Atmospheric Absorption in the VAS Split-Window Channels

Abstract

The Visible Infrared Spin-Scan Radiometer (VISSR) Atmospheric Sounder (VAS) split-window channels at 10?12.5 ?m and 12.6?12.8 ?m can be used to give measurements of sea surface temperature (SST) and precipitable water amount in the lower troposphere. Empirical algorithms for providing these quantities have been developed by comparing conventional ground based measurements with the satellite data. Chesters et al. (1987) produced new differential absorption coefficients for the VAS split-window channels which, when used in a transmission model of the atmosphere, reproduce their optimized precipitable water algorithm. These new coefficients are used here in a spectral band model to see if they also improve the match between empirical and theoretical (model derived) SST algorithms. Some improvement is found but the analysis suggests that the absorption coefficient of a dry atmosphere in the 12.7 ?m channel should be less than that for the 10?12.5 ?m channel. In contrast, the differential absorption coefficient (12.7 ?m minus 10?12.5 ?m) for water vapor should be increased. Differential absorption coefficients that match the theoretical SST retrieval algorithm to that used empirically by Bates and Smith (1985) are given.