Computing the Atmospheric Absorption for the DMSP Operational Linescan System Infrared Channel

Abstract

An accurate and rapid means is presented for computing the atmospheric absorption for the infrared channel (10.2?12.7 ?m) on the Defense Meteorological Satellite Program operational linescan system (OLS) for use in remote sensing studies of surface and cloud properties. The method is a new approach to correlated k-distribution theory that keeps track of spectral information 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-line (LBL) results demonstrate that calculations using only 60 g-space intervals produce total atmospheric transmittance errors of 0.24% for a tropical atmosphere and 1.2% for a midlatitude winter atmosphere. In terms of upwelling equivalent blackbody (EBB) temperatures computed at the top of the atmosphere (TOA), the errors are less than 0.5 K over a wide range of atmospheric profiles and zenith angles when compared to LBL radiative transfer calculations. Errors are smallest (<0.1 K) for tropical environments. For downwelling EBB temperatures at the surface the errors become somewhat larger, especially for the winter atmosphere (maximum error of 1.66 K). Errors also generally increase slightly with increasing zenith angle. Reducing the number of g-space intervals to 17 can still provide reasonable results with a maximum error of 0.72 K for the TOA upwelling EBB temperature in a midlatitude winter atmosphere.