational Land Imager (OLI) on Landsat-8. Infrared data are superimposed on natural-color wavelengths to emphasize detail through areas of thin clouds (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
- In the past, large icebergs would break from Antarctica’s Pine Island Glacier every four to six years. Calving now occurs almost annually, and the bergs tend to more easily break up into smaller pieces. The fracturing indicates just how weak the thinning ice shelf has become, as relatively warm water in Pine Island Bay is partly melting it from below. Thinning of the floating ice tongue destabilizes the overall shelf by reducing the ice’s contact with underwater “pinning points” that slow ice flow and influence how the shelf calves.
- The last major iceberg to break from Pine Island Glacier was B-46 in October 2018. Around that time, the main flow of the glacier lost contact with thicker ice from a tributary flowing from the southwest. As a result, Pine Island Glacier (PIG) lost ice at the front of its southwest shear margin—visible in these images as the crumbled ice between the edge of the fast flow of the glacier and the South Ice Shelf.
- “When Pine Island Glacier lost contact with the thicker ice of the southwest tributary it was like the loss of protection on the glacier’s flank,” said NASA/UMBC glaciologist Christopher Shuman. “The growing indentation into the shear margin was likely a factor in the formation of all the rifts that then caused PIG’s ice to fall apart in the last calving. This area is likely to continue to breakdown as Pine Island Glacier pushes past the thinner South Ice Shelf, further exposing that flank.”
Figure 100: Retreat at Pine Island Glacier. Pine Island Glacier is one of the fastest-retreating glaciers in Antarctica. Watch the glacier’s ice front as it retreats and sheds some notable icebergs over the past two decades. Images were acquired by the MODIS instrument on NASA’s Terra and Aqua satellites from 2000 to 2020. Notice that there are times when the front appears to stay in the same place or even advance, though the overall trend is toward retreat (video credit: NASA Earth Observatory)
- Pine Island Glacier, along with neighboring Thwaites Glacier, is one of the main pathways for ice entering the Amundsen Sea from the West Antarctic Ice Sheet. Pine Island is also one the fastest-retreating glaciers in Antarctica. It is a normal part of life for the floating ice from huge glaciers to fracture near the seaward edge and calve off as icebergs. If the icebergs break off at a rate that matches the glacier’s forward flow, the ice front stays in place. But the calving rate at Pine Island has increased more than the glacier been able to move inland ice forward into Pine Island Bay.
• February 6, 2020: Antarctica’s Thwaites Glacier has been in the spotlight in recent years, as scientists have undertaken a multi-part international project to study the vast glacier from all angles. The urgency stems from observations and analyses showing that the amount of ice flowing from Thwaites—and contributing to sea level rise—has doubled in the span of three decades. Scientists think the glacier could undergo even more dramatic changes in the near future. 74)
Figure 101: This Thwaites Glacier image was observed with ETM+ (Enhanced Thematic Mapper Plus) on Landsat-7 on 2 December 2001 [image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen, with image interpretation by Christopher Shuman (NASA/UMBC) and Ted Scambos (University of Colorado)].
Figure 102: This Thwaites Glacier image was observed with OLI (Operational Land Imager) on Landsat-8 on 28 December 2019 [image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen, with image interpretation by Christopher Shuman (NASA/UMBC) and Ted Scambos (University of Colorado)].
- This image pair of Figures 101 and 102 demonstrates the changes that have occurred since the start of this century. Both images show the glacier where it exits the land in West Antarctica and stretches over the Amundsen Sea as thick floating ice. Ice that originates on land can raise sea level if it is delivered to the ocean at a faster rate than it is being replaced inland by snowfall. Indeed, Thwaites Glacier is one of the largest contributors to global sea level rise from the West Antarctic Ice Sheet. The flow speed of Thwaites has been increasing, while inland snowfall has not changed significantly.
- Notice the size of the glacier’s main ice tongue in 2001, when the glacier was advancing by about 4 kilometers per year. The large rift across the glacier eventually spawned Iceberg B-22 in 2002.
- In the past ten years, the tongue has continued to fracture and separate from the Thwaites Eastern Ice Shelf. By the time the 2019 image was acquired, the main tongue had retreated substantially, and the ocean in front of Thwaites had become filled with mélange, a mixture of icebergs and sea ice.
- Unlike Pine Island Glacier—which tends to shed large icebergs every few years (now almost annually)—the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits.
- The melting of floating ice as it makes contact with the ocean is a key reason why the glacier is coming unglued. Seawater that is a few degrees above freezing is melting the ice shelf from below. Warm water has recently been recorded near the Thwaites Glacier grounding line—the location where the glacial ice rests on the seafloor.
- “What the satellites are showing us is a glacier coming apart at the seams,” said Ted Scambos, a senior scientist at the University of Colorado. “Every few years a new area seems to be letting go and accelerating. Like taffy being stretched out, this glacier is being drawn into the ocean.”
• February 1, 2020: Natural-color satellite images can capture art-like beauty when sediments trace water currents and eddies. Other kinds of data can make that art intersect with scientific understanding. 75)
- See, for example, the colorful details in the Mediterranean Sea (Figure 103). When paired with a false-color observation of temperature, scientists can say more about the likely source of the color.
Figure 103: Aida Alvera-Azcárate, an ocean scientist at University of Liège, noticed colorful swirls off the coast of western Italy starting in late December 2019, as observed by the European Space Agency’s Sentinel-3 and Sentinel-2 satellites. The Operational Land Imager (OLI) on Landsat 8 acquired a similar scene on December 26 (top) showing colorful waters between the island of Elba and the Italian mainland (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
- The colors are primarily the result of suspended sediments that were carried by several rivers into the sea. (There might be some phytoplankton contributing as well). Water with more sediment appears green-brown, and water with less sediment is light blue.
- When there is ample sediment in a body of water, it becomes easy to see otherwise invisible motions. Along the west coast of Italy, a strong current flows south. As the water is channeled between the island and mainland, the current encounters a shallow bay where it becomes unstable. It starts to swirl and produce numerous small-scale eddies.
- Small features like these—less than 10 km diameter—are common in the oceans. According to Alvera-Azcárate, they can contribute to the total movement of water, nutrients, and heat around the planet. “But their precise role in this is very difficult to assess because they are not easy to model or measure,” she said.
- Sediments and phytoplankton are not always present to act as tracers, and the features can be short-lived, quickly erased by stronger currents. Still, satellites are helping scientists compile the observations needed to better understand how the role of small-scale eddies compares to larger and more long-lived flows.
Figure 104: False-color images offer a different but equally compelling view. The Thermal Infrared Sensor (TIRS) on Landsat-8 acquired the second image at the same time that the natural-color image was acquired. TIRS measures the water’s relative warmth (yellows and oranges) and coolness (blues and white). The spatial resolution is lower, but you can still see some of the same swirling patterns (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
- Temperature is useful for revealing the origin of the waters. River water is cooler than the seawater here, so the white plume —where water from the Corina River enters the bay—stands out. Interestingly, that same plume is not apparent in the natural-color image, which means the river might not be contributing much sediment. Alvera-Azcárate thinks the main sources of sediment come from larger rivers to the north along the Italian coast. She notes: “Having the two variables—color and temperature—helps to better understand what is going on.”
• January 30, 2020: For several decades, scientists and astronauts observing Lake Baikal have noticed giant rings in the spring ice on one of the world’s oldest and deepest lakes. Russian researchers first spotted them in satellite images in the early 2000s, but it was after astronauts on the International Space Station photographed two ice rings in April 2009 that the phenomenon become a topic of international study and fascination. 76)
- While the rings have attracted speculation and a few conspiracy theories, decades of satellite data and field-based studies have shed light on why they form. “Results of our field surveys show that before and during ice ring manifestation, there are warm eddies that circulate in a clockwise direction under the ice cover,” explained Alexei Kouraev, a hydrologist at the University of Toulouse. “In the eddy center, the ice does not melt — even though the water is warm — because the currents are weak. But on the eddy boundary, the currents are strong and warmer water leads to rapid melting.”
- During field work, Kouraev and his colleagues from France, Russia, and Mongolia drilled holes near ice rings and deployed sensors capable of measuring the temperature and salinity of the water column to a depth of 200 meters. Typically the water in the eddies was 1 to 2 degrees Celsius warmer than the surrounding water.
- The research team is still investigating what causes the eddies, but an analysis of meteorological and hydrological data suggests that they typically get going in autumn, before ice has covered the lake. They likely form because of persistent wind patterns and the inflow of water from certain rivers. The shape of the coastline and lake bottom also play a role in determining where the eddies form and move.
Figure 105: The puzzling features are most easily seen from above, but they pose real risks at the surface. The Landsat-8 image shows an ice ring in the central part of the lake on April 1, 2016. That ring was particularly well-studied because Kouraev and colleagues were nearby, taking measurements of the ice and underlying water. The thin ice of the ring appears darker and more transparent than the whiter, thicker ice surrounding it (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
- This particular ring was more than just a scientific oddity; it posed a serious hazard because Russians often drive over the ice to get across the lake in the winter. In fact, a few weeks before the satellite image was captured, a van broke through and sank along the edge of this ice ring; the driver and passengers escaped and were rescued. A few days later, a second van (Figure 106) broke through and got stuck along the eastern boundary of the ice ring.
- To better understand where and how often giant ice rings form, scientists mined all the available satellite imagery of Lake Baikal back to 1969 and identified dozens of rings. Most appeared in March or April and had diameters of about 5 to 7 kilometers (3 to 4 miles) — too big to recognize from the ground but easily seen from above. Some rings were ephemeral, lasting a day or two. Others persisted for weeks or months.
Figure 107: On April 25, 2019, the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Terra satellite acquired an image of the most recent Baikal ice rings detected by satellites (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview)
- The ring in the image of Figure 105 formed off the Nizhneye Izgolovye Cape, one of the most common places for rings to occur. Of the 57 rings detected on Baikal, about 13 formed in this area. According to Kouraev, that is likely because a sharp slope on the lake bed tends to “trap” eddies in this area. “People often drive a direct line between Nizhneye Izgolovye Cape and Khoboy Cape,” he said, “but we strongly advise that they take a more southerly route to avoid the frequent ice rings in this dangerous region.”
- For a number of years, one of the most discussed theories in both the scientific community and the news media was that gas hydrates — an ice-like form of methane found at the bottom of the lake — may play a role. Work by Kouraev and colleagues suggests otherwise. When combing through Landsat and MODIS satellite image archives for evidence of rings, scientists identified several over shallow parts of the lake where conditions are not right for gas hydrates. They have also discovered giant rings in satellite imagery of Lake Hovsgol in Mongolia and Lake Teletskoye in Russia’s Altai Republic, both of which are shallower than Lake Baikal and are not known to have gas emissions.
• January 24, 2020: Fifty years ago, Cancún was virtually unknown to the world. With a population of roughly 100 people, the town was located in one of the poorest regions of Mexico. It had odd-shaped sand dunes and a coast occupied by marshes, mangroves, and a snake-infested jungle. Over the past five decades, though, Cancún has been transformed into one of Mexico’s top tourist attractions. The growth didn’t happen by chance. 77)
- In the late 1960s, the Mexican government took an interest in developing the country’s tourism sector to boost the economy. To determine the perfect place, government officials analyzed statistics from several successful resort locations such as Miami Beach and Acapulco. They compiled information on the number of tourists, number of hotel rooms, average temperatures, average rainfall, and hurricane events and fed them into a computer program. The computer selected several candidates for a new resort town. Officials then visited each site along Mexico’s approximately 10,000 km of coastline to personally inspect the beaches, swimming, and living conditions.
- In the end, they selected Cancún because it had good weather year-round, blue seas, and white sand beaches. It was also located near great archeological treasures, such as the Mayan ruins at Chichen Itza and Tulum. It also had a high level of poverty and no existing industry.
- In January 1970, technicians arrived and began building the resort town. By September 1974, Cancún’s first hotel opened its doors. Within a year, Cancún added more hotels and welcomed around 100,000 tourists. Today, Cancún accommodates around two million visitors annually and generates around one-fourth of the country’s tourism revenue.
Figure 108: Image of Cancún acquired by the TM instrument of Landsat-5 on 28 March 1985 (image credit: NASA, image by Allison Nussbaum, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- The image pair of Figures 108 and 109 show the growth of Cancún between 28 March 1985, and 11 April 2019. The images were acquired by the Thematic Mapper (TM) on Landsat 5 and the Operational Land Imager (OLI) on Landsat-8, respectively. In the late 1980s, Cancún’s population registered around 120,000. A census report in 2015 conducted by the National Institute of Statistics and Geography (INEGI) reported around 740,000 people. Most of the hotels are located on a 27 km stretch of beach known as the Hotel Zone.
Figure 109: Image of Cancún acquired by the OLI instrument on Landsat-8 on 11 April 2019 (image credit: NASA, image by Allison Nussbaum, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- While creating a large source of revenue, Cancún’s tourism also has had major impacts on the environment. One of the biggest issues is water pollution due to sewage from hotels (about 95 percent of all sewage from the area)—significantly more than the local treatment plants can handle. Untreated sewage ends up in the sea and becomes a threat to aquatic ecosystems, sometimes introducing pathogens that affect coral growth. The resort has also significantly increased the amount of garbage produced, a share of which is sent to illegal garbage dumps. Hotel construction and human presence have also eroded beaches, threatening local reef and coral systems.
• January 18, 2020: Approximately 4,000 years ago, a volcano in the South Ocean launched massive amounts of rock and magma—between 30 and 60 km3—into the sky. The eruption had the same severity as the cataclysmic 1991 eruption of Mount Pinatubo. It was the biggest eruption around Antarctica in the past 12,000 years. 78)
- As the volcano’s magma chamber emptied, the sudden drop in pressure inside the volcano caused the top to collapse and form a caldera. The caldera had a diameter of eight to ten kilometers (five to six miles). A collapse at this magnitude is large enough to induce multiple, intense high-magnitude earthquakes, according to researchers.
- These two natural-color images show Deception Island in early autumn (March 23, 2018, Figure 110) and early spring (September 21,2017, Figure 111), as observed by OLI (Operational Land Imager) on Landsat-8.
Figure 110: This image shows the island on March 23, 2018, when the top of the volcano was visible (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- Deception Island is one of two active volcanoes around Antarctica, and it has erupted more than twenty times since the 19th century. The most recent eruptions occurred between 1967 and 1970, while seismic activity occurred as recently as 2014-2015. Deception Island remains the one of the only places in the world where ships can sail directly into the center of a restless volcano.
Figure 111: This image, taken on September 21, 2017, shows the volcano and caldera covered in snow and ice (image credit: NASA Earth Observatory, image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
- Despite the island’s eruptive history, its harbor—Port Foster—is considered one of the safest in Antarctica due to the absence of large glaciers. At the beginning of the 19th century, people began visiting the island to hunt seals, a popular commercial frenzy at the time. When the seals were nearly hunted to extinction by the early 1900s, seafarers switched to whaling and set up operations at Whalers Bay on the east side of the port.
- Today, Deception Island is home to scientific research stations, although some have been wiped away by past volcanic activity. The island is also a popular place for tourists, who can haul out on the beach and sit in geothermal baths. Visitors can also see one of the world’s largest rookeries of chinstrap penguins located on the island.
• January 2, 2020: Mountains of sand, some as tall as 300 meters (1000 feet), reach from the floor of Africa’s Namib Desert toward the sky. Driven by wind, these dunes march across the desert, bordered to the west by the Atlantic Ocean and in other directions by solid, rocky land. 79)
- The images show a region along the northern boundary of the Namib Sand Sea, which generally traces the path of the Kuiseb River. The sporadic flow of the Kuiseb River depends on flooding rains that can occur during the rainy season, typically from November to March. Floods, such as one in April 2011, wash away accumulated sand and temporarily halt the northward progression of the dunes. The occasional floodwaters also bring life to the desert, sustaining vegetation along the banks. Analysis of satellite data has shown that extreme floods lead to fast plant growth and a “green-up” that can last for up to two years.
- Without much water, vegetation elsewhere in the sand sea is limited--though not completely absent, thanks to fog from the ocean.
Figure 113: The abrupt transition from sand to land is visible in these images (Figures 112 & 113), acquired on November 13, 2019, by the Operational Land Imager (OLI) on Landsat-8. They show the northern extent of the Namib Sand Sea—a field of sand dunes spanning more than 3 million hectares (more than 10,000 square miles) within the Namib-Naukluft Park, which was named a UNESCO World Heritage site in 2013. Sand appears red, painted by a layer of iron oxide (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)
Landsat-8 Initial imagery until May 2013 when Landsat-8 was declared operational
• 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. 80)
• 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. 81)
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 114 and 115 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 115 are simply not visible in the natural color image of Figure 114. This new analysis feature will give scientists a better handle to study the changing environment.
• 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. 82) 83) 84) 85)
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. 86) 87)
Figure 116: 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 117).
Legend to Figure 117: 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. 88)
• 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. 89) 90)
• Since April 4, 2013, LDCM is on WRS-2 (Worldwide Reference System-2),
Figure 118: 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. 90)
Legend to Figure 118: 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. 91)
• 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. 92)
- 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.
Figure 119: First image of LDCM released in March 2013 (image credit: NASA) 93)
Legend to Figure 119:
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.
• March 18, 2013: First day of simultaneous OLI and TIRS Earth imaging (Ref. 90).
• 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. 94)
• 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).
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). 95) 96)
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.
Figure 120: 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: 97)
• 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.
Table 2: 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).
Figure 121: Spectral parameter comparison of OLI and ETM+ instruments
Figure 122: OLI and ETM spectral bands (image credit: NASA)
The OLI design features a multispectral imager with a pushbroom architecture (Figure 123) 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.. 98) 99) 100) 101) 102)
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 124). 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 125) 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.
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).
Table 3: 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. 103)
The OLI calibration subsystem (Figures 126 and 127) 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). 104) 105)
• 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. 104):
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.
Figure 128: Illustration of the OLI instrument (image credit: NASA, BATC)
In Nov. 2008, the OLI instrument passed the ICDR (Instrument Critical Design Review). 106)
Figure 129: 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. 107) 108)
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.
Figure 130: Functional block diagram of TIRS (image credit: NASA, Ref. 105)
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). 109) 110) 111)
Table 4: 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. 110).
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. 112)
Advantages of QWIP technology:
- Large lattice-matched substrates
- Mature materials technology
- No unstable mid-gap traps
- Inherently, radiation hard.
Figure 131: QWIP quantum state diagram (image credit: NASA/JPL)
Figure 132: TIRS 10-13 µm QWIP spectral response requirement (image credit: NASA)
Figure 133: Overview of the TIRS focal plane layout (image credit: NASA, Ref. 105)
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.
Figure 134: Schematic view of the FPA (Focal Plane Assembly), image credit: NASA
Legend to Figure 135: 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 136).
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.
Figure 137: Schematic view of the TIRS instrument internal assembly (image credit: NASA, Ref. 105)
Legend to Figure 137: 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. 113) 114)
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
Figure 138: 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.
Figure 139: Illustration of the TIRS calibration system (image credit: USGS)
Figure 140: 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. 115)
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.
Figure 141: Cutaway view of the SSM (image credit: NASA)
Table 5: SSM driving requirements
Table 6: Comparison of Landsat and GMES/Sentinel-2 imager specifications 116)
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 142. 117)
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.
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 143.
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.
End to end mission data flow is represented in Figure144 . 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.
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:
- 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 121)
- 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.
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.
Figure 146: Overview of the LDCM system architecture (image credit: USGS)
Table 7: 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
Figure 147: Overview of the IC (International Cooperator) network (image credit: USGS)
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. 103).
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.
Figure 148: 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. 103).
Table 8: Landsat 8 operational characteristics
• 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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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 (firstname.lastname@example.org).