AIRS Deconvolution and the Translation of AIRS-to-CrIS Radiances With Applications for the IR Climate Record

Abstract

Spectra of the earth’s thermal emission as measured by the Atmospheric InfraRed Sounder (AIRS), Cross-track Infrared Sounder (CrIS), and Infrared Atmospheric Sounding Interferometer (IASI) hyperspectral sounders are becoming a significant part of the long-term climate record. These instruments have broadly similar spatial sampling, spectral resolution, and band spans. However, the spectral response functions differ in detail, leading to significant differences in observed spectra. To address this, we translate channel radiances from one sounder to another, including simulation of the response functions of the translation target. We make regular use of such translations from AIRS to CrIS and IASI to CrIS and have implemented and tested IASI-to-AIRS and CrIS-to-AIRS translations as well. Our translation from AIRS to CrIS has some novel features. AIRS is a grating spectrometer with a distinct response function for each channel, whereas CrIS is a Michaelson interferometer with a sinc response function after calibration and corrections. We use our detailed knowledge of the AIRS spectral response functions to deconvolve AIRS channel radiances to a resolution-enhanced intermediate representation. This is reconvolved to CrIS or other instrument specifications. The resulting translation is shown to be more accurate than interpolation or regression.