Sensitivity of AIRS and IASI radiometric calibration to scene temperature

High radiometric accuracy under all conditions (such as scene temperature and scan angle) is critical for establishing a climate-quality data record. In this study we compare radiances of both AIRS and IASI using the difference each instrument sees between the brightness temperature at 1231 cm-1 and that at 961 cm-1. We collected spectra at 17 different sites distributed around the world in tropical, temperate, desert, and arctic climates. For perfectly calibrated instruments, the brightness temperature differences should closely agree, since diurnal differences caused by the differing orbits cancel to first order. We examine observed differences (indicative of calibration artifacts) as functions of scene temperature, time of day, and scan angle. AIRS is a cooled grating array spectrometer with 2378 spectral channels in the wavelength range from 3.7 to 15.4 microns. AIRS began routine operations in September 2002. IASI is a Fourier Transform spectrometer covering the range 3.6 to 15.5 microns in three bands. The spectral resolutions of AIRS and IASI are similar. IASI data have been available since July 2007.