AIRS

Frequently Asked Questions


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Q.  Can you improve the meaurements of the temperature of the ground (earth)
by correcting any atmospheric disturbance? In other words, can AIRS get
better results than MODIS?  

A.  The AIRS physical retrieval combines data from the AMSU microwave
instrument and the AIRS infrared instrument. Within the 50km (nominal,
at nadir) AMSU field of view are nine 15km (nominal, at nadir) AIRS
fields of view. Our Level 1B radiance products provide the observed
instrument radiances/spectra at native instrument resolution. Our
Level 2 cloud-cleared radiance product and Level 2 physical product
are reported at the AMSU field of view spatial resolution.

The AIRS physical products include the atmospheric temperature and
water vapor profiles as well as the surface parameters. Thus our
surface temperature retrievals do include corrections for atmospheric
effects. However, our retrieval results in a spectrum of surface
radiance, and we must separate the surface emissivity from the surface
skin temperature. Over ocean this is relatively easy, as the sea
surface emissivity is mainly modified by surface winds and that
modification is relatively small. Over fully vegitated land the
retrieval is also relatively straightforward. The most difficulty is
encountered in the case of naked soil. You can appreciate the
variability of soil types within a spot 50km in diameter! We are
continuing to refine our surface retrieval algorithm, but deserts are
particularly difficult. MODIS is a true imaging instrument, with much
higher spatial resolution than AIRS. Thus the soil variability in
their footprint is not as severe. AIRS is complementary to MODIS-
poorer spatial resolution but greater resolution in the spectral
domain. We also cloud-clear through our algorithm combining the AIRS
radiances within the AMSU field of view.

You may not be aware of our trace gas retrievals, which will begin to
be standard products in our Version 5 release. One of them is a
detection of SO2. We have given NOAA our updated algorithm for their
near real time feed to the forecast community. Included in that
product is the SO2 detection, and that is now being shared with the
Washington Volcanic Ash Advisory Center (VAAC, W-vaac@noaa.gov), which
now rebroadcasts that flag. It has already been responsible for same-
day detection of several remote volcanic eruptions (Augustine and
Manam). Fred Prata of the Norwegian Institue for AIR Research is
generating SO2 retrievals from AIRS and HIRS data products.

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