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 were involved in completing the instrument test phase, after which Aqua went 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):

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.

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.

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:

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:

Released simultaneously were images from the AIRS group of 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:

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

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

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

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 multisensor 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.

AIRS also measures the total water vapor content of the atmosphere from its base to the outer limits of H₂O occurrence. This can be done globally for an extended period of time, as shown in this map which uses daily averages summed up for January 2004 to arrive at estimates of rainfall potential expressed in millimeters. The tropical zones can thus produce more than a half meter of precipitation over that period.

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 2002 (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.

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:

The first MODIS images were released near the end of June, 2002. An example of its large area coverage is this 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 on both Terra and Aqua took measurements of CO₂ throughout 2002. From knowledge of the Carbon Cycle (page 16-4) relations between CO₂ 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.

MODIS has also proved its value at detecting plankton and thus complements SeaWiFS and other ocean-dedicated satellites. This image shows chlorophyll distribution in the Arabian Sea between Pakistan and Oman. The higher than normal concentrations of planktonic life are due to a period of significant rainfall in the region.

Other satellites in the EOS program are now operational. ICESat (Ice, Clouds, and land Experiment Satellite; see page 14-14), whose sole instrument is GLAS (Geoscience Laser Altimeter System) and SORCE (Solar Radiation and Climate Experiment) were both successfully launched in 2003 but large quantities of data are still forthcoming.

Aura, discussed below, will concentrate on atmospheric chemistry and climate conditions, looking with its instruments also at the dynamics involved in climate change.

ENVISAT

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 (10). Count these in this artist's drawing - you should find 10. These are described in the Envisat component of ESA's Web site.

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:

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.

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 right.

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.

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

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 barrels did escape, some reaching coastal beaches, as seen here in this ASAR image.

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 right panel was made from MERIS images. The bottom 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.

One of Envisat's tasks is to monitor various chemicals (including pollutants) in the global atmosphere. Its Scanning Imaging Absorption Spectrometer for Atmospheric Cartography is capable of determining the amount and distributon of the noxious gas NO₂, released largely in auto emissions. Here is a map of the distribution of this gas over the eastern U.S. in June, 2003; yellows and browns are higher concentrations.

Aura will extend this compositional capability for air analysis and will dovetail results with Envisat.

AURA

The natural chemistry of the Earth's atmosphere is dominated by three elemental gases: O₂, N₂, and Argon; much of the CO₂ in air is introduced by natural processes such as transpiration. Some sulphur compound gases also are brought into the atmosphere by volcanic processes. Ozone, O₃, is likewise in large part present naturally. But as we have seen earlier in this Section, man's activities have altered natural balances of the above chemicals and added still others, mostly in burning fuels. A general diagram illustrating chemical transfer in the atmosphere is as follows:

The EOS program has included a spacecraft designed to primarily monitor the Earth's atmosphere. The third flagship in NASA's Earth Observatory spacecraft, AURA, was successfully launched in the early morning of July 15 2004 from the Vandenberg Air Force Base facility near Lompoc, California. Being a night launch, the visual effect of its takeoff, after 6 delays, was a "glorious" sight for the many scientists, engineers, and technicians who had patiently waited until all systems were finally set at "GO".

Aura, like the other EOS spacecraft, has its own website.

Aura was inserted along an orbital path and altitude that allows its to follow just 8 minutes behind Aqua, so that here is an example of formation flying, discussed on the next page. With two assemblages of different instruments, the Aqua-Aura pair are acquiring complementary data sets.

Its primary mission is to determine the "health" of the world's air envelope. This includes an inventory of global three-dimensional distribution of various chemicals (most as pollutants) in the atmosphere, as well as more detailed measurements of ozone, and evidence of short- and long-term climate change. We show here the $736 million dollar spacecraft (as big as a small bus and weighing over 3 tons) :

Below is the spacecraft "innards" in the assembly facility before its outer cover was emplaced.

Here is a chart indicating the chemicals that can be detected and quantified

The tasks of its four principal sensors are:

The joint U.K./U.S. High Resolution Dynamics Limb Sounder (HIRDLS) instrument will measure trace gases, temperature and aerosols in the upper troposphere, stratosphere, and mesosphere.

The Microwave Limb Sounder (MLS) will measure important ozone-destroying chemical species in the upper troposphere and stratosphere and measure trace gases in the presence of ice clouds and volcanic aerosols. MLS was built by the Netherlands and Finland in conjunction with NASA.

Ozone Monitoring Instrument (OMI) is Aura's primary sensor for tracking global ozone change and will continue the record of space-based ozone monitoring that began in 1970. NASA's Jet Propulsion Laboratory built OMI.

Tropospheric Emission Spectrometer (TES) will measure tropospheric ozone directly and other gases important to tropospheric pollution. JPL also made TES.

All four images are capable of making ozone measurements.

As with most satellites of this size and complexity, it took almost 90 days to purge the system of unwanted gases, check out instruments, adjust orbit, and do other appropriate housekeeping.

One major disappointment soon was evident. The Sun Shield on HIRDLS had upon opening become clogged with some debris in this instrument shaken loose during launch. The Shield had deployed only 20% of its full open condition. This severely compromises data acquisition because of the limited field of view. Hence, images from this sensor have not been released.

Far better luck befell the other three instruments. We look first at some MLS images; read their captions for brief descriptions.

Here are two ozone measurements made by the OMI:

Another example of the OMI data is this map of the a Pacific island group in a small nation called Vanuatu. Here the Ambrym volcano is exuding S0₂ gases through vents filled with lake water in large enough amounts to be dangerous to livestock.

NO₂ concentrations in the eastern United States measured by OMI on January 29, 2005 are plotted in this map:

A solar flare on January 17, 2005 apparently had a distinct effect on O₃ and OH in the Antarctic atmosphere which the OMI was able to detect and map; read the description in the diagram for details.

The TES has measured CO levels worldwide at two different altitudes (in atmospheric pressure terms):

The TES obtained vertical variation data for ozone and water along an orbital path from northern Canada to the Yucatan in Mexico.

The next is a short-term aerosol map made at a global scale.

The three Earth Observing satellites are all functioning well as of mid-2005. Imagery covering new types of data will be added from time to time.

As the EOS program moves on, some of the companion satellites shown in the diagram on Page 16-7 will be launched. One of these, JASON-1, was placed in orbit on Dec. 7, 2001. A joint endeavor between NASA JPL and the French Space Agency, it will provide improved wind speed measurements over the oceans and will yield data giving more detailed ocean surface topography. Here is one of the first products made public in 2002.

When these EOS satellites are all up and flying, they will represent one type of Satellite Formation Flying configuration. Another is the NPOESS program which will be developed in the first decade of th 21st Century. Page 16-11 discusses these innovations.

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Primary Contact: Nicholas M. Short, Sr.