AIRS

Frequently Asked Questions


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Q.  1) How are "surface temperatures" determined for forrests and other
areas where the land is covered?
2) What is the accuracy of land surface measurements (+/- degrees C)
3) What is the effect of cloud cover on accuracy?  

A.  1) Surface Skin Temperature is the specific AIRS product. It is
determined by the combined retrieval algorithm which determines the
cloud-cleared radiance (brightness temperature) and the surface
emissivity. Dividing the first by the second yields the physical skin
temperature, which may be ground (if bare surface), ocean skin
temperature (not to be confused with bulk temperature), or forest
canopy skin temperature.

2) Land surface temperature is problematical, since the emissivity of
bare earth will vary greatly over the 50 km diameter spot in which our
retrieval is made. Our estimated uncertainty at present is 2->3 K.

3) We have found no correlation with fraction of cloud cover, beyond
our retrieval yield dropping when it reaches about 80%. Low stratus
clouds are problematical, as we cannot discriminate between a field
covered 100% by low stratus and a clear field. The temperature of the
cloud tops of low stratus is close to that which would be encountered
on the surface.

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