Skip navigationGetting the global picture


1. Storms of dust and tanks

2. Big eyes upstairs

3. Eyeing melting ice

4. At the big disconnects

5. Finding fish - by satellite

6. Fire and brimstone

This movie shows how the Atmospheric Infrared Sounder on the EOS Aqua satellite reads temperature at various levels of the atmosphere (1.5 MB).NASA.




Thermal radiation leaving Earth, seen by the EOS Terra satellite. Radiation is fairly uniform over the oceans. The blue swaths across the central Pacific are the tops of thick clouds. Their highest points (white) are among the coldest places on Earth. Notice the intense outgoing radiation from the U.S. Southwest (upper right edge). The area had a heat wave when the image was made on Sept. 30, 2001. It's so dry that little solar energy gets absorbed. And there's little cloud cover to block outgoing radiation. Image from Clouds and the Earth's Radiant Energy System.







Satellites are really the only way to get the big picture on what's happening on Earth.


A fixation with space
thumbnail image of movie: Satellite image shows western United States enshrouded in clouds. The clouds are being swept away graphically by an arm of the satellite to reveal a clean picture of the land below. Why are earth scientists so fixated on space? Access, access, access. Say you want to know the temperature of the atmosphere -- a reasonable request in this global warming era. But you don't want to measure only in cities, and only near the ground. You want the entire atmosphere, over the whole globe, at all levels.

The same rule applies to measuring energy entering or leaving the planet, and water vapor, ozone and trace gases. Where are they in the atmosphere? How common? How much do they vary?

The EOS satellites are designed to answer this type of question. For example, Aqua, launched May 4, 2002, carries six instruments, including the Atmospheric Infrared Sounder, which will measure 2,378 infrared wavelengths, plus four on the red end of the visible spectrum. With sufficient computerized massaging, they will be turned into "soundings" (measurements at various depths) of the atmosphere.

Sphere in bright shades of orange and yellow, with sparse blue and white patches and strips, against a black background. Colors indicate longwave flux.

"The object is to get the best atmospheric temperature and humidity readings of any spaceborne system," says Claire Parkinson, project scientist for Aqua, at the Goddard Space Flight Center in Maryland... "to get the same level of accuracy, or better, as radiosondes." About 3,000 to 4,000 of these balloon-borne atmospheric instrument packages are released every day. They can reach up to about 30 kilometers, and send data back by radio.

Parkinson admits the effort may seem redundant. "People could say it's only the same level of accuracy as something you already have," but that ignores the critical advantage of satellites. While radiosondes require people to release them, the satellite, she says, "is getting the same level of accuracy, all around the globe, day after day. With radiosondes... in the vast reaches of the Pacific, you don't have measurements," she adds.

Furthermore, Aqua takes 400,000 readings per day, about 100 times as radiosondes. The orbiting gadget sends down 89 gigabytes of data - day after day.

Aqua's velvet data
Many of Aqua's instruments also orbit on a sister satellite, Terra, launched in 1999. A key finding of that satellite was rapid changes in energy flow through the upper atmosphere over the tropics. "People thought it stayed on an even keel year after year," Parkinson says, "but they are finding it's not nearly as stable as we once thought." The changes in outgoing radiation could stem from changes in Earth's reflectivity, or more likely in changing cloud cover.

 A brown balloon seen against blue-black sky, with two packages trailing beneath it to carry instruments.The weather balloon, or radiosonde, is a classic tool of meteorology. But satellites are threatening to replace it. NASA.

This business matters. Solar energy heats up the planet, making life possible. But we would cook if Earth can't dump the same amount of energy to space. But it does: the warm land, ocean and atmosphere all emit long-wave (thermal) radiation.

The question for global warming folks is this: how fast is that taking place. In dollars-and-cents terms, the critical question is the overall "energy budget" for our planet.

Armed with new data on the energy budget, the Clouds and the Earth's Radiant Energy System (CERES) science team is looking closely at the impact of clouds, says Parkinson. Years after clouds were first identified as a key unknown in the emerging study of global warming, Parkinson says, clouds are still "considered to be one of the definite key elements where more information is needed on."

Can EOS also measure big ice?

The Why Files

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