The AIRS hyperspectral IR radiance climate data record

The Atmospheric Infrared Sounder (AIRS) is a hyperspectral infrared instrument on the EOS Aqua Spacecraft, launched on May 4, 2002. AIRS has 2378 infrared channels ranging from 3.7 um to 15.4 um and a 13.5 km footprint. The AIRS is a “facility” instrument developed by NASA as an experimental demonstration of advanced technology for remote sensing and the benefits of high resolution infrared spectra to science investigations. AIRS radiances are routinely assimilated by National Weather Prediction Centers worldwide. This paper will identify several uses of AIRS radiance data for climate applications and cross-calibration, provide key information on subtle performance characteristics of the AIRS instrument that affect the radiances, and identify how to apply new correction algorithms to improve accuracy and stability for climate applications.

Scientists have found the calibrated radiances from AIRS, Level 1B, to be particularly valuable for studying earth system processes affecting climate. The radiances have been demonstrated to be extremely stable and well calibrated making them ideal for seasonal and interannual investigations. AIRS radiances have been useful for comparisons with OLR from CERES and valuable in determining the contribution from the various spectral regions to the total OLR allowing attribution of the observations.

Use of AIRS radiances requires some explanation. Of the 2378 infrared channels a small fraction have high or unusual noise properties or are unusable. AIRS frequencies have a very small drift with time that if uncorrected could contribute to radiometric drift. New corrections to the scan angle dependence will allow the high calibration accuracy to be applied at all scan angles. These and other instrument subtleties will impact climate investigations if uncorrected, but if considered will allow the user to benefit from the long, stable, and accurate characteristics of the AIRS hyperspectral IR radiance climate data record.