AIRS

Frequently Asked Questions


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Q.  How does data collected through the AIRS program compare with data that
could be gathered using radio occultation?  

A.  AIRS and radio occultation (GPS) are very different types of programs.
AIRS looks down and scans from side to side across its track to map the
three-dimensional temperature and water vapor distribution. Radio
occultation (satellite-to-satellite using GPS constellation) looks along
a path drawn between two satellites that is tangent to the Earth's
surface at some point.

The major difference between the programs is two-fold:

1) Spatial coverage - AIRS blankets the globe in the course of a single
day, making observations equivalent to 300,000 balloon-borne
radiosondes. GPS provides (using all combinations of satellites so
instrumented) perhaps several thousand observations at a particular
level in the atmosphere in the course of a day. The GPS observation,
where it occurs, has a higher vertical resolution than AIRS, but coarser
horizontal resolution.

2) Atmospheric parameters retrieved - AIRS retrieves both the
temperature profile and the water vapor profile at the same time. The
GPS observation must assume either a temperature profile or a water
vapor profile, at which point it can recover the unknown one. Usually
GPS takes temperature profiles from models or satellites (like AIRS) and
then retrieves water vapor at the tangent point.

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