Information Content of METEOSAT and Nimbus/THIR Water Vapor Channel Data: Altitude Association of Observed Phenomena

Abstract

Significant information can he extracted from satellite measurements in water vapor bands so that an accurate association of the observable phenomena in corresponding satellite images and the altitude level is required. In order to evaluate rapidly the contribution of different atmospheric layers with the desired high accuracy for spectrally wide channels, transmittance functions for 25 cm?1 intervals covering the whole 6.3 ?m band have been fitted to line-by-line calculations. Contribution functions have been determined for varying atmospheric conditions and viewing angles, taking into account the different spectral response functions of the METEOSAT and Nimbus/THIR radiometers. Given mean atmospheric models for different latitudes and seasons, the summarized results, which agree approximately for both instruments, are as follows: 1) the contribution function depends particularly on the vertical water vapor profile and viewing angle, 2) the sensitivity to temperature changes in the atmosphere is comparatively small, and 3) the half-width center of the contribution function lies between 560 and 360 mb. The major contributing layer is ?320 mb thick and its location varies between the 800 and 250 mb levels.