Aqua Mission (EOS/PM-1)
The Aqua mission is a part of the NASA's international Earth Observing System (EOS). Aqua was formerly named EOS/PM-1, signifying its afternoon equatorial crossing time. NASA renamed the EOS/PM-1 satellite to Aqua on Oct. 18, 1999. The Aqua mission is part of NASA's ESE (Earth Science Enterprise) program. 1) 2) 3)
The focus of the Aqua mission is the multi-disciplinary study of the Earth's water cycle, including the interrelated processes (atmosphere, oceans, and land surface) and their relationship to Earth system changes. The data sets of Aqua provide information on cloud formation, precipitation, and radiative properties, air-sea fluxes of energy, carbon, and moisture (AIRS, AMSU, AMSR-E, HSB, CERES, MODIS); and sea ice concentrations and extents (AMSR-E).
The Aqua spacecraft is based on TRW's modular, standardized AB1200 bus design (also referred to as T-330 platform) with common subsystems (Note: Northrop Grumman purchased TRW in Dec. 2002). The satellite dimensions are: 2.68 m x 2.47 m x 6.49 m (stowed) and 4.81 m x 16.70 m x 8.04 m (deployed). Aqua is three-axis stabilized, with a total mass of 2,934 kg at launch, S/C mass of 1,750 kg, payload mass =1,082 kg, propellant mass = 102 kg; power = 4.86 kW (EOL). Propulsion: hydrazine blow-down system; 4 pairs of thrusters. The design life is six years.
RF communications: X-band, S-band (TDRSS and Deep Space Network/Ground Network compatible). All communications are based on CCSDS protocols. Like the Terra mission, Aqua provides various means of payload data downlinks, among them Direct Broadcast (DB).
Figure 2: The Aqua spacecraft in launch preparation at VAFB (image credit: NASA)
Launch: The Aqua spacecraft was launched on May 4, 2002 with a Delta-2 7920-10L vehicle from VAFB, CA. Aqua is the second satellite in NASA's series of EOS spacecraft. - Aura, the third of the three large satellites in the EOS series, was launched in July 2004 and is lined up behind Aqua, in the same orbit.
Orbit: Sun-synchronous circular orbit, altitude = 705 km (nominal), inclination = 98.2º, local equator crossing at 13:30 (1:30 PM) on ascending node, period = 98.8 minutes, the repeat cycle is 16 days (233 orbits).
The Aqua spacecraft is part of the “A-train” (Aqua in the lead and Aura at the tail, the nominal separation between Aqua and Aura is about 15 minutes) or “afternoon constellation” (a loose formation flight which started sometime after the Aura launch July 15, 2004). The objective is to coordinate observations and to provide a coincident set of data on aerosol and cloud properties, radiative fluxes and atmospheric state essential for accurate quantification of aerosol and cloud radiative effects.
The PARASOL spacecraft of CNES (launch on Dec. 18, 2004) is part of the A-train as of February 2005. The OCO mission (launch in 2009) will be the newest member of the A-train. Once completed, the A-train will be led by OCO, followed by Aqua, then CloudSat, CALIPSO, PARASOL, and, in the rear, Aura. 4)
Note: The OCO (Orbiting Carbon Observatory) spacecraft experienced a launch failure on Feb. 24, 2009 - hence, it is not part of the A-train.
Figure 3: Illustration of Aqua in the A-train (image credit: NASA)
Figure 4: Anintroduction to Aqua (video credit: NASA)
Note: As of 12 March 2020, the previously single large Aqua file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the Aqua mission and its imagery in the period 2020
Mission status and sample imagery
• June 24, 2020: Eastern Siberia is famous for some of the coldest wintertime temperatures in the Northern Hemisphere. But in 2020, it has been the region’s wildly high temperatures and wildfires that have wowed meteorologists. 5)
- After several months of warm weather, the Russian town of Verkhoyansk reported a daytime temperature of 38°C (100.4°F) on June 20—likely a record high for the town. (The previous high was 37.3°C, recorded on July 25, 1988.) If verified, this will be the northernmost temperature reading above 100°F ever observed and the highest temperature on record in the Arctic, according to the Capital Weather Gang.
- “This event seems very anomalous in the last hundred years or so,” said NASA Goddard Institute for Space Studies Director Gavin Schmidt. “The background trends in temperature in this region are about 3 degrees Celsius since the 19th century, so the probabilities of breaking records there are increasing fast.”
- Note that the map depicts land surface temperatures (LSTs), not air temperatures. LSTs reflect how hot the surface of the Earth would feel to the touch and can sometimes be significantly hotter or cooler than air temperatures. — To learn more about land surface temperatures and air temperatures, read: Where is the Hottest Place on Earth?
Figure 5: This map shows land surface temperature anomalies from March 19 to June 20, 2020. Red colors depict areas that were hotter than average for the same period from 2003-2018; blues were colder than average. The map is based on data from the MODIS instrument on NASA’s Aqua satellite (image credit: NASA Earth Observatory images by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE), and data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi NPP. Story by Adam Voiland)
- In a report about the remarkably warm temperatures in Siberia, European scientists examined historical temperature data in their global ERA5 reanalysis, finding that temperatures have been unusually warm in the region since January 2020. Since the ERA5 data begins in 1979, the European team also looked to GISTEMP, a NASA temperature record with data through 1880. They could not find any other examples in either dataset of such an intense heat wave in this part of Siberia persisting for such an extended period.
- The persistent high-pressure atmospheric pattern that brought the extreme heat has exacerbated wildfires, prompting dozens to burn in the region’s forest and shrub ecosystems. Some of those ecosystems grow on top of carbon-rich layers of peat and permafrost. The natural-color image below shows smoke streaming from several active wildfires in Russia's Sakha region.
- “Most of Earth’s terrestrial carbon is stored in the upper latitudes of the northern hemisphere,” explained Amber Soja, a NASA scientist who has conducted field research in the region. Soja noted that many forests in the region are dominated by a coniferous tree—Dahurian larch—that drops its needles each winter. “But because the winters are so cold, there are few decomposers around to break the needles down. Over time, you end up with lots of buried fuel that has built up over centuries, even millennia, and stores huge quantities of carbon in peat and soils.”
- Intense heat waves can thaw the permafrost layer and make long-frozen deposits susceptible to fires, which move carbon from the ground to the atmosphere and contribute to global concentrations of greenhouse gases. “In this part of Siberia, the signs of climate change are already here. It’s not some distant future. It’s now,” she said. “The heat and fires this year are just adding more evidence to the climate change signal that we have seen in these forests for years.”
- Though it is still early in the fire season, satellite observations of active fires by NASA and NOAA’s MODIS and VIIRS sensors show the number of fire detections to be among the highest observed in any year since 2003. “Over the Russian Far East, there has been about the same amount of fire as last year, another very active year,” said NASA and Columbia University scientist Robert Field. “Both 2020 and 2019 were about twice the 2003–2020 average, and about half as much as 2011, the most active year.”
Figure 6: Fires are raging in eastern Siberia in the midst of an unusually long-lived heat wave. This image was acquired on 23 June 2020 (image credit: NASA Earth Observatory)
• June 9, 2020: As ships cruise across the ocean, they emit a large number of small airborne particles—aerosols—into the lower atmosphere. Under the right conditions, these exhaust particles cause long, thin cloud patterns referred to as “ship tracks.” For decades, scientists have theorized that these cloud changes might alter climate by affecting the amount of sunlight reaching Earth’s surface. 6)
- Now, for the first time, researchers have measured exactly how ship emissions affect clouds at a regional scale. University of Washington scientist Michael Diamond and colleagues examined more than a decade of cloud patterns over a busy shipping lane in the southeast Atlantic that connects Europe to southern Africa and Asia.
- The team measured the cloud properties inside the shipping corridor using satellite data and compared them to what they estimated the values would be without shipping activity. The scientists found that the shipping activity increased the number of cloud droplets over the shipping lane. They further showed that those clouds prevented about 2 Watts of solar energy from reaching each square meter of ocean surface along the shipping lane. The team’s results agreed with previous computer modeling studies that predicted a sizeable cooling effect due to shipping.
- “If you look at a satellite image of a high-traffic shipping area, when the weather conditions are right, you can clearly see bright lines of clouds right along where those ships are traveling and emitting aerosols,” said Diamond, an atmospheric scientist. ”Ship tracks are a prime example of how tiny particles of pollution in the atmosphere can influence cloud properties. The clearly visible ship tracks are only the tip of the iceberg, however, so our study looked at how shipping could affect cloud properties on average over a long time period.“
Figure 7: The natural-color image shows an example of ship tracks over the southeast Atlantic Ocean as observed on January 18, 2018, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite (image credit: NASA Earth Observatory, image by Lauren Dauphin using MODIS image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response. Story by Kasha Patel)
Figure 8: The maps show the average cloud droplet concentrations from 2003 to 2015 during the cloudiest months for the region (September, October, and November). The map on the left shows the cloud droplet concentrations observed by MODIS on NASA’s Aqua and Terra satellites. The map on the right shows the expected cloud droplet concentrations without shipping activity. The expected values were calculated based on statistical patterns from nearby, unpolluted areas. The team then calculated the difference in the amount of sunlight reflected back into space between the two scenarios. The team used data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) instruments, which monitor the solar energy reflected by Earth and the heat energy emitted by the planet (NASA Earth Observatory, image by Lauren Dauphin, using data from Michael Diamond, et al. (2020). Story by Kasha Patel)
- Diamond explained that the aerosols from the ships create “seeds” in the atmosphere that water vapor can latch onto and condense into small cloud droplets. These smaller droplets make clouds brighter so that they reflect more sunlight, which creates a local cooling effect at the planet’s surface.
- That change is small on a regional scale, but it could be enough to affect global temperatures if the same phenomenon occurs worldwide, according to study co-author Hannah Director of the University of Washington. When the team scaled their findings across the planet, they found that changes in low-lying clouds from all industrial pollution sources could block about 1 Watt of energy per square meter globally. For context, greenhouse gases from industrial activities have trapped roughly 3 Watts per square meter so far.
- “Cloud changes caused by industrial pollution have produced a global cooling effect that is about one-third as strong as the warming from increased greenhouse gases,” said Diamond.
- Diamond explains that even though these ship emissions have a short-term cooling effect, they create other issues. Pollutants from ship exhaust have detrimental effects on human health, while also adding carbon dioxide to the atmosphere.
- The algorithms developed for this study could be applied to study other anthropogenic sources of pollution around the world. “We can use a similar methodology to determine the effects of other human sources of aerosols like power plants,” said Diamond. “We could model the world with and without various human activities and better understand our impact on Earth's climate.”
• May 28,2020: Spend time on China’s Hainan Island, and chances are good that you will witness a lightning storm. Hainan and neighboring Guangdong province have the highest density of cloud-to-ground flashes and the most lightning related casualties in the country. 7)
Figure 9: This image was acquired at 2 p.m. China Standard Time (06:00 Universal Time) on May 11, 2020, with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite (image credit: NASA Earth Observatory, images by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE, Story by Kathryn Hansen)
Figure 10: The time-series animation shows the growth of the clouds over the course of the day, as observed by Japan’s Himawari-8 satellite (image credit: NASA Earth Observatory, using GIBS/Worldview and Natural-color animation based on Himawari imagery, courtesy of the Japan Meteorological Agency)
- “It’s definitely a cumulonimbus cloud,” said Paul Markowski, a professor of meteorology at Pennsylvania State University. “And it’s sitting over the highest terrain in the center of the island.”
- The south-central part of the island is mountainous, with elevations of more than 1800 m (5,900 feet) surrounded by plains extending to the island’s northeast. The rugged topography creates orographic lift: when air moves across the plains and encounters the mountains, it is forced upward. So, when moist ocean air moves from low to high elevations, it cools and condenses into clouds.
- The terrain enhances the convection. But even if the island were completely flat, cumulonimbus could still develop, as the collision of air masses also forces air upward. Starting in the morning, the Sun quickly heats up the land and warms the air above it. The warm air rises it leaves behind a pocket of low pressure. Air within high pressure areas over the ocean moves in to fill the void, producing an onshore wind known as a “sea breeze.”
- As the cool, moist air from over the South China Sea moves toward the island’s interior, it can collide with warm air along the sea breeze front. The cool air forces the less dense warm air to rapidly rise, producing the vertical towers of clouds. Convection can be particularly intense in areas where sea breezes from opposite sides of the island ultimately collide.
- The whole process takes time, which explains why the storm clouds tend to develop in the afternoon. For example, similar clouds show up in the afternoon of May 10. In contrast, images from the mornings of May 10 and May 11 show cumulus-free skies.
• May 09, 2020: Almost like clockwork, the right conditions develop in different parts of the world and vibrant blooms of phytoplankton color the oceans. Spring and summer, for example, are common times to see blooms in places like the North Sea or off the Alaskan coast. In a bay off the coast of northwest Africa, however, conditions are almost always just right. 8)
- The color of Figure 11 is due to a combination of phytoplankton and sediments. Physical samples collected in recent decades off Mauritania have turned up large numbers of diatoms, a type of microscopic algae with silica shells and plenty of chlorophyll. They are one of the most common types of phytoplankton in the ocean.
- Diatoms tend to thrive in waters that are rich in nutrients. They often show up after strong storms mix the ocean layers and bring up nutrients from the depths. (In contrast, a type of phytoplankton called coccolithophores can flourish in the more layered, or “stratified” waters common during summer and autumn.)
- But the waters off Mauritania don’t need storms to mix. Trade winds constantly displace the surface water—blowing it west and away from the African coast—which is then replaced by cold, nutrient-rich waters from below (a process known as “upwelling”). The sediments here are especially rich with iron from Saharan dust.
- While the upwelling off Mauritania is constant, it is strongest in March and October. It is part of the Canary Upwelling System, one of the main upwelling systems that occur along the eastern edges of the planet’s ocean basins. Other such systems show up off of southern Africa (Benguela), Chile and Peru (Humboldt), and the United States (California). These areas are known to be among the most biologically productive regions of the planet’s oceans.
Figure 11: The MODIS instrument on NASA’s Aqua satellite acquired this image of colorful surface waters off of Mauritania on May 5, 2020. Scrolling through satellite images of the area reveals that there is nothing particularly unique about the May 5 image; the tongue of green water is present constantly throughout the year (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kathryn Hansen, with image interpretation by Oscar Romero and Gerhard Fischer/University of Bremen, and Violeta Sanjuan Calzado/NASA GSFC)
• April 29, 2020: For much of March and April 2020, satellites have detected signatures of heat and smoke from fires burning in northwestern Venezuela. Some of them burned in and near Ciénagas del Catatumbo National Park, a flat swampy area west of Lake Maracaibo known for its rainforests full of unusual plant and animal life. 9)
- Throughout March, satellites detected short-lived fires in the northwestern state of Zulia—likely crop or other small-scale fires. But in mid-March a larger, smokier, and more sustained fire cluster emerged in the park in a forested area west of the lake.
Figure 12: On March 27, 2020, the MODIS instrument on NASA’s Aqua satellite acquired an image of a sizable smoke plume over the park. Places where the sensor detected unusually warm temperatures—signs of fires—are shown with red. As seen in the image of Figure 13, the fire was still smoldering in late-April (image credit: NASA Earth Observatory, images by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview)
- It is not clear what triggered the fire, but Venezuela is in the midst of an ongoing drought. Recent observations from the Gravity Recovery and Climate Experiment Follow On (GRACE-FO) satellites show stark deficits in soil moisture and shallow groundwater in Zulia. The dry weather may be exacerbating Zulia’s normal fire season, which typically runs from January to April in MODIS records of active fire data.
- The state’s 2020 fire season is registering as one of the most active in the MODIS record since 2003, according to data analyzed by Robert Field, a scientist at Columbia University and NASA’s Goddard Institute for Space Studies. Satellites observations also show that nearby mountain ranges have been channeling smoke southwest toward the city of Cucuta, noted Jean-Paul Vernier of NASA’s Earth applied sciences disasters program.
• April 16, 2020: Severe storms with high winds ripped through much of the southern and eastern United States in mid-April, with tornado warnings stretching from Florida to Virginia. More than a dozen tornadoes were confirmed in Mississippi, including one on April 12, 2020, that scarred the landscape to such a degree that it could be seen from space. 10)
Figure 14: The scar is visible in this natural-color image, acquired on April 14, 2020, with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. It shows where the tornado uprooted vegetation and spread debris along a path nearly 70 miles long from Jefferson Davis County to Clarke County in the southeast part in the state of Mississippi. Preliminary reports from the National Weather Service indicate that the storm was an EF4—the second-highest intensity on the Enhanced Fujita scale (image credit: NASA Earth Observatory images by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview, and the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE). Story by Kathryn Hansen)
Figure 15: The signature of the scar is also apparent in this image, which shows land surface temperature data also acquired by Aqua MODIS. Damaged areas appear warmer than the surrounding landscape because bare ground heats up faster than vegetated areas (A similar phenomenon was observed in 2018 in the damage associated with hail storms), image credit: NASA Earth Observatory
- Other tornados also marked the landscape in the area, although the scars appear more subtle in satellite images. For example, an EF3 tornado tracked for nearly 83 miles from Lawrence to Jasper counties in southeast Mississippi. According to news reports, the deadly outbreak of storms left tens of thousands of people in the state without power and destroyed hundreds of homes.
• April 9, 2020: In early April 2020, satellites observed several wildfires in northern Ukraine around the Chernobyl Exclusion Zone. Hundreds of firefighters and at least eight airborne units were working to extinguish fires in the Denysovets, Kotovsky, and Korogodsky forests. 11)
- Officials have been fighting fires in the exclusion zone since April 4, 2020. As of April 9, police evacuated residents from the village of Poliske, which is located within the zone.
- The soils and forests of the exclusion zone, which spans about 2,600 km2 (1,000 square miles), were contaminated in 1986 by radioactive fallout from the Chernobyl nuclear accident. Fires in the exclusion zone are not uncommon, but the severity and intensity of the fires has grown over the years as more forests and grasslands have recovered. Research has also shown that fires in heavily contaminated areas can resuspend radioactive elements in smoke plumes that then get carried across long distances.
- On April 5, officials tested the air in Kiev and nearby suburbs for radioactivity, but they did not report finding any man-made contamination. As of April 9, the State Emergency Service of Ukraine reported that background radiation levels continue to be within the normal range around Kiev. Additionally, no spikes in radiation have been reported in Belarus.
Figure 16: The natural-color image shows the fires on April 9, as observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. Forecasts called for winds to blow the plumes of smoke toward the Chernihiv region and the border with Belarus (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kasha Patel)
• March 26, 2020: Spring has arrived in Central Asia. And over the Aral Sea, that means there is dust in the air. The shrinking of this once-vast inland lake means winds more frequently pick up dust from the exposed lakebed. 12)
Figure 17: On March 24, 2020, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image of a dust storm over the once-vast inland lake. Much of the dust appeared to be coming from the Aralkum Desert, which has emerged as the Aral Sea has dried in recent decades. Dried lake beds are abundant sources of atmospheric dust because they are filled with light, fine-grained sediment that winds can easily lift (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Adam Voiland)
- Scientists use satellites to track when and where winds transport the most dust. One analysis of nearly a decade of data from the NASA’s Aura satellite found that dust transport from the Aral Sea peaks in the spring (March-May) and early winter (November-January). In the spring, northeasterly and southwesterly winds often prevail, with 42 percent of dust plumes blowing to the north, 32 percent to the south, and 26 percent to the west.
Figure 18: The Aral Sea has been shrinking since the 1960s, when the former Soviet Union undertook a major water diversion project on the arid plains of Kazakhstan, Uzbekistan, and Turkmenistan and diverted river water for crops that otherwise would have poured into the Aral Sea. As the lake dried, river runoff enriched the increasingly salty water with fertilizers and pesticides. As a result, the salty dust that blows from the exposed lake bed poses public health hazards and can degrade the fertility of soils in the surrounding area (video credit: NASA Earth Observatory)
• March 18, 2020: As observed during previous years in Southeast Asia, large numbers of seasonal agricultural fires and wildfires are creating clouds of smoke over northern Thailand and Burma (Myanmar). The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this natural-color image (Figure 19) on March 18, 2020. 13)
Figure 19: The haze and smoke has resulted in unhealthy levels of air pollution, particularly in Chiang Mai in northern Thailand, which has had the most polluted air in the world several times this month (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Text by Kasha Patel)
• March 12, 2020: Over the past few decades, the bison population in Yellowstone National Park has grown substantially. Some of that is due to longstanding conservation efforts, but some of it is also due to a greater abundance of food for the animals to graze on. A new study by a NASA scientist has found a link between the effects of climate change, the productivity of grasslands, and the proliferation of bison in Yellowstone. 14)
- Using 20 years of data from NASA’s Aqua and Terra satellites, earth scientist Christopher Potter examined the length of the growing season in Yellowstone—from snowmelt in springtime to the first snowfall in autumn—and the health and abundance of vegetation during that time. He found that the annual period of vegetation growth has been getting longer, likely due to the decreasing severity of winters and warming average temperatures (year-round) as a result of climate change.
- The National Park Service first approached NASA about ten years ago for insight into patterns of growth across Yellowstone’s grasslands. They thought tracking such growth could provide wildlife managers with clues about where bison and other animals might move. Potter became part of that effort.
- As the new research shows, the grass-growing season is getting longer and bison have more opportunities to feed, likely fueling their population growth. But as they follow the development of new and better grazing spots, they become more likely to leave the protected areas of the park. This creates challenges for the Park Service because bison can carry brucellosis, a bacterial disease that can spread among other wild species and domesticated livestock. Getting regular updates on grassland growth patterns can help wildlife managers better predict the movements of the bison herds.
- Scientists also see national parks as natural laboratories for climate research because land use is restricted, so the fingerprints of climate change are easier to detect than in settled areas. A decade ago, there was enough satellite data to make some projections about vegetation growth and animal movements, but not enough to draw conclusions about climate effects. Now the 20-year record allows for deeper insights about Yellowstone.
- MODIS instruments acquire images across nearly the entire surface of Earth every day. For his study, Potter compiled cloud-free images of Yellowstone across 20 years and also developed tools to make maps of vegetation and snow cover. Wildlife managers can check such maps to anticipate where and when confrontations between bison and human communities are likely to happen and to prepare appropriate conservation actions at the park boundaries.
- “By compiling daily satellite data, we created a near-real-time online tool that resource managers can consult much like a weather map,” said Potter, who is based at NASA’s Ames Research Center. “MODIS is the silver bullet for these large-scale wilderness situations, where daily updates make all the difference in planning a response.”
Figure 20: A new study has found a link between the effects of climate change, the productivity of grasslands, and the proliferation of bison in Yellowstone National Park. The map depicts one aspect of that change: how the end of the growing season fluctuated around Yellowstone National Park between 2001 and 2017. The map is based on measurements of vegetation greenness, the NDVI (Normalized Difference Vegetation Index), as observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on Aqua and Terra (image credit: NASA Earth Observatory image by Joshua Stevens, using data from Potter, C. (2020). Story by Abby Tabor, NASA Ames Research Center, and Mike Carlowicz)
• March 9, 2020: It is not every day that a textbook high-pressure system, cold front, and warm front all reveal themselves on the same natural-color satellite image. But that is exactly what NASA research meteorologist Galina Wind recently noticed over the Eastern United States as she was browsing old satellite imagery. 15)
- On weather maps, the center of a high is generally marked with a blue H. “But in natural-color satellite images, you usually see clear skies because the downward movement of the air is strong enough to prevent any convective clouds from rising up as the Sun heats the surface,” explained Wind. “In this case, the descending air was weak enough that some fair-weather cumulus clouds were able to bubble up anyway.”
- The cold front, marked with blue triangles on a weather map, is visible here as a curving line of clouds with intense convection running through Minnesota, Iowa, Missouri, Kansas, and Oklahoma. While highs generally lead to sunny, calm conditions, cold fronts often produce turbulent, unsettled skies.
- “If you have ever seen a snowplow going at full speed, you will have a sense of how cold fronts work,” said Wind. “Cold air is heavier than warm air, so it literally shoves warm air up in front and over it.” As the displaced, warmer air rises and cools, water vapor condenses, yielding clouds, rain, and often thunderstorms.
Figure 21: This image is a mosaic based on data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite and the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP on September 12, 2019. In the Southeast, thin rows of cumulus clouds trace the location of the high, with the center of circulation near Mississippi. High pressure systems typically have cool, descending air flow in their centers and winds that move in a clockwise direction in the Northern Hemisphere (image credit: NASA Earth Observatory, images by Joshua Stevens, using GOES-16 data from the NOAA-NASA GOES-R Mission, and MODIS and VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi National Polar-orbiting Partnership. Story by Adam Voiland)
Figure 22: This video, based on imagery from the Advanced Baseline Imager (ABI) on GOES 16 (GOES-East), shows how the weather system developed between 7 a.m. and 3 p.m. on September 12. The images were taken at 5 minute intervals (video credit: NASA Earth Observatory, using GOES-16 data from the NOAA-NASA GOES-R Mission)
- As storm clouds bubbled up around the cold front, clouds swirled in a counter-clockwise direction around an area of low-pressure centered on South Dakota. East of the cold front, notice how the winds circulating around the high-pressure area flowed in the opposite direction. Though clouds in the high were generally small, look for the larger, deeper clouds that developed as air was forced upward by the Appalachian Mountains.
- “Conditions can become quite fierce along cold fronts,” said Wind, noting that false-color imagery of the cold front does a particularly good job of highlighting the deep convection and thunderstorms that developed along it. (For instance, the pinks in this false-color view of the cold front show clouds that have grown tall enough for water droplets to turn into ice particles.)
- The warm front, normally shown with red half circles on a weather map, is marked here by the wide band of clouds through Minnesota, Wisconsin, and Michigan. “Warm front events are much calmer. They are basically just layers and layers of clouds,” said Wind. “Sometimes warm fronts can produce drizzle, but they generally come and go as gently as a lamb.”
- However, the leading wave of clouds that precedes a warm front can often indicate that more serious weather may be on the way. “If it is a clear, sunny day and you suddenly notice the arrival of large numbers of thin, feathery cirrus clouds, that is a clue that the weather could be changing soon,” said Wind.
• February 18, 2020: Scientists previously established that the world is greener than it was in the early 1980s. Updated maps show that the trend has continued, and researchers say reduced global warming is among the consequences. 16)
Figure 23: This map shows where greenness increased (green) and decreased (brown) across the planet between 2000 and 2018. Specifically, it shows the trend in the “leaf area index”—the amount of leaf area relative to ground area—during the growing season. The index is computed using data from the MODIS instrument on NASA’s Terra and Aqua satellites. White areas are where the land is barren, built upon, or covered with ice, wetlands, or water (image credit: NASA Earth Observatory, image by Joshua Stevens, using data from Shilong, P., et al. (2020). Story by Kathryn Hansen)
- Note that the map does not show overall greenness, which is why it does not exactly match heavily forested areas like the Amazon or the Congo Basin. Instead, the map shows how greenness has changed —a phenomenon most obvious in places like China and India where agriculture has intensified and governments have made efforts to conserve and expand forests.
- There is a clear greening trend in boreal and Arctic regions, a result of rising temperatures. For example, Svalbard in the high-Arctic has seen a 30 percent increase in greenness, according to Rama Nemani of NASA’s Ames Research Center, a co-author of the review paper in Nature Reviews Earth & Environment. The greening was concurrent with an increase in mean summer temperature from 2.9° to 4.7° Celsius (37.2° to 40.5° Fahrenheit) between 1986 and 2015.
- The paper’s authors reviewed more than 250 published articles that have used satellite data, modeling, and field observations, to understand the causes and consequences of global greening. Among the key results, the authors noted that on a global scale greening can be attributed to the increase of carbon dioxide in the atmosphere. Rising levels of carbon dioxide increase the rate of photosynthesis and growth in plants.
- There is an interesting consequence of this global green up: as vegetation consumes some of the heat-trapping carbon dioxide it also performs evapotranspiration—a function similar to human sweating—which can have a cooling effect on the air. Scientists say that global greening since the early 1980s may have reduced global warming by as much as 0.2° to 0.25° Celsius (0.36° to 0.45° Fahrenheit). In other words, the world would be even warmer than it is if not for the surge in plant growth.
- “It is ironic that the very same carbon emissions responsible for harmful changes to climate are also fertilizing plant growth,” said co-author Jarle Bjerke of the Norwegian Institute for Nature Research, “which in turn is somewhat moderating global warming.”
- According to climate models, the future looks even greener. The map of Figure 24 shows what the green-up might look like in the future based on the Coupled Model Intercomparison Project (CMIP5) climate model, under a scenario in which increases in greenhouse gases lead to almost 5° Celsius (9° Fahrenheit) of warming by the end of the 21st century. Specifically, it shows the predicted change in the growing season’s “leaf area index” from 2081-2100 relative to 1981-2000.
Figure 25: This chart shows the predicted changes by latitude. Notice that high latitudes in the Northern Hemisphere are still expected to change the most (image credit: NASA Earth Observatory, image by Joshua Stevens, using data from Shilong, P., et al. (2020). Story by Kathryn Hansen)
• January 29, 2020: There is plenty of plant-like life around Antarctica; you just have to know when and where to look. During the austral spring and summer, coastal waters sometimes swirl with vibrant green color—the surface expression of a huge phytoplankton bloom. 17)
Figure 26: Off the coast of Antarctica, vibrant green phytoplankton swirls amidst the sea ice. The floating, microscopic plant-like organisms were abundant in Terra Nova Bay and McMurdo Sound on January 21, 2020, when the MODIS instrument on NASA’s Aqua satellite acquired this image. Such colorful swirls in coastal waters are sometimes caused by sediments stirred up by waves and currents. But scientists say the source of the color this month has a biological origin (image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Text by Kathryn Hansen)
- “It is definitely a phytoplankton bloom,” said Kevin Arrigo, a biological oceanographer at Stanford University. “They tend to form every year in Terra Nova Bay around January.” Robert Dunbar, a fellow researcher at Stanford, agrees that the color is a phytoplankton bloom. “These kinds of features are common in Antarctica’s coastal polynyas in summer and late summer.”
- Polynyas are areas where winds sustain a persistent opening in the sea ice. Sunlight and near-surface nutrients are plentiful in these areas, making them havens for phytoplankton. Blooms can even occur in polynyas in late summer when the water is covered by thin, new frazil crystals and pancake ice. Research by Dunbar and colleagues has shown that late summer blooms can accumulate in this ice and turn it green. The phenomenon—most widespread in February and March—is visible in the photograph of Figure 27, shot by Dunbar in 2018.
• January 21,2020: Among the most useful and longest-lived dust-monitoring sensors in space today is the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites. Terra MODIS has collected more than 20 years of dust data; Aqua MODIS has observed for 18 years. 18)
Figure 28: Changing winds and more vegetation are probably contributing to the trend. The image was acquired on 22 March 2019 with MODIS on Aqua (image credit: NASA Earth Observatory, image by Joshua Stevens, story by Adam Voiland)
- “Two decades is long enough to look for meaningful trends in atmospheric dust,” said NASA atmospheric scientist Hongbin Yu. In a new study in Atmospheric Chemistry and Physics, Yu and colleagues detailed their efforts to do just that. “We looked at the world’s six major dust outflow regions. We found lots of year-to-year variability, but in most areas we did not see obvious increases or decreases in dust. The one exception was the area we defined as the northwestern Pacific. In other words, the dust that blows east from deserts in western China and Mongolia, such as the Taklamakan and Gobi deserts.” 19)
Figure 29: In this area, dust activity has declined since the early 2000s. Over the course of the MODIS record, the researchers found a 1.5 percent decrease in the atmospheric dust detected by the sensor each year. “More detailed analysis showed that the trend was due to changes in the spring—March, April, and May,” said Yu. “Trends were negligible in other seasons.”(image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi National Polar-orbiting Partnership, and data courtesy of Hongbin Yu, et al. (2020). Story by Adam Voiland)
- In this area, dust activity has declined since the early 2000s. Over the course of the MODIS record, the researchers found a 1.5 percent decrease in the atmospheric dust detected by the sensor each year. “More detailed analysis showed that the trend was due to changes in the spring—March, April, and May,” said Yu. “Trends were negligible in other seasons.”
- Scientists using other sensors and analysis techniques have noted the same pattern. Ground-based lidars in Japan detected a 4.3 percent decrease in spring dust. A team of Chinese scientists analyzed data from ground-based weather stations and an atmospheric model and concluded that spring dust storm frequency in arid and semiarid regions of China had decreased by 15 storms per year on average over a period of 25 years.
- Several research teams have addressed the obvious question: why? “There are three main factors that people have looked at: changes in winds, changes in vegetation cover, and changes in soil moisture,” said Yu. Changes in wind speeds, as well as wind shear, can affect how much dust winds can pick up. The presence of vegetation reduces how much dust winds can lift. And winds more easily lift dust from drier surfaces than wetter ones.
- “I haven’t personally tested which of these is the most important,” said Yu. “Based on what I have seen in the scientific literature, it is likely that a combination of all three is contributing to the decline.”
- For instance, some research shows a weakening in the polar vortex over the past few decades, a change that would limit the number of cold fronts (which elevate dust) and reduce maximum wind speeds of storm systems. Several studies also show increases in green vegetation and forests, likely due to global warming, reforestation projects, and efforts to prevent overgrazing.
• January 17, 2020: Afternoon storms are a typical phenomenon during summertime in Australia. They are a reminder that everyday natural events can be strikingly beautiful. 20)
- According to Bastiaan Van Diedenhoven, a researcher for Columbia University and NASA’s Goddard Institute for Space Studies, the cloud is a cumulonimbus—a type capable of producing thunderstorms and heavy rain.
- “Afternoon storms form often in the Austral summer as the land heats up, leading the air to rise and condense into clouds,” Van Diedenhoven said. “The storm looks very round from the top probably because there’s not much wind shear. When the top reaches its highest point near the tropopause, its top will expand horizontally.”
- While clouds like this are normal, they don’t turn up too often in MODIS or VIIRS imagery. The clouds usually grow large later in the afternoon, after the satellites have passed over and acquired their once-a-day imagery. Satellites with a geostationary orbit—giving a constant view of an area—can more easily capture full weather events. Watch the cumulonimbus evolve in this animation of images from Japan’s Himawari-8 satellite.
- Earlier in the week, thunderstorms had developed as a result Tropical Cyclone Claudia, which spun off the coast of Western Australia. And to the east, areas that previously saw thunderstorms triggered by the bush fires are now seeing the more typical type of thunderstorms, providing much-needed rain to the area.
- The cumulonimbus of Figure 30, however, was likely just a typical summer storm. Van Diedenhoven noted: “The cyclone or the fires should have nothing to do with it.”
Figure 30: These images show the evolution of a storm over Western Australia on January 14, 2020. Morning skies appear clear in the left image, acquired around 11 a.m. local time. The storm starts growing in the afternoon at about 1 p.m. (middle) and even larger an hour later (right image). The natural-color images were acquired (from left to right) with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite; MODIS on NASA’s Aqua satellite, and the Visible Infrared Imaging Radiometer Suite (VIIRS) on the NOAA-NASA Suomi NPP satellite (image credit: NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview and VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview and the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
• January 9, 2020: Satellite observations show how far winds normally spread North African dust particles before rain and gravity pull them down to the ocean. — Individual particles of dust are small and easy to ignore, but on a grand scale, atmospheric dust directly affects all of us, and the planet, in many ways. 21)
- Particles of dust are typically comprised of metal oxides, clays, and carbonates. They most often accumulate in low-lying desert basins, often dried rivers or lakes. When winds lift particles up, they can spread across thousands of miles, circling the planet and fertilizing key parts of oceans and rainforests with critical nutrients, notably iron. They also can spread diseases, trigger asthma and other respiratory health problems, and darken skies so much that they cause traffic accidents and problems for pilots.
- One of the most difficult to study—but far reaching—effects of dust is its influence on weather and climate. Dust particles can change air temperatures by blocking light, influence where clouds form and how they behave, and affect whether hurricanes or other types of storms break out. By fertilizing the sea, dust also helps influence the size and frequency of blooms of carbon dioxide-consuming phytoplankton, which could play a role in dialing global temperatures up or down.
- North Africa is the largest source of atmospheric dust in the world by far. “It has the key ingredients: plenty of strong winds, sediment piled up in basins, dry weather, and little vegetation,” explained NASA atmospheric scientist Hongbin Yu, noting the El Djouf region in Mauritania and Mali and the Bodélé Depression in northern Chad are the sources of much of the dust.
- Notice the seasonality in the distribution of dust. In December and January, strong northeasterly winds—the Harmattan—from West Africa carry dust southwestward, putting the highest concentrations over the Gulf of Guinea, and extending dust plumes west toward South America. Over the course of the year, as wind patterns and the location of the Intertropical Convergence Zone (ITCZ) shift, the most concentrated dust band moves north. From June through August, particles stream from West Africa toward the Caribbean.
- “Measuring the distribution of atmospheric dust is just the first piece of our research,” said Yu, who has been using satellites and other tools to study dust and other aerosol particles for two decades. “In order to understand the effect African dust has on the ocean, we have to determine how much dust gets removed from the atmosphere by rainfall.” That is where other NASA satellite sensors, like the Multi-angle Imaging SpectroRadiometer (MISR) on Terra and the lidar on the CALIPSO satellite, play a critical role. The CALIPSO lidar makes it possible to observe the height of different parts of dust plumes, which is key for estimating where dust drops into the sea. MISR excels at observing particle shapes in order to distinguish dust from other airborne material.
- By analyzing observations from all three sensors—as well as the European Infrared Atmospheric Sounding Interferometer (IASI)—Yu and colleagues have created maps showing how much dust gets deposited in the ocean and where. The most efficient removal of dust occurs in winter, when the dust is following the more southerly trajectory. The researchers found that it tends to be at low altitudes then and gets intercepted by rains along the ITCZ.
- “One of the most important things that comes out of this line of research is that we've realized that leading atmospheric circulation models like the Goddard Earth Observing System (GEOS) overestimate how fast dust is falling into the Atlantic ocean by 2 to 5 times,” Yu said. "Since in situ measurements [from ships or sensors on islands] of dust over the Atlantic Ocean are quite limited, satellites help fill data gaps, but models are still incredibly important for assessing the overall effects of dust.”
Figure 31: These maps, based on data analyzed by Yu and colleagues, show where the MODIS instrument observed dust moving out from Africa and over the Atlantic Ocean from 2007 to 2016. These optical depth observations are based on the amount of light dust particles scatter and absorb. The measurements capture dust throughout all levels of the atmosphere, not specific altitudes. The maps were first published in 2019 in the Journal of Geophysical Research–Atmospheres (image credit: NASA Earth Observatory, images by Joshua Stevens, using data courtesy of Yu, H., et al. (2019). Story by Adam Voiland)
• January 6, 2020: Forecasters predicted extreme fire conditions in southeastern Australia for the weekend of January 4–5, 2020, and they were correct in their assessment. The natural-color image of Figure 32 was acquired on January 4, 2020, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. Smoke has a tan color, while clouds are bright white. It is likely that some of the white patches above the smoke are pyrocumulonimbus clouds—clouds created by the convection and heat rising from a fire. 22)
Figure 32: As predicted, the weekend brought extreme fire weather.(image credit: NASA Earth Observatory, image by Joshua Stevens, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Text by Michael Carlowicz)
Sensor complement: (AIRS, AMSU/HSB, AMSR-E, CERES, MODIS)
Aqua has six Earth-observing instruments on board, collecting a variety of global data sets. 23)
Note: The descriptions of CERES and MODIS can be found under Terra.
Table 1: Overview of sensor complement on the Aqua spacecraft
AIRS (Atmospheric Infrared Sounder):
AIRS is a NASA/JPL instrument, PI: M. T. Chahine; prime contractor is BAE Systems (Infrared and Imaging Systems Division (LMIRIS) of BAE Systems, in Lexington, MA). AIRS, along with AMSU and HSB, is of HIRS and MSU heritage flown on the NOAA POES series. Objective: High-spectral-resolution measurement of global temperature/humidity profiles in the atmosphere in support of operational weather forecasting by NOAA. Measurement of the Earth's upwelling infrared radiances in the spectral range of 3.74 - 15.4 µm, simultaneously at 2378 frequencies (bands). Four visible wavelength channels are also present. 24) 25) 26) 27) 28) 29) 30)
Figure 33: Photo of the AIRS instrument (image credit: NASA)
The AIRS spectrometer is a pupil imaging, multi-aperture echelle grating design that utilizes a coarse 13 lines/mm grating at high orders (3-11) to disperse infrared energy across a series of detector arrays. The typical entrance slit of a spectrometer is subdivided into a series of eleven apertures, each of which is imaged onto the focal plane. The grating serves to spectrally disperse each image, which in turn is overlaid onto a HgCdTe detector array with each detector in the array viewing a unique wavelength by virtue of the grating dispersion. Rejection of overlapping grating orders and background photon suppression is provided by a series of IR bandpass filters located within the spectrometer and directly on the focal plane. Use of the grating in combination with the filter set provides a two-dimensional color map on the focal plane with a high degree of design flexibility in terms of color arrangement and spacing. Cooling of the spectrometer to 155 K is provided by a two stage passive radiator assembly with 10 Watt cooling capacity at 155 K.
Figure 34: Isometric view of the AIRS instrument (image credit: NASA/JPL)
Dispersed energy exiting the spectrometer is imaged onto a state-of-the-art hybrid PV/PC: HgCdTe focal plane assembly (FPA) consisting of a series of multi-linear arrays each associated with a specific entrance aperture. The assembly consists of 17 arrays arranged in 12 modules with each module individually optimized for wavelength and photon flux. The module set includes 10 photovoltaic (PV) modules covering the 3.7 - 13.7 µm region and 2 photoconductive (PC) modules for the 13.7 - 15.4 µm region. The more advanced PV modules include on-focal plane signal processing via a custom CMOS Readout IC (ROIC) specifically designed for AIRS temperature, photon flux and radiation conditions. The ROIC provides the first stage of signal integration at a 1.4 ms subsample rate, which are summed off focal plane in groups of 16 to meet full footprint dwell time requirements. The IR FPA provides simultaneous measurement of 2378 spectral samples across the 3.7 - 15.4 µm region with two samples per resolution element. Additionally, each PV sample is further divided by two in the cross-dispersed direction to provide increased yield and a measure of spectral redundancy. As a consequence, the IR FPA contains a total of 4482 active detectors. The complex FPA is packaged in a vacuum dewar maintained at the 155 K spectrometer operating temperature, with the IR FPA cooled to 58 K via a redundant, 1.5 W capacity Split Stirling pulse tube cryocooler.
Figure 35: Illustration of the FPA (Focal Plane Assembly), image credit: NASA/JPL)
Figure 36: The AIRS spectrometer assembly (image credit: NASA/JPL)
Figure 37: AIRS scan assembly (image credit: NASA/JPL)
Figure 38: Illustration of the cryocooler assembly (image credit: NASA/JPL)
The infrared region of 3.74-15.4 µm has a spectral resolution of 1200 (lambda/ delta lambda). The high spectral resolution permits the separation of unwanted spectral emissions and, in particular, provides spectrally clean “super windows,” ideal for surface observations. - This is supplemented by a VNIR photometer of four bands in the range between 0.4 and 1.0 µm. The VNIR channels are used to discriminate between low-level clouds and different terrain and surface covers, including snow and ice. The AIRS infrared bands have an IFOV of 1.1º and FOV = ± 49.5º scanning capability perpendicular to the spacecraft ground track (swath width = 1650 km, 13.5 km horizontal resolution in nadir, 1 km vertical). It takes 22.41 ms for each footprint of 1.1º in diameter (or 13.5 km). Each IR scan produces 90 footprints across the flight track and takes 2.67 s (see Figure 39). The VNIR channels have a footprint of 0.185º or about 2.3 km on the ground, nine VNIR footprints are within a 40 km swath. The VNIR photometer is boresighted to the spectrometer to allow simultaneous VNIR observations.
The VNIR photometer uses optical filters to define the four spectral bands. It operates at ambient temperatures (293-300 K). Inflight calibration is performed during each scan period. In addition, AIRS uses four independent cold-space views.
The major data products derived from AIRS are atmospheric temperature profiles, humidity profiles (from channels in the 6.3 µm water vapor band and the 11 µm windows, sensitive to the water vapor continuum), and land skin surface temperature.
AIRS is flown on the Aqua satellite with two operational microwave sounders: NOAA's AMSU and Brazil's HSB (Humidity Sounder Brazil). Together, the three sensors constitute constitute a possible advanced operational sounding system for future NOAA missions - offering increased accuracy of short-term weather predictions, improved tracking of severe weather events like hurricanes, and advances in climate research.
Table 2: Overview of some AIRS parameters
Some AIRS results in 2010:
The excellent sensitivity and stability of the AIRS instrument has recently allowed the AIRS team to successfully retrieve Carbon Dioxide (CO2) concentrations in the mid-troposphere (8-10 km) with a horizontal resolution of 100 km and an accuracy of better than 2 ppm. 31)
Originally designed to retrieve temperature and water vapor profiles for weather forecast improvement, the AIRS (Atmospheric Infrared Sounder) has become a valuable tool for the measurement and mapping of mid-tropospheric carbon dioxide concentrations. Several researchers have demonstrated the ability to retrieve mid-tropospheric CO2 from AIRS by different methods. The retrieval method selected for processing and distribution is called the method of “Vanishing Partial Derivatives” and results in over 15,000 CO2 retrievals per 24-hour period with global coverage and an accuracy better than 2 ppm.
The AIRS CO2 accuracy has been validated against a variety of mid-tropospheric aircraft measurements as well as upward looking interferometers (FTIR) from the ground.
Mid-tropospheric CO2 concentrations are an indicator for atmospheric transport and several interesting findings have resulted from analysis of the data.
- First is the non-uniformity of CO2, primarily caused by weather.
- Second is the ability to identify stratospheric-tropospheric exchange during a sudden stratospheric warming event.
- Third is the presence of a seasonally varying belt of enhanced CO2 concentrations in the Southern Hemisphere.
Figure 40: AIRS yields about 15,000 mid-tropospheric CO2 measurements per day (image credit: NASA/JPL)
Carbon dioxide turns out to be an excellent tracer gas since it does not react with other gases in the atmosphere. The project is finding that the AIRS mid-tropospheric CO2 is a good indicator of vertical motion in the atmosphere. It is a known fact that the majority of atmospheric CO2 is produced and absorbed near the surface and that there are no sources or sinks in the free troposphere. Thus elevated levels of mid-tropospheric CO2 are the result of airflow into the mid-troposphere from the near surface.
The most obvious finding from the AIRS retrievals is that the distribution of CO2 is not uniform as indicated in the models. Strong latitudinal and longitudinal gradients exist particularly over the large land masses in the Northern Hemisphere. This phenomenon is referred to as “CO2 weather”. The large variability in atmospheric circulation due to convection and global and mesoscale transport is responsible for most of the variability seen in the AIRS data. This implies that the AIRS CO2 data will be extremely useful for validating global scale transport in GCMs (Global Circulation Models).
Figure 41: AIRS mid-tropospheric CO2 is a tracer for atmospheric motion particularly in the vertical direction. July, 2010 monthly average (image credit: NASA/JPL)
AMSU/HSB (Advanced Microwave Sounding Unit (NASA Instrument)/ (Humidity Sounder for Brazil), provided by INPE. Both instruments operate in conjunction.
AMSU was designed and developed by Aerojet of Azusa, CA (a GenCorp company). AMSU primarily provides temperature soundings, whereas HSB provides humidity soundings. AMSU is a 15-channel microwave radiometer. AMSU and HSB have a total of 19 channels, 15 are assigned to AMSU, each having a 3.3º beamwidth, and four are assigned to HSB, each having a beamwidth of 1.1º. AMSU comprises two separate units: AMSU-A1 (channels 3-15), and AMSU-A2 (channels 1 and 2). Channels 3 - 14 use the 50 to 60 GHz oxygen band to provide data for vertical temperature profiles up to 50 km. The “window” channels (1, 2, and 15) provide data to enhance the temperature sounding by correcting for surface emissivity, atmospheric liquid water, and total precipitable water. HSB channels 17 - 20 use the 183.3 GHz water vapor absorption line to provide data for the humidity profile. 32) 33)
AMSU-A1 measures temperature profiles from the surface up to 50 km in 15 channels. Temperature resolution: 0.25 - 1.2 K. The AMSU-A1 instrument has two 15 cm diameter antennas (reflectors with momentum compensation), each with a 3.3º nominal IFOV at the half power points or FWHM (Full width Half maximum). Each antenna provides a cross-track scan of ±49.5º from nadir with a total of 30 Earth views (scan positions) per scan line. The total scan period is eight seconds. The footprint (resolution) at nadir is 40 km. The swath width is approximately 1690 km. Internal calibration is performed with internal warm loads and cold space.
AMSU-A2 has a single 28 cm diameter antenna (reflector without momentum compensation) with a 3.3º nominal IFOV. All other instrument/observation parameters are the same as those of AMSU-A1.
AMSU parameters: mass = 91 kg (49 kg for AMSU-A1, 42 kg for AMSU-A2); power = 101 W; data rate = 2.0 kbit/s; thermal control by heater, central thermal bus, radiator; thermal operating range= 0-20º C.
Table 3: Spectral parameters of the AMSU-A and HSB instruments
Figure 42: View of AMSU-A1 (left) and AMSU-A2 (right), image credit: Aerojet
Table 4: Summary of AMSU instrument parameters
HSB (Humidity Sounder for Brazil):
HSB is an INPE-provided instrument of AMSU-B heritage (built by MMS (Matra Marconi Space) of Bristol, UK (now EADS Astrium Ltd) with participation of Equatorial Sistemas of Brazil), and sponsored by AEB (Brazilian Space Agency). HSB is a microwave radiometer with the objective to measure atmospheric radiation, to obtain atmospheric water vapor profile measurements and to detect precipitation under clouds with 13.5 km horizontal nadir resolution (humidity profiles for weather foresting). 34) 35) 36)
HSB is a four-channel self-calibrating instrument (passive sounder) providing a humidity profiling capability in the frequency range of 150 - 190 GHz, spanning the height from surface to about 42 km. The measured signals are also sensitive to a) liquid water in clouds (cloud liquid water content) and b) graupel and large water droplets in precipitating clouds (qualitative estimate of precipitation rate). HSB scans in the cross-track direction at a rate of 2.67 seconds in continuous mode. The instrument features a momentum-compensated scan mirror system. HSB is operated in combination with AMSU-A, they have a total of 19 channels: 15 are assigned to AMSU-A, each having a 3.3º beamwidth, and four assigned to HSB, each having a 1.1º beamwidth. The HSB receiver channels are configured to operate in DSB (Double Sideband).
The HSB collected valuable data for the first nine months of the mission but ceased operating in February 2003 (scanner anomaly).
Table 5: Specification of the HSB instrument
Figure 43: Photo of the HSB instrument (image credit: NASA)
AMSR-E (Advanced Microwave Scanning Radiometer-EOS):
AMSR-E is a JAXA/NASA cooperative instrument, of AMSR heritage, built by Mitsubishi Electronics Corporation (PIs: A. Shibata, R. W. Spencer). The objective is the measurement of geophysical parameters such as: cloud properties, radiative energy flux, precipitation, land surface wetness (moisture), sea ice, snow cover, sea surface temperature (SST), and sea surface wind fields. AMSR-E is a modified design of AMSR on ADEOS-II (Japan).
The AMSR-E instrument is a conically scanning total power passive microwave radiometer sensing microwave radiation (brightness temperatures) at 12 channels and 6 frequencies ranging from 6.9 to 89.0 GHz (6.925, 10.65, 18.7, 23.8, 36.5, and 89.0 GHz). Horizontally and vertically polarized radiation are measured separately at each frequency. 37) 38) 39)
AMSR-E consists of an offset parabolic reflector 1.6 m in diameter, fed by an array of six feedhorns. The reflector and feedhorn arrays are mounted on a drum which contains the radiometers, digital data subsystem, mechanical scanning subsystem, and power subsystem. The reflector/feed/drum assembly is rotated about the axis of the drum by a coaxially mounted bearing and power transfer assembly. All data, commands, timing and telemetry signals, and power pass through the assembly on slip ring connectors to the rotating assembly. The AMSR-E instrument has a mass of 314 kg, power = 350 W, a duty cycle of 100%, and an average data rate of 87.4 kbit/s.
Table 6: Performance parameters of AMSR-E
Figure 44: Schematic view of the AMSR-E instrument (image credit: NASA)
The AMSR-E instrument rotates continuously about an axis parallel to the local spacecraft vertical at 40 rpm. At an altitude of 705 km, it measures the upwelling scene brightness temperatures over an angular sector of ± 61º about the subsatellite track, resulting in a swath width of 1445 km. During a period of 1.5 seconds the S/C subsatellite point travels 10 km. Even though the IFOV for each channel is different, active scene measurements are recorded at equal intervals of 10 km (5 km for the 89 GHz channels) along the scan. The half cone angle at which the reflector is fixed is 47.4º which results in an Earth incidence angle of 55.0º.
Figure 45: Line drawing of the AMSR-E instrument (image credit: NASA)
Instrument calibration. The radiometer calibration accuracy budget, exclusive of antenna pattern correction effects, is composed of three major contributors: warm load reference error, cold load reference error, radiometer electronics nonlinearities and errors.
Some data products from AMSR-E are:
• Level 2A brightness temperatures
• Level 2 rainfall
• Level 3 rainfall
• Columnar cloud water over the oceans
• Columnar water vapor over the oceans
• Sea surface temperature (SST)
• Sea surface wind speed
• Sea ice concentration
• Sea ice temperature
• Snow depth on sea ice
• Snow-water equivalent on land
• Surface soil moisture
Figure 46: The Aqua spacecraft and instrument accommodations (image credit: NASA, JAXA)
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30) Stuart MacCallum, “The Atmospheric InfraRed Sounder,” 2005, URL: http://xweb.geos.ed.ac.uk/~stuart/Presentations/stuart_firbush2005.pdf
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34) Information provided by Janio Kono of INPE, Sao José dos Campos, Brazil
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36) Ezio Castejon Garcia, Marcio Bueno dos Santos, “The Environmental Simulation of the Humidity Sounder for Brazil,” 54th Astronautical Congress of the IAF, Sept. 29 - Oct. 3, 2003, Bremen, Germany
38) AMSR-E Data Users Handbook, 4th Edition, JAXA, March 2006, NCX-030021
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 (email@example.com).