Terra Mission (EOS/AM-1)Spacecraft Launch Mission Status Sensor Complement EOS References
Terra (formerly known as EOS/AM-1) is a joint Earth observing mission within NASA's ESE (Earth Science Enterprise) program between the United States, Japan, and Canada. The US provided the spacecraft, the launch, and three instruments developed by NASA (CERES, MISR, MODIS). Japan provided ASTER and Canada MOPITT. The Terra spacecraft is considered the flagship of NASA's EOS (Earth Observing Satellite) program. In February 1999, the EOS/AM-1 satellite was renamed by NASA to “Terra”. 1) 2) 3) 4)
The objective of the mission is to obtain information about the physical and radiative properties of clouds (ASTER, CERES, MISR, MODIS); air-land and air-sea exchanges of energy, carbon, and water (ASTER, MISR, MODIS); measurements of trace gases (MOPITT); and volcanology (ASTER, MISR, MODIS). The science objectives are:
• To provide the first global and seasonal measurements of the Earth system, including such critical functions as biological productivity of the land and oceans, snow and ice, surface temperature, clouds, water vapor, and land cover;
• To improve the ability to detect human impacts on the Earth system and climate, identify the “fingerprint” of human activity on climate, and predict climate change by using the new global observations in climate models;
• To help develop technologies for disaster prediction, characterization, and risk reduction from wildfires, volcanoes, floods, and droughts
• To start long-term monitoring of global climate change and environmental change.
Complemented by aircraft and ground-based measurements, Terra data will enable scientists to distinguish between natural and human-induced changes.
Figure 1: Illustration of the Terra spacecraft (image credit: NASA)
Terra consists of a spacecraft bus built by Lockheed Martin Missiles and Space (LMMS) in Valley Forge, PA. The spacecraft is constructed with a truss-like primary structure built of graphite-epoxy tubular members. This lightweight structure provides the strength and stiffness needed to support the spacecraft throughout its various mission phases. The zenith face of the spacecraft is populated with equipment modules (EMs) housing the various spacecraft bus components. The EMs are sized and partitioned to facilitate pre-launch integration and test of the spacecraft.
EPS (Electrical Power Subsystem): A large single-wing solar array (size of 9 m x 5 m = 45 m2), deployed on the sunlit side of the spacecraft, maximizes both its power generation capability and the cold-space FOV (Field of View) available to instrument and equipment module radiators. The average power of the satellite is 2.53 kW provided by a GaAs/Ge solar array (max of 7.5 kW @ 120 V at BOL). The solar array is based on on a prototype lightweight flexible blanket solar array technology developed by TRW (use of single-junction GaAs/Ge photovoltaics). A coilable mast is used for the deployment of the solar array. The Terra spacecraft represents the first orbiting application of a 120 VDC high voltage spacecraft electrical power system implemented by NASA. A PDU (Power Distribution Unit) has been designed to provide 120 DC (±4%) under any load conditions. This regulated voltage, in turn, is achieved via a sequential shunt unit (SSU) and the 2 BCDUs. A NiH2 (nickel hydrogen) battery is used (54 cells series connected) to provide power during eclipse phases of the orbit. 5) 6) 7)
Figure 2: Coilable mast deployer for the Terra solar array (image credit: NASA)
GN&C (Guidance Navigation and Control) subsystem: Terra is a three-axis stabilized design with a single rotating solar array. The GN&C subsystem is made up of sensors, actuators, an ACE (Attitude Control Electronics) unit, and software. A three-channel IRU (Inertial Reference Unit) determines body rates in all control modes. Solid-state star trackers provide fine attitude updates, processed by a Kalman filter to maintain precise 3-axis inertial knowledge. A 3-axis magnetometer senses the Earth's geomagnetic field, primarily for magnetic unloading of reaction wheels, but also as a sensor to determine an attitude failure during a deep space calibration maneuver. 8)
The backup sensors include an ESA (Earth Sensor Assembly) for roll and pitch sensing, and coarse sun sensors for pitch and yaw sensing of the sun line relative to the solar array. A fine sun sensor is used in the event that one star tracker fails or during the backup stellar acquisition mode. In addition to these sensors, a gyro-compassing computation is performed for backup yaw attitude determination.
A reaction wheel assembly provides primary attitude control. During normal mode, a wheel speed controller is available to bias the wheel speeds at a range that avoids zero rpm crossings (stagnation point). Magnetic torquer rods regulate the wheel momentum to < 25% capacity in four-wheel mode and < 50% capacity in the three-wheel mode (backup mode). Thrusters are used for attitude control during all velocity change maneuvers and for backup attitude control and wheel momentum unloading.
GN&C is a fault-tolerant system that includes an FDIR (Fault Detection, Isolation and Recovery) capability unique to each of the different operational control modes. If an attitude fault is detected, FDIR transfers all control functions to the ACE unit configured to use all redundant hardware. Once in safe mode, FDIR is disabled.
Table 1: Overview of GN&C sensors and actuators
Figure 3: Artist' view of the Terra spacecraft in orbit (image credit: NASA)
The design life of the Terra spacecraft is six years. The spacecraft bus is of size of 6.8 m (length) x 3.5 m (diameter) and has a total launch mass of 5,190 kg. The total payload mass is 1155 kg.
RF communications: The primary Terra telemetry data transmissions are via TDRS (Tracking & Data Relay Satellite) system. A steerable HGA (High Gain Antenna) and associated electronics are mounted on a deployed boom extending from the zenith side of the spacecraft. This location maximizes the amount of time available for TDRS communications via this antenna without obstruction by other pads of the spacecraft. Emergency communication is done via the nadir or zenith omni antenna. Command and engineering telemetry data are transmitted in S-band. The science data recorded onboard are transmitted via Ku-band at 150 Mbit/s. The nominal mode of operation is to acquire two 12 minute TDRSS contacts per orbit. During each TDRSS contact, both S-band and Ku-band transmission is being used.
The average data rate of the payload is 18.545 Mbit/s (109 Mbit/s peak); onboard recorders for data collection of one orbit. Mission operations are performed at GSFC. 9)
Broadcast of data: Besides Ku-band and S-band communication, Terra is also capable of downlinking science data via X-band. The X-band communication can be operated in three different modes, Direct Broadcast (DB), Direct Downlink (DDL) and Direct Playback (DP). DB and DDL is used to directly transmit real-time MODIS and ASTER science data respectively to users.
The DAS (Direct Access System) provides a backup option for direct transmission in X-band. DAS supports transmission of data to ground stations of qualified EOS users around the world. These users fall into three categories:
- EOS team participants and interdisciplinary scientists
- International meteorological and environmental agencies
- International partners who require data from their EOS instruments
Figure 4: The Terra spacecraft in the cleanroom of LMMS at Valley Forge (image credit: LMMS)
Launch: The launch of the Terra spacecraft took place on Dec. 18, 1999 from VAFB, CA, on an Atlas-Centaur IIAS rocket.
Figure 5: Photo of the Terra satellite launch on 18 Decmber 1999 (6:57 UTC) from VAFB, CA (image credit: NASA)
Orbit: Sun-synchronous circular orbit, altitude = 705 km, inclination = 98.5º, period = 99 minutes (16 orbits per day, 233 orbit repeat cycles). The descending nodal crossing is at 10:30 AM.
Orbit determination is performed by TONS (TDRS Onboard Navigation System) which estimates Terra's position and velocity, drag coefficient, and master oscillator frequency bias. TONS is updated by Doppler measurements at the spacecraft's receivers and provides the attitude control software with a desired pointing ephemeris. Ground-based orbital elements are uplinked daily for backup navigation.
As of March 1, 2001, the Landsat-7, EO-1, SAC-C and Terra satellites are flying the so-called “morning constellation” or “morning train” (a loose formation demonstration of a single virtual platform). There is 1 minute separation between Landsat-7 and EO-1, a 15 minute separation between EO-1 and SAC-C, and a 1 minute separation between SAC-C and Terra. The objective is to compare coincident observations (imagery) from various instruments (synergistic effects). 10)
Figure 6: NASA's Terra mission at 10 years on-orbit (video credit: NASA)
• November 19, 2021: Terra's Orbital Drift 11)
Figure 7: In 2020, Terra completed its final inclination maneuver, using some of its limited fuel supply, to maintain that crossing time. Since that final inclination maneuver, Terra has continuously drifted to an earlier equatorial crossing time. To ensure Terra, with limited fuel supplies, is a safe distance from other missions in the Earth Observing Satellite constellation orbit, Terra will be lowered to a new orbit in 2022, where it will be able to collect valuable data at an even earlier crossing time. As Terra’s crossing time creeps earlier, small changes will be noticeable in the data and imagery collected by the instruments aboard Terra. The impact on science is expected to be minimal. In fact, some impacts could prove beneficial to some areas of research, like land morphology, surface temperature, and climate research (video credit: NASA's Goddard Space Flight Center/Scientific Visualization Studio, Liz Wilk, Kel Elkins)
Note: As of April 2022, the previously large Terra 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 Terra mission and its imagery in the period 2022, in addition to some of the mission milestones.
• Terra status and imagery in the period 2021-2020
Mission status and imagery for the period 2022
• May 12, 2022: The Red River Valley in Minnesota, North Dakota, and Manitoba is facing some of its worst flooding in a decade. An extreme spring blizzard, multiple rainstorms, and melting winter ice swelled the Red River of the North and its tributaries, driving them out of their banks and across a broad, flat floodplain. The deluge comes one year after the same region endured extreme drought. 12)
Figure 8: A blizzard, multiple rainstorms, and melting winter ice swelled rivers out of their banks and across a flat floodplain in Minnesota, North Dakota, and Manitoba. The false-color image was acquired with the MODIS instrument on NASA’s Terra satellite. This image shows the flooded valley as observed by Terra on May 10, 2022. The image combines shortwave infrared and visible light (MODIS bands 7-2-1) to better distinguish river water out of its banks (image credit: NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Michael Carlowicz)
- According to the U.S. National Weather Service, the water level on the Red River at Pembina, North Dakota (near the U.S.–Canada border) crested at 52.27 feet (15.93 m) on May 8; flood stage there is 39 feet (11.88 m). The Red River has mostly been dropping at Grand Forks, after cresting just below major flood stage last week. The Red River remained in major flood stage at Oslo, Minnesota: river gauges measured 36.09 feet on May 11, while flood stage is 26 feet. According to news reports, water managers in northeast North Dakota remain concerned about the 65-year-old Bourbanis Dam, which has been battered by weeks of high water.
- In Canada, at least 26 municipalities remain in states of emergency across southern Manitoba Province. Roads have been flooded on both sides of the international border, and some towns have been isolated by the high water. According to Canadian authorities, the Red River flood this year is already the sixth largest on record (by volume) at Emerson, Manitoba. Forecasters were calling for more rain in the region on May 12.
- The flow and topography of the Red River basin are unusual, leading to somewhat regular spring flooding. The river runs north from the Dakotas and Minnesota, through Manitoba, toward Hudson Bay. As a result, the upper reaches of the river (to the south) typically warm, thaw, and flow with spring meltwater and rain when channels to the north are still frozen or choked with ice. This can lead the river to slow or back up onto the floodplain.
- The river valley is also nearly flat, and it runs through a trough that was shaped by continental glaciers about 10,000 years ago. The elevation drop along the river from Fargo, North Dakota to the Canadian border is roughly 130 feet (40 meters). The minimal slope allows the river to meander across the landscape; meanwhile, the areas surrounding the trough are steeper and more rugged. The combination of steeper slopes on the edges and merging streams in the flat middle allows water to spread out and rise, while also slowing drainage.
Figure 9: This Aqua image was acquired on 11 May 2020 under more typical spring conditions (image credit: NASA Earth Observatory)
• April 4, 2022: Formed between 3.6 billion and 2.8 billion years ago, the rocks of the Pilbara Craton in Western Australia are some of the oldest on Earth. The iron-rich rocks here began forming before there was oxygen in Earth’s atmosphere or even life itself. The area also harbors evidence of some of the earliest life—3.45-billion-year-old fossil colonies of microbial cyanobacteria, the oldest known stromatolites on Earth. 13)
- The false-color image shows part of the Hamersley Basin in Western Australia, which lies on the southern Pilbara Craton. A craton is the stable, geologically inactive core of an ancient continent. The Pilbara Craton has remained intact, surviving the affronts of plate tectonics and erosion since the Archean Eon (4 billion to 2.5 billion years ago). The imagery of the Pilbara Craton reveals billions of years of the rich geologic history of Western Australia.
Figure 10: The image was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite on October 12, 2004. It is a composite of ASTER bands 4-2-1. These bands detect shortwave-infrared light, near-infrared and visible red light, and green light, which are displayed as red, green, and blue, respectively. In this display, iron-rich rocks appear yellow to green. Light-colored, iron-poor rocks appear white, while dark-colored iron-poor rocks are dark blue. Areas with more vegetation cover appear dark red. This is because plants reflect more near-infrared than green light. A linear contrast stretch has also been applied to the image to enhance the color contrast and help distinguish rock types (image credit: NASA Earth Observatory image by Joshua Stevens, using data from NASA/METI/AIST/Japan Space Systems, and the U.S./Japan ASTER Science Team. Story by Sara E. Pratt)
- During the Archean, and the Proterozoic Eon that followed, multiple cratons assembled to form the Australian continent, leaving multiple basins and belts of buckled and folded rocks at their margins. The main cratons that formed Western Australia are the Pilbara and Yilgarn. They began to assemble about 2.2 billion years ago during a mountain-building episode called the Capricorn Orogeny.
- The land that is today known as the Hamersley Basin was then at the bottom of an ocean lying between the two cratons. The rocks of the basin preserve a record of the last ocean environment in the area before the cratons converged and closed the basin.
- Atop the granite and greenstone rocks of the Pilbara Craton lie the younger rocks of the Fortescue, Hamersley, and Turee groups, which were deposited between 2.7 billion and 2.3 billion years ago. Together these rocks form the Mount Bruce Supergroup, which holds a singular place in Australia’s geologic history.
- According to the Geological Survey of Western Australia, not only do these rocks hold the best-preserved sequence of Archean volcanic rocks, but they also include the most continuous rock record of the transition from the Archean to the Proterozoic 2.5 billion years ago (including a record of the Great Oxidation Event). In addition, they are the most economically important ores on the Australian continent. These iron-rich rocks, including the world’s thickest and most extensive banded iron formations, form the basis of the iron-ore mining industry in the region.
- For example, in the top center of the image, the knob-shaped outcrop colored blue and green shows the rocks of the Hamersley Group—which includes four major banded-iron formations separated by sequences of iron-poor dolomites, shales, and volcanics.
- At the top left of the image, the white area shows the southeast portion of the Rocklea Dome, which is composed of light-colored granites. The dome is the remnant core of a plunging anticline—a buckled-up ridge that tilts down into the ground. Erosion of the fold’s surface exposed the dome’s granite core, which intruded into the surrounding rock during the Archaean Eon. The dome is also visibly crosscut with basalt intrusions. To the north, these rocks underlie the Hamersley Group, but here they are exposed at the surface.
- The rest of the image largely shows the area underlain by the volcanic and sedimentary rocks of the Fortescue Group. Much of this land is vegetated, mostly Spinifex grasses, shrubs, and bushes. The bottom of the image shows the town of Paraburdoo and its airport.
• April 2, 2022: Sea ice around Antarctica started to regrow after reaching the lowest extent ever observed in the satellite record in late February 2022. But on local scales, this transition from melting to freezing can display nuance. For example, near Land Glacier in West Antarctica, an area of old sea ice broke up as new ice formed in March. Around the same time, part of the glacier’s ice tongue crumbled away. 14)
- Michael Lowe, an analyst at the U.S. National Ice Center who pointed out the changes, has been closely watching this part of the Antarctic coastline, known as Marie Byrd Land. “I've had my eye on that area over the past two months as a large area of very old fast ice began to break apart,” Lowe said. “When comparing two SAR images from consecutive days I saw that the tip of the Land Glacier was starting to break up.”
Figure 11: The changes are also apparent in this pair of natural-color images acquired on February 24 and March 23, 2022, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites, respectively [image credit: NASA Earth Observatory images by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Kathryn Hansen with input from Christopher Shuman (UMBC/GSFC), Michael Lowe (USNIC), and Frazer Christie (U. Cambridge)]
- The February image displays a vast expanse of sea ice fastened to the edge of the coastline, and to the Land Glacier’s ice tongue and icebergs. Lowe explained that this “fast ice” often has a symbiotic relationship with glaciers and icebergs. “The glaciers and grounded bergs allow sea ice to accumulate and ‘fast’ in a stable fashion,” he said. “This fast ice then helps anchor those bergs and glaciers as it thickens into old ice over years.”
- But recent research using satellite observations showed that fast ice around parts of Antarctica, including off the coast of Marie Byrd Land, has been decreasing since MODIS records began around 2000. Still, a substantial patch remained at the time of the February image. By March, much of this old fast ice had broken apart.
Figure 12: MODIS image on NASA's Aqua satellite observed on 23 March 2022. In March 2022, old sea ice crumbled away as new ice formed off the coast of Antarctica’s Marie Byrd Land (image credit: NASA Earth Observatory)
- According to Frazer Christie, a glacier geophysicist at the Scott Polar Research Institute at the University of Cambridge, the loss of fast ice may have had further consequences. It is possible, he said, that the quick evacuation of fast ice between February and March, in addition to the longer-term losses, may have contributed to the rifting and ultimate calving of Land Glacier’s ice tongue.
- Christie points to a similar instance at the fast-flowing Totten Glacier in East Antarctica. There, losses of seasonal fast ice have caused the glacier’s front to speed up by as much as 100 meters per year. “An increasing body of research has begun to show the important role sea ice plays in congealing together and buttressing both ice tongues and ice shelves,” he said.
- Notice in the March image that the icebergs appear to be turning west into the direction of the remaining sea ice. Christie explained that the bergs are being carried along with the Antarctic Coastal Current, which flows westward around the continent parallel to the coastline. The Coriolis effect will also influence the bergs’ flow, deflecting them toward the left of their path.
- Iceberg calving is a natural process for glaciers that terminate in the ocean. “While Land Glacier has been observed to retreat, thin, and speed up in recent years, there is no evidence to suggest that its recent calving is related to anthropogenically forced climate change,” Christie said. “Instead, its behavior most likely reflects the natural calving lifecycle common to all Antarctic ice shelves and marine terminating glaciers.” The glacier last lost a similar amount of floating ice during the austral winter of 2004.
- Another stage in the natural lifecycle of sea ice is visible in the March image: the growth of new sea ice. The smooth streaks and swirls are “nilas”—young ice that often forms thin sheets, generally no more than 10 centimeters thick. (Note that the green-yellow tinge is largely an effect of low light and automatic color corrections.) New ice that appears streaky is lining up with the direction of surface winds; ice that displays a swirling pattern is likely being pushed around by winds and ocean circulation patterns, or “eddies.”
- As the next few winter and summer seasons come and go, scientists are curious to see what becomes of the glacier, icebergs, and sea ice off this part of Marie Byrd Land. Lowe added: “We’ll be watching to see if the bergs that broke off the Land Glacier ground and allow a new area of old fast ice to form over the next few years, restabilizing this area.”
• March 31, 2022: In March 2022, several large storms carried clouds of Saharan dust to Europe. One of them also brought long-lasting, high-altitude cirrus clouds infused with dust, which led to extensive cloud cover—from Iberia to the Arctic—for more than a week. It was an unusual type of storm that scientists have only recently come to understand. Called a dust-infused baroclinic storm (DIBS), its hallmarks are icy clouds permeated with dust. 15)
- In mid-March, an atmospheric river of Saharan dust was entrained by a DIBS and lifted into the troposphere, reaching altitudes up to 10 km (6 miles). The dust acted as nucleation particles for ice, leading to the formation of icy high-altitude, dust-infused cirrus clouds. They persisted for nearly a week and covered large parts of Europe and Asia.
Figure 13: In this image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite on March 17, 2022, the cloud tops exhibit a dimpled appearance. “We still don’t know why that happens,” Fromm said, “but it is peculiar to DIBS.” (image credit: NASA Earth Observatory images by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview, and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Sara E. Pratt)
- In March 2022, several large storms carried clouds of Saharan dust to Europe. One of them also brought long-lasting, high-altitude cirrus clouds infused with dust, which led to extensive cloud cover—from Iberia to the Arctic—for more than a week. It was an unusual type of storm that scientists have only recently come to understand. Called a dust-infused baroclinic storm (DIBS), its hallmarks are icy clouds permeated with dust.
- In mid-March, an atmospheric river of Saharan dust was entrained by a DIBS and lifted into the troposphere, reaching altitudes up to 10 kilometers (6 miles). The dust acted as nucleation particles for ice, leading to the formation of icy high-altitude, dust-infused cirrus clouds. They persisted for nearly a week and covered large parts of Europe and Asia.
- “Actually, two DIBS were formed,” said Mike Fromm, a meteorologist at the U.S. Naval Research Laboratory. “The fact that the dust river fed two separate DIBS makes this notable” as it is more common to see a single storm arise from an influx of dust.
- The first storm started on March 15, 2022, over north central Europe and spread from Poland, Czechia, and Austria south to the eastern Mediterranean. This was also unusual, Fromm said, as there is “usually a direct connection of a DIBS to its dry dust source, closer to the desert itself.”
- On March 16, a second storm followed the classic pattern, spinning up closer to the source of the dust in Africa. The large, widespread dust cloud continued moving north over Europe toward Scandinavia and the Arctic Ocean. It then moved east over northern Russia before taking an anticyclonic turn and curving back down into Eastern Europe and the Black Sea region on March 20.
- Analysis of the mid-March storms by Colin Seftor, an atmospheric scientist at NASA’s Goddard Space Flight Center, showed that much of the dust was circulating at the top of the cloud deck. “This means there is enough dust at the cloud tops to give the normally white clouds a dusty tinge, ergo the ‘infused’ part of the name,” Fromm said. “In the DIBS, the dust and storm cloud are one.”
- The high, dusty cloud layers produced by DIBS have been observed to travel around the world, Fromm said, and can sometimes be mistaken for volcanic ash that could affect flight paths. They have local effects as well. The dust that gets drawn up into them tends to linger after the clouds evaporate, Fromm added. Also, longer-lasting cirrus clouds can affect forecasts of temperature and precipitation.
- In late March, yet another large dust storm started making its way north carrying Saharan dust over the Mediterranean and Europe. Although the latest storm appears to be similarly large, it may not be as long-lasting, Seftor said. “Two large [storms] like this almost back-to-back is somewhat unusual, but the weather patterns over northern Africa and Europe during the spring seem to be more conducive to producing dust storms that reach Europe than at other times of the year.”
Figure 14: Long-lasting, icy cirrus clouds filled with Saharan dust covered many parts of the continent in March. The map shows a model of the dust movement on March 17 based on the Goddard Earth Observing System Model, Version 5 (GEOS-5), image credit: NASA Earth Observatory (image credit: NASA Earth Observatory)
• March 9, 2022: The Pilbara in northwestern Australia exposes some of the oldest rocks on Earth, over 3.6 billion years old. The iron-rich rocks formed before the presence of atmospheric oxygen, and life itself. Found upon these rocks are 3.45 billion-year-old fossil stromatolites, colonies of microbial cyanobacteria. The image, acquired in October 2004, is a composite of ASTER bands 4-2-1 displayed in RGB. 16)
- With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of about 50 to 300 feet (15 to 90 meters), ASTER images Earth to map and monitor the changing surface of our planet and is one of five Earth-observing instruments launched Dec. 18, 1999, on the Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and data products.
Figure 15: The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and temporal change. Example applications are monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance (image credit: NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team)
• March 1, 2022: The journey of every Antarctic iceberg is unique. Some drift many thousands of kilometers in the Southern Ocean before disintegrating and melting away. Others, like Iceberg B-22A, stay closer to home. In the span of 20 years, B-22A has strayed just 100 km (60 miles) from its birthplace, the floating ice tongue of Thwaites Glacier. 17)
Figure 16: These images, acquired with the MODIS instrument on NASA’s Terra satellite, show the iceberg around the time it broke from the shelf in March 2002 and two decades later in February 2022 (image credit: NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Kathryn Hansen with image interpretation by Christopher Shuman, NASA/UMBC)
- Notice the wide rift in the March 2002 image where the berg was detaching from the ice tongue. At the time that it broke away, Iceberg B-22 measured 85 km (53 miles) long and 64 km (40 miles) wide—about twice the size of Rhode Island. A few sizable pieces broke off from the berg, and the main piece was renamed B-22A. Two decades later, the berg still measures 71 km (44 miles) by 45 km (28 miles).
- After the initial break, the ice tongue accelerated and caught up to the drifting berg, giving it a push out to sea. But overall, B-22A has not moved far, as it is stuck or “grounded” in a relatively shallow part of the Amundsen Sea.
- Studies have shown that the grounded iceberg plays an important role in stabilizing sea ice in the area. In some years, a band of landfast sea ice has anchored to the iceberg and ice tongue. This landfast ice is thought to help buttress the Thwaites ice tongue and ice shelf, slowing the flow of ice toward the sea.
Figure 17: Terra image of B-22A on 2 February 2022. In the span of 20 years, Iceberg B-22A has strayed just 100 km from its birthplace at Thwaites Glacier (image credit: NASA Earth Observatory)
- Plenty of sea ice persisted in the area throughout the austral summer of 2022, but instead of landfast ice, it consisted primarily of broken sea ice and icebergs, or “mélange.” Scientists were sidetracked this season from an international project to study Thwaites Glacier because sea ice and icebergs blocked ships from accessing the ice shelf. A series of bergs—smaller than B-22A but larger than the pieces now breaking from modern-day Thwaites—are visible near the edge of the Crosson Ice Shelf, which spawned them.
- Though B-22A remains grounded, plenty has changed in the area since 2002. The ice tongue stopped advancing and has retreated substantially, as it continues to fracture and separate from the Thwaites Eastern Ice Shelf. And the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits. As Ted Scambos, a senior scientist at the University of Colorado, said in 2020: “What the satellites are showing us is a glacier coming apart at the seams.”
• February 5, 2022: After being soaked in mid-January 2022 by persistent, flooding rainstorms and Tropical Storm Ana, citizens of Madagascar are bracing for the arrival of another potent cyclone. Forecasters from the U.S. Joint Typhoon Warning Center suggest Cyclone Batsirai is likely to make landfall on February 5 in central Madagascar between Mahanoro and Mananjary as a category 2 storm. 18)
- The United Nations Office for the Coordination of Humanitarian Affairs estimated that 4.5 million people live within the projected path of the storm. Meteo Madagascar predicted 20 to 40 cm (8 to 16 inches) of rainfall and warned of the potential for widespread flooding in the east, southeast, and central highlands.
Figure 18: The MODIS instrument on NASA’s Terra satellite acquired a natural-color image of Cyclone Batsirai in the late morning on February 4, 2022. Around that time, Batsirai had sustained winds of 210 kilometers (130 miles) per hour, a category 4 storm. The storm brushed by Mauritius and Réunion, with strong winds in the outer bands of the storm knocking out electricity in some places (image credit: NASA Earth Observatory images by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview and GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Michael Carlowicz)
Figure 19: This map shows the total precipitable water vapor in the atmosphere at noon East Africa Time on February 4, 2022. The image was derived from the Goddard Earth Observing System 5 (GEOS-5) model, which uses satellite data and mathematical representations of physical processes to calculate what is happening in the atmosphere. Total precipitable water vapor is the depth of water in a column of the atmosphere if all the water vapor in that column were condensed into liquid. Not all precipitable water vapor necessarily falls as rain; nor is it a limit on the amount of rain that can fall. It is, however, a useful indicator of regions where rainfall could be excessive (image credit: NASA Earth Observatory)
- Jeff Masters, meteorologist and blogger, noted that Madagascar has been hit by a major tropical cyclone about once every three years. “The damage potential is higher than for previous storms of similar intensity,” he said, “because of the considerable deforestation Madagascar has experienced over the past 20 years.”
- Batsirai will be crossing over a landscape that has already been soaked and ravaged by damaging floods. A series of heavy rainstorms in mid-January were followed within a week by Tropical Storm Ana. Flooding and landslides killed at least 58 people and displaced more than 70,000.
- “Frequent cyclones during the agricultural season mean loss of harvest, high food prices, and increased food insecurity,” said Margaret Malu, deputy regional director for the UN World Food Programme. “The people of Southern Africa have been on the front lines of climate extremes for many years now and each passing storm sets them back, resetting the progress made.”
• February 4, 2022: In southeastern Québec lies one of the world’s largest and oldest impact craters. Manicouagan Crater was formed 214 million years ago, near the end of the Triassic Period, when an asteroid 5 kilometers (3 miles) wide struck what is now Canada. Today, the remnants of the crater are made visible by water and, sometimes, ice. 19)
Figure 20: These images of Manicouagan Lake were acquired by the MODIS instrument on NASA’s Terra satellite on January 20, 2022. A natural-color image of the frozen lake is compared with a false-color image of Figure 21 (image credit: NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Sara E. Pratt)
- Sometimes called the "Eye of Québec," the 1,940 km2 (750-square-mile) ring-shaped lake is readily identifiable from space. The unique shape makes it a popular feature in satellite imagery and a favorite subject of astronaut photography. Despite the crater’s ancient age, the events that gave rise to the lake coincided with the dawn of the Space Age.
- In the 1960s, Hydro-Québec constructed the Daniel-Johnson Dam — the largest multiple arch-and-buttress concrete dam in the world—on the Manicouagan River. Prior to the dam’s completion in 1968, two separate crescent-shaped lakes flanked the sides of the impact crater: Manicouagan Lake on the east and Mouchalagane (Mushalagan) Lake on the west. As the water levels rose over the next few years, the previously isolated water bodies joined to form the Manicouagan Reservoir, which finished filling in 1977.
Figure 21: In the false-color image, which uses MODIS bands 7-2-1, snow or ice appears electric blue and vegetation appears green. A blanket of snow covering the surrounding vegetation gives it a greenish-blue color (image credit: NASA Earth Observatory)
- Today, the reservoir reaches a depth of roughly 350 m and holds 140 km3 (34 cubic miles) of water, making it one of the largest freshwater reservoirs in the world. The outflow from the dam drains south into the Manicouagan River, which empties into the St. Lawrence River.
- After the river was impounded, water rising behind the dam encircled the higher land in the center of the impact crater; René-Levasseur Island was formed. The highest point on the island is Mount Babel, which rises 600 m (1,970 feet) above the lake level on its northern end.
- Mount Babel is the crater’s central peak, which formed in the aftermath of the impact when shattered rock and debris was uplifted. Geologists estimate that the crater was initially about 100 km (60 miles) wide. It has since been heavily eroded and scoured by ice sheets and today measures 72 km (45 miles) in diameter.
• January 28, 2022: Phytoplankton are sometimes called “the grass of the sea.” Like green plants on land, these floating, microscopic organisms play several key roles in making life on Earth possible. First, they are a source of food for zooplankton, shellfish, and marine creatures that eventually become food for other, larger creatures. They also produce a sizable amount of the oxygen in our oceans and atmosphere. And phytoplankton help remove carbon dioxide from Earth’s atmosphere, consuming it during photosynthesis and sinking it to the ocean depths in decaying cells and fecal matter from marine life (a phenomenon known as marine snow). 20)
Figure 22: In January 2022, the Atlantic Ocean off of South America was teeming with phytoplankton, as it does most austral summers. On January 24, the MODIS instrument on NASA’s Terra satellite acquired a natural-color image of blooms stretching across hundreds of kilometers (image credit: NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Michael Carlowicz)
Figure 23: This closeup was captured the same day (24 January) by the MODIS sensor on NASA’s Aqua satellite. MODIS sensors have been observing nearly continuous blooms in the area since the end of November (image credit: NASA Earth Observatory)
- It is not possible to detect specific species from space, but the aquamarine stripes and swirls are likely coccolithophores—phytoplankton with microscopic calcite shells that give water a chalky color. The various shades of green are probably diatoms, dinoflagellates, and related species. Ship-based studies have shown that Emiliania huxleyi coccolithophores and Prorocentrum sp. dinoflagellates tend to dominate in this region. Imagers planned for future satellite missions should make it easier to identify types of phytoplankton from space.
- The patches of color not only reveal the presence of phytoplankton, but also trace the edges of the dynamic eddies and currents that carry them. Off the coast of Argentina, Uruguay, and Brazil, warm currents from the tropics flow south and run into cooler currents flowing north from the Southern Ocean. They meet in a place known as the Brazil-Malvinas Confluence. At least seven different water masses of varying temperature, depth, and salinity arrive at this turbulent intersection, leading to vertical and horizontal mixing. With all of the churning—plus nutrient-rich outflows from rivers (such as Rio de la Plata) and windblown dust from Patagonia—this patch of ocean is incredibly productive and home to one of the richest fisheries in the world.
• January 17, 2022: Mid-winter in North America often brings blasts of cold wind blowing south from the Arctic or the Canadian interior. In addition to stirring up snowy weather and freezing the Great Lakes, the winds can create features that look like long white highways across the sky. 21)
- Cloud streets are parallel bands of cumulus clouds that form when frigid air near the surface blows over warmer waters, while a warmer air layer (a temperature inversion) rests over the top of both. The comparatively warm water gives up heat and moisture to the cold air, leading columns of heated air (thermals) to rise through the atmosphere.
- The warm air in the temperature inversion acts like a lid such that the moist, rising thermals hit the air mass above and roll over on themselves. This creates parallel horizontal cylinders of rotating air. On the upward side of the cylinders (rising air), the moisture cools and condenses into flat-bottomed, fluffy-topped cumulus clouds that line up parallel to the direction of the wind. Along the downward side (descending air), skies remain clear to make a cloudy-clear-cloudy striping pattern.
Figure 24: Winter winds can create long, thin cloud bands that stretch hundreds of kilometers across the sky. The MODIS instrument on NASA’s Terra satellite spied such an event over the Great Lakes on January 10, 2022. The image is a composite of natural color, shortwave infrared, and near infrared—a combo that helps distinguish snow and ice (blue/cyan) from clouds (white). The cloud streets that day stretched across hundreds of kilometers, mostly arising from Lake Superior and Lake Michigan (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Michael Carlowicz and Adam Voiland)
- Cloud streets are more common over the Great Lakes in the early part of winter, as the fresh water is still cooling down from summer and winter ice is starting to form. The cloud phenomenon also coincides sometimes with lake-effect snow downwind.
• January 7, 2022: Following three consecutive failed rainy seasons, more than 20 million people in eastern Africa now face some of the worst food security risks in 35 years. Climate and agriculture experts are advising governments and relief agencies to expect a significant need for food assistance in Somalia, Kenya, and Ethiopia. Climate change and ongoing La Niña conditions in the Pacific Ocean, half a world away, have contributed to the persistent dry weather and might bring more of it during the next rainy season. 22)
- The warnings come from the Famine Early Warning Systems Network (FEWS NET), a program supported by the U.S. Agency for International Development (USAID). FEWS NET assembles global and regional analyses of food security (particularly conditions for farming and livestock husbandry) to help governments and relief agencies plan for and respond to humanitarian crises. Several U.S agencies support FEWS NET; NASA provides satellite imagery and climate and weather data.
Figure 25: The map at the right shows anomalies in the Normalized Difference Vegetation Index (NDVI), a satellite-derived product used to assess crop conditions. NDVI measures the health, or “greenness,” of vegetation based on how much red and near-infrared light the leaves reflect. Healthy vegetation reflects more infrared light and less visible light than stressed vegetation. The map compares NDVI from December 2021 with the long-term average from 2000 to 2013. The data come from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite and the analysis comes from the USGS FEWS NET Data Portal [image credit: NASA Earth Observatory images by Joshua Stevens, using data from the Climate Hazards Center, the Famine Early Warning System Network (FEWS Net), and modified Copernicus Sentinel data (2021) processed by the European Space Agency courtesy of Josh Willis/NASA/JPL-Caltech. Story by Michael Carlowicz)]
- Tropical countries within the Horn of Africa tend to have two rainy seasons: the gu in March, April, and May, and the deyr in October, November, and December. The 2020 and 2021 deyr seasons were both substantially drier than normal, and the 2021 gu also came up short. Levels of precipitation have been the lowest on record in some areas; the Shabelle-Juba river basins have seen their lowest rainfall totals since 1981. Kenya and Somalia have declared drought emergencies; similar conditions have also prevailed in southern and eastern Ethiopia.
- “These back-to-back blows are hard for the farmers to take,” said Ashutosh Limaye, a scientist at NASA’s Marshall Space Flight Center and a close collaborator with the SERVIR Eastern and Southern Africa Hub (a NASA-USAID collaboration). “We are heading into a dry season, and the seasonal outlook does not look favorable either. The challenge is not just the soil moisture or the rainfall anomalies; it is the resilience of the population to drought.”
- In its December 2021 report, FEWS NET declared: “A poor March-May 2022 season would result in an unprecedented (since 1981) sequence of four below-normal rainfall seasons. ... Even if March-April-May rains are normal, the region will experience lingering long-term rainfall deficits.” Many areas in the Horn of Africa are expected to face “crisis” and “emergency” levels of food insecurity.
- The map of Figure 25 left shows precipitation anomalies for the 2021 deyr season, or how much rainfall was above or below average for the October through December period. Measurements come from the Climate Hazards Center Infrared Precipitation with Stations (CHIRPS) data set.
- The map of Figure 25 right shows anomalies in the Normalized Difference Vegetation Index (NDVI), a satellite-derived product used to assess crop conditions. NDVI measures the health, or “greenness,” of vegetation based on how much red and near-infrared light the leaves reflect. Healthy vegetation reflects more infrared light and less visible light than stressed vegetation. The map compares NDVI from December 2021 with the long-term average from 2000 to 2013. The data come from the MODIS instrument on NASA’s Terra satellite and the analysis comes from the USGS FEWS NET Data Portal.
- Successive rain shortfalls in eastern Africa have had a cumulative effect: smaller crop harvests; shortages of forage; depleted water supplies; and weakened and depleted livestock herds. The UN Food and Agriculture Organization reported that at least 60,000 animals have been lost to starvation, and milk production is 80 percent below average. Production of cereals during the 2021 deyr was reduced by 50 to 70 percent, while maize and sorghum production were down 15 to 25 percent in 2020 and 50 percent in 2021.
- Current soil moisture forecasts from the NASA Hydrologic Analysis and Forecast System (NHyFAS) indicate there could be further reductions in soil moisture in the common months. As the 2021 rainy season draws to a close, hot and dry air conditions and further drying soils, watering holes, and pasturelands.
- The dire agricultural conditions have been exacerbated by the COVID-19 pandemic and by violent regional conflicts. East Africans are simultaneously dealing with rising prices for commodities (locally and globally) and with the loss of income from failed harvests and depleted livestock. And the region still has not fully recovered from the losses of a deep drought in 2016-17.
- Scientists who study climate and weather teleconnections point to human-induced warming in the western Pacific and the ongoing La Niña as causes of the troubles in eastern Africa. The cooling of the eastern tropical Pacific and the warming of the western Pacific disrupts weather patterns all over the world. While rainfall increases substantially around Indonesia, the effect in eastern Africa is suppressed rainfall. With La Niña still dominating the conditions in the western Pacific—shown above in December 2021—and expected to persist through the first few months of 2022, food security researchers fear there may be another failed gu rainy season ahead.
- In their report, FEWS NET analysts wrote: “A long sequence like this is very rare, with the last possibly being nearly 40 years ago during 1983-84. Since 1983, the population of Kenya, Ethiopia, and Somalia has tripled, dramatically increasing the number of people exposed to drought hazards.”
- “Climate change, interacting with natural La Niña climate conditions, has increased the frequency of droughts in this region,” said Chris Funk, director of the Climate Hazards Center at the University of California, Santa Barbara. “But using the latest generation of climate models, we can now predict—and have predicted—many of the recent poor rainy seasons.”
- “Satellites tell us that the 2021 October-December season was similar to the disastrous 2010 season, and our forecast models are suggesting a high chance of a March-May 2022 season similar to 2011,” he added. “A poor March-May 2022 season would result in an unprecedented sequence of four below-normal rainfall seasons, which would further exacerbate the current humanitarian challenges.”
Figure 26: The MODIS instrument on NASA’s Terra satellite acquired this natural-color image of northeastern China on January 3, 2022. A pall of gray haze hangs over valleys and other low-lying areas, partially obscuring cities, farmland, lakes, and other features that would normally be more visible. The bright areas on the lower left of the image are clouds (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Adam Voiland)
- On the day that the image was acquired, several ground-based sensors in the region reported levels of fine particulate matter (PM2.5) in the very unhealthy and hazardous range, according to data published by The World Air Quality Project. That means PM2.5 levels were several times higher than the World Health Organization’s recommended limit of an average of 15 micrograms averaged over a day.
- Outbreaks of haze generally occur during the winter because of temperature inversions. Air normally cools with altitude, but during an inversion warm air settles above a layer of cool air near the surface. The warm air acts like a lid and traps pollutants near the surface, especially in basins and valleys. Common sources of pollution in the winter include coal and wood burning for heat, industrial activity, and vehicle emissions. Smoke from fires and dust storms can also contribute to poor air quality.
- One likely component of the haze in this image is nitrate particles. According to one recent analysis led by Harvard University researchers, levels of nitrates have remained stubbornly high over China in recent years even as emission controls have significantly reduced concentrations of other types of particles that contribute to PM2.5. “Nitrate is now the principal component of Beijing winter haze pollution, contributing to 30-40 percent of PM2.5M mass during winter haze days,” the authors wrote. “There is an urgent need to better understand why nitrate is not decreasing.”
- The storm blanketed the region with snow, closed schools, and snarled traffic.
- Some motorists were stranded overnight after accidents on Interstate 95 shut the highway down in both directions.
Figure 27: The MODIS instrument on NASA’s Terra satellite captured this image of the snow band on January 4, 2022. Parts of southern Virginia and southern Maryland saw some of the highest accumulations, with more than 14 inches (36 cm) falling in Spotsylvania, Stafford, and Calvert counties (image credit: NASA Earth Observatory image by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Adam Voiland)
• January 03, 2022: The English porcelain industry began with the 1745 discovery of kaolinite, or “china clay,” at Tregonning Hill, Cornwall. By the early 19th century, the Cornish deposits were the largest known to the world. By 1910, Cornwall was producing 50 percent of the world’s china clay. The mines produced a million metric tons of clay each year, exporting 75 percent of it. Domestically, the clay was used to produce Wedgwood, Spode, and Minton china. 25)
- Prior to the discovery of a U.K. source for the clay, the earthenware and stoneware made by the British pottery industry was prone to cracking, often when exposed to temperature changes. The addition of kaolinite produced porcelain that was both more delicate and more durable. Today, some of the U.K. deposits are still being mined, but many others have been abandoned in favor of other sources of clay, mainly from Brazil.
Figure 28: This image shows the clay pits northwest of St Austell. It was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite on September 10, 2014. Note that the image is synthetic natural color, combining several different spectral ranges to simulate the look of natural color. Some colors may appear slightly brighter than they would in an aerial photograph (image credit: NASA/METI/AIST/Japan Space Systems, and the U.S./Japan ASTER Science Team. Story by Sara E. Pratt)
- Clay mining left significant marks on the English landscape. Rain has since collected in many of the abandoned pits, forming ponds of various shades of blue (dependent on the amount of suspended clay minerals). Also, each ton of clay extracted from the ground resulted in multiple tons of waste products, which were piled in spoil tips. These pyramid-shaped mounds still dot the skyline and are sometimes called the Cornish Alps.
- Cornwall’s clay deposits owe their existence to the weathering and alteration of granites that are rich in feldspar and mica and low in iron minerals, giving the clay a white color desirable for porcelain. The granites formed when magma intruded into the crust about 280 million years ago during the assembly of the supercontinent Pangea. This process also produced the ores of tin, copper, lead, zinc, and tungsten that have made Cornwall a mining center for centuries.
- Much of the geology of southwestern England was deciphered in the late 1800s and early 1900s by William A.E. Ussher, a descendant of the Irish Archbishop James Ussher. The earlier Ussher is known for his dubious 1650 declaration, based on a biblical chronology, that Earth was roughly 6,000 years old, having been created on the morning of October 23, 4004 B.C.E.
- The Ussher Society, founded in 1962 to promote the study of geology and geomorphology in southwest England, was named after William Ussher to honor his contributions in establishing the stratigraphical succession of the rocks in Devon and Cornwall. He found that much of the rock was formed during the Devonian, Carboniferous, Permian, and Triassic periods between 420 million and 200 million years ago.
Terra Mission continued
Sensor complement: (ASTER, CERES (2 units), MISR, MODIS, MOPITT)
Table 2: Overview of major physical process measurements of the Terra instruments
ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer):
ASTER is a Japanese instrument sponsored by METI (Ministry of Economy, Trade and Industry) and a cooperative project with NASA. The ASTER team leaders are Hiroji Tsu of ERSDAC (Japan) and Anne B. Kahle of JPL. ASTER management is provided by JAROS (Japan Resources Observation System Organization). ASTER was built by NEC, MELCO, Fujitsu, and Hitachi. A Joint US/Japan Science Team is responsible for instrument design, calibration, and validation. Previous instrument name: ITIR (Intermediate Thermal Infrared Radiometer).
Objective: Provision of high-resolution and multispectral imagery of the Earth's surface and clouds for a better understanding of the physical processes that affect climate change. Applications: studies of the surface energy balance (surface brightness temperature), plant evaporation, vegetation and soil characteristics, hydrologic cycle, volcanic processes, etc. 26) 27) 28) 29) 30) 31)
The ASTER instrument consists of three separate instrument subsystems; each subsystem operates in a different spectral region, has its own telescope(s), and is built by a different Japanese company. The subsystems are in the VNIR (Visible Near Infrared), SWIR (Shortwave Infrared) and TIR (Thermal Infrared) spectral regions. The VNIR and SWIR subsystems employ pushbroom imaging while the TIR subsystem performes whiskbroom imaging. ASTER is pointable in the cross-track direction such that any point on the globe may be observed at least once within 16 days in all 14 bands and once every 5 days in the VNIR bands. The absolute temperature accuracy is 3K in the 200-240 K range, 2K in the 240-270 K range, and 2 k in the 340-370 K range for TIR bands.
Total instrument mass=421 kg; power=463 W average, 646 W peak; data rate = 8.3 Mbit/s average and 89.2 Mbit/s peak; thermal control by 80 K Stirling cycle coolers, heaters, cold plate/capillary pumped loop, and radiators; pointing accuracy: for control = 1 km on ground (all axes), knowledge= 342 m on ground (per axis), stability=2 pixels for 60 seconds. shown in this figure.
Table 3: ASTER instrument parameters of the three subsystems
The cooling capacity of the SWIR cryocooler is a nominal value of 1.2 W at 70 K; the measured power consumption is 43.5 W, which satisfies the requirement that it be less than 55 W. The cooling capacity of the TIR cryocooler is a nominal value of 1.2 W at 70 K; the measured power consumption is 50 W, which satisfies the requirement that it be less than 55 W. 32)
The VNIR subsystem, built by NEC Corporation, is a reflecting-refracting improved Schmidt design. VNIR features two telescopes, one nadir-looking with a three-spectral-band detector, and the other backward-looking with a single-band detector. The backward-looking telescope provides a second view of the target area in band 3B for stereo observations. Cross-track pointing is accomplished by rotating the entire telescope assembly. Band separation is through a combination of dichroic elements and interference filters that allow all three bands to view the same ground area simultaneously. Calibration of the nadir-pointing detectors is performed with two halogen lamps.
Table 4: Spectral range comparison of ASTER and TM (on Landsat)
The SWIR subsystem, built by MELCO (Mitsubishi Electric Company), uses a nadir-pointing aspheric refracting telescope. Cross-track pointing is accomplished by a pointing mirror. The size of the detector/filter combination requires a wide spacing of the detectors, causing in turn a parallax error of about 0.5 pixels per 900 m of elevation. This error is correctable if elevation data (DEM) are available. Two halogen lamps are used for calibration. The maximum data rate is 23 Mbit/s. 33)
The TIR subsystem employs a Newtonian catadioptric system with aspheric primary mirror and lenses for aberration correction. The telescope of the TIR subsystem is fixed to the platform, pointing and scanning is done with a single mirror. The line of sight can be pointed anywhere in the range ± 8.54º in the cross-track direction of nadir, allowing coverage of any point on Earth over the platform's 16 day repeat cycle. Each channel uses 10 mercury cadmium telluride (HgCdTe) detectors in a staggered array with optical bandpass filters over each detector element to define the spectral response. Each detector has its own pre- and post-amplifier for a total of 50. The detectors are being operated at 80 K using a mechanical split-cycle Stirling cooler. - In scanning mode, the mirror oscillates at about 7 Hz with data collection occurring over half the cycle. The scanning mirror is capable of rotating 180º from the nadir position to view an internal full-aperture reference surface, which can be heated to 340 K. 34)
Overview of some ASTER instrument characteristics:
• The Visible Near InfraRed (VNIR) telescope subsystem features a backward viewing band (next to a nadir viewing band) for high-resolution along-track stereoscopic observation (two-line VNIR imager)
• Provision of multispectral thermal infrared data of high spatial resolution (8 to 12 µm window region, globally)
• ASTER provides the highest spatial resolution surface spectral reflectance, temperature, and emissivity data within the Terra instrument suite
• The instrument provides the capability to schedule on-demand data acquisition requests
• The VNIR and SWIR subsystems employ pushbroom imaging while the TIR subsystem performes whiskbroom imaging
• ASTER provides band-to-band registration of the 14 spectral bands, not only within each subsystem, but also among the three subsystems. Accuracies of 0.2 pixels within each subsystem and 0.3 pixels among different subsystems are achieved.
Figure 29: Illustration of the VNIR and SWIR subsystems of ASTER (image credit: JPL)
Figure 30: Illustration of the TIR subsystem of ASTER (image credit: JPL)
CERES (Clouds and the Earth's Radiant Energy System):
The CERES instrument of NASA/LaRC was built by Northrop Grumman (formerly TRW Space and Technology Group) of Redondo Beach, CA (PI: Bruce Wielicki). Objective: Long-term measurement of the Earth's radiation budget and atmospheric radiation from the top of the atmosphere to the surface; provision of an accurate and self-consistent cloud and radiation database (input to WCRP international programs like TOGA, WOCE, and GEWEX). Retrieval of cloud parameters in terms of measured areal coverage, altitude, liquid water content, and shortwave and longwave optical depths. Specific science objectives are: 35) 36) 37) 38)
• For climate change analysis, provide a continuation of the ERBE record of radiative fluxes at the top of the atmosphere (TOA), analyzed using the same algorithms that produced the ERBE data.
• Double the accuracy of estimates of radiative fluxes at TOA and the Earth's surface.
• Provide the first long-term global estimates of the radiative fluxes within the Earth's atmosphere.
• Provide cloud property estimates that are consistent with the radiative fluxes from surface to TOA.
Figure 31: View of one CERES radiometer and location of instruments on the Terra spacecraft (image credit: NASA/LaRC)
Figure 32: Observation geometry of the CERES instruments on Terra (image credit: NASA/LaRC)
The CERES instrument assembly (of ERBE heritage) consists of a pair of broadband scanning radiometers (two identical instruments), referred to as FM-1 (Flight Module-1) and FM-2; one instrument operates in the cross-track mode for complete spatial coverage from limb to limb; the other one operates in a rotating scan plane (biaxial scanning) mode to provide angular sampling. The cross-track radiometer measurements are a continuation of the ERBS mission. The biaxially scanning radiometer provides angular flux information to improve model accuracy. A single cross-track CERES instrument is flown on TRMM (Tropical Rainfall Measuring Mission), while the dual-scanner instrument is flown on Terra (EOS/AM-1) and Aqua (EOS/PM-1).
The CERES instrument consists of three major subassemblies: 1) Cassegrain telescope, 2) baffle for stray light, and 3) detector assembly, consisting of an active and compensating element. Radiation enters the unit through the baffle, passes through the telescope and is imaged onto the IR detector. Uncooled infrared detection is employed.
Figure 33: Schematic view of the CERES instrument (image credit: NASA/LaRC)
Instrument parameters (2 identical scanners): total mass of 100 kg , power = 103 W (average, 2 instruments), data rate = 20 kbit/s, duty cycle = 100%, thermal control by heaters and radiators, pointing knowledge = 180 arcsec. The design life is six years. CERES measures longwave (LW) and shortwave (SW) infrared radiation using thermistor bolometers to determine the Earth's radiation budget. There are three spectral channels in each radiometer:
- VNIR+SWIR: 0.3 - 5.0 µm (also referred to as SW channel); measurement of reflected sunlight to an accuracy of 1%.
- Atmospheric window: 8.0 - 12.0 µm (also referred to as LW channel); measurement of Earth-emitted radiation, this includes coverage of water vapor
-Total channel radiance in the spectral range of 0.35 - 125 µm;. reflected or emitted infrared radiation of the Earth-atmosphere system, measurement accuracy of 0.3%.
Limb-to-limb scanning with a nadir IFOV (Instantaneous Field of View) of 14 mrad, FOV = ±78º cross-track, 360º azimuth. Spatial resolution = 10-20 km at nadir. Each channel consists of a precision thermistor-bolometer detector located in a Cassegrain telescope.
Instrument calibration: CERES is a very precisely calibrated radiometer. The instrument is measuring emitted and reflected radiative energy from the surface of the Earth and the atmosphere. A variety of independent methods used to verify calibration: 39)
• Internal calibration sources (blackbody, lamps)
• MAM (Mirror Attenuator Mosaic) solar diffuser plate. MAM is used to define in-orbit shifts or drifts in the sensor responses. The shortwave and total sensors are calibrated using the solar radiances reflected from the MAM's. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument FOV of the shortwave and total sensor units.
• 3-channel deep convective cloud test
- Use night-time 8-12 µm window to predict longwave radiation (LW): cloud < 205K
- Total - SW = LW vs Window predicted LW in daytime for same clouds <205K temperatures
• 3-channel day/night tropical ocean test
• Instrument calibration:
- Rotate scan plane to align scanning instruments TRMM, Terra during orbital crossings (Haeffelin: reached 0.1% LW, window, 0.5% SW 95% configuration in 6 weeks of orbital crossings of Terra and TRMM)
- FM-1 and FM-2 instruments on Terra at nadir
Table 5: CERES instrument parameters
The international CERES Science Team includes scientists from NASA, NOAA, US universities, France (CNRS), and Belgium (RMIB).
Data: A key element in the success of CERES, beyond the development of an instrument, is the development of data analysis and interpretation techniques for producing radiation and cloud products that meet the scientific objectives of the project.
MISR (Multi-angle Imaging SpectroRadiometer):
The MISR instrument was designed and developed by NASA/JPL (PI: D. J. Diner). Objective: provision of multiple-angle continuous sunlight coverage of the Earth with high spatial resolution (multidirectional observations of each scene within a time scale of minutes). MISR uses nine CCD pushbroom cameras to observe the Earth at nine discrete viewing angles: one at nadir, plus eight other symmetrical views at 26.1º, 45.6º, 60.0º, and 70.5º forward and aft of nadir. Images at each angle are obtained in four spectral bands centered at 0.446, 0.558, 0.672, and 0.866 µm. Each of the 36 instrument data channels (i.e. four spectral bands for each of the nine cameras) is individually commandable to provide ground sampling of 275 m, 550 m, or 1100 m. The swath is 360 km; multi-angle coverage (repeat cycle) of the entire Earth in nine days at the equator, and in two days at higher latitudes. By design, MISR is an along-track nine-line camera system, offering multidirectional observations of each ground (or target) scene. 40) 41) 42) 43)
Table 6: MISR as-built camera pointing specifications
Application: MISR provides global maps of planetary and surface albedo (brightness temperature), and aerosols and vegetation properties. Monitoring of global and regional trends in radiatively important optical properties (eg., opacity, single scattering albedo, and scattering phase function) of natural and anthropogenic aerosols.
Figure 34: A camera of the MISR instrument with support electronics (image credit: NASA/JPL)
Figure 35: Cut-away view of the MISR instrument (image credit: NASA/JPL)
MISR images are acquired in two observing modes: global and local. The global mode provides continuous planet-wide observations, with most channels operating at moderate resolution; some selected channels operate at the highest resolution for cloud screening and classification, image navigation, and stereo-photogrammetry. The local mode provides data at the highest resolution in all spectral bands and all cameras for selected 300 km x 300 km regions. In addition to data products providing radiometrically calibrated and geo-rectified images, global mode data will be used to generate two standard (level 2) science products: TOA (Top-of-Atmosphere)/Cloud Product and the Aerosol/Surface Product.
MISR on-orbit radiometric calibration is performed bi-monthly, using deployable white spectralon panels to reflect diffuse sunlight into the cameras, and a set of photodiodes to measure the reflected radiance. Additionally, vicarious calibrations using field and AirMISR data are done on six-month intervals. Geometric calibration of the cameras is done using ground control points.
Table 7: MISR instrument specification
Figure 36: Illustration of the MISR observing concept from Terra (image credit: NASA/JPL)
MODIS (Moderate-Resolution Imaging Spectroradiometer):
MODIS is a NASA/GSFC instrument; prime contractor is Raytheon SBRS, Goleta, CA, formerly Hughes SBRS (Science team leader: V. Salomonson); MODIS algorithm development by an international team of scientists from USA, UK, Australia, and France; there are four discipline groups: Atmosphere, Land, Oceans, and Calibration. 44) 45) 46) 47)
The instrument is flown on the Terra and Aqua satellites (prime instrument). Objective: to measure biological and physical processes on a global basis on time scales of 1 to 2 days. Specific science goals are:
• To determine surface temperature at 1 km resolution, day and night, with an absolute accuracy of 0.2 K for ocean and 1 K for land
• To obtain ocean color (ocean-leaving spectral radiance) from 415 to 653 nm
• To determine chlorophyll fluorescence within 50% at surface water concentrations of 0.5 mg per cubic meter of chlorophyll a
• To obtain chlorophyll a concentrations within 35%
• To obtain information on vegetation and land surface properties, land cover type, vegetation indices, and snow cover and snow reflectance
• To obtain cloud cover with 500 m resolution by day and 1000 m resolution at night
• To obtain cloud properties and aerosol properties
• To determine information on biomass burning
• To obtain global distribution of atmospheric stability and total precipitable water.
Figure 37: Artist's rendition of the MODIS instrument showing the 360º scan mirror (image credit: Hughes SBRS, NASA)
Figure 38: Schematic view of the MODIS instrument (image credit: Raytheon SBRS, NASA)
Table 8: Some specification parameters of the MODIS instrument
MODIS is an optomechanical imaging spectroradiometer (whiskbroom type), consisting of a cross-track scan mirror (continuously rotating double-sided scan mirror assembly) and collecting optics, and a set of linear detector arrays with spectral interference filters located in four focal planes. To accommodate frequent infrared calibration (every 1.47 s), a 360º rotating paddle-mirror is centered within a scan cavity to provide the optical subsystem with sequential views of the five calibrators and the Earth.
The optical arrangement provides imagery in 36 discrete bands between 0.4 and 14.5 µm (21 bands within 0.4-3.0 µm range, 15 bands within 3-14.5 µm range). The spectral bands provide a spatial resolution of 250 m, 500 m, and at 1 km at nadir. MODIS heritage: AVHRR (POES), HIRS (POES), TM (Landsat), CZCS (Nimbus-7). In fact, the MODIS instrument is considered to be a next-generation AVHRR instrument, having 36 bands (AVHRR/3 has 6) and a spatial resolution of 250 m (AVHRR has 1 km).
A high-performance passive radiative cooler provides cooling to 83 K for the infrared bands on two HgCdTe FPAs (Focal Plane Assemblies). A new photodiode-silicon readout technology for the VNIR range provides unsurpassed quantum efficiency and low-noise readout with a very good dynamic range.
Figure 39: Functional architecture of the MODIS instrument (image credit: Raytheon SBRS)
Figure 40: Major elements of the MODIS instrument (image credit: NASA)
MODIS polarization sensitivity < 2% for the visible range out to 2.2 µm; the performance goal for SNR (Signal-to-Noise Ratio) and NEΔT (Noise-Equivalent Temperature Difference) values is 30-40% better than the required values in Table 9.; absolute irradiance accuracy of 5% for <3 µm and 1% for >3 µm; absolute temperature accuracy of 0.2 K for oceans and 1 K for land; daylight reflection and day/night emission spectral imaging; swath width of 2330 km at 110º FOV; scan rate = 20.3 rpm across track; instrument mass = 250 kg; duty cycle = 100%; power = 225 W (average); data rate = 6.2 Mbit/s (average), 10.6 Mbit/s (peak daytime), 3.2 Mbit/s (night); quantization = 12 bit. Instrument IFOV (spatial resolution) = 250 m (bands 1-2), =500 m (bands 3-7), = 1000 m (bands 8-36).
The observations are made at three spatial resolutions (nadir): 0.25 km for bands 1-2 with 40 detectors per band, 0.5 km for bands 3-7 with 20 detectors per band, and 1 km for bands 8-36 with 10 detectors per band. All the detectors, aligned in the along-track direction, are distributed on four focal plane assemblies (FPAs) according to their wavelengths: visible (VIS), near infrared (NIR), short- and mid-wave infrared (SMIR), and long-wave infrared (LWIR).
Table 9: MODIS spectral performance parameters
• Spectroradiometric Calibration Assembly (SRCA)
- Spectral calibration of reflective channel channel bandpasses
- Verification of spectral band registration
- DC restoration on every scan using a direct view of space
- Lunar calibration via the space-view port as well as periodic rotations of the S/C to enable full scans across the moon through the active scan aperture
• Blackbody (BB) calibration of thermal bands on every scan (a v-groove blackbody)
• Solar Diffuser (SD) reference
• Solar Diffuser Stability Monitor (SDSM)
The spectral mode of the SRCA device consists of a light source, a grating monochromator, and a beam collimator. The light source is a SIS (Spectral Integration Sphere) with lamps distributed inside. By combining the use of the spectral filters mounted on the filter wheel assembly and the grating monochromator, the SRCA is capable of performing spectral characterizations of the RSB (Reflective Solar Bands) ranging from 0.41 to 2.2 µm. Its spectral calibration is referenced to the ground equipment (SpMA) with high accuracy.
Figure 41: Schematic view of the SRCA device (image credit: NASA/GSFC)
The SD/SDSM system is used for the RSB calibration and BB for the TEB (Thermal Emissive Bands) calibration. The SRCA is primarily used for the sensor's spectral (RSB only) and spatial (TEB and RSB) characterization. The RSB calibration is reflectance based using a sensor’s view of diffusely reflected sunlight from a solar diffuser (SD) plate with a known bi-directional reflectance and distribution function (BRDF). Because of the solar exposure onto the SD plate, its reflectance properties slowly degrade on-orbit.
The Blackbody is located in front of and slightly above the Scan Mirror, which views the BB with every revolution. The BB assembly provides a full-aperture radiometric calibration source of the MWIR and LWIR bands to within 1 percent absolute accuracy. It provides known radiance levels and is also used in the DC restore operation (a space-view signal level provides the second level for all bands in the two-point calibration). In normal operation the BB is kept at the instrument’s ambient temperature (nominally 273 K), though it is possible to heat and control the BB to 315K. Twelve sensors below the assembly's surface monitor its temperature. Each sensor is calibrated to National Institute of Standards & Technology (NIST) traceable standards, and can determine the temperature of the assembly to within ± 0.1 K.
Figure 42: View of the BB assembly (image credit: NASA/GSFC)
To maintain the calibration and data quality, a solar diffuser stability monitor (SDSM) is used in tandem with the SD to track its degradation or BRDF changes. The SDSM system has a small integration sphere (SIS) with a single input aperture and nine filtered detectors. Each filter has a narrow spectral bandpass so that the change in reflectance is effectively monitored at nine discrete wavelengths between 0.4 µm and 1.0 µm. A three-position fold mirror enables the detectors to view sequentially a dark scene, direct sunlight, and illumination from the SD (Solar Diffuser). The direct sunlight is attenuated via a two-percent transmitting screen to keep the radiance within the dynamic range of the SDSM’s detector/amplifier combination.
Figure 43: The MODIS SD device (image credit: NASA/GSFC)
Figure 44: The SDSM device (image credit: NASA/GSFC)
MODIS product overview: MODIS provides global coverage every 1 to 2 days. It provides specific global survey data, which includes the following (some standard data products):
• Cloud mask: at 250 m and 1 km resolution by day and at night
• Aerosol concentration and optical properties: at 5 km resolution over oceans and 10 km over land during the day
• Cloud properties: characterized by optical thickness, effective particle radius, cloud droplet phase, cloud-top altitude, cloud-top temperature
• Vegetation and land-surface cover, conditions, and productivity, defined as:
- Vegetation indices corrected for atmospheric effects, soil, polarization, and directional effects
- Surface reflectance
- Land-cover type with identification and detection of change
- Net primary productivity, leaf-area index, and intercepted photosynthetically active radiation
• Snow and sea-ice cover and reflectance
• Surface temperature with 1 km resolution, day and night, with absolute accuracy goals of 0.3-0.5ºC for oceans and 1ºC for land surfaces.
• Ocean color: defined as ocean-leaving spectral radiance within 5% from 415-653 nm, based on adequate atmospheric correction from NIR sensor channels
• Concentration of chlorophyll-a within 35% from 0.05 to 50 mg/m3 for case 1 waters
• Chlorophyll fluorescence within 50% at surface water concentrations of 0.5 mg/m3 of chlorophyll-a.
MOPITT (Measurement of Pollution in the Troposphere):
MOPITT is a Canadian sensor supported by CSA, built by COM DEV, Cambridge, Ontario (PI: J. R. Drummond, University of Toronto). The MOPITT instrument design is of MAPS (Measurements of Air Pollution from Space) heritage, flown on STS-2 (November 12.-14, 1981), then on STS-13 (October 5 -13, 1984), and then twice in 1994 (STS-59, STS-68). MOPITT is the first satellite sensor to use gas correlation spectroscopy (A technique to increase the sensitivity of the instrument to the gas of interest by separating out the regions of the spectrum where the gas has absorption lines and integrating the signal from just those regions. The specific wavelengths are located using a sample of the gas as a reference for the spectrum). By using correlation cells of differing pressures, some height resolution can be obtained. Thus MOPITT has multiple channels to provide height resolution, it also carries multiple channels to afford some redundancy. Definitions of acronyms in Table 10: LMC (Length Modulator Cell), PMC (Pressure Modulator Cell). 52) 53) 54) 55) 56) 57) 58) 59)
The CO profile measurements are made using upwelling thermal radiance in the 4.6 µm fundamental band. The troposphere is resolved into about four layers with approximately 3 km vertical resolution, 22 km horizontal resolution and 10% accuracy. Pressure Modulated Cells (PMCs) are used to view the upper layers whilst Length Modulated Cells (LMCs) are used for the lower troposphere measurements. By varying the cell pressures the modulators can be biased to view the different layers.
The MOPITT instrument contains four optical chains initiated by four scan mechanisms, which are split into eight independent channels. Each channel uses a technique known as correlation spectroscopy to perform the science measurements. This uses a sample of gas in the optical path. By performing synchronous demodulation of the detected infrared signal, the system functions as a complex filter, providing very good spectral resolution and good sensitivity by incorporating several molecular lines simultaneously.
Figure 45: Isometric optical system layout of the MOPITT instrument (image credit: University of Toronto)
Figure 46: Schematic illustration of the MOPITT instrument (image credit: University of Toronto)
Figure 47: Schematic view of the correlation radiometry concept (image credit: NCAR, University of Toronto)
Figure 48: Photograph showing the finished PMC for MOPITT (image credit: Oxford Physics)
Table 10: Channel definition of MOPITT
The instrument measures emitted and reflected infrared radiance in the atmospheric column. Analysis of these data permit retrieval of tropospheric CO profiles and total column CH4. Objective: study of how these gases interact with the surface, ocean, and biomass systems (distribution, transport, sources and sinks). Measurements are performed on the principle of correlation spectroscopy utilizing both pressure-modulated and length-modulated gas cells, with detectors at 2.3, 2.4, and 4.7 µm. Vertical profile of CO (carbon monoxide) and total column of CH4 (methane) are to be measured; CO concentration in 4 km layers with an accuracy of 10%; CH4 column abundance accuracy is 1%.
Swath width = 616 km, spatial resolution = 22 x 22 km; instrument mass = 182 kg; power = 243 W; duty cycle = 100%; data rate = 25 kbit/s; thermal control by an 80 K Stirling cycle cooler, capillary-pumped cold plate and passive radiation; thermal operating range = 25º C (instrument) and 100 K (detectors).
MOPITT is designed as a scanning instrument. IFOV = 1.8º x 1.8º (22 km x 22 km at nadir). The instrument scan line consists of 29 pixels, each at 1.8º increments. The maximum scan angle is 26.1º off-axis which is equivalent to a swath width of 640 km. - MOPITT data products include gridded retrievals of CH4 with a horizontal resolution of 22 km and a precision of 1%. Gridded CO soundings are retrieved with 10% accuracy in three vertical layers between 0 and 15 km. Three-dimensional maps to model global tropospheric chemistry.
The instrument is self-calibrating in orbit and performs a zero measurement every 120 seconds and a reference measurement every 660 seconds. The instrument operation is practically autonomous, requiring very little commanding to keep it within the mission profile at all times. 60)
Figure 49: View of the MOPITT instrument (image credit: COM DEV)
MOPITT operations: MOPITT has suffered two anomalies since launch. On May 7, 2001 one of the two Stirling cycle coolers, which are used to keep the detectors at about 80 K, failed. The cooler fault compromised half of the instrument. After the fault, only channels 5, 6, 7, and 8 are delivering useful data. On Aug. 4, 2001 chopper 3 failed. Fortunately, it stopped in the completely open state, which permits to continue to use the data by adjusting the data processing algorithm accordingly.
EOS (Earth Observing System)
EOS is the centerpiece of NASA's Earth Science Enterprise (ESE). It consists of a science component and a data system supporting a coordinated series of polar-orbiting and low inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans. 61) 62) 63) 64)
Background: The EOS program is a NASA initiative of the US Global Change Research Program (USGCRP). Planning for EOS began in the early 1980s, and an AO (Announcement of Opportunity) for the selection of instruments and science teams was issued in 1988. Early in 1990 NASA announced the selection of 30 instruments to be developed for EOS. Major budget constraints imposed by the US Congress forced the EOS program into a restructuring process in the time frame of 1991-92. In addition a rescoping of the EOS program occurred in 1992 leading to just half of the 1990 budget allocation (the HIRIS sensor was eliminated). The instruments adopted as part of the restructured/rescoped EOS program were chosen to address the key scientific issues associated with global climate change. This action reduced the required instruments to 17 that needed to fly by the year 2002 (six were deferred and seven instruments were deselected from the original 30). Furthermore, a shift occurred in the conceptual design of the EOS satellite platforms from “large observatories” to intermediate and smaller spacecraft that may be launched by smaller and existing launch vehicles. The EOS program experienced a further rebaselining process in 1994, due to a budget reduction of about 9%. This resulted in the cancellation of the combined EOS Radar and Laser Altimeter Mission (but rephasing the latter as two separate missions), deferring the development of some sensors and spreading the launch of missions by increasing the basic re-flight periods of missions from 5 to 6 years, and flying some EOS instruments on missions of partner space agencies (NASDA, RKA, CNES, ESA) in a framework of international cooperation. The EOS program includes instruments provided by international partners (ASTER, MOPITT, HSB, OMI) as well as an instrument developed by a joint US/UK partnership (HIRDLS).
The overall goal of the EOS program is to determine the extent, causes, and regional consequences of global climate change. The following science and policy priorities are defined for EOS observations (established by the EOS investigators working group and in coordination with the national and international Earth science community):
• Water and Energy Cycles: Cloud formation, dissipation, and radiative properties which influence the response of the atmosphere to greenhouse forcing, large-scale hydrology, evaporation
• Oceans: Exchange of energy, water, and chemicals between the ocean and atmosphere, and between the upper layers of the ocean and the deep ocean (including sea ice and formation of bottom water)
• Chemistry of the Troposphere and Lower Stratosphere: Links to the hydrologic cycle and ecosystems, transformations of greenhouse gases in the atmosphere, and interactions including climate change
• Land-Surface Hydrology and Ecosystem Processes: Improved estimates of runoff over the land surface and into the oceans. Sources and sinks of greenhouse gases. Exchange of moisture and energy between the land surface and the atmosphere. Changes in land cover
• Glaciers and Polar Ice Sheets: Predictions of sea level and global water balance
• Chemistry of the Middle and Upper Stratosphere: Chemical reactions, solar-atmosphere relations, and sources and sinks of radiatively important gases
• Solid Earth: Volcanoes and their role in climate change.
The original EOS mission elements (AM S/C series, PM S/C series, Chemistry S/C series) was redefined again in 1999. The EOS program space segment elements are now: Landsat-7, QuikSCAT, Terra, ACRIMSat, Aqua, Aura and ICESat.
Table 11: Specification of Direct Broadcast (DB) service of Terra and Aqua satellites
EOS policy includes providing Direct Broadcast (DB) service to the user community; this applies to real-time MODIS data from the Terra spacecraft, as well as to the entire real-time data stream of the Aqua satellite. These data may be received by anyone with the appropriate receiving station, without charge. The broadcast data are transmitted in X-band. A 3 m antenna dish (minimum) should be sufficient for X-band data reception.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).
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