Aqua (EOS/PM-1)

Quick facts

Overview

Summary

Mission Capabilities

Aqua has six instruments: the Atmospheric Infra-red Sounder (AIRS), the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), the Advanced Microwave Sounding Unit-A (AMSU-A), the Cloud and the Earth’s Radiant Energy System (CERES), the Humidity Sounder for Brazil (HSB), and the Moderate-Resolution Imaging Spectroradiometer (MODIS). 
The AIRS instrument is a medium resolution infrared spectrometer that provides high spectral resolution measurements of temperature and humidity profiles in the atmosphere. These include long-wave Earth surface emissivity, cloud diagnostics, surface temperatures and trace gas profiles. The instrument contains one infrared band and four near-infrared bands. 
AMSU-A functions as an absorption-band microwave spectrometer that allows the satellite to capture all-weather night-day temperature sounding to an altitude of 45 km. HSB is also an absorption-band microwave spectrometer that records humidity soundings for climatological and atmospheric dynamics applications. 
AMSR-E is a multi-purpose imaging microwave radiometer that attains measurements of water vapour, cloud liquid water, precipitation, winds, sea surface temperature, sea ice concentration, and soil moisture. The radiation measurements are collected via the CERES module and provide long term measurements of Earth’s radiation budget. 
MODIS collects data on biological and physical processes on the Earth’s surface, in the lower atmosphere and on global dynamics, as well as surface temperatures of ocean and land processes, chlorophyll fluorescence, land and cloud cover. 
 

Performance Specifications

AIRS contains more than 2300 spectral channels that have a spatial resolution of 0.4 - 14.4 μm, with an instantaneous field of view (IFOV) of 1.1°, field of view (FOV) of ± 49.5°, and swath width of 1650 km (13.5 km horizontal at nadir, 1km vertically positioned). The AMSU and HSB modules have a total of nineteen channels, with fifteen used by AMSU. AMSU is divided into two units, AMSU-A1 measures temperature profiles and has a swath width of approximately 1690 km, while AMSU-A2 is a smaller unit and has a nominal instantaneous field of view of 3.3°. The HSB module has a swath width of 1650 km with an IFOV of 1.1° or 13.5 km at nadir.

The AMSR-E instrument has a swath width of greater than 1450 km and an incidence angle of 55°. The instrument senses microwave radiation at 12 channels with 6 specific frequency ranges: 6.925, 10.65, 18.7, 23.8, 36.5 and 89.0 GHz. CERES has a resolution of 20 km and three specific channels of 0.3 - 5 um, 0.3 - 100 um, and 8 - 12 um. MODIS has a swath width of 2330 km and thirty-six bands in the range of 0.4 - 14.4 um. 

Aqua is in sun-synchronous orbit at an altitude of 705 km with an orbital inclination of 98.2° and a repeat cycle of 16 days. 
 

Space and Hardware Components

The Aqua spacecraft is based on the AB1200 bus design by TRW (now Northrop Grumman) and has a total mass of 2,934 kg. The propulsion system is a hydrazine blow-down system with four pairs of thrusters. The spacecraft had a design life of six years, which it has outlasted, and achieves radio-frequency communications based on the Consultative Committee for Space Data Systems (CCSDS) protocol and through Direct Broadcast (DB). 

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).

Spacecraft

The Aqua spacecraft is based on TRW's modular, standardised 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 stabilised, 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).

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.

Note: As of 19 April 2022, the previously single large Aqua file has been split into three 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 2022

• Aqua imagery in the period 2021-2020
• ​​Aqua imagery in the period 2019-2002

Mission Status

• July 19, 2022: During the first week of July, NASA satellites began detecting signs that several wildland fires were burning in Russia’s far east. Two weeks later, several fires had grown much larger and more intense, creating rivers of smoke that flowed over parts of Khabarovsk and the neighbouring Republic of Sakha (Yakutia). ⁵⁾ According to Sakha’s emergencies ministry, 51 fires burned across roughly 9,737 hectares (38 square miles) on July 18. More than 500 people were fighting the fires in Sakha, and thousands more were deployed to fire fronts across Russia, according to Russia’s ministry of emergency situations (EMERCOM). For the previous two years, Sakha endured unusually severe fire seasons. In 2021, more than 8.4 million hectares (84,000 km²) of forests burned in Sakha, nearly four times the long-term average. Fires were not the only hazard facing the region. Flooding along the Yana River displaced hundreds of people in Sakha.

• June 24, 2022: Torrential monsoon rains, lightning, and landslides are common in Bangladesh and the northeastern Indian states of Assam and Meghalaya during the summer. But the intensity of the severe weather that pummeled the low-lying region in mid-June 2022 stands out. ⁶⁾ After weeks of downpours, flooding swamped millions of homes and displaced hundreds of thousands of people in India and Bangladesh, according to reports from humanitarian agencies. Officials from the hard-hit Sylhet region of Bangladesh called the floods the worst to hit the area in more than a century.

• June 15, 2022: On June 4–5, 2022, thunderstorms moved across south-central and southwest Alaska, delivering nearly 5,000 lightning strikes and igniting dozens of wildfires. It was the latest outbreak in an unusually active fire season so far. ⁷⁾ In the Yukon Delta, the East Fork fire has become the largest tundra fire on record. Ignited on May 31 by a lightning strike, it has burned more than 150,000 acres along the Yukon River north of the village of St. Mary’s. Northerly winds drove the East Fork fire within about 3.5 miles (6 km) of the village of St. Mary’s. To the east, the Hog Butte fire had so far burned about 58,000 acres about 125 miles (200 kilometers) west of Denali National Park. On June 11, 2022, the Hog Butte fire spawned a pyrocumulonimbus cloud (pyroCb) that reached an altitude of about 6 miles (10 kilometers). It was the first pyroCb over Alaska in two years. According to a report from the Alaska Interagency Coordination Center, by mid-June 2022, 250 wildfires had already burned more than 770,000 acres, not counting prescribed burns. Over the last 30 years, the median area burned by mid-June has been about 50,000 acres. Smoke from the wildfires drifted over the Alaska Range into Anchorage and northeast across the state causing reduced visibility and poor air quality.

• June 8, 2022: The Gulf of Maine is growing warmer and saltier, and those changes have led to a substantial decrease in the productivity of phytoplankton that are the center of the marine food web. Specifically, phytoplankton in the gulf are now about 65 percent less productive than they were two decades ago, scientists from Bigelow Laboratory for Ocean Sciences reported in research published on June 7, 2022. ⁸⁾ The Gulf of Maine supports New England’s marine ecosystems and economy, with phytoplankton playing a vital role in absorbing carbon dioxide and fueling the food web. Disruptions to their productivity can impact fisheries and coastal communities. Research published in 2021 revealed that the Gulf is warming faster than most ocean basins, affecting phytoplankton. A 23-year study, the Gulf of Maine North Atlantic Time Series (GNATS), tracks changes in temperature, salinity, and other properties, highlighting the Gulf's connection to the Atlantic. Since 1998, Bigelow Laboratory has monitored biogeochemical changes using water samples from ferries, research vessels, and autonomous gliders. These measurements validate satellite data and address gaps from cloudy or foggy days. NASA satellites like Aqua and Terra collect ocean colour data, and the upcoming Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission will enhance observations. The GNATS dataset is publicly available via NASA’s repository.

• June 4, 2022: Early summer blooms coloured the seas off of southern Wales and southwestern England when NASA’s Aqua satellite passed over the region on June 3, 2022. Bright blue-green waters indicated an abundance of phytoplankton just beyond Bristol Channel. ⁹⁾ Phytoplankton are usually most abundant in the far North Atlantic and the North Sea in late spring and early summer, when dissolved nutrient levels are high. The milky, light-coloured waters are likely filled with coccolithophores, phytoplankton with calcium carbonate plates that appear chalky white when amassed in great numbers. Greener patches may be rich with diatoms. The Bristol Channel is the largest natural inlet of the United Kingdom. Freshwater from the River Severn (the UK’s longest) pours into an estuary here and mixes sediment and nutrients into the saltwater. In a recent study by Plymouth University, scientists reported that the types and abundances of plankton in the waters around the United Kingdom have changed significantly in the past six decades. The shifts are likely related to climate change—particularly warming temperatures—and could have long-term effects on the health and distribution of fish, marine mammals, and sea birds in the region. ¹⁰⁾

• May 18, 2022: Since the beginning of April 2022, Iraq and other parts of the Middle East had been hit by a series of severe dust storms. Two major storms in the past two weeks have sent thousands of people to the hospital, as poor air quality from airborne dust can aggravate asthma and other respiratory diseases. ¹¹⁾ The skies above Baghdad, Najaf, Sulaimaniyah, and other cities turned orange as visibility dropped to a few hundred meters. Several airports were closed during the dust events, and schools were closed nationwide. Dust storms in Iraq are most common in late spring and summer, provoked by seasonal winds such as the “shamal” that blows in from the northwest. Researchers suggested in a 2016 paper that La Niña conditions in the equatorial Pacific can lead to an earlier onset of shamal winds. Recent observations suggest that La Niña may be persisting into a third consecutive year. Those strong seasonal winds blow across abundant sources of dust. According to The World Bank, northern Iraq—between the Tigris and Euphrates rivers—has the highest density of dust sources in the Middle East.  News media reported that Iraq has been hit by at least eight dust storms in the past six weeks. Researchers have found that dust events have become more frequent in Iraq.

• May 14, 2022: The Calf Canyon-Hermits Peak fire continued to rage across northern New Mexico in mid-May 2022, entering its second month. On May 13, it was the largest fire burning in the United States and the second largest in New Mexico’s history. ¹²⁾ The burned area spanned more than 270,000 acres east of Santa Fe and stretched 50 miles (80 km) from its northern to southern perimeter in the Sangre de Cristo mountains. Evacuation orders remained in effect in San Miguel, Moro, and Colfax counties, and have been expanded into the ski resort town of Angel Fire. Extremely low humidity and high winds helped spread the fire through dry grass, brush, and trees.  Researchers at the Cooperative Institute for Meteorological Satellite Studies measured a cloud-top temperature of -59°C (-75°F). This indicated that the cloud had reached the tropopause, the boundary between the troposphere and the stratosphere at an altitude of about 12 km. Most of the state continues to experience extreme to exceptional drought in the midst of the Southwest megadrought. New Mexico has had 244 fires by that point in the year, burning more than 360,000 acres, according to the National Interagency Fire Center.

• May 6, 2022: As another winter ends with the U.S. West still in the grip of the worst megadrought in 1,200 years, scientists and water managers are looking at the state of the snowpack. Mountain snowpack is a natural reservoir: As it melts out over the course of the spring and summer, it provides a steady supply of water for millions of people who rely upon it for agriculture, industry, and municipal and residential use. ^{13) 14)} To forecast water supplies for the coming year, hydrologists and water managers rely on measurements of snowpack, particularly the snow water equivalent (SWE), a measure of how much liquid water is stored within snow. In the western U.S., snowpacks usually peak around April 1. Assessment of the snowpack on this date has traditionally been used to help predict streamflows, reservoir storage levels, and potential wildfire conditions for the rest of the year. While satellites can show where snow is, they cannot yet directly measure snow depth or snow water equivalents. Measurements of snow have been made manually since the early 1900s. In the late 1970s, automated ground-based monitoring began with the SNOTEL network which has used over 900 automated stations in remote, high-elevation watersheds to monitor snowpack, precipitation, and climate conditions. However, SNOTEL data represents narrow locations, requiring extrapolation to estimate snowpack across broader areas.

- Most areas of the Colorado River Basin have Snow Water Equivalent (SWE) ranging from 46% to 95% of the 2000–2020 average, despite isolated high-SWE pockets. Data from NASA’s Terra satellite (MODIS) and models incorporating elevation, slope, and historical melting patterns inform these estimates. An April 18 report from the Colorado Basin River Forecast Center predicted near- to below-average water supply from April to July 2022. The Colorado River Basin spans 246,000 square miles, supplying water to tens of millions, including urban areas like Denver, Salt Lake City, and Los Angeles. Meltwater is stored in reservoirs like Lake Mead and Lake Powell, with Glen Canyon Dam providing hydropower to 5 million people.

• May 5, 2022: On April 13, a blizzard dropped 4 feet of snow on Minot, North Dakota, as a drought-fueled wildfire burned in Ruidoso, New Mexico, and severe storms spawned eight tornadoes in Kentucky. NASA’s Atmospheric Infrared Sounder (AIRS) helped weather forecasters predict these events, as it’s been doing since it was launched in 2002. But now AIRS also helps researchers calculate the role climate change plays in these extreme weather events. ¹⁵⁾ AIRS measures infrared – heat – radiation from the air below the satellite to create three-dimensional maps of atmospheric temperature and water vapour, the main ingredients for any kind of weather.

- The AIRS instrument is a spectrometer that breaks radiation into wavelengths, just as a prism does. Researchers recently used AIRS data to detect atmospheric waves from the eruption of the Hunga Tonga-Hunga Ha’apai volcano. Earlier this year, researchers also used AIRS data to quantify the link between humidity and influenza outbreaks. In addition, AIRS data is used to track clouds, carbon dioxide, methane, ozone, and other gases and pollutants whose spectral signatures fall within the range of infrared wavelengths AIRS detects.

• May 4, 2022: Early season wildfires continued to rage in the first week of May 2022 in northern New Mexico. The blazes have been driven by high winds, low humidity, and exceptionally dry tinder—grass, brush, and timber—that are providing ample fuel for burning. The fires have destroyed hundreds of structures and prompted the evacuation of thousands of homes. On May 3, 2022, seven large fires were still burning across the state. ¹⁶⁾ According to the U.S. Drought Monitor on April 26, 2022, approximately 99 percent of the state was experiencing drought, with 83 percent facing extreme to exceptional dryness. New Mexico has had 211 fires so far this year, burning a total of 230,000 acres. In all of 2021, 672 fires burned nearly 124,000 acres, according to the National Interagency Fire Center. MODIS sensors have also imaged burn scars from the New Mexico fires. Many NASA satellites and instruments are used to detect actively burning fires, track the transport of smoke, provide information for fire managers, and map the extent and severity of burn scars. Satellites are often the first to detect wildfires in remote regions.

• May 2, 2022: A dust storm over the Middle East in late April 2022 was triggered by thunderstorms that also brought hail and flash floods. The dust turned skies yellow, reduced visibility, disrupted aviation, and degraded air quality. ¹⁷⁾ In Jordan, low-visibility conditions caused by gusting winds carrying dust and sand disrupted aviation. Heavy thunder and hail showers and flash flooding also prompted emergency alerts. In Saudi Arabia, large hail and thunderstorms caused flash flooding. The storm arose due to an Red Sea depression. Also called a Red Sea low, this weather system brings a hot air mass from the Arabian Peninsula, increasing atmospheric instability that triggers thunderstorms and dust storms, usually during the spring and autumn. In Jordan, most spring dust storms occur in April and form when strong winds blowing over dry, desert soils in eastern and southern Jordan become hotter and drier, According to a World Bank report on sand and dust storms, land-use changes in the past few decades have increased the number of dust sources in the Middle East.

• April 28, 2022: A few times every spring, the skies over the Labrador Sea fill with row after row of long, parallel bands of cumulus clouds. The organisation of these clouds, known as cloud streets, was on full display when this image was acquired on April 19, 2022. ¹⁸⁾ The appearance of cloud streets indicates that strong, cold winds were blowing toward the southeast over comparatively warmer water. There is also enough open water from which that air can draw moisture and form clouds. The pattern is the result of the ice-chilled air being warmed by the ocean surface and forming strong currents of upward moving air, or thermals. The moist air rises until it hits a temperature inversion, which acts like a cap and causes the air to roll over and form parallel cylinders of rotating air. On the upper side of these cylinders (the rising air), clouds form. Along the downward side (descending air), skies are clear. In research published in November 2021, scientists found that burned acreage from wildfires in the western United States doubled between the period of 1984–2000 and 2001–2018. They attributed the increase in fire to a significant change in the vapour pressure deficit, a measurement of how hot and dry the atmosphere can get. ²⁰⁾

• April 19, 2022: Only half of the citizens of Ethiopia had access to electricity, a lower percentage than most other countries in Africa and a much lower percentage than most other countries in the world. To change this, the Ethiopian government began constructing a dam on the Blue Nile in 2011 that will rank as Africa’s largest hydroelectric dam when completed in 2023. ²¹⁾ The Grand Ethiopian Renaissance Dam (GERD), a 145-meter (475-foot) concrete structure with three spillways and 13 turbines, will create a 1,874 km² (724 square mile) reservoir—about the size of Houston, Texas. Once operational, GERD is expected to more than double Ethiopia's electricity output, illuminating a country where much of the population lacks power, as seen in satellite images contrasting Ethiopia’s darkness with Egypt’s brightly lit Nile corridor, where World Bank data indicates that 100 percent of the population has access to electricity. GERD could also temper seasonal floods in Sudan, provide irrigation water to boost Ethiopia's food supply, and reduce sediment buildup in downstream dams.

• March 22, 2022: High winds, low humidity, and drought-parched grasses fueled a rash of wildfires in Texas, Oklahoma, and Arkansas in mid-March 2022. According to the Texas A&M Forest Service, at least 178 wildfires have burned more than 108,000 acres across Texas in the past seven days, including one of the largest blazes (by area) in state history. At least three first responders have died in Texas and Oklahoma while responding to the fires. ²⁴⁾ About 125 miles west of Dallas, the Kidd Fire ignited on March 17 amid days of strong, dry winds. (This short time-lapse sequence shows dust and clouds caught up in the winds.) More than 42,000 acres (65 square miles) have burned so far in a fire that is about 40 percent contained. At least 147 homes and structures have been consumed, including most of the town of Carbon. The Kidd Fire is one of seven that have been grouped into the Eastland Complex by firefighting agencies; more than 54,000 acres (84 square miles) of wildland and property have burned near the town of Eastland.

• February 28, 2022: Bolivia’s Salar de Uyuni is the largest salt flat (or playa) in the world. For much of the year, it stretches out in a seemingly endless expanse of white, with a salt crust covering 10,000 km² (4,000 square miles). During the rainy season, water can fill part of the salt flat and give it a stunning, mirror-like appearance. In early 2022, that watery mirror grew larger and lingered longer than it has in several years. ²⁵⁾ Abundant rainfall around the Altiplano in November, December, and early January had the Salar de Uyuni brimming with water nearly to its edges. In fact, local newspapers reported flooding in some areas and temporary prohibitions on travel across the salar during the busy tourist season. Salar de Uyuni is rich in minerals—especially lithium (used in batteries), halite (common table salt), and ulexite and gypsum (for fertiliser and plaster)—some of which have been harvested here since at least the 1600s. The flat landscape draws many tourists who come to see the salty crust in the dry season and the mirror lakes in the wet season. The salt flat is also popular with remote sensing scientists, who use the landscape to calibrate satellite imagers and altimeters.

• February 13, 2022: Tropical Cyclone Batsirai swept over the Indian Ocean and into central and southern Madagascar on February 5–6, 2022, bringing torrential rain, flooding, and high winds. The storm devastated entire villages, killing at least 120 people and leaving tens of thousands displaced, according to the country’s Office of Risks and Disasters. ²⁶⁾ The cyclone came just two weeks after the island nation was struck by Tropical Storm Ana, which followed a series of heavy rainstorms in mid-January. Flooding and landslides killed at least 58 people and displaced more than 70,000. Batsirai made landfall on February 5 on the southeast coast near Mananjary as a category 3 storm with sustained winds of 165 km (105 miles) per hour and gusts up to 230 km (145 miles) per hour. Heavy rain continued to fall on February 7–8 as the storm moved over the island and off to the southwest. In its wake, Batsirai left water and power outages, along with destroyed or damaged buildings and schools. Relief efforts were underway, although washed out roads and bridges have made some areas inaccessible, according to the United Nations Office for the Coordination of Humanitarian Affairs.

• February 1, 2022: After several mostly uneventful months of winter, the densely populated northeastern United States was buried in mounds of snow and blasted by gale-force winds on January 28-29, 2022. Twelve states from North Carolina to Maine received measurable snowfall from the nor’easter; eight of them had towns report more than a foot (30 cm) of snow. ²⁷⁾ Due to the moderating effect of warmth and moisture from the ocean, coastal areas often see less snow during winter storms. But in this case heavy snowfalls were brought to the New Jersey shore, Long Island, and coastal New England. According to National Weather Service (NWS) reports snow fell at rates of 3–4 inches per hour, with totals exceeding 21 inches in Providence, Rhode Island; 29 inches in Norton, Massachusetts; 30 inches in Quincy; and 22 inches in Norwich, Connecticut. Boston tied its record for 24-hour snowfall at 23.6 inches, while Islip, New York, recorded its second-highest daily total of 23.2 inches. The storm also brought near-hurricane-force winds, with blizzard conditions confirmed in parts of Rhode Island and Massachusetts, impacting 11 million people.

• January 29, 2022: The Gulf of Khambhat lies on the west coast of India between the Saurashtra Peninsula and mainland Gujarat. Several major river systems—including the Narmada, Tapi, Mahi, Sabarmati, and Shetrunji—deliver abundant freshwater and heavy sediment loads to the gulf. The gulf measures 80 km (50 miles) wide at its mouth in the Arabian Sea but narrows to about 25 km (15 miles) at its head, where the deltas of the Sabarmati and Mahi rivers meet. ²⁸⁾ Natural-colour images from NASA’s Aqua satellite on April 16 and October 16, 2021, show sediment discharge concentrated at the northern end of the gulf. The monsoon season (June–September) increases sediment discharge, evident in the October image, where sediment reflectivity shifts from brown to green as freshwater disperses and sinks. Strong tides dominate the gulf, flowing at 1.5 to 2 m/s (3.3 to 4.5 mph). With depths under 20 meters (65 feet) in most areas, receding tides expose intertidal zones up to 5 km (3 miles) wide. Extensive mudflats, shoals, and banks make navigation hazardous, as seen in the April image. Dynamic water flows rapidly alter the gulf’s bathymetry, posing additional navigation risks. This has prompted some researchers to develop a bathymetry model based on satellite radar data to enable quicker updates to navigation charts.

• January 15, 2022: For much of 2021, drought affected southern Iran, parching crops, drying wells, and fueling protests over water. The first week of 2022 brought the opposite problem—a series of potent rain and snow storms overwhelmed rivers and unleashed widespread flooding. ²⁹⁾ News and social media reports showed destructive flood waters that washed out bridges, swept away cars, swamped homes, and inundated farmland. The floods killed at least 10 people and damaged hundreds of homes and vehicles, according to the Iranian Red Crescent Society. The recent burst of rain will not necessarily end Iran’s drought or water challenges immediately. While storms can replenish moisture on the surface, it takes a sustained period of wet weather to replenish groundwater, which many people in this region rely on for irrigation. Data collected by the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites show that reserves of shallow groundwater in the region’s aquifers, though improved, were still low in some parts of southern Iran on January 10, 2021, according to GRACE-FO data published by the University of Nebraska.

• January 13, 2022: Beachgoers in the Brazilian state of Rio de Janeiro contended in late 2021 with unwelcome ocean-dwelling visitors. Starting in November, countless microscopic phytoplankton amassed along the coast, colouring the clear, blue waters a dark, reddish-brown. The bloom—known as a red tide or harmful algal bloom (HAB) event—was unusually widespread and long-lived. ³⁰⁾ Phytoplankton blooms are common near Rio during this season and usually benefit the ecosystem. Harmful algal blooms, however, can occur year-round, driven by sewage and heat waves, though they are typically short-lived. This red tide, spanning over 200 km and lasting eight weeks, was an exception.

- From September to January, upwelling near Arraial do Cabo brings nutrient-rich waters that fuel phytoplankton blooms, turning Rio’s blue waters green. In spring 2021, prolonged clouds and rain delayed diatom growth, leaving clear, nutrient-rich waters. When sunlight returned in November, ideal conditions triggered the red tide. It was first observed on November 3 and confirmed by water samples on November 16. The waters darkened rapidly, with red seafoam accumulating along Rio’s beaches. By early December, satellite images showed the bloom spanning the coast from Rio to Arraial do Cabo. After the phytoplankton die, the process of decomposition by bacteria can deplete the water of oxygen (hypoxia) and cause fish kills. Also, the red tide species can replace other phytoplankton species that usually support a region’s fish and marine food webs.

• January 5, 2022: On December 30, 2021, high winds roared out of the west and down the front slope of the Rocky Mountains in Colorado. Northwest of Denver, peak gusts reached 115 miles (185 kilometers) per hour—the equivalent of a category 3 hurricane. Those winds whipped up intense grass and brush fires in south Boulder and blew them east toward the towns of Superior and Louisville, igniting a firestorm. By the time it was over, nearly 1,100 houses had been destroyed or damaged, two people were reported missing, and thousands were displaced. ³¹⁾ The Marshall Fire, at the time Colorado’s most destructive wildfire, burned 6,200 acres and was fully contained by January 3, 2022. Unlike typical Western megafires in forests, it spread rapidly into neighborhoods, becoming an urban conflagration. Hurricane-force winds created an “ember storm,” driving flames through streets, trees, and buildings, and forcing tens of thousands to evacuate.

- A cold front brought over 10 inches (25 cm) of snow, helping extinguish the fire but complicating the response. High winds and wildfires are not uncommon on the Front Range, but a December wildfire was; the normal fire season lasts from May to September. At the time, eastern Boulder County was under extreme drought, with Standardized Precipitation-Evapotranspiration Index (SPEI) values below minus 2, indicating severe warm and dry conditions. Meanwhile, western Colorado had near or above-average snowpack, highlighting a stark contrast in moisture levels across the state. Denver saw its first winter snowfall on December 10.

Sensor Complement

Aqua has six Earth-observing instruments on board, collecting a variety of global data sets. ³²⁾

Note: The descriptions of CERES and MODIS can be found under Terra.

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. ^{33) 34) 35) 36) 37) 38) 39)}

The AIRS spectrometer is a pupil imaging, multi-aperture echelle grating design that utilises 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 colour map on the focal plane with a high degree of design flexibility in terms of colour 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.

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 optimised 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.

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 49). 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 vapour band and the 11 µm windows, sensitive to the water vapour 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.

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. ⁴⁰⁾

Originally designed to retrieve temperature and water vapour 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.

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).

AMSU/HSB

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 vapour absorption line to provide data for the humidity profile. ^{41) 42)}

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.

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 vapour profile measurements and to detect precipitation under clouds with 13.5 km horizontal nadir resolution (humidity profiles for weather foresting). ^{43) 44) 45)}

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).

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 polarised radiation are measured separately at each frequency. ^{46) 47) 48)}

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.

​​​​​​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.

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 vapour 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

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