THERMAL IMAGING THROUGH THE ATMOSPHERE - ATMOSPHERIC MODULATION TRANSFER-FUNCTION THEORY AND VERIFICATION

Atmospheric modulation transfer function (MTF) measurements carried ou t simultaneously in both thermal imaging atmospheric windows using bot h passive and actively heated targets are presented. Results indicate rather significant angular spatial frequency dependence of the MTF, in contradiction to the conventional approach, which assumes contrast tr ansfer is atmospheric transmission only. A theoretical explanation is discussed, based on aerosol forward scattering and absorption effects, which is shown to be angular spatial frequency dependent and yields M TF results similar to those measured. This means that small details ar e blurred much more than large details by the atmosphere, thus also af fecting target acquisition probabilities.