A Fast Line-by-Line Method for Atmospheric Absorption Computations: The Automatized Atmospheric Absorption Atlas

Abstract

A computationally fast line-by-line method for the determination of atmospheric absorption is described. This method is based on the creation of an Automatized Atmospheric Absorption Atlas (4A) covering all possible plausible atmospheric conditions (temperature, mixing ratios of absorbing gases, zenith angle). It is applied to synthetic computations of atmospheric transmittances and radiant energies associated with three types of satellite observations: radiometric measurements made by HIRS/2 (High-Resolution Infrared Sounder) on TIROS-N; infrared images taken from the geostationary satellite METEOSAT; interferometric experiment IRIS (Infrared Interferometer Spectrometer) on VOYAGER (NASA's mission to Jupiter, Saturn and possibly Uranus). For all three experiments, comparisons were made with real observations and are presented associated with radiosonde data for the first. Concerning computation times, a gain of a factor varying between 15 and 40 is obtained when using the 4A line-by-line method rather than a standard line-by-line method.