Computing the atmospheric absorption for the DMSP operational linescan system infrared channel

An accurate and rapid means is presented for computing the atmospheric abso rption for the infrared channel (10.2-12.7 mu m) on the Defense Meteorologi cal Satellite Program operational linescan system (OLS) for use in remote s ensing studies of surface and cloud properties. The method is a new approac h to correlated k-distribution theory that keeps track of spectral informat ion at the cumulative probability (g) level and more effectively addresses overlapping absorption through a recursive procedure. It also incorporates details of the instrument's response function. Comparisons with line-by-lin e (LBL) results demonstrate that calculations using only 60 g-space interva ls produce total atmospheric transmittance errors of 0.24% for a tropical a tmosphere and 1.2% for a midlatitude winter atmosphere. In terms of upwelli ng equivalent blackbody (EBB) temperatures computed at the top of the atmos phere (TOA), the errors are less than 0.5 K over a wide range of atmospheri c profiles and zenith angles when compared co LBL radiative transfer calcul ations. Errors are smallest (<0.1 K) for tropical environments. For downwel ling EBB temperatures at the surface the errors become somewhat larger, esp ecially for the winter atmosphere (maximum error of 1.66 K). Errors also ge nerally increase slightly with increasing zenith angle. Reducing the number of g-space intervals to 17 can still provide reasonable results with a max imum error of 0.72 K for the TOA upwelling EBB temperature in a midlatitude winter atmosphere.