Minimize Landsat-8

Landsat-8 / LDCM (Landsat Data Continuity Mission)

Spacecraft     Launch    Mission Status     Sensor Complement    Ground Segment    References

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

The following are the major mission objectives: 3)

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

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

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

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

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

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

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

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

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

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

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

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

Overall science objectives of the LDCM imager observations are:

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

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

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

• To make the data available to the user community.

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

LS82021_Auto9E

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

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

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

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

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

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




Spacecraft

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

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

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

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

LS82021_Auto9D

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

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

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

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

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

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

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

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

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

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

LS82021_Auto9C

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

LS82021_Auto9B

Figure 4: Block diagram of the C&DH subsystem (image credit: NASA, USGS, Ref. 123)

- 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.

LS82021_Auto9A

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.

LS82021_Auto99

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

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

The spacecraft FSW (Flight Software) plays an integral role in the management of the file directory system for recording and file playback. FSW creates file attributes for identifier, size, priority, protection based upon instructions from the ground defining the length of imaging in the interval request, and its associated priority. FSW also maintains the file directory, and creates the ordered lists for autonomous playback based upon image priority. FSW automatically updates and maintains the spacecraft directory while recording or performing playback, and it periodically updates the SSR FSW directory when no recording is occurring to synchronize the two directories (Ref. 123).

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

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

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

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

Spacecraft platform

SA-200HP (High Performance) bus

Spacecraft mass

Launch mass of 2780 kg; dry mass of 1512 kg

Spacecraft design life

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

EPS (Electric Power Subsystem)

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

ADCS (Attitude Determination &
Control Subsystem)

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

C&DH (Command & Data Handling)

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

Propulsion subsystem

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

Table 1: Overview of spacecraft parameters

LS82021_Auto98

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. 123).

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).

LS82021_Auto97

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

LS82021_Auto96

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

LS82021_Auto95

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 2021, in addition to some of the mission milestones.

Landsat-8 imagery in the period 2020

LandSat-8 imagery in the period 2019

Landsat-8 imagery in the period 2018

Landsat-8 imagery in the period 2017 to June 2013




Mission status and some imagery of 2021

• September 20, 2021: Numerous craters on Earth are exceptionally compelling when viewed from space, displaying clearly visible rims and well-defined bowls. Not Sudbury Basin. It can take a moment looking at images to discern the shape of this impact structure amid the modern landscape. But few craters are as large or as old. 30)

- The object responsible for creating Sudbury Basin crashed into Earth about 1.8 billion years ago. That makes this crater in Canada fifty times older than Popigai—one of the world’s most well-preserved craters—which was created a mere 36 million years ago. Much of Sudbury’s original crater, thought to have measured at least 200 km (120 miles) across, has been deformed and eroded. Despite this, the crater has had a lasting impact on the region.

LS82021_Auto94

Figure 13: The OLI instrument on Landsat-8 acquired this image of Sudbury Basin in southeastern Ontario on September 11, 2020. Notice the many mines located around the basin, particularly along the rim. This is due to the abundance of ore deposits rich in nickel and copper, which were discovered here long before people were aware of the basin’s cosmic origin (image credit: NASA Earth Observatory images 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)

- This region of Canada owes its unique geology to that powerful collision—initially thought to be an asteroid and later interpreted as a comet. The collision punctured Earth’s crust, allowing material from the mantle to well up from below and fill the basin with melted rock. Then after a shockwave shattered the surrounding rocks, minerals from the melted rock below infiltrated the cracks.

LS82021_Auto93

Figure 14: The relief of the basin is apparent in this map. Data for the map comes from a digital elevation model acquired by the Shuttle Radar Topography Mission (SRTM). Few craters are as large, or as old, as this impact structure in southeastern Ontario, Canada. (image credit: NASA Earth Observatory)

- People have been making use of the minerals in Sudbury Basin for thousands of years. Large-scale mining operations started with the Murray Mine (now defunct) in the late 1800s. The mining took a toll on the landscape, polluting the region with sulfur dioxide and metals released during smelting processes. In recent decades, efforts have been made to capture emissions and restore the health of the basin’s land and water.

• September 17, 2021: In the midst of another brutal fire season that has threatened many lives, homes, and businesses, several of California’s natural treasures have also been threatened. Still burning after nearly nine weeks, the Caldor fire has encroached on Lake Tahoe. Now some of the world’s oldest and largest trees are being threatened by fires at the southern end of the Sierra Nevada range. 31)

LS82021_Auto92

Figure 15: On September 15, 2021, the OLI instrument on Landsat-8 acquired imagery of the KNP fire complex (Kings-Canyon National Park), the Windy fire, and the thick smoke plumes both have released (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- According to InciWeb and other sources, the KNP complex was ignited by a significant lightning storm on September 9–10. The Paradise fire and the Colony fire started separately near Sequoia National Park and have been marching across the drought-ravaged landscape toward a merger. By the morning of September 16, the KNP complex had burned 8,940 acres (36 km2). (A complex includes two or more separate fires that burn in very close proximity, have the potential to merge, and are managed by a unified firefighting group.)

- The KNP complex has led to the closure of Sequoia National Park and the evacuation of parts of the nearby community of Three Rivers. Fire officials told The Los Angeles Times on September 15 that the blazes were about a mile from the “Giant Forest,” the largest concentration of giant sequoias in the park and home to the 275-foot (83 m) General Sherman tree. Nearby Kings Canyon National Park remains open, but air quality is poor.

- The KNP fires are raging in very steep, dangerous terrain, so most of the firefighting has been done by aircraft so far. The National Park Service wrote in an update: “In the case of the Paradise Fire, extremely steep topography and a total lack of access has prevented any ground crew operations, and in the case of the Colony Fire, only a limited amount of ground crew access has been possible. Both fires are utilizing extensive aerial resources performing water and retardant drops.”

- Due south of the KNP complex, the Windy fire is burning in Sierra National Forest. It started in the Tule River Reservation during the September 9–10 lightning storm. About 2,800 acres have burned so far in an area not far from Giant Sequoia National Monument.

- According to CalFire, 1.97 million acres (nearly 3,100 square miles) have burned in California so far this year, and the fire season still has several months to go. The total is about half of the 2020 fire season—the worst on record—and roughly equal to the total burned in all of 2018. Near the end of the last severe drought in the state (2012-16), fire totals were 30 to 40 percent of the 2021 count.

LS82021_Auto91

Figure 16: In the midst of another brutal fire season, several of California’s natural treasures have also been threatened. This image includes infrared data with the thermal signature of some fire fronts beneath the plumes. NASA’s Terra satellite acquired broad-area images of the same region from September 10-16 (image credit: NASA Earth Observatory)

• September 12, 2021: Hurricane Ida left an extensive trail of damaged homes, infrastructure, and lives from Louisiana to New England. It also has left a stain on the sea. Two weeks after the storm, several federal and state agencies and some private companies are working to find and contain oil leaks in the Gulf of Mexico. 32)

- The U.S. Coast Guard has assessed more than 1,500 reports of pollution in the Gulf and in Louisiana, and it “is prioritizing nearly 350 reported incidents for further investigation by state, local, and federal authorities in the aftermath of Hurricane Ida.” The Coast Guard is working with the Environmental Protection Agency, the state of Louisiana, the National Ocean Service, and other agencies to chronicle and monitor the state of coastal waters and infrastructure.

LS82021_Auto90

Figure 17: Federal and state agencies and private companies are working to find and contain oil leaks in the Gulf of Mexico. On September 3, 2021, the Operational Land Imager (OLI) on Landsat-8 acquired this natural-color image of apparent oil slicks off the southeastern Louisiana coast near Port Fourchon, a major hub of the oil and gas industry (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- Hurricane Ida caused the disruption of 90 to 95 percent of the region’s crude oil and gas production, while also damaging current and abandoned pipelines and structures. According to many news reports, the surface oil slicks near Port Fourchon (shown above) are likely related to as many as three damaged or ruptured submarine pipelines. It is unclear how much oil has spilled into the Gulf of Mexico.

- NOAA (National Oceanic and Atmospheric Administration) has conducted aerial surveys of some offshore waters and has released the photos online. The NASA-sponsored Delta-X research team has also been working in the area and was called upon to make some observations of the slicks and other coastal changes with synthetic aperture radar.

- Beyond active oil and gas extraction platforms, the seafloor of the Gulf of Mexico is covered in a maze of pipelines, capped wellheads, and other infrastructure that can be vulnerable to storm events. In a report issued earlier this year, the U.S. Government Accountability Office stated: “Since the 1960s, the Bureau of Safety and Environmental Enforcement has allowed the offshore oil and gas industry to leave 97 percent of pipelines (18,000 miles) on the seafloor when no longer in use. Pipelines can contain oil or gas if not properly cleaned in decommissioning.”

• August 30, 2021: Lake Mead is the largest reservoir in the United States and part of a system that supplies water to at least 40 million people across seven states and northern Mexico. It stands today at its lowest level since Franklin Delano Roosevelt was president. This means less water will be portioned out to some states in the 2022 water year. 33)

LS82021_Auto8F

Figure 18: As of August 22, 2021, Lake Mead was filled to just 35% of its capacity. The low water level comes at a time when 95 percent of the land in nine Western states is affected by some level of drought (64% is extreme or worse). It continues a 22-year megadrought that may be the region’s worst dry spell in twelve centuries. This natural color image was acquired by Landsat-8. The tan fringes along the shoreline are areas of the lakebed that would be underwater when the reservoir is filled closer to capacity. The phenomenon is often referred to as a “bathtub ring.”(image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and lake elevation data from the Bureau of Reclamation. Story by Michael Carlowicz and Kathryn Hansen)

- The lake elevation data below come from the U.S. Bureau of Reclamation, which manages Lake Mead, Lake Powell, and other portions of the Colorado River watershed. At the end of July 2021, the water elevation at the Hoover Dam was 1067.65 feet (325 meters) above sea level, the lowest since April 1937, when the lake was still being filled. The elevation at the end of July 2000—around the time of the Landsat 7 images above and below—was 1199.97 feet (341 meters).

LS82021_Auto8E

Figure 19: Lake Meade elevation levels at Hoover Dam (image credit: NASA Earth Observatory)

- At maximum capacity, Lake Mead reaches an elevation 1,220 feet (372 meters) near the dam and would hold 9.3 trillion gallons (36 trillion liters, corresponding to 36,000 km3) of water. The lake last approached full capacity in the summers of 1983 and 1999. It has been dropping ever since.

- In most years, about 10% of the water in the lake comes from local precipitation and groundwater, with the rest coming from snowmelt in the Rocky Mountains that melts and flows down to rivers, traveling through Lake Powell, Glen Canyon, and the Grand Canyon on the way. The Colorado River basin is managed to provide water to millions of people—most notably the cities of San Diego, Las Vegas, Phoenix, and Los Angeles—and 4-5 million acres of farmland in the Southwest. The river is allotted to states and to Mexico through laws like the 1922 Colorado River Compact and by a recent drought contingency plan announced in 2019.

- With the Lake Mead reservoir at 35 percent of capacity, Lake Powell at 31 percent, and the entire Lower Colorado system at 40 percent, the Bureau of Reclamation announced on August 16 that water allocations would be cut over the next year. “The Upper [Colorado] Basin experienced an exceptionally dry spring in 2021, with April to July runoff into Lake Powell totaling just 26 percent of average despite near-average snowfall last winter,” the USBR statement said. ”Given ongoing historic drought and low runoff conditions in the Colorado River Basin, downstream releases from Glen Canyon Dam and Hoover Dam will be reduced in 2022 due to declining reservoir levels. In the Lower Basin the reductions represent the first “shortage” declaration—demonstrating the severity of the drought and low reservoir conditions.”

LS82021_Auto8D

Figure 20: The Overton Arm of Lake Meade on August 7, 2000 (left) and on August 9, 2021 (image credit: NASA Earth Observatory)

- For the 2022 water year, which begins October 1, Mexico will receive 80,000 fewer acre-feet, approximately 5% of the country’s annual allotment and Nevada’s take will be cut by: 21,000 acre-feet (about 7% of the state’s annual apportionment). The biggest cuts will come to Arizona, which will receive 512,000 fewer acre-feet, approximately 18 % of the state’s annual apportionment and 8 % of the state’s total water use (for agriculture and human consumption). An acre-foot is enough water to supply one to two households a year.

• August 26, 2021: Since 2017, August 26 has been known as Katherine Johnson Day in West Virginia. The celebration commemorates the birthday of the ground-breaking NASA mathematician who was born on August 26, 1918, in White Sulphur Springs. 34)

- Katherine Johnson contributed her mathematical expertise to the first human space travel missions in the United States. In 1953, in a time of racial segregation, she started a job as a human “computer” with the National Advisory Committee for Aeronautics (NACA), the predecessor to NASA. She worked in the West Area Computing section at Langley Research Center on a team of Black women headed by fellow West Virginian Dorothy Vaughan.

- In 1961, Johnson did trajectory analysis for Alan Shepard’s Freedom 7 mission, America’s first human spaceflight. Her work was also instrumental in John Glenn’s successful orbit around Earth in 1962.

- Glenn became a household name in the United States, but it wasn’t until recently that Katherine Johnson’s name became well-known. Her story came to light in 2016 through the book and film Hidden Figures by Margot Lee Shetterly. In a pivotal scene in the movie, John Glenn hesitated over trusting his fate in space to a network of new IBM computers. He asked Johnson to check the equations for his orbit against the computer output. “If she says they’re good, I am ready to go,” said Glenn.

LS82021_Auto8C

Figure 21: Johnson’s birthplace, White Sulphur Springs, is shown in this image, acquired by the Landsat-8 satellite in 2019. The small city sits in the Allegheny Mountains, one of the smaller ranges running through the Appalachians. The city was settled in the 18th century around a natural freshwater spring, which is now on the grounds of the Greenbrier Hotel. Katherine’s father, Joshua Johnson, worked at that resort as a bellman, but he was determined to get his talented daughter an education that allowed her to excel (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Photograph by NASA. Story by Emily Cassidy, NASA Earthdata)

- Because of the segregated school system at the time, Black Americans could not attend high school in White Sulphur Springs. Her father moved the family to Institute, West Virginia, so that Katherine and her siblings could attend a high school that was on the West Virginia State University campus. Johnson graduated high school at 14, and then graduated summa cum laude from West Virginia State when she was 18, earning a double major in mathematics and French.

LS82021_Auto8B

Figure 22: Katherine Johnson at work in her office at NASA in 1966 (photo credit: NASA)

- Johnson’s fingerprints are on some of NASA’s greatest achievements. She precisely calculated trajectories for the 1969 Apollo 11 flight to the Moon, and she worked on the Space Shuttle and the Earth Resources Technology Satellite (later renamed Landsat 1). Across three decades at Langley, she authored or co-authored more than two dozen research reports before retiring in 1986.

- In 2015, President Barack Obama awarded Johnson the Presidential Medal of Freedom, citing her as a pioneering example of African-American women in science, technology, engineering, and mathematics. “Katherine G. Johnson refused to be limited by society’s expectations of her gender and race, while expanding the boundaries of humanity’s reach,” said Charles Bolden, NASA's first Black administrator and a former astronaut.

- In 2019, NASA renamed its Independent Verification and Validation Facility in Fairmont, West Virginia, for Katherine Johnson. When she died on February 24, 2020, then-NASA Administrator James Bridenstine said: “She was an American hero and her pioneering legacy will never be forgotten.”

• August 17, 2021: Eleven years after an earthquake devastated the Haitian capital of Port-Au-Prince, another major earthquake has shaken the Caribbean nation. The epicenter of the magnitude 7.2 earthquake was centered about 100 km (60 miles) west of the 2010 quake, in a mountainous area between Petit-Trou-de-Nippes and Aquin. Like the previous event, this earthquake occurred along the Enriquillo-Plantain Garden fault, an area where two tectonic plates grind against each other. 35)

LS82021_Auto8A

Figure 23: A break in the clouds allowed the Operational Land Imager (OLI) on Landsat-8 to acquire this natural-color view of landslides in and around Pic Macaya National Park in southwestern Haiti on August 14, 2021, the same day the earthquake hit (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- The earthquake exposed more than one million people to very strong to severe shaking, according to the U.S. Geological Survey. In preliminary estimates, news media and Haiti’s civil protection agency are reporting large numbers of deaths and extensive damage to buildings and infrastructure.

- Many of the landslides in this image appear to be in sparsely populated areas. It is possible that landslides also occurred in areas south and east of the park that experienced intense shaking, but cloud cover on August 14 prevented Landsat from acquiring a clear view. Additional imagery from Landsat and other satellites should eventually provide more clarity about the extent of the landslides.

- The situation could be exacerbated in the coming days by heavy rains from tropical depression Grace. Some forecasts call for the storm to drop between 13 to 25 cm (5 to 10 inches) of rain on the areas hit hardest by the earthquake.

LS82021_Auto89

Figure 24: For comparison, this second image shows the same area on a clear day on 2 January 2021 (image credit: NASA Earth Observatory)

- “Some hillslopes that have been destabilized by the earthquake but did not become landslides may be pushed past the limit of stability by the rain, leading to further landslides,” said Robert Emberson, a landslide expert with NASA’s Earth Applied Sciences Disasters Program. “Debris and rock already mobilized by the earthquake may be transported by flash flooding as devastating debris flows. The material is mostly at the base of hills currently, but rivers quickly filled by rain could push that downstream and cause severe impacts to communities living farther from the location of the landslides.”

- NASA’s disasters program is monitoring the situation and coordinating with the United States Agency for International Development and other partners to share relevant data about the event with emergency responders. Data and updates from the team will be shared here.

• August 12, 2021: In the first two weeks of August 2021, Greece has endured a series of wildland fires that have charred a large swath of the island of Evia and several areas of the Peloponnese region. The fires followed closely after one of the worst heatwaves in the country since the 1980s, which dried up scarce moisture and left forests primed to burn. Greek Prime Minister Kyriakos Mitsotakis told several news agencies that the fire outbreak has been a “disaster of unprecedented proportions.” 36)

LS82021_Auto88

Figure 25: Fires in the country have consumed five times as much land as they do in an average year. The OLI instrument on Landsat-8 acquired natural- and false-color views (Figure 26) of the north end of Evia on August 10, 2021 (image credit: NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Michael Carlowicz)

- According to data from the European Forest Fire Information System (EFFIS), more than 110,000 hectares (424 square miles) have burned in Greece this year, more than five times the yearly average from 2008 to 2020 (21,000 hectares). EFFIS counted 58 fires (30 hectares or larger) in the country in 2021, already above the yearly average total of 46.

LS82021_Auto87

Figure 26: This false-color image combines shortwave infrared, near infrared, and red light (OLI bands 6-5-4). In this view, burned vegetation appears dark brown, and greens and yellows indicate a combination of unburned trees and scrub (image credit: NASA Earth Observatory)

- Some of the worst fires in the country have burned on Evia, the second largest island in Greece and a major hub for tourism. Much of the island has been in a state of high fire alert for a week. The Associated Press reported that an estimated 50,000 hectares (123,000 acres) have burned on Evia, as well as hundreds of homes.

- Significant fires also broke out near Athens, Olympia, and Arcadia, and 63 organized evacuations have been reported across Greece in the past nine days. Firefighters and equipment have been sent from at least 15 countries to help Greek authorities.

- As of August 11, EFFIS reported that more than 338,000 hectares (1,300 square miles) have already burned across Europe in 2021, more than the 2008-2020 average for an entire year (295,000). More than 109,000 hectares have burned so far in Italy, 2.5 times the annual average. Large fires have also been burning in Algeria and Turkey.

LS82021_Auto86

Figure 27: On August 8, the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP acquired a wider view of the fires and smoke in Greece. NASA Worldview imagery from August 3–11 shows the evolution of the smoke plumes with changing winds (image credit: NASA Earth Observatory)

- The heatwaves and fires fit with patterns described in the latest assessment report from the Intergovernmental Panel on Climate Change (IPCC), to which NASA-funded scientists contribute. In its summary of climate conditions in Europe, the IPCC noted: “The frequency and intensity of hot extremes ... have increased in recent decades and are projected to keep increasing regardless of the greenhouse gas emissions scenario. Despite strong internal variability, observed trends in European mean and extreme temperatures cannot be explained without accounting for anthropogenic factors.”

• August 11, 2021: Every year, scientists at the University of Maryland publish new data about the state of Earth’s forests based on observations from Landsat satellites. As has often been the case in recent years, the update for 2020 painted a bleak picture. In that one year, Earth lost nearly 26 million hectares of tree cover—an area larger than the United Kingdom. 37)

LS82021_Auto85

Figure 28: Using satellite data from the past two decades, scientists are starting to pinpoint which crops and farming styles have lasting impacts on forests. This map is based on an analysis of Landsat data by The Sustainability Consortium and WRI, highlights several key drivers of forest loss. Shifting agriculture (yellow) typically involves the clearing of small plots within forests in Africa, Central America, and parts of South America. The clearing is done by subsistence farmers, often families, who raise a mixture of vegetables, fruits, grains, and small livestock herds for a few years and then let fields go fallow and move on as soil loses its fertility. The practice is especially common in Africa, and has become more so since 2000 due to increasing human populations. (image credit: NASA Earth Observatory images by Lauren Dauphin, using data from Curtis, P.G., et al. (2018), data from Goldman, Elizabeth, et al. (2020), and Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- The raw numbers can tell us how much and where forests were lost, but they do not explain what was driving those losses. How much deforestation was due to wildfires? Food production? Forestry management? An ongoing effort by researchers from The Sustainability Consortium and the World Resources Institute (WRI) attempts to answer such questions with maps and datasets that categorize and quantify the major drivers of annual forest losses. In doing so, the researchers have put a spotlight on the impact that food production has on forests, particularly in the tropics.

- In 2020, for instance, Earth lost about 4.2 million hectares (16,000 square miles) of humid tropical primary forest—an area about the size of the Netherlands. Nearly half of that, their analysis shows, was due to food production, and half of that was due to commodity crops. In recent years, commodity crop production has pushed rates of forest loss to record levels.

LS82021_Auto3E

Figure 29: In South America and Southeast Asia, commodity crops (tan on the map) have become the dominant driver of forest loss. Common commodity crops include beef, soybeans, palm oil, corn, and cotton. They are typically grown on an industrial scale and traded internationally. Unlike the temporary forest clearings associated with small-scale agriculture, commodity-scale production often involves clear-cutting and results in significant impacts on forests (like the Indonesian palm oil plantation in this image), image credit: NASA Earth Observatory

- “In many cases, commodity-driven deforestation is essentially a permanent change compared to shifting agriculture,” explained Christy Slay, a conservation ecologist and the senior director of science and research applications at The Sustainability Consortium. “These areas will likely never be forests again.”

- In contrast, forests cleared for forestry management or by wildfires generally grow back over time. In the U.S. Southeast, for instance, managers maintain certain ecosystems and animal habitats by periodically burning and planting forests to mimic natural cycles of burning and regrowth. Likewise, forests in the Pacific Northwest and Europe are often managed for timber in ways that cycle between periods of forest clearing and periods of regrowth.

- Note that food production was once a major driver of deforestation in North America and Europe, but much of the clearing happened a hundred or more years ago. Since many forests in these areas were already gone by 2000, their absence does not register as forest loss. Nor does the map capture the impact of large-scale conversion of natural grasslands to agriculture, a common practice in both North and South America.

Figure 30: The NASA/USGS Landsat satellite mission is helping scientists study how the Amazon rainforest has changed over decades. The Amazon is the largest tropical rainforest in the world, but every year, less of that forest is still standing. Today's deforestation across the Amazon (video credit: NASA Goddard)

- With tropical forest cover dwindling and the effect of climate change becoming more acute, some companies and consumers are trying to ensure that food production does not lead to new deforestation. In recent years, hundreds of companies have committed to eliminating or reducing products in their supply chains that cause deforestation. But ensuring that is often challenging.

- “Global supply chains can be complicated and opaque,” said Slay. “You often have companies buying commodities off the spot market, such that the source regions change frequently or even daily. Retailers and food manufacturers often don't know the source of their ingredients down to the individual farm and field scale.”

- By regularly collecting data on the health of forests, satellites are making it easier for scientists to untangle which commodities and regions are the biggest contributors to deforestation. Doug Morton, a forest ecologist at NASA’s Goddard Space Flight Center, has witnessed a shift in the dominant drivers of deforestation.

- “Forty years ago, we often saw small-scale deforestation creating roads that look like fishbone patterns,” said Morton, who monitors agricultural frontiers in the Amazon. At the time, many people were moving into the Amazon to escape drought and hunger in eastern Brazil. “By the middle of the Landsat record, we see large-scale commodity production taking hold. Today’s deforestation isn’t about individual families. It’s often tractors and bulldozers clearing large tracts of forest for industrial scale cattle ranching and crops.”

- For companies trying to keep their supply chains free of deforestation, knowing which commodity crops are being grown where is critical. “If we know where deforestation is common and what crops are involved, we can go to companies and say: ‘Be careful if you’re working with suppliers that are sourcing this particular product from this particular part of the world,’ ” said Slay. “Satellite data of forest change and loss is the first step in the process.”

- One recent WRI analysis combined Landsat imagery with economic and land-use data to parse the impact of seven different commodities on forests around the world. “One of the big things you notice in the data is the outsized role of cattle pastures in driving deforestation,” said Mikaela Weisse, one of the report’s authors. “Cattle pastures caused about five times more deforestation than any of the other commodities we analyzed.”

LS82021_Auto84

Figure 31: The map shows forests being cleared for cattle all over the world, but particularly in Brazil, where deforestation has been on the rise. Large tracts of forest have also been cleared in Paraguay, Bolivia, and Peru according to WRI data (image credit: NASA Earth Observatory)

- In Southeast Asia, where deforestation rates have dropped recently, most forest losses are associated with palm oil, which is used in many types of processed foods and various health and beauty products like deodorant, shampoo, toothpaste, soap, and lipstick. Deforestation for cocoa production had a sizable impact in certain countries—notably Ghana and Côte d'Ivoire—but only represented 3 percent of total forests losses. Other commodities with similarly modest effects on global forests included rubber, coffee, and wood fiber.

- While new tools are making it easier to understand where food production is intersecting with new deforestation, huge challenges remain. “Deforestation rates are going up instead of down,” said Elizabeth Goldman of WRI. “There’s a lot of work left to do.”

• August 4, 2021: In the midst of a severe heatwave and following months of dry weather, Turkey is facing some of its worst wildfires in years. Over the past seven days, more than 130 wildfires have been reported across 30 Turkish provinces. Most of the fires have ignited along the Mediterranean and Aegean Sea coasts, several in resort areas around Antalya, Mugla, and Marmaris. 38)

LS82021_Auto83

Figure 32: On 31 July 2021, the OLI instrument on Landsat-8 acquired natural-color imagery of fires near the coastal towns of Alanya and Manavgat (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Michael Carlowicz)

LS82021_Auto82

Figure 33: Detail image of Landsat-8. More land has been consumed already this year than usually burns in an entire year in the country (image credit: NASA Earth Observatory)

- The European Forest Fire Information Service reported more than 136,000 hectares (525 square miles) have burned in Turkey already this year, about three times the average for an entire year. The European Space Agency’s Sentinel-3 satellite also acquired a view of the fires on July 30.

LS82021_Auto81

Figure 34: As of August 3, at least nine wildfires were still burning across Turkey. The MODIS instrument on NASA’s Aqua satellite captured a wider natural-color image of several of them near Antalya and Marmaris (image credit: NASA Earth Observatory)

- Fires were still being fed by strong winds, air temperatures above 40º Celsius (104° Fahrenheit), and low humidity. Croatia, Iran, Spain, Russia, Ukraine, and Azerbaijan provided equipment and personnel to help Turkish firefighters bring the blazes under control.

- Much of southern Europe has been baking for weeks under extreme heat not seen since the 1980s. National temperature records were set in both Greece and Turkey in the past month. Air temperatures reached 45°C (113°F) in Greece and surrounding areas yesterday, and the heat is forecasted to continue for several days. Fires are also burning this week in Greece and Lebanon.

• July 21, 2021: Covered with lakes, forests, and mountains, Dalarna County has been called “Sweden in miniature.” But the same region that today draws people to its idyllic lakeside villages and midsummer celebrations was also the site of an ancient, catastrophic impact. 39)

LS82021_Auto80

Figure 35: The idyllic region of Dalarna County is the site of an ancient, powerful collision. The Siljan impact structure, or “Siljan Ring,” is visible in this image, acquired on June 24, 2020, with the Operational Land Imager (OLI) on Landsat-8. Measuring more than 50 kilometers (30 miles) across, Siljan is the largest-known impact structure in Europe and among the top-20 largest on Earth (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Around 380 million years ago, in the Late Devonian period, an asteroid slammed into the land that is now south-central Sweden. The impact left quite a mark. Even after hundreds of millions of years of erosion, the scar is still recognizable. It is especially apparent when viewed from above.

- Surveys of the structure have shown that the ground is slightly raised up across parts of the crater’s center. It is surrounded by a ring-like graben, or depression, which today is partially filled with water. Lake Siljan, on the crater’s southwest side, is the largest lake; it connects to Lake Orsa via a small river.

- People have lived for millennia near the crater without knowing its cosmic origin. In the late 1960s, scientists used drill cores to uncover the complex and ancient geology deep below the ground.

- Research at Siljan is ongoing today. In a 2019 study, scientists described how they used drill cores to find that the deep, fractured rocks in the crater were suitable for ancient life. A subsequent paper in 2021 described the fossilized remains of fungi discovered at a depth of more than 500 meters.

• July 19, 2021: For several months, communities along the west coast of Florida have observed substantial blooms of the harmful algae Karenia brevis. The algae occur naturally in the waters around Florida, but the bloom in 2021 has been particularly bad near Tampa Bay, causing large-scale fish kills in what some people refer to as a ‘red tide’ event. The bloom is also unusual for how early it is occurring. 40)

LS82021_Auto7F

Figure 36: The natural-color images of Figures 36 and 37 were acquired on July 14, 2021, by the OLI instrument on Landsat-8. The scene from Tampa Bay north to Horseshoe Beach shows dynamic coastal waters, with plumes of dissolved organic matter (dark brown to black) running off from the land; shallow seafloors and re-suspended sediment from the bottom (brighter greens and blues); and some hints of algae and phytoplankton (often diatoms) in green (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the USGS and chlorophyll data from the Harmful Algal Bloom Monitoring System from the National Centers for Coastal Ocean Science/NOAA using modified Copernicus Sentinel data (2021) processed by the European Space Agency. Story by Michael Carlowicz)

- Karenia brevis is a microscopic algae that, like other phytoplankton, can multiply into massive blooms when there are enough nutrients in the water—often in the autumn along the Gulf Coast. The algae produce neurotoxins that can kill fish and cause skin irritation and respiratory problems for humans, particularly those prone to asthma and other lung diseases. In extreme concentrations, K. brevis can turn water brown, red, black, or green; however, it is not always visible from space.

LS82021_Auto7E

Figure 37: Tampa Bay is teeming with Karenia brevis months before it usually blooms (image credit: NASA Earth Observatory)

- “This Karenia brevis ‘red tide’ bloom is doubly unusual,” said Richard Stumpf, an oceanographer for the National Oceanic and Atmospheric Administration (NOAA). “It is summer, which is rare, and it is intense well into Tampa Bay, which is rare even during a ‘normal’ fall bloom.”

- “If a bloom is out on the continental shelf, it is more easily diluted,” said Chuanmin Hu, an optical oceanographer at the University of South Florida (USF). “The bloom this year is so troublesome because it is both inside Tampa Bay and around the Tampa Bay mouth.”

LS82021_Auto7D

Figure 38: This map, based on data processed by the NOAA National Centers for Coastal Ocean Science, shows measurements of chlorophyll fluorescence on July 11, 2021. Scientists can use fluorescence and distinct wavelengths of light to detect signatures of algae and phytoplankton amid turbid, churning waters along the coast. The data are collected by the Copernicus Sentinel-3 satellite of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Similar observations from July 13 are available from the Optical Oceanography Laboratory at the University of South Florida (image credit: NASA Earth Observatory)

- “Although Karenia brevis blooms are common to the West Florida Shelf and have been observed in almost every coastal region of the Gulf of Mexico, I have never seen anything like that inside Tampa Bay,” said Inia Soto Ramos, an ocean color specialist at NASA’s Goddard Space Flight Center (GSFC) and former researcher at USF. “Massive blooms were observed back in the late 1990s, and even the Spanish conquistadors described them in their books. But the bloom this year inside the bay is worrisome. It could be a one-year thing, and hopefully it is. But if water quality in the bay continues to decline, residents should prepare for more blooms, and not only K. brevis.”

- Since early June 2021, Karenia brevis has been abundant along the Gulf Coast from just north of Clearwater to Sarasota. In a July 14 report, the Florida Fish and Wildlife Conservation Commission noted: “A bloom of the red tide organism, Karenia brevis, persists on the Florida Gulf Coast. Over the past week, K. brevis was detected in 107 samples.”

- According to the Sarasota Herald-Tribune, coastal work crews have collected more than 600 tons of dead fish and marine life killed by the bloom. On July 15, the city council of St Petersburg asked the governor to declare a state of emergency over the bloom. Officials are still trying to pinpoint the trigger for the event, but many scientists note that the area has been unusually rich with algae-sustaining nutrients in 2021.

- “Karenia brevis blooms, although studied for decades, do not follow a strict recipe. Some years, circulation and advection are the main drivers,” said Soto Ramos. “However, we know if there is an excess of nutrients, the algae will utilize them. I think the bloom right now is due to a combination of available nutrients, warm temperatures, and circulation patterns keeping the algae contained within the bay. Once the algae are there, they stay for a while.”

- NASA is currently developing the Plankton, Aerosol, Cloud, ocean-Ecosystem (PACE) satellite mission for launch around 2024. The satellite is being designed with sensors tuned to the signatures of blooms. “Whereas heritage ocean color instruments observe roughly six visible wavelengths, PACE will collect a continuum of colors that span the visible rainbow,” said Jeremy Werdell, project scientist for PACE at NASA GSFC. “Its ocean color instrument will be the first of its kind to collect hyperspectral radiometry on global scales, which will allow unique and highly advanced identification of aquatic phytoplankton communities, including potentially harmful algae such as these on the West Florida Shelf.”

• July 17, 2021: In recent decades, aquaculture has boomed in Andhra Pradesh. The state has become one of India’s largest producers of farmed fish and shrimp. Among the reasons for the boom:a major expansion a of inland aquaculture farms along rivers and canals where people once raised crops. 41)

LS82021_Auto7C

Figure 39: The OLI instrument on Landsat-8 acquired this natural-color detail image of an area dense with inland aquaculture ponds along the Upputeru River on June 8, 2021. Aquaculture ponds appear dark green. Farmland is generally brown. Coastal areas with mangrove forests are lighter green (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- According to satellite imagery, aquaculture was scarce in this area in the mid-1980s. Now carp, catfish, and other types of finned fish are commonly raised in the area. There are numerous shrimp ponds, too, which tend to be the narrow according to one satellite survey of the area.

- The Indian government established the first aquaculture ponds in this area in the 1970s around Lake Kolleru. Since then, the initial success of those projects has made aquaculture an appealing and profitable choice for many farmers in the region who regularly dealt with crops being flooded, the intrusion of salt into water used for irrigation, and Bay of Bengal cyclones.

LS82021_Auto7B

Figure 40: Inland areas along rivers and canals where people once raised crops are now dotted with fish and shrimp ponds (image credit: NASA Earth Observatory)

- Despite the expansion, India’s aquaculture sector has faced challenges recently. One recent study calculated that its shrimp farming sector may have lost as much as $1.5 billion in 2020-2021 due to disruptions related to the pandemic. The state of Andhra Pradesh accounts for about 70 percent of India’s shrimp production.

• July 11, 2021: In research published in 2017, scientists reported that summer pulses of freshwater from melting glaciers along Greenland’s southwest coast often coincide with phytoplankton blooms. The flow of fresh meltwater out to sea carries nutrients that can sustain and promote abundant growth of the floating, plant-like organisms that form the center of the ocean food web. 42)

LS82021_Auto7A

Figure 41: Pulses of fresh glacial meltwater and nutrients provoke summertime phytoplankton blooms. That appears to be what was happening in the waters off of Nuuk, Greenland, when the Operational Land Imager (OLI) on Landsat-8 flew over on July 8, 2021. Close to the coast, the water in Ameralik Fjord and other inlets is stained chalky tan and gray by sediments and glacial flour—rock that has been ground to powder by the ice sheets. Offshore in the Labrador Sea and Davis Strait, light green swirls indicate the presence of phytoplankton in summer bloom. Chlorophyll measurements confirm this (image credit: NASA Earth Observatory image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- The waters of the Labrador Sea, Davis Strait, and Baffin Bay—between Greenland and Nunavut, Canada—form a transitional zone between the Arctic and Atlantic oceans. Fresh meltwater from the ice sheets and strong regional tides (which promote nutrient mixing) help make these waters biologically rich, particularly in summertime. The abundant phytoplankton draw in copepods and other grazers that ultimately feed shrimp, cod, and other species up to the size of whales.

- In the 2017 paper, Stanford University ocean scientist Kevin Arrigo and colleagues noted that summer blooms tend to start in early July and can extend as far as 300 kilometers (200 miles) offshore from Greenland. Fed by sunlight and water rich in iron, silicate, and phosphorous, the blooms account for about 40 percent of annual net primary production for the region.

- Blooms in high-latitude and Arctic waters are happening more often and lasting longer, according to another study published in 2020 by Arrigo’s research group. Incorporating satellite data from NASA’s SeaWiFS and MODIS instruments, they found that the rate of growth of phytoplankton biomass across the Arctic Ocean increased by 57 percent between 1998 and 2018. The study contradicted an older idea that increasing glacier melting might lead to fewer nutrients and blooms.

• July 8, 2021: Toward the end of the last Ice Age, as mile-thick glaciers weighed down the land surface and then melted, parts of New England and eastern Canada became inundated by water. Some lowlands flooded and formed inland basins like the Champlain Sea. 43)

- Ten thousand years later, with seas now rising because of global warming, scientists are combing through an array of data and building increasingly detailed models to understand the processes that drive regional and local changes in sea level. The goal is to project when, where, and how much seas are likely to rise in the coming decades and centuries. It's an incredibly complicated set of interdependent calculations.

LS82021_Auto79

Figure 42: While scientists have grown more confident about projections of sea level rise for the next few decades, many competing factors make it hard to see far into the coastal future (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and sea level rise projections courtesy of Benjamin Hamlington/NASA/JPL-Caltech. Story by Adam Voiland)

- “People tend to think that sea level is like a bathtub with the water level simply rising and falling depending on how much water is coming out of the faucet,” said paleoclimatologist Anders Carlson of the Oregon Glaciers Institute. “In reality, it’s more like a spinning bathtub that’s changing shape, moving up and down, and has water pouring into and out of different drains and over the sides. Where the water will ultimately slosh over the edge of the tub is influenced by many things, making it difficult to say where the overtopping will occur.”

- Despite the complexities, the scientific understanding of the factors that control sea level has improved dramatically in recent decades, as have measurements of past sea level change and projections of future change.

- “We can tell you how much the ocean has warmed in recent decades, and how much more space the water takes up. We have satellites and other tools that have measured that,” said Ben Hamlington, the current lead of NASA’s sea level change team. “The same thing is true for several of other factors that influence sea level, such as the mass of the ocean, the salinity, and how much water is stored on land.”

- That growing knowledge base is why scientific organizations like the Intergovernmental Panel on Climate Change (IPCC) are publishing sea level rise projections with increasing levels of confidence. In its 2019 report, the IPCC projected (chart Figure 42) 0.6 to 1.1 meters (1 to 3 feet) of global sea level rise by 2100 (or about 15 mm per year) if greenhouse gas emissions remain at high rates (RCP8.5). By 2300, seas could stand as much as 5 meters higher under the worst-case scenario. If countries do cut their emissions significantly (RCP2.6), the IPCC expects 0.3 to 0.6 meters of sea level rise by 2100.

- A host of competing factors will influence how global sea changes translate to regional and local scales. Among them: the rising or falling of the land surface due to plate tectonics and human activity; gravity anomalies that can create regional bulges and dips in sea surface height; variations in the temperature and salinity of seawater; changes in the amount of water stored on land in reservoirs; isostatic adjustment due to the addition, loss, and movement of land ice; and changes in erosion and how much sediment rivers carry to coastal areas.

LS82021_Auto78

Figure 43: Sorting out how river deltas will respond is a particularly thorny and consequential issue. Tens of millions of people live on river deltas around the world (such as India’s Krishna Delta), and many of them are subsiding (sinking), often at twice the mean rate of sea level rise. The subsidence is due to a combination of factors like the natural settling of sediments, groundwater and oil extraction, and the extra weight of buildings. Inland dam construction and land management practices can also starve deltas of the raw material needed to replenish and build coastal land (image credit: NASA Earth Observatory, Landsat-8 image of 8 June 2021)

- But it is hard to predict human settlement patterns—and the subsidence it causes—decades or centuries from now. Many IPCC projections do not even attempt to incorporate estimates of this subsidence partly because of the uncertainties in future land use and human behavior and because there is a lack of readily available, large-scale data on vertical land motion to feed into models of sea level rise.

LS82021_Auto77

Figure 44: The current shortage of land motion data is poised to become an abundance with the launch of the NASA-ISRO Synthetic Aperture Radar (NISAR) mission in 2022. The radar will make daily, global measurements of land motion that sea level experts like Manoochehr Shirzaei of Virginia Tech say will lead to major improvements in regional sea level rise projections (image credit: NASA Earth Observatory)

- Likewise, teams of scientists have been surveying the fast-sinking Mississippi River Delta to get a better understanding of how changes in sediment and vegetation affect the delta. Scientists participating in NASA’s Delta-X campaign have collected several types of data to develop and calibrate a model of how the delta might respond to rising sea levels in the next century.

- “The combination of anthropogenic subsidence and increasing rates of sea level rise is a five-alarm fire for many delta cities,” said Shirzaei. “Places like New Orleans, Kolkata, Yangon, Bangkok, Ho Chi Min City, and Jakarta will undoubtedly face increasing pressures from flooding and saltwater intrusion.”

- Still, the long-term picture—hundreds of years into the future—is unlikely to be perfectly clear. “When you think about future impacts of sea level rise, you also have to consider what people might do in response," said Hamlington. Some countries—like The Netherlands and the United States—have already built elaborate sea walls and water-control systems that protect vulnerable deltas like the Rhine and the Sacramento-San Joaquin. They will likely continue reinforcing these systems as sea levels rise. In others deltas, like the Krishna (Figure 43) or Ganges in India, the Chao Phraya in Thailand, and the Mekong in Vietnam, coastal defenses are more limited so far.

Figure 45: It's hard to "see" sea level rise by just looking at the ocean, but its effects are very real. A new video covers some of the basics (video credit: NASA/JPL-Caltech)

- “The reason people within the scientific community are working so hard on regional sea level rise projections is that if we can get them right, it will give cities and nations a chance to prepare,” said Hamlington. “Even if some of the more distant projections are inexact, they still provide critical constraints that could end up being the difference between places that successfully adapt to rising seas and those that experience the most damaging consequences.”

• July 6, 2021: With heights ranging from 600 to 1800 meters (2,000 to 5,900 feet), the Barberton Makhonjwa Mountains in South Africa and Eswatini are not particularly tall. What distinguishes the belt of greenstone rock formations found here is their age. 44)

LS82021_Auto76

Figure 46: Rare igneous rock and early signs of life are found beneath the grassy hills of the mountain range in South Africa and Eswatini. The natural-color image shows part of the Komati River Valley in South Africa. Lava flows made of komatiites were first identified within this valley in 1969. The image was acquired by the Operational Land Imager (OLI) on Landsat-8 on March 10, 2021. The United Nations Educational, Scientific and Cultural Organization declared the mountains a World Heritage Site in 2018 (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- Beneath the rolling, grassy uplands and forested valleys of the mountain range, lie some of the oldest, best-preserved, and diverse sequences of volcanic and sedimentary rock layers found anywhere on the planet. They hold evidence of some of Earth’s earliest forms of life, including microfossils, stromatolites, and other biologically derived material. Geological sampling indicates that some rock formations in these mountains are 3.2 to 3.6 billion years old.

- One type of rock in this area that especially intrigues geologists is komatiite. The rare igneous rock formed from magmas that were hotter, more liquid, and denser than any lavas found on Earth today. Geologists still debate what conditions allowed komatiite to form, but many think Earth’s mantle was likely hotter or wetter 3 billion years ago than today, and that likely played an important role.

• July 3, 2021: On March 19, 2021, the Fagradalsfjall volcano erupted after lying dormant for 800 years. Three months later, the volcano on Iceland’s Reykjanes peninsula is still spewing lava and expanding its flow field. 45)

LS82021_Auto75

Figure 47: Lava flows from the Icelandic volcano were estimated to cover a total area of 3 km2, three months after the eruption began. The natural-color images show the lava flow progression from March, May, and June 2021. Note the ground around the volcano was still covered in snow in March. The darkest areas in May and June show where lava has cooled and piled up across the valley floors. Fresh lava flows that are still hot appear orange. All of the images were acquired by the Operational Land Imager (OLI) on Landsat-8 (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- The Icelandic Met Office reported that by May 3, the lava flow was largely confined to one main crater, a fifth fissure that opened in April. In late May, lava flows broke through an artificial barrier built to contain it; the lava continued flowing south towards Nátthagi Valley. The lava flow has since cut off access to the most popular hiking trail to the eruption site. As of June 15, the lava flows were estimated to cover a total area of 3 square kilometers (about 1 square mile), with an estimated volume of 63 million cubic meters.

- Icelandic officials are concerned that a prolonged eruption will cause lava to flow south and cross the Suðurstrandarvegur, a road used to transport goods and connects Reykjanes peninsula to South Iceland. After crossing the road, the lava flow could continue toward the ocean.

• June 30, 2021: Skies were clear and the waters of Mistastin Lake were placid when the Operational Land Imager (OLI) on Landsat 8 captured this natural-color image of Labrador, Canada, on a fall day in 2017. 46)

LS82021_Auto74

Figure 48: The lake covers part of a crater where an asteroid once slammed into Labrador, Canada (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- The scene would have looked quite different about 36 million years ago when an asteroid smashed into Earth and left an impact crater where the lake (called Kamestastin by the Innu people) now sits. While erosion has changed and obscured some of the features, a 50-meter (164-foot) wall still rings much of the crater. Geologists estimate the original crater had a diameter of about 28 kilometers (17 miles)—about twice the size of the current lake.

- Parts of the central peak are also visible in the lake as Horseshoe Island. These mound-like features are often found in the center of large craters as a product of the melting and rebound of subsurface rocks. Meanwhile, the elongated, elliptical appearance of the crater is a result of periods when glaciers slid across this area during several ice ages.

- Based on the presence of an unusual diamond-like mineral called cubic zirconia, the asteroid impact must have heated rocks at the site to at least 2370°C (4,300°F). That would be the hottest-known temperature recorded by a surface rock on Earth, according to one team of researchers.

• June 21, 2021: The Yukon-Kuskokswim Delta is one of the world’s largest deltas, and it stands as remarkable example of how water and ice can shape the land. These images show the delta’s northern lobe, where the Yukon River spills into the Bering Sea along the west coast of Alaska. 47)

LS82021_Auto73

Figure 49: One of the world’s largest deltas stands as remarkable example of how water and ice can shape the land. “The Yukon Delta is an exceptionally vivid landscape, whether viewed from the ground, from the air, or from low-Earth orbit,” said Gerald Frost, a scientist at ABR, Inc.—Environmental Research and Services in Fairbanks, Alaska. The vivid landscape is captured in these images acquired with the Operational Land Imager (OLI) on Landsat-8 on May 29, 2021. The images are composites, blending natural-color imagery of water with a false-color image of the land (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- While the image could be considered a work of art, there are some useful aspects to looking at the land this way. For example, you can easily distinguish areas of live vegetation (green) from land that is bare or contains dead vegetation (light brown) from the network of sediment-rich rivers and ponded flood water (dark brown). A sprinkling of thermokarst lakes are also part of the scene.

LS82021_Auto72

Figure 50: Detail image of the Yukon Delta (image credit: NASA Earth Observatory)

- In general, the green areas across the delta are tall willow shrublands. They are especially apparent on either side of the river channels in the detailed image above. The light-brown areas are primarily moist sedge meadows; they appear brown because much of it is the dead remains of last year’s growth. Away from the delta (right side of the image) the vegetation is shrub-tussock tundra.

- “To me, one of the interesting things about the delta is that it is a highly transitional area, with some elements of Arctic tundra and some of boreal forest,” Frost said.

- The delta also transitions with the seasons. At the time of this image, the signature of spring flooding is written across the delta. Melting snow and ice cause the rivers to spill over their banks and by late May, many of the marshes are filled with floodwater, which appears as dark-brown ponds.

- According to Lawrence Vulis, a graduate student at the University of California, Irvine, the delta would have appeared much more inundated immediately following the melting of snow and ice a few weeks prior to this image. Stream gauges and satellite images suggest that the bulk of the flooding had already subsided. Still, the flooding was recent enough that the plenty of ponding remained on May 29. As summer advances, the floodwater will continue to recede and the wetlands will continue to green up with vegetation.

- Also notice the colorful water where the delta meets the Bering Sea. This is a product of glacial runoff far upstream, which carries a large amount of sediment toward the coast. This sediment is also instrumental to the formation of tall “levees” on the sides of the channels, deposited there when floodwaters spill over their banks. These “levees” support stands of tall willows—important habitat for moose.

- “Interestingly, tall shrubs have expanded a lot on the delta in recent decades, and the moose have followed,” Frost said. “Today, the delta has one of the highest moose densities in the state of Alaska.”

- The delta did not always look this way. Studies have shown that the modern Yukon Delta is just a few thousand years old. It’s young age “is incredible to think about,” Vulis said. “We are used to thinking about relatively ancient landscapes, but modern river deltas have only formed in the last 10,000 to 8,000 years since global sea level has stabilized.”

- The delta could quite possibly look different in the future. “The Yukon and other Arctic deltas are thought to be particularly vulnerable to climate change,” Vulis noted, “due to the roles of permafrost and ice in shaping these deltas.”