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As of July, 2002. Aqua has been launched successfully but as of this date only limited imagery or other data have been released. The present page will be fleshed out as the materials become available. Meanwhile, this is a brief synopsis of the program, plus a further look at the European Space Agency satellite Envisat, which is a companion to the Terra and Aqua pair but is also equipped with sensors that supplement the data needed for Earth Observations:


The afternoon segment (PM) of the EOS flagships, Aqua, was successfully launched by a Delta II rocket from Vandenberg Air Force base at 2:55 AM PDT on May 4, 2002. Here is an artist's painting of the spacecraft:

The Aqua spacecraft from an artist's perspective
Aqua's initial orbit of 705 km (438 miles) leads to an average equatorial crossing time (going north) of 1:30 PM. Its mission is to complement Terra observations by providing data later in the day; however, the new sensors on Aqua are designed to obtain information of interest primarily to meteorologists and oceanographers. A better understanding of the planet's water cycle is the goal, as these sensors will lead to improved data on global precipitation and evaporation, radiative balances, humidity and temperature profils through the atmosphere, soil moisture, etc. The overall objective is to integrate the water studies into a better general understanding of the world's environments. The three host participants in Aqua are the United States, Japan, and Brazil, although other nations are close associates.

Aqua carries six state-of-the-art instruments in a near-polar low-Earth orbit. The six instruments are the Atmospheric Infrared Sounder (AIRS), managed by JPL, the Advanced Microwave Sounding Unit (AMSU-A), the Humidity Sounder for Brazil (HSB), the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), the Moderate-Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth's Radiant Energy System (CERES). Each has unique characteristics and capabilities, and all six serve together to form a powerful package for Earth observations. Information about each of these sensor systems is rather involved and will not be summarized here, but the reader is encouraged to consult the section on Instruments at the Aqua Home Page.

Several months are involved in completing the instrument test phase, after which Aqua goes operational. (There were a few minor glitches during this period.) The first imagery released by the Aqua team is this AMSR-E pair that give improved sea surface and brightness temperatures on June 2-4 (three days data integrated):

The first ocean water temperatures, both sea surface and surface brightness, obtained by the AMSR-E on Aqua.

AMSR-E has been used also to locate and measure rainfall on the continents. This set of data maps shows measurements made simultaneously within the same hour on June 5, 2002 by AMSR-E from space and by the U.S. Weather Bureau's ground-based NEXRAD Doppler radar and by TRMM (see page 14-5) three hours later, with corresponding NEXRAD readings. The space and ground measurements were 0.31 and 0.29 mm/hr respectively.

AMSR-E and TRMM determinations of rainfall distribution on the night of June 5, 2002, both compared with NEXRAD scans from the ground.

A very important task in applying microwaves to the Earth's surface is the detection of soil moisture and estimation of its amount. Here is a map of the generalized variations in soil moisture on a global basis as determined by AMSR in June 2001.

Global variations in soil moisture, as mapped by Aqua's AMSR-E.

The second sensor to "go public" with data is CERES. We have described this sensor on the previous page. Recall that CERES measures reflected thermal radiation from the Sun and heat from the Earth's surface warmed by the Sun. Here is another pair of images centered on North America and acquired on June 22, 2002:/p>

CERES images from the Aqua spacecraft, showing reflected and emitted radiation over a broad region centered on the United States.

Then, on July 6, images from the AIRS (Atmospheric Infrared Sounder) group were released. The sensors making up this instrument are designed to measure temperatures along vertical profiles so as to derive a three-dimensional map of the atmosphere. The first image is a Visible view of Tropical Cyclone Ramasun in Asia:

Visible bands image of Cyclone Ramasun.

Released simultaneously were images from the AIRS group sensors for a region from Italy east to Turkey and south to the North African Coast. This is the Visible image obtained from AIRS itself:

AIRS group Visible image of the Mediterranean area of Europe/Asia.

Beneath this visible view as a geographic reference in succession are:

AIRS infrared image

1) An AIRS infrared image at 11 µm, which measures surface and cloud temperatures

AMSU temperatures

2) An AMSU (Advanced Microwave Sounding Unit) temperature plot, sensed in the microwave at 31.4 GHz

HSB mid-troposphere temperatures.

3) An HSB (Humidity Sounder, developed and operated by Brazil) map, made from a sensor operating at 150 GHz, designed to obtain mid-troposphere temperatures, and sensistive to moisture, precipitation, and ice crystals; its dry land temperatures are close to those of AIRS.

Three-dimensional atmospheric maps developed from observations such as the above three data sets have now been released. Here is the western Mediterranean (France on left and North Africa on right) with the bottom shown as a landscape image, and atmospheric layers at 8 and 12 km shown in colors with red the warmest and purples coolest.

Generalized temperature ranges in two layers above the Mediterranean Sea (view looks east towards the top).

AMSU measures surface emissivities in the microwave region as well as atmospheric emissivities. These in turn are used to calculate temperatures. An excellent illustration of end products from this sensor is given by these observations of the eastern half of the U.S. before and after passage of Hurricane Isidore in late September of 2000 (these dates are determined by the 16-day orbital repeat cycle of Aqua). The left image was obtained on September 12; the right on the 28th, one day after the hurricane made landfall.

AMSU images on Sept. 12 and 28, 2000 of the eastern U.S.

Increasing temperatures range from the colder blues to the warmest reds. In the right image, the blues around the Mississippi River drainage basin result mainly from surface soils that have absorbed water from the hurricane (it appears further north as a blue area) such that the cooling effect of the rainfall into these soils has lowered emissivity. In the image below, differences in temperature determined by subtracting the second from the first AMSU image show a new map in which the hurricane cooling effects stand out in blue and red pinpoints an area of warmer temperatures in the air evident in the Carolinas:

AMSU temperature difference map.

The first MODIS images were released near the end of June, 2002. Shown next, in a rather large size to preserve detail, is a natural color MODIS image, taken on June 24, that shows West Coast states from northern Oregon to the Mexican border. The red spots are active wildfires in the Klamath Mountains of SW Oregon, and elsewhere in that state. Most of the clouds off northern California are actually a thick fog bank.

MODIS natural color image of Oregon and California (Nevada inland) taken on June 24th, 2002 during a time of several major (100000 acres plus) wildfires (in bright red).

MODIS on both Terra and Aqua took measurements of CO2 throughout 2002. From knowledge of the Carbon Cycle (page 16-4) relations between COs and the amount fixed in vegetation (land and ocean), a measure of productivity could be made at different times of the year. The first pair of plots below show the distribution of global productivity in June and December of that year. The next map indicates the net productivity for the year.

Primary Productivity (as a function of kg/ worldwide at the end of June and December 2002, based on MODIS data

Net Primary Productivity for the year 2002.

Other satellites in the EOS program are now operational. ICESat (Ice, Clouds, and land Experiment Satellite), whose sole instrument is GLAS (Geoscience Laser Altimeter System) and SORCE (Solar Radiation and Climate Experiment) were both successfully launched in 2003 but data are still forthcoming.


We previously described the ESA (European Space Agency) environmentally-oriented program with its Envisat as the lead satellite, near the second page of the Overview.Check this for details, and note that Envisat was also launched in May of 2002. ESA claims their satellite is the biggest of the EOS family and has the most sensors. Count these in this artist's drawing - you should find 10. These are described at the Envisat Web Site.

ESA's Envisat; the two prime sensors are MERIS and ASAR.

Several images from Envisat appear elsewhere in the Tutorial. Two excellent MERIS (for Medium Resolution Imaging Spectrometer) images are found in the Overview. Here is another MERIS wide swath image showing France, the Alps, and a cloud bank over Germany:

MERIS image of France and neighboring regions.

As an example of a scene that has strong environmental information is this MERIS image of the West Coast of Africa, including part of Senegal. The Kaffrine River delta is densely vegetated with brackish water coastal vegetation. Dakar is at the end of the westernmost peninsula. Note the sediment from the river.

MERIS image of Senegal, with the westernmost tip of Africa.

Data taken by AATRS (Advanced Along Track Scanning Radiometer) are used primarily to determine sea surface temperatures. But several bands can be processed in images that resemble false color composites. These tend to look "funny" because of their extended elongation (along the orbital track) but they have the advantage of being a continuous "picture" taken at one time. Here is one that begins in Kenya and ends in the Sinai Peninsula across the Gulf of Suez; to fit better on the page it has been turned 90° so that north is to the east.

AATRS image of East Africa.

We have seen several ASAR (Advanced SAR) images in Section 8, page 8-7. Here is another, showing the Elbe River south of Berlin, in color because several band modes were used.

ASAR image of the Elbe River.

Many of the ASAR images are in black and white. Here is one showing Patagonia in Argentina, with the Andes to the left (west):

ASAR image of the Patagonia plateau and the Andes, in Venezuela.

As an example of the environmental utility of Envisat, we look again at the oil spill in the eastern Atlantic of Galicia in northwest Spain, which occurred in November of 2002 when the tanker Prestige sank with most of its cargo of 25 million barrels of oil. About 1.5 million did escape, some reaching coastal beaches, as seen here in this ASAR image.

ASAR (radar) image of the oil spill off the Spanish coast in late 2002.

As with several other satellites that mount both visible-NIR sensors and radar, these images can be combined. The three panels below show parts of Corsica and Sardinia in the Tyrranean Sea and the west coast of Italy just north of Rome. The left panel is an ASAR radar image; the center panel was made from MERIS images. The right panel is a registered combination of both - red areas over the water are rain clouds; red on land is NOT vegetation, but in the band combinations used this color coincides with vegetation-poor land areas.

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