Minimize Landsat-8

Landsat-8 / LDCM (Landsat Data Continuity Mission)

Spacecraft     Launch    Mission Status     Sensor Complement    Ground Segment    References

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

The following are the major mission objectives: 3)

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

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

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

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

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

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

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

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

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

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

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

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

Overall science objectives of the LDCM imager observations are:

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

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

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

• To make the data available to the user community.

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

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

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

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

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

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

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




Spacecraft:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Figure 4: Block diagram of the C&DH subsystem (image credit: NASA, USGS, Ref. 138)

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

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

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

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

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

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

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

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

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

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

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

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

The spacecraft FSW (Flight Software) plays an integral role in the management of the file directory system for recording and file playback. FSW creates file attributes for identifier, size, priority, protection based upon instructions from the ground defining the length of imaging in the interval request, and its associated priority. FSW also maintains the file directory, and creates the ordered lists for autonomous playback based upon image priority. FSW automatically updates and maintains the spacecraft directory while recording or performing playback, and it periodically updates the SSR FSW directory when no recording is occurring to synchronize the two directories (Ref. 138).

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

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

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

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

Spacecraft platform

SA-200HP (High Performance) bus

Spacecraft mass

Launch mass of 2780 kg; dry mass of 1512 kg

Spacecraft design life

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

EPS (Electric Power Subsystem)

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

ADCS (Attitude Determination &
Control Subsystem)

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

C&DH (Command & Data Handling)

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

Propulsion subsystem

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

Table 1: Overview of spacecraft parameters

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

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

The X-band transmitter is a single customized unit, including the LDPC FEC algorithms, the modulator, and up converter circuits. The transmitter uses a local TXCO (Thermally Controlled Crystal Oscillator) as a clock source for tight spectral quality and minimum data jitter. This clock is provided to the PIE XIB to clock mission data up to a 384Mbit/s data rate to the transmitter. The X-band transmitter includes an on-board synthesized clock operating at 441.625 Mbit/s coded data rate using the local 48 MHz clock as a reference. Using the on-board FIFO buffer, this architecture provides a continuous data flow through the transmitter (Ref. 138).

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

Onboard data transmission from an earth-coverage antenna:

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

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

• To three LGN (LDCM Ground Network) stations

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

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

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

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

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

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

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


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

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

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

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.

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 2020 + 2021

• January 11, 2021: With its population rising three times faster than the national average, the Charleston metropolitan area in South Carolina is among the fastest growing places in the United States. 30)

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Figure 13: Large tracts of coastal forests and farmland have been cleared and developed in recent decades to accommodate new residents to the area. The pair of natural-color Landsat images above—this image from 1985 (on Landsat-5, TM) and the image of Figure 14 from 27 December 2020—show some of the changes. Forests and marshes appear green; developed areas are gray. Places where widespread development has occurred include James Island, Johns Island, Daniel Island, West Ashley, and Mount Pleasant (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey)

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Figure 14: Sea level rise and new development are on a collision course in South Carolina lowcountry.. Charleston metropolitan area observed by OLI on Landsat-8 on 27 December 2020 (image credit: NASA Earth Observatory)

- A similar story is playing out in cities all across the United States, but the Charleston area stands out in one critical way—much of the new development has happened on low-lying land that is especially vulnerable to sea level rise and flooding. Older, more established parts of Charleston—often on slightly higher land but surrounded by water on three sides—faces similar challenges. As one form of remediation, local and federal government officials are moving forward with plans to build a seawall to protect the city’s historic downtown from encroaching water.

- “Other southeastern coastal cities face similar problems but with one caveat: the lowcountry of South Carolina is low,” said Norman Levine, director of the Santee Cooper GIS Laboratory and Lowcountry Hazards Center at the College of Charleston. “Over one-third of all homes are built on land that sits below 10 feet (3 meters) of elevation.”

- However, hurricane storm surges up to 9 feet have been measured in the past, and climatologists expect surges to grow larger as global climate warms and storms become more intense.

- High tide, or “nuisance flooding,” is already far more common now than it was decades ago, according to Dale Morris, the coauthor of a 2019 report that assessed the region’s flood risks. On average, Charleston saw 10 to 25 tidal floods per year in the 1990s. There were 89 such events in 2019 and 69 in 2020, he said. In other words, the city now sees tidal flooding every 4 to 5 days.

- Both problems are amplified by sea level rise. Relative sea level in Charleston has risen by 10 inches (25 cm) since 1950, with an acceleration to 1 inch (3 cm) every 2 years since 2010.

- “If you look at a lot of the recent development, it impinges upon or is in low-lying floodplains and adjacent land,” said Morris. “These areas used to flood and no one really noticed. Now they flood and impact people’s lives, resources, and livelihoods.”

- The report offers some general principals and recommendations for future development. Development should respect the landscape's natural drainage patterns and soil qualities. Coastal forests—which sponge up water—should be preserved wherever possible. And according to the report authors, development on the lowest-lying areas should not happen.

- “We are not saying don’t develop at all,” said Morris. “We are saying to develop wisely, carefully, sensibly given the current and future flood risks. Those risks are not going to decrease.”

• January 7, 2021: Popocatépetl volcano—the name is Aztec for “smoking mountain”—is one of Mexico’s most active volcanoes. The glacier-clad stratovolcano has been erupting since January 2005, with daily low-intensity emissions of gas, steam, and ash. 31)

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Figure 15: Ash and gas emissions continue from one of Mexico’s most active volcanoes. On January 2, 2021, the Operational Land Imager (OLI) on Landsat-8 captured this image of a plume rising from Popocatépetl (nicknamed El Popo), image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel

- On January 6, the Washington Volcanic Ash Advisory Center (VAAC) reported a volcanic ash plume that rose to around 6,400 meters (21,000 feet) above the volcano. Mexico’s National Center for Prevention of Disasters (CENAPRED), which continuously monitors Popo, warned people not to approach the volcano or its crater due to falling ash and rock fragments. Some ashfall was blown downwind to the city of Puebla, located about 45 kilometers (30 miles) away from the volcano.

- At 5,426 meters (17,802 feet) above sea level, Popocatépetl is the second tallest volcano in Mexico (after Citlaltépetl). It is comprised of alternating layers of volcanic ash, lava, and rocks from earlier eruptions. The volcano is located around 70 kilometers (40 miles) southeast of Mexico City and more than 20 million people live close enough to be affected by a major eruption. However, most of the eruptions in the past 600 years have been relatively mild.

• December 30, 2020: The Caspian Sea is the world’s largest landlocked body of water. Stretching 1,200 km (750 miles) from north to south, it intersects five countries in Asia and Europe. The lake passes through several geological landscapes, creating a beautiful array of visual textures. 32)

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Figure 16: The image shows the northeastern portion of the Caspian on November 20, 2020. The lake is bordered by Kazakhstan in the northeast, Turkmenistan in the southeast, Iran in the south, Azerbaijan in the southwest, and Russia in the northwest. The images below offer six different closeups of the northeastern section as winter arrived. All images were acquired by the Operational Land Imager (OLI) on Landsat-8 (image credit: NASA image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

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Figure 17: The world’s largest landlocked body of water stretches across several types of landscapes (image credit: NASA Earth Observatory)

The first inset (top-left) shows ice forming around the edges of the lake. In the winter, ice typically forms in the north, while central and southern areas remain ice free. The contrast is a result of differences in water depth and salinity. In the north, the lake is shallower and fresher than the south. Freshwater freezes at a slightly warmer temperature than salt water, allowing the ice to form more readily once the temperatures start to drop. The shallower depth also allows water to cool more quickly through the water column.

The second and third images (top row) depict areas around Dead Kultuk Bay. Since the 1990s, water levels in the Caspian Sea have risen and obscured the bay’s coastlines. As a result, water now reaches farther into the bay and creates waterlogged marshes. The surrounding area also contains oil fields.

The fourth image (bottom-left) shows the Buzachi Peninsula, south of Dead Kultuk. The peninsula is a low-lying desert environment, with some areas 30 meters (100 feet) below sea level. The northern part of the peninsula contains many salt marshes and salt lakes. The area has also become a popular site for oil and gas drilling.

The fifth image (bottom center) shows part of the Mangyshlak Peninsula, which is also very dry, low in elevation, and contains little vegetation. It is mostly uninhabited desert, but it includes Mount Otpan-tau, the highest point in Mangystau province at 530 meters (1,700 feet) above sea level. Today, a historical and spiritual complex sits atop the mountain. Legend holds that in the past, fire was lit at the peak to warn locals about a potential attack or danger.

The sixth image (bottom right) shows green swirls in the Caspian Sea, which contrasts with the lake’s typically bluer waters. The swirls could be phytoplankton blooms, which occur in the Caspian Sea when there is adequate sunlight and nutrients. The blooms are usually harmless and can be an important food source for marine life.

• December 29, 2020: Roughly 70 million years ago, the land that is now Washington County, Georgia, was covered by a shallow tropical sea with a chain of young mountains nearby. As erosion wore away at the mountains over tens of millions of years, large deposits of mineral-rich silt accumulated in deltas, bays, and estuaries along the ancient coastline. 33)

- The process left behind deposits of a silica- and aluminum-rich mineral clay called kaolin in a narrow band along the coastline, which is marked today by the “fall line” that runs diagonally across Georgia and divides the hilly piedmont region from the flatter coastal plain. The soft white rock is widely used in the production of glossy papers, ceramics, bricks, cosmetics, paint, and many other products.

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Figure 18: People have long extracted the soft clay from central Georgia for use in paper, ceramics, and other products. Signs of the industry are apparent in this natural-color satellite image, where mining pits appear white. Rain has collected in many of the pits, forming ponds with a crystal blue color. Some of the forested areas around the active pits were mined in previous decades but have since been replanted with trees and other vegetation. The Operational Land Imager (OLI) on Landsat-8 captured this image on April 13, 2020 (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- While kaolin deposits are present in several places in Georgia and other southeastern states, few areas have deposits that are as pure, white, and easily mined as those in Washington County. According to the U.S. Geological Survey, Georgia mines $1 billion worth of the clay every year, more than any other state.

- Kaolin mining has a long history in the U.S. Southeast. Before Europeans arrived, the Cherokee people used the white clay in their homes and in pottery. As early as 1767, an English potter negotiated a deal with the Cherokee Nation to ship five tons of Georgia clay back to the Wedgewood, a pottery company in England, for use in porcelain. Still, it was not until the 1950s that companies set up large-scale mines and processing facilities similar to those in this image.

- Kaolin has had a particularly strong impact on the town of Sandersville, which brands itself as the “kaolin capital of the world.” Each October, the town hosts a festival that includes a parade of heavy mining machinery, kaolin mine tours, and a beauty pageant that crowns Miss Kaolin. There is even a long-running tradition of locals eating kaolin, particularly women during pregnancy.

• December 26, 2020: If you accidentally stumbled upon the town of Huacachina, you might think it is a mirage. Huacachina is centered around a lagoon lined with lush vegetation—all located in the driest desert in the world. Snuggled between the biggest sand dunes in South America, it is the only natural oasis on the continent. 34)

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Figure 19: A popular place for sandboarding, Huacachina is the only natural desert oasis in South America. On August 15, 2020, the Operational Land Imager (OLI) on Landsat-8 captured this image of Huacachina and the adjacent sand dunes. Huacachina is located in southwestern Peru on the edge of the Atacama desert. The town is located about 5 kilometers (3 miles) from the city of Ica (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey.. Story by Kasha Patel)

- Roughly translating to “weeping woman” in Quechua, Huacachina has several mythological origin stories. One legend says a beautiful Incan princess named Huacachina was mourning the loss of her lover, and her tears created the lagoon. One day, a warrior saw her and startled the princess, who ran into the water to hide for hours. When she tried to leave, she had transformed into a mermaid. Another version says the princess was holding a mirror and admiring herself when the warrior saw her. When she ran away startled, the mirror fell and shattered. The glass became the tiny pool in the desert and consumed the princess, turning her into a mermaid. Many legends say Huacachina still lives in the pool and comes out at night to tempt swimmers.

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Figure 20: Photograph by Havardtl and used under the Creative Commons Attribution 4.0 International license (credit: NASA Earth Observatory)

- The oasis is actually formed by water from underground aquifers that seeps through the sand and helps promote the growth of palm trees, eucalyptus, and carob trees around the pool. The lagoon, which only covers about 2 acres, is encircled by businesses, hotels, and restaurants on its rim. The oasis town has a population of around 100 year-round residents. In recent years, water levels in the lagoon have decreased due to the drilling of nearby wells and increased evaporation during the hot summers. Consequently, the town has been feeding water into the lagoon from outside sources.

- Located about a five-hour bus ride from Lima, Huacachina has served as a popular tourist destination for more than 70 years. The town entertained many of Peru’s financial elite in the 1940s, and today entertains tens of thousands of tourists per year. Once called the “oasis of America,” Huacachina was featured on the 50 Nueva Sol currency note until 2006.

- The soaring sand dunes beyond the oasis rise several hundred feet in elevation—as tall as small mountains. They provide excellent sandboarding adventures: Adrenaline junkies can slide down the dunes like tubers or snowboarders. Visitors can also ride dune buggies across the dunes or hike, although the sand makes hiking strenuous.

• December 19, 2020: The Sea of Galilee in northern Israel—one of the lowest-lying bodies of water in the world—has long been a source of religious inspiration and intrigue. It was along the shores of the shallow freshwater lake where the Christian gospels say Jesus performed some of his ministry and certain miracles. Jewish settlers established the first kibbutz nearby. And it appears in certain Islamic prophesies. 35)

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Figure 21: The OLI instrument on Landsat-8 captured this false-color image (bands 6-5-4) of the lake and its surrounding landscape on October 27, 2020. The image was overlaid on a digital elevation model from the Shuttle Radar Topography Mission (SRTM) to give a sense of the topography (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 Adam Voiland)

- Some underground springs drain into the lake, but most of its water arrives through the Jordan River, which flows from Lebanon in the north to Israel and Jordan in the south. The Sea of Galilee (sometimes called Lake Tiberias or Lake Kinneret) lies within the Jordan Rift Valley, a narrow depression that began forming tens of millions of years ago as the Arabian plate tore away from Africa. Many of the marshy floodplains around the lake and to the south have been converted into farmland, which appears bright green.

- The Sea of Galilee has long been a popular destination for pilgrims. Yet the condition of the lake has grown increasingly tenuous in recent decades. Water levels dropped significantly during the past two decades, nearly hitting an all-time low in 2018. Less water causes the lake to become saltier, making it less viable as a source of drinking water. Such changes also threaten fish populations and encourage problematic algae blooms.

- The Sea of Galilee has long been a popular destination for pilgrims. Yet the condition of the lake has grown increasingly tenuous in recent decades. Water levels dropped significantly during the past two decades, nearly hitting an all-time low in 2018. Less water causes the lake to become saltier, making it less viable as a source of drinking water. Such changes also threaten fish populations and encourage problematic algae blooms.

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Figure 22: Larger area image of Landsat-8 acquired on 27 October 2020. A few wet years have helped reverse a decades-long decline in water levels on one of the world’s most cherished lakes (image credit: NASA Earth Observatory)

- Understanding those declining water levels and finding ways to keep them stable is a topic of much research in the region. Explanations for the decline include a lack of rain, increased water usage upstream in Lebanon, rising temperatures (which increase evaporation), and the expansion of farmland and irrigation around the lake. One research team recently investigated all of these possibilities by analyzing meteorological data, information from stream gauges, and Landsat satellite observations to estimate farmland extent. They found the expansion of agriculture and diversions for water use in Israel over the past two decades to be the best explanation for the decline.

- Recent years have been better, as two wet winters have helped the lake rebound considerably. The water level stood at 209.9 meters (688.6 feet) on December 16, 2020, high enough that hydrologists consider it nearly full. The last time it reached such heights was nearly two decades ago. Israel’s water authority has considered opening a dam at the southern end of the lake to prevent flooding, according to The Jerusalem Post.

• December 8, 2020: Svalbard, an archipelago between mainland Norway and the North Pole, is known as something of a mecca for geologists. It is one of the few places in the world that has easily accessible rocks from nearly every geological time period. There is little soil or vegetation to cover up the remarkable geologic diversity. And despite the Arctic location, ocean currents moderate the weather enough to keep much of the land clear of snow in the summer. 36)

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Figure 23: Among the more striking geologic attractions, at least when viewed from above, are glaciers on the archipelago’s northwestern island of Spitsbergen. The ice there seems to “bleed” meltwater that is an intense shade of red. The OLI instrument on Landsat-8 acquired this natural-color image of red water pooling in a shallow meltwater lake near the terminus of Holmström glacier. The image was captured on August 23, 2020, shortly after an unusual heatwave brought record-breaking temperatures to Svalbard (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

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Figure 24: This image shows a wider view. Note that the image has been rotated to combat relief inversion, an optical illusion that can make valleys look like mountains (image credit: NASA Earth Observatory)

- The red color is due to an abundance of sediment that has sloughed off from a particularly iron-rich layer of rock that formed roughly 400 million years ago (during the Devonian Period). Sometimes called the Old Red Sandstone, the rock layer formed on land when sand and other sediments were trapped in a basin enclosed by series of mountain ranges. The mountain ranges emerged when several of the world’s land masses were smashed together in a supercontinent called Laurussia, sometimes called the Old Red Continent.

- “The red Devonian rock is fairly soft and erodes easily,” explained University of Edinburgh geologist Geoffrey Boulton. “Glacial grinding produces a great deal of silt. These very small—and in this case red—particles are easily suspended in flowing meltwater and take a long time to settle in still water.”

- The silty meltwater pooled first in a shallow lake that had formed behind Holmström’s push moraine—a dam-like pile of sediment bulldozed by the front of the glacier when it surged about a century ago. Since then, a drainage stream has carved a narrow channel through the folded sediments of the moraine. The stream eventually widens and meanders some as it moves through mud flats as it approaches the sea. “When the silty water reaches seawater in Ekmanfjorden, it stays at the surface because the freshwater has a lower density than saltwater,” explained Boulton.

• December 2, 2020: Within an expanse of boreal forest in northwestern Alaska, two treeless stretches of sand stand out—the Great Kobuk Sand Dunes. With crests that rise as high as 100 feet (30 meters) above the surrounding forests, the dunes look like they belong in the Saharan Desert more than in the Arctic. 37)

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Figure 25: Dune fields of interest to scientists who study the Red Planet stand out in the Kobuk Valley amid a backdrop of green. The OLI instrument on Landsat-8 acquired this image of the Kobuk Valley and its dunes on August 16, 2020. While tundra grasses and forests have encroached upon and now cover about 90 percent of the sand that blankets Kobuk Valley, shifting winds still freely sculpt roughly 25 square miles (65 km2) of active dunes fields. Ridge-like transverse dunes are common in the northern part of the Great Kobuk Dune Field, while crescent-shaped barchan and parabolic dunes appear in significant numbers in the southern part (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland)

- The dunes owe their existence to glacial ice. During recent ice age cycles, massive sheets of ice bulldozed mountains and other rocky surfaces in the region, creating an abundance of sand, silt, and loess that collected along the banks of glacial streams. Over time, sediment-laden streams and dust-filled winds deposited much of that material in the ice-free Kobuk Valley, which is sheltered by the Baird Mountains to the north and the Waring Mountains to the south (Figure 26).

- One notable group has made the journey to Kobuk: geologists who study dunes on Mars. Since the Great Kobuk dunes are frozen and crusted with snow and frost for much of the year, they move quite slowly in comparison to dunes in warmer areas. They are akin to sand dunes on Mars, some of which have ice-like layers of frozen carbon dioxide frost during the winter. In fact, scientists from the Southwest Research Institute first discovered that sand dunes on Mars can move by using a satellite-based technique that they initially developed and tested among the Great Kobuk dunes.

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Figure 26: The dunes are one of the highlights of Kobuk Valley National Park—one of the most remote sites in the U.S. national park system. While hundreds of thousands of caribou migrate through the park each year, the absence of roads and other facilities means the number of human visitors to the park is typically less than 20,000, and often much lower (image credit: NASA Earth Observatory)

• November 28, 2020: Along with the plentiful harvest of crops in North America, one of the gifts of autumn is the gorgeous palette of colors created by the chemical transition and fall of leaves from deciduous trees. It is an aesthetic wonder from the ground, from the mountaintop, and from satellites. 38)

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Figure 27: The folded mountains of central Pennsylvania were past peak leaf-peeping but still colorful when the Operational Land Imager (OLI) on the Landsat-8 satellite passed over on November 9, 2020. The natural-color images above show the hilly region around State College, Pennsylvania (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and data from NASA/METI/AIST/Japan Space Systems, and the U.S./Japan ASTER Science Team. Story by Joshua Stevens and Michael Carlowicz)

- The region of rolling hills and valleys is part of a geologic formation known as the Valley and Ridge Province that stretches from New York to Alabama. These prominent folds of rock were mostly raised up during several plate tectonic collisions and mountain-building episodes in the Ordovician Period and later in the creation of Pangea—when what is now North America was connected with Africa in a supercontinent. Those events created the long chain of the Appalachians, one of the oldest mountain ranges in the world. The Appalachians once stood as tall at the Rockies and Alps, but hundreds of millions of years of erosion have worn them down.

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Figure 28: Detail image of State College, Pennsylvania. The close-up and oblique satellite views capture Mount Nittany, State College, and University Park, home of The Pennsylvania State University. The mascot of the university and several other groups in the area is the Nittany Lion, a localized name for the now-extinct eastern cougar (image credit: NASA Earth Observatory)

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Figure 29: This image shows the same scene overlaid on a digital elevation model to highlight the topography of the area (image credit: NASA Earth Observatory)

- The river valleys between and beside these mountains are quite popular with fishermen. Spring Creek is considered one of Pennsylvania’s best trout fisheries and is a popular destination for fly fishing. Fishermans Paradise was the first special regulation area for trout in the United States, and Penn State was the first university in America to offer credited courses in fly fishing.

• November 23, 2020: When he first encountered Lituya Bay in 1786, the French explorer Jean-François de Galaup La Pérouse was intrigued by an odd line in the forests that surrounded the narrow fjord in southeastern Alaska. It was as though the forests “had been cut cleanly with a razor blade,” he noted in his log. 39)

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Figure 30: Evidence of the cataclysmic wave is still visible from space more than 60 years later. As seen in the false-color Landsat-8 image (bands 7-5-3) at the top of the page, the damaged trimline is still imprinted in the forest. The lighter green areas along the shore indicate places where forests are younger than older trees (darker areas) that were not affected by the tsunami. When the tsunami hit, it snapped all of the trees and scoured away almost all vegetation. Some 2 square miles (4 km2) of forest were sheared and swept away by the tsunami waves (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Aerial photos of Lituya Bay and the source of the rockslide by Don Miller for the USGS. Story by Adam Voiland)

- It was the first clue that the seemingly placid, protected waters of the bay had a more destructive side. Another came when he dispatched three small boats to measure the depth of the water near the entrance of the bay. Despite the weather being calm, two of the three boats capsized after being drawn into roiling tidal currents that had been amplified by the fjord’s narrow shape. Twenty-six men lost their lives, their remains never to be found. It was in their honor that the lone island in the bay was given the name Cenotaph, a Greek word meaning “empty tomb.”

- The name turned out to be all too fitting. In 1899, an earthquake triggered a giant wave that destroyed a native village and drowned 5 people on the island. Another tsunami wave hit in 1936. But it was in 1958 that Lituya Bay’s unpredictable waters reared up in truly apocalyptic fashion. After a 7.8 earthquake throttled the nearby Fairweather Fault, a rockslide sent 90 million tons of rock plunging into the bay—an amount equivalent to 8 million dump truck loads.

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Figure 31: Aerial photo of Lituya Bay of 1958 after a 7.8 earthquake throttled the nearby Fairweather Fault (image credit: NASA Earth Observatory)

- Eyewitness reports describe a chaotic and surreal scene: Intense shaking for several minutes, an explosive boom, and a shattered glacier soaring hundreds of feet into the air. Then a series of giant waves dotted with hunks of ice raced through the bay. One fisherman described his boat being lofted over a forested spit on the crest of one wave and looking down at trees below. The wave obliterated a cabin on Cenotaph island and swept away a lighthouse near the mouth of the bay. One couple that had been fishing when the wave hit were never heard from again.

- The damage line in the forest—geologists call it a trimline—generally extended to an elevation of 700 feet (200 m) around much of the bay. On one ridge opposite the slide, waves splashed up to an elevation of 1,720 feet (524 m)—taller than New York’s Empire State Building. The event at Lituya Bay still stands as one of the tallest tsunami waves known to science. The photo above, taken in 1958 after the tsunami, shows the ring of damage around much of the bay.

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Figure 32: One of the causes of the enormous waves in Lituya Bay was that an entire chunk of a mountain peak—estimated to be 2,400 feet by 3,000 feet by 300 feet—broke free from a cliff and dropped 2,000 feet. “In some respects, it created a similar reaction to that which would have occurred if an asteroid had fallen into the water,” said the authors of a summary from the Western States Seismic Policy Council. This photo, taken in 1958, shows the scar left behind after the rock slide. After the initial blast, Lituya Bay’s narrow shape and U-shaped seafloor also amplified the waves, causing them to slosh back and forth like swells in a huge bath tub (image credit: NASA Earth Observatory)

- Lituya Bay’s steep walls, the geometry of its seafloor, and the fact that it intersects a fault that is often a source of earthquakes suggests that Lituya Bay will see more tsunamis in the future. After scrutinizing the bay’s geology and history for years, one scientist calculated giant waves happen there once every quarter century—a 1 in 9000 chance on any given day. The threat from the tidal currents that thwarted La Pérouse is more constant. Since the 1958 wave, an average of one fishing boat has been lost at the entrance of the bay per year, reports Philip Fradkin in the book, Wildest Alaska: Journeys of Great Peril in Lituya Bay.

• November 21, 2020: Across most of Earth’s coasts, tides typically vary no more than two meters from high to low. At Broad Sound, though, daily high tide can stand as much as ten meters above the low—the largest tidal swings on the eastern shore of Australia. 40)

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Figure 33: Tidal swings here are greater than at any other place on the east coast of Australia. The image shows Broad Sound around 10 a.m. Australian Eastern Standard Time on October 29, 2020, as the Moon-driven high tide crested. The image was acquired by the Operational Land Imager (OLI) on the Landsat-8 satellite. The image processing is a blend of art and science. Like a photographer adjusting lighting and using filters, Norman Kuring of NASA’s Ocean Biology group works color-filtering techniques to draw out the fine details in the water (image credit: NASA Earth Observatory, image by Norman Kuring/NASA’s Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Explorer Matthew Flinders first documented the unusual bay tides in the early 1800s. At new and full Moon, he noted the tide was “not less than thirty, and perhaps reache[d] thirty-five feet” and occurred hours later than expected. Other researchers in the 20th century also observed the bay’s daily tides are six times higher and occurred three hours later than anywhere else on the eastern shore. Peculiar local geography plays a key role in the phenomenon.

- Broad Sound is a large funnel-shaped bay near the southern end of the Great Barrier Reef. It is 50 km (30 miles) long and stretches to about 20 km (12 miles) wide at its greatest extent. The bay contains 48 islands, collectively part of Broad Sound Islands National Park.

- In this image, suspended sediments and phytoplankton trace the water flow into the bay, around islands and other shallow spots. The sediments near the shore are likely mud from the erosion of rocks on land, while sediments near the outer reefs are coarse-grained carbonate. Since no major rivers flow into the bay, the sediments are mainly stirred up by incoming tide.

- The gravitational pull of the Moon causes tides in Broad Sound like everywhere else on Earth, but these tides are further amplified by the shape of the bay and shallowness of the nearby Great Barrier Reef. The reef network inhibits the normal astronomical tidal patterns, concentrating the flows through nearby channels—Flinders Passage to the north and Capricorn Channel to the southeast. The delayed tidal flows from these channels converge in Broad Sound and cause waters to rise significantly. Due to the shape and size of the bay, different areas may experience higher tide than others. The head of the bay experiences the greatest tidal range, sometimes exceeding ten meters.

- Due to the high tidal range and the turbidity of the water, seagrass is not common in Broad Sound. However, the area serves as a nesting habitat for Australian east coast flatback turtles. It also supports Australian snubfin dolphins, humpback whales, koalas, and a variety of land and sea birds.

• November 12, 2020: Four blackwater rivers—the Waccamaw, Pee Dee, Black, and Sampit—feed into Winyah Bay, an estuary in eastern South Carolina. All of them flow through swamps, wetlands, and forests that are rich with decaying vegetation and other organic matter. The dead leaves and debris stain the rivers and wetlands a transparent brown color as several natural chemical substances found in plants—tannin, phenol, and humic acid—seep into the water. The same process gives tea its yellow or brown color. 41)

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Figure 34: One of the first attempts to set up a permanent European colony in the contiguous United States ended in disaster. After heavy rains, stained floodwaters can get flushed out of swamps and wetlands into the estuary and ocean. That was happening on October 1, 2020, when the Operational Land Imager (OLI) on Landsat-8 acquired this natural-color image of Winyah Bay. Many waterways were swollen following heavy rains from Hurricane Sally. [image credit: NASA image by Norman Kuring/NASA's Ocean Color Web, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland, with information from James Morris (University of South Carolina)]

- When measuring the phenomenon with optical instruments, scientists describe heavily stained waters as being high in colored dissolved organic matter (CDOM). On October 1, a National Oceanic and Atmospheric Administration water quality monitoring system at North Inlet-Winyah Bay National Estuarine Research Reserve measured CDOM levels that were roughly 50 percent higher than the long-term average for that date, said Erik Smith, the head of the research reserve.

- Blackwater flows can have important consequences for aquatic ecosystems because they change the color of the light available to phytoplankton for photosynthesis. “The compounds that make up CDOM absorb blue light wavelengths extremely well, so blue light does not penetrate very deep into the water. The red wavelengths are the ones left behind, hence the brownish-red appearance of the water,” explained Tammi Richardson, an oceanographer at the University of South Carolina. “If phytoplankton do not have pigments that can absorb red light, then they will not be able to photosynthesize.”

- Since phytoplankton photosynthesis is a centerpiece of the ocean food web, CDOM levels can affect the productivity of the entire Winyah Bay estuary. In practice, cryptophytes and diatoms tend to do well in blackwater, while other types of phytoplankton tend to suffer.

- Blackwater holds an interesting place in maritime history in this region. In the early years of European exploration and colonization of North America, mariners sought out blackwater streams to refill their casks because the water was thought to minimize the spread of disease. Sailors did not know why at the time, but the high acidity and presence of certain phenols have anti-bacterial properties.

- Among those early sailors may have been the Spanish explorer Lucas Vázquez de Ayllón. He led an expedition of six ships that reached Winyah Bay in August 1526, and established San Miguel de Gualdape, the first European settlement in the contiguous United States. It preceded Pensacola, Roanoke, and Jamestown by decades, but is often overlooked by historians because of how unsuccessful and short-lived it was.

- Upon arrival in Winyah Bay, the Spaniards immediately lost their main supply ship—the Capitana—when it ran aground on a sandbar near the modern town of Georgetown. In the chaos that followed, the Native American guides and interpreters they had captured from the area during a previous expedition deserted and slipped into the forest. After about a month in Winyah Bay, Ayllón moved the colony of 500 Europeans and 100 enslaved Africans to a new location. Where exactly they went is unclear, but historians think they settled along Sapelo Sound in what is now Georgia.

- However, unusually cold weather, disease, and lack of food quickly turned a difficult situation into a catastrophe for the colonists. Settlers died in large numbers by mid-October, including Ayllón himself. His death triggered a battle for leadership of the struggling colony. In the confusion, the African slaves revolted and escaped, meaning the first ever documented slave uprising in North America happened at San Miguel de Gualdape. The 150 Europeans who were still alive after the uprising soon abandoned the colony and set sail for Hispaniola. The escaped slaves, meanwhile, were likely taken in by Native American communities in the area.

• November 8, 2020: Conditions for phytoplankton blooms are often just right off in southern spring and summer in the South Atlantic between South America and the Falkland Islands. Phytoplankton are microscopic, plant-like organisms that use chlorophyll to harness sunlight for energy. They form the center of the marine food web, serving as a primary food source for zooplankton, fish, and other marine animals. They are also critical to the global carbon cycle and key producers of the oxygen that makes the planet livable. 42)

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Figure 35: Detail image. These natural-color images were acquired by the OLI instrument on the Landsat-8 satellite on October 18, 2020. Swirls of milky blue water indicate the presence of substantial numbers of phytoplankton around the western Jason Islands, an archipelago off of West Falkland Island. The floating, plant-like organisms get piled up along the edges of currents and eddies, making visible some of the turbulent, dynamic ocean mixing patterns (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Michael Carlowicz)

- The waters in this area are rich with nutrients carried on the Malvinas Current. Spun off of the Circumpolar Current of the Southern Ocean, the Malvinas flows north and east and is enriched by iron and other nutrients from Antarctica and Patagonia. The waters are made even richer by the interaction of ocean currents along shelfbreak fronts, where underwater ridges slope down to the deep ocean.

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Figure 36: Dynamic mixing and churning of currents around some South Atlantic islands makes for biologically productive waters (image credit: NASA Earth Observatory)

- “The bright color suggests this might be coccolithophores, although its hard to say for sure,” said Marina Marrari, a biological oceanographer with the Costa Rica Fishing Federation. “In general, there is a species succession at the shelfbreak from diatoms in spring to dinoflagellates to coccolithophores in summer, and this also varies with latitude. October seems early in the season but with the right nutrients it is possible.”

- “This is such a beautiful image. To me it really looks like a patch of coccolithophorids because there are no rivers in the Falklands capable of providing such an amount of sediments,” said Priscilla Lange of the Blue Marble Space Institute of Science. “It is a pretty large patch, and blooms of coccolithophorids are so common in this area. It is also possible to see blooms of other phytoplankton (dark patches) in the middle of the white swirls.”

- “These sub-mesoscale features are common in the shelfbreak region and north of Malvinas. The Malvinas current interacts with the bathymetry in that region, stirring the water column and likely causing nutrient input that promotes production in those features,” Marrari added. “There is a recent paper that discusses that the interaction of the bathymetry with the current and how it could bring iron to the surface promoting these blooms.”

- The area is also on the edge of what oceanographers call the “great calcite belt.” Spanning large swaths of ocean in far southerly latitudes, the calcite belt often shows up as bright, reflective areas in satellite imagery because of the abundance of calcite-rich coccolithophores.

- The nearby Jason Islands were first noted on Spanish maps in the 16th century; evidence suggests they might have first been sighted by Ferdinand Magellan or Amerigo Vespucci. Much later, they were named for the British survey vessel HMS Jason; the Spanish name for the archipelago is Islas Sebaldes.

- In general, there are no permanent human inhabitants of the islands these days, other than occasional research teams and a few seasonal visitors. Many of these rocky islands are protected by the Falklands government and private conservation groups as nature reserves. The area is important bird habitat, with sizable populations of gentoo and rockhopper penguins, black-browed albatrosses, and other species.

• November 5, 2020: Dust storms are relatively common in places like the Sahara Desert. But they can happen at high latitudes, too, in places that are icy and dry. This image shows one of a handful of dust clouds that streamed over the Gulf of Alaska in autumn 2020. 43)

- The dust pictured here originated upstream in the Copper River Valley, where glaciers have crushed rocks into a very fine silt, or “glacial flour.” River water carries the silt south and deposits it along the delta and shore. Because the silt particles are so fine, they are easily lofted into the air by a stiff breeze.

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Figure 37: Winds were especially strong on October 22, 2020, when the Operational Land Imager (OLI) on Landsat-8 acquired this natural-color image. A pressure gradient caused low-level air to accelerate out of the valley—a phenomenon known as a “gap wind”—and stir up a substantial amount of the silt (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- Strong seasonal winds are just one reason why dust clouds occur across southern Alaska between late September and mid-November, explained Santiago Gassó, an atmospheric scientist at NASA’s Goddard Space Flight Center. This is also the time of year when river levels start to decline because glacial melt has tapered off; this leaves more silt exposed to the wind. The amount of exposed silt also depends on the amount of snow cover, which was mostly absent along the Copper River’s shoreline and delta in late October.

- Dust clouds from Alaska produce some spectacular satellite images, but they could also play an important role in the region’s ecosystem. The dust contains iron, a micronutrient that phytoplankton can use once the dust settles and dissolves in the Gulf of Alaska. “Although the magnitude of Alaskan dust events is not as massive as those seen in the North Atlantic, they may be more effective in terms of fertilization potential per unit of mass of dust because glacial silt is more soluble,” Gassó said.

- Exactly how much dust in southern Alaska becomes airborne is still uncertain, as is the relative importance of the multiple sources of micronutrient iron in this part of the North Pacific Ocean. But scientists are working to find out.

- “Until a few years ago, we knew about dust activity in this part of the world in very anecdotal way,” Gassó said. “But with the advent of better online platforms to search for images, as well as the increase of number of satellites in operation, the surveillance of this area—and other high latitude dust sources such as Greenland—is easier to carry out. This has contributed to the discovery that high latitude dust activity is fairly common, and it dispels the belief that dust storms are a purely hot-environment phenomenon.”

• October 27, 2020: On October 14, 2020, a small fire started north of Hot Sulphur Springs in north-central Colorado. Within ten days, the East Troublesome fire had burned through more than 190,000 acres (77,000 hectares) and had become Colorado’s second largest fire (by area) on record. As of October 26, 2020, it was 15 percent contained. 44)

East Troublesome experienced extensive growth on October 21, growing from 30,000 acres to 170,000 acres in about 24 hours. The rapid growth was fueled by strong winds that blew flames east into the Rocky Mountains. The fire burned quickly through lodge pole pine forests, which had already been weakened by drought and an infestation of bark beetles. The blaze has killed at least two people, destroyed hundreds of homes, and prompted evacuations in several nearby areas, including the entire town of Grand Lake.

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Figure 38: On October 22, OLI on Landsat-8 captured this false-color image of the East Troublesome fire. The image combines shortwave infrared, near-infrared, and green light (bands 7-5-2) to show active fires (bright red), scarred land consumed by fire (darker red), and intact vegetation (green), image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- The fire has since split into two fingers in Rocky Mountain National Park. One section, now known as the Thompson Zone, moved northeast along Big Thompson River and crossed the rocky terrain of the continental divide.

- Snowfall on October 25 slowed the spread of the fire and helped firefighters keep the blaze away from Estes Park, where more than 6,000 residents were evacuated. The snow also slowed the Cameron Peak fire, located about 10 miles north of East Troublesome. Cameron Peak has burned more than 200,000 acres (8,000 hectares) and is the largest fire in state history by acre. As of October 26, the fire areas received about 6 to 12 inches (15 to 30 cm) of snow, with light snow predicted to continue through the day.

- Despite the snow, authorities say large downed logs and other fuels under the forest canopy are still expected to burn. Temperatures are also expected to increase again on October 27. U.S. Forest Service officials estimate East Troublesome and Cameron Peak will be fully contained by early November.

• October 26, 2020: With its colorful soils, salt caves and mountains, and ocher-stained streams and beaches, Iran’s Hormuz island is rich with memorable geology. 45)

- The island is a salt dome — a teardrop-shaped mound of rock salt, gypsum, anhydrite, and other evaporites that has risen upward through overlying layers of rock. Rock salt, or halite, is weak and buoyant, so it loses its brittleness and flows more like a liquid when under high pressure.

- The rising mass is not purely made of salt. Embedded within it are layers of clay, carbonates, shale, and iron-rich volcanic rocks, some of which have taken on vivid shades of red, yellow, and orange as they moved upward and interacted with water and minerals from other rock layers.

- The ocher soils on the island have proven appealing to cooks, artists, and miners alike. Locals reportedly use the red soil to season a certain type of bread. Groups of artists have used it to create expansive sand carpets. Sand from a mine in the northern part of the island has also been used in paints, cosmetics, ceramic tiles, and for the exteriors of buildings.

- One nongeological feature of the island stands out in the image: At the northern end, a small inlet hosts a concentrated patch of mangroves that appear green. Known locally as a hara forest, the area serves as habitat for numerous types of fish, mollusks, crustaceans, and migratory birds.

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Figure 39: A mix of uplifting salt and other sedimentary and metamorphic rocks make for colorful landscapes in the Persian Gulf. The concentric ring structure of the uplifted salt dome is visible in this natural-color image acquired by the OLI instrument on Landsat-8. Uplifted halite is widespread near the central and southern two-thirds of the island, which appear reddish amid outcrops of weathered, volcanic rocks that appear gray. The tan northern third of the island is covered by a layer of sand and other sediment that was deposited by other processes (image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey)

• October 19, 2020: Ice lingered on Hudson Bay as recently as July 2020 and will start to freeze up again in autumn when snowfall and chilly breezes return. In the meantime, this image captures the unique beauty of the region in late summer. 46)

- The saltwater bay receives fresh water from more than 40 major rivers that flow through various ecosystems and zones of permafrost. The rivers carry sediment and dissolved organic matter, which colors the water brown. In this image, a small dark brown plume is visible at the mouth of the Niskibi River, while a more prominent plume from the Severn River flows around Partridge Island. There is also ample sediment from the seafloor that has become suspended in the water.

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Figure 40: Located in northeastern Canada, just south of the Arctic Circle, Hudson Bay is the world’s second-largest bay and spans 1,230,000 km2. This image, acquired on September 19, 2020, with the Operational Land Imager (OLI) on Landsat-8, shows the bay’s southern side where it is bordered by Ontario Province. Raised beaches around the bay show how the landscape responded after the last ice age (image credit: NASA Earth Observatory, image by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen, with image interpretation by Lynda Dredge/Geological Survey of Canada, and Robie Macdonald/University of Manitoba)

- According to Robie Macdonald, a scientist at the University of Manitoba, the colorful swirls occur as fresh water from land enters the bay and drives a cyclonic circulation. This circulation moves material around the shallow coastal zone from the northwest to the southeast corner of the bay, and out into Hudson Strait. Part of that transport process is visible in this image.

- The coastal lands are equally interesting, telling a story about how the landscape responded after the last ice age. At the height of the last ice age, ice sheets spanned much of Canada and parts of the northern United States. The weight of the Laurentide ice sheet, centered over Hudson Bay, depressed the surface of the land. Then, as the ice sheets melted at the end of the ice age, the land started to rebound—a process that continues today.

- The rebound led to a series of abandoned beaches, visible in this image as a sequence of near-linear ridges and spits separated by flatter areas. Lynda Dredge, an emeritus scientist with the Geological Survey of Canada, noted that the oldest and highest beaches farthest inland developed about 7,500 years ago when the bay’s relative sea level was about 130 meters above its present level. As the land rebounded and relative sea level dropped, old beaches were left behind. The process continued, forming successively lower beaches all the way down to the present sea level.

- Today, the abandoned beaches inland and at higher elevations are covered with grasses and scrubby trees; dry, unvegetated beaches closer to the shore appear light tan. Between the ridges, shallow wetland areas containing fens and bogs appear red-brown.

- The landscape is still evolving as the land continues to rebound. According to Dredge: “Future beaches will form in the area now covered in tidal flats.”

• October 14, 2020: Romania’s landscape has seen plenty of transition in recent decades, as farmers have responded to changes in land management policies and in the natural environment. As a result, many farms display a compelling array of shapes and sizes when viewed from above. 47)

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Figure 41: On April 8, 2020, the Operational Land Imager (OLI) on Landsat-8 acquired these images of southwest Romania’s historic Oltenia province. The images are false color (bands 6-5-2) to better distinguish the types of land cover amid the region’s mountains, foothills, and plains (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 Dan Bălteanu/Romanian Academy)

- Figure 41 shows a wide view of the province, bordered to the east by the Olt River, to the south by the Danube River, and to the north by the South Carpathian Mountains. Snow and ice (light blue) cap the range’s higher elevations, which reach up to more than 2500 meters (8200 feet) high. Forested areas of the Carpathians—with ample conifers and deciduous trees—appear dark green and orange.

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Figure 42: This image shows a detailed view of the foothills along the Jiu River. The gray patch on the river bank is Târgu Jiu, the capital city of Gorj County. Away from the city, long, narrow farms are generally laid out perpendicular to the rivers and streams. Orchards and vineyards are common across the hilly region, as is pastoral sheep farming (image credit: NASA Earth Observatory)

- Forested areas of Figure 42 (primarily orange), with plenty of oak and beech trees, also show up in the foothills spanning between 300 and 800 meters in elevation. Notice the bright green color tracing the valleys in the foothills; this is the signature of healthy crops. The relatively flat land along river channels offers suitable terrain for farming in an otherwise rugged landscape.

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Figure 43: Farther south beyond the foothills, farming on the Oltenia Plain appears even more widespread. This image shows a detailed view of bright green crops mixed with brown and red bare ground. The square-shaped boundaries of villages, such as Visina Nouă and Visina, add to the geometric patchwork. Only the thin lake (Balta Obârsia) breaks up the scene with a natural shape (image credit: NASA Earth Observatory)

- In all of the images, the fields are extremely long and narrow. The narrow shape is due to land fragmentation; that is, farms that were already small have been divided into even smaller parcels. Researchers note numerous reasons for this. For example, land that belonged to cooperatives during the years of communist rule was returned to former land owners, dividing large plots of land into smaller plots. Private plots across the plain span on average just 1-2 hectares (2-5 acres).

- Not all land on the Oltenia Plain can currently support crops. Desertification has given way to sand dunes in some areas, while others have been abandoned or deforested.

• October 01, 2020: “Spalte” is a Danish verb meaning “to split.” The aptly named Spalte Glacier in northeast Greenland once branched off from its parent glacier, Nioghalvfjerdsbrae (79 N), which is the Arctic’s largest remaining ice shelf. In late June 2020, Spalte completely split off from its parent and crumbled away into numerous icebergs. 48)

- Scientists have been watching Spalte Glacier crack, shed ice, and retreat for decades. But the loss of 113 km2 (44 square miles) of ice in summer 2020 means that the branch of floating ice on the northeast side of 79 N is essentially gone for good. Scientists say the recent loss of Spalte, and the subtler changes to the adjacent 79 N, are part of a “progressive disintegration” that has happened amid unusually warm temperatures in recent years.

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Figure 44: The pair of satellite images show changes in the region across three decades. The right image was acquired with the OLI instrument on Landsat-8 on July 24, 2020, nearly one month after Spalte Glacier broke up. For comparison, the left image from Landsat-5 shows the glacier system on August 16, 1986 (image credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen)

- The icebergs in the 2020 image had already started drifting north in Dijmphna Sound after breaking away on June 30. “More rifts are already visible just southwest of the calving front indicate the 79 N floating ice tongue is not in good shape,” said NASA/UMBC glaciologist Christopher Shuman.

- Also visible in the 2020 image is a long, gray line with curves that resemble the line plot from a seismograph; this is actually a seasonal river of liquid water that runs along the top of the glacier. The location of the bends in the river, which move with the glacier, can be correlated to stationary rocky landmarks and used to track the overall flow of the ice. For now, the ice at the main front of 79 N in Nioghalvfjerd Fjord is relatively steady, but recent research indicates further changes are likely to come.

- About six small islands and submerged rocky “pinning points” help hold the floating front of 79 N in place. Two of the larger islands are clearly visible in these images. According to Shuman, another small island in the northern fjord may once have been crucial for holding Spalte Glacier in place into the 1970s. “This is the only ice shelf I know of that is fronted by so many distinct bedrock features,” he said.

- Even after the loss of Spalte Glacier, 79 North remains the Arctic’s largest ice shelf, measuring about 70 kilometers long and 20 kilometers wide. Together with neighboring glaciers Zachariæ Isstrøm and Storstrømmen, the three glaciers are part of the Northeast Greenland Ice Stream and are the main outlets through which land-based ice can be drained from a 200,000 km2 section of the Greenland Ice Sheet.

• September 28, 2020: After burning more than 180 square miles (460 km2) of the San Gabriel Mountains in September 2020, the Bobcat fire now ranks among the largest fires on record for Los Angeles County, California. The blaze began on September 6 near Cogswell Dam, and grew steadily over the next three weeks in the midst of unusually hot, dry conditions. 49)

- “Strong winds that have shifted direction several times over the course of the fire helped it spread over such a large area,” explained Natasha Stavros, a wildfire expert with NASA’s Jet Propulsion Laboratory. “And the fire is burning on steep terrain with limited access to roads, which made it challenging to contain.”

- Stavros sees the fingerprints of climate change in the Bobcat fire and in California's historic 2020 fire season. “Four of the five largest fires ever recorded in California were burning at the same time as the Bobcat fire,” she said. “Climate change contributes to megafires like these by heating fuels up, drying them out, and making them more flammable.”

- As the fire worked its way through the national forest, it consumed large areas of chaparral, brush, and grass. While flames have mostly stayed clear of populated areas, they veered into parts of the Juniper Hills and Littlerock neighborhoods near Palmdale, leading to more than two dozen homes being destroyed or damaged. Flames also threatened historic Mount Wilson Observatory for several days, but the site appears to have escaped serious damage.

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Figure 45: The fire is among the largest Los Angeles County has ever faced. Stavros and other NASA fire experts have been monitoring the blazes using a suite of satellite sensors. One of them, the OLI instrument on the Landsat-8 satellite, acquired an image of the burn scar on September 21, 2020, while the fire was still raging in Angeles National Forest. False color makes it easier to distinguish the burn scar. The image combines shortwave infrared, near-infrared, and green light (OLI bands 7-5-2) to show active fires (bright red), scarred land that has been consumed by the fire (darker red), intact vegetation (green), and cities and infrastructure (gray) [image credit: NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. AVIRIS photograph by Tim Williams on 21 September 2020 (NASA Armstrong Flight Research Center). Story by Adam Voiland]

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Figure 46: While Landsat and other satellites constantly collect data from space that is useful for monitoring fires, NASA sometimes deploys aircraft for advanced fire management research. In this case, the high-flying ER-2 surveyed the Bobcat fire on September 17, 2020, from a height of 65,000 feet (20,000 meters), about twice as high as commercial airliners fly. The pilot of the aircraft took the photograph of smoke rising from the fire shown above. Meanwhile, the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) sensor on board observed fine details of the fire’s temperature, the water content of vegetation canopies, characteristics of the smoke, and burn severity (image credit: NASA Earth observatory)

- “The ER-2 with AVIRIS was able to image the Bobcat fire on a checkout flight for the NASA Western Diversity Time Series airborne campaign,” said Robert Green, a senior research scientist at NASA’s Jet Propulsion Laboratory and the AVIRIS experiment scientist. “These advanced measurements are supporting development and testing of new algorithms that will be used with the space instruments planned for the next decade.”

- “We use airborne ‘missions of opportunity’, like the Bobcat fire flight, to improve our understanding of dynamic fire physics and Earth processes,” added Vincent Ambrosia, the associate program manager for wildfire research in NASA’s Earth Applied Sciences Program. “The agency supports the adaptation and operationalization of unique sensor data derived from NASA Earth Observations, such as AVIRIS, to improve national and international disaster management agencies efforts to understand and mitigate wildfire effects.”

- According to InciWeb, the blaze was 50 percent contained as of September 24 thanks to the efforts of more than 1,600 firefighters. While cooler weather and lighter winds helped firefighters slow the spread in recent days, forecasters anticipate that red flag burning conditions could soon return as another heat wave and stronger winds return to southern California in the coming days.

• September 26, 2020: In the past three decades, several of Iraq’s largest lakes have experienced fluctuating water levels due to droughts, dam management, and conflict. Two lakes in particular—Milh and Habbaniyah—experienced substantial declines in water levels and lost much of their reputation as bustling resort areas. 50)

- After decades of low water levels, two of Iraq’s popular lakes appear to be filling again.

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Figure 47: Now satellite imagery shows the two lakes are refilling. The natural-color images shows Lake Milh on August 16, 2018 (Figure 47) compared to August 21, 2020 Figure 48. The red color is most likely due to the presence of algae and bacteria with red pigments; a similar phenomenon occurs in a lake in nearby Iran. The images were captured by the Operational Land Imager (OLI) on Landsat 8. Older satellite imagery suggests that the lake has not appeared this full since 2009, although 2015 came close (image credit: NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Kasha Patel)

- Lake Milh, also known as Lake Razzaza, was completed in the 1970s to receive excess water from Habbaniya Lake during flood season. Milh was one of Iraq’s largest lakes and a popular recreation spot in the 1980s. The islands within the lake served as important breeding areas for many birds, such as the flamingo.

- But due to droughts and closures of connecting waterways, water levels began to dwindle. The lake’s changing water levels and increasing salinity caused several fish species to disappear. Tourism also decreased as the lake and nearby communities suffered through drought and war.

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Figure 48: Image of Lake Milh acquired with the Landsat-8 OLI instrument on 21 August 2020 (image credit: NASA Earth Observatory)

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Figure 49: This image shows Habbaniya Lake (also known as Lake Ramadi), as observed by Landsat-8. In the 1980s, Habbaniya was also a popular tourist destination. However, the resort suffered after several conflicts in the 1990s and 2000s. Companies have since tried to revive the vacation spot by rebuilding facilities (image credit: NASA Earth Observatory)

- The reasons for the recent increases in the water levels are not clear. Preliminary satellite precipitation data analysis and data from ground stations do not show obvious flooding in the vicinity of the lakes recently, but heavy rains did fall in locations farther upstream in northern and central Iraq this year. Additionally, it is possible that there were changes in water storage and release patterns upstream at dams along the Euphrates River. Dams and reservoirs along the Tigris and Euphrates can significantly alter the amount of water in locations further downstream. In 2019, Mosul Dam Lake in northern Iraq displayed a similar increase in water levels, which was due from a combination of heavy rain and changes in dam management.

- The Iraqi National Investment Commission has been interested in restoring both Habbaniya and Milh. In January 2018, the group unveiled a $25 million investment project to develop the areas with hotels, a marina, and an amusement park.

• 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. 51)

- 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.

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Figure 50: 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.”

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Figure 51: Landsat-8 image of the west arm of Glacier Bay acquired with OLI (Operational Land Imager) on 17 September 2019 (image credit: NASA Earth Observatory)

- “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.”

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Figure 52: 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 50 and 51, 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 53: 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 (video 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. 52) 53)

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Figure 54: 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.

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Figure 55: 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. 54)

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Figure 56: The false-color images show the spread of water hyacinths across Mexico’s Valsequillo reservoir from January 10, 2000 (Figures 56), to January 9, 2020 (Figure 57). 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.

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Figure 57: OLI false-color image on Landsat-8, acquired on 9 January 2020 (image credit: NASA Earth Observatory)

- “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.

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Figure 58: The natural-color image of OLI shows the same scene in 2020; the water hyacinths are dark green (image credit: NASA Earth Observatory)

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Figure 59: 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. 55)

- 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.

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Figure 60: 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.

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Figure 61: 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.

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Figure 62: 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. 56)

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Figure 63: 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.

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Figure 64: 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. 57)

- 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.

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Figure 65: 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)

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Figure 66: 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. 58)

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Figure 67: 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.

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Figure 68: 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. 59)

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Figure 69: 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)

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Figure 70: 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.”

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Figure 71: 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. 60)

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Figure 72: 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 73) 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.

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Figure 73: 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. 61)

- 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.

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Figure 74: 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)

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Figure 75: 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.

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Figure 76: 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. 62)

- 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.

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Figure 77: 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.

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Figure 78: 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. 63)

- 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.

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Figure 79: 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.

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Figure 80: 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. 64)

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Figure 81: 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. 65)

- 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).

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Figure 82: 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.”

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Figure 83: 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.

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Figure 84: 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. 66)

- 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.

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Figure 85: 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.

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Figure 86: 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. 67)

- 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.”

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Figure 87: 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)

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Figure 88: 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. 68)

- 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.

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Figure 89: The satellite images (Figures 89 and 90) 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)

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Figure 90: Overall Bush fire burn scar of the Arizona fire on June 14 2020 (image credit: NASA Earth Observatory)

- The red lines across the detailed image (Figure 89) 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. 69)

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Figure 91: 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. 70)

- “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.

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Figure 92: 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. 71)

- 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.

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Figure 93: 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. 72)

- 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.

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Figure 94: 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)

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Figure 95: 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.

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Figure 96: 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)

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Figure 97: 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.

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Figure 98: 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. 73)

- 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.”