Abstract:
The Atmospheric Infrared Sounder (AIRS) is a hyper-spectral infrared sounder which covers the 3.7 to 15,4 micron
region with 2378 spectral channels. The AIRS instrument specification called for spatial co-registration of all channels to
better than 2% of the field of view. Pre-launch testing confirmed that this requirement was met, since the standard
deviations in the centroids was about 1% of the 13.5 km IFOV in scan and 3% in track. Detailed analysis of global AIRS
data show that the typical scene gradient in 10 micron window channels is about I .3K/km rms. The way these gradients,
which are predominantly caused by clouds, manifest themselves in the data depends on the details of the instrument
design and the way the spectral channels are used in the data analysis, AIRS temperature and moisture retrievals use 328
of the 2378 channels from 17 independent arrays. As a result, the effect of the boresight misalignment averages to zero
mean. Any increase in the effective noise is less than 0.2K. Also, there is no discernable performance degradation of
products at the 45 km spatial resolution in the presence of partially cloudy scenes with up to 80% cloudiness. Single
pixel radiometric differences between channels with boresight alignment differences can be appreciable and can affect
scientific investigations on a single 15km footprint scale, particularly near coastlines, thunderstorms and surface
emissivity inhomogeneities.
