Determination of Semi-Transparent Cirrus Cloud Temperature from Infrared Radiances: Application to METEOSAT

Abstract

The use of simultaneous infrared measurements to derive the temperature and emissivity of semi-transparent cirrus clouds is experimentally investigated. Results from the NASA/CONVAIR-990 Winter Experiment Program, 1977 (WEP) are discussed. It is shown that the mean effective emissivities of cirrus in the water vapor absorption channel 5.7–7.1 μm and in the window channel 10.5–12.5 μm are equal to within 6%. A method is then developed to derive the cirrus temperature and emissivity from simultaneous measurements in the two infrared channels. This method is applied to 14 cirrus cloud cases observed during the WEP experiment. The infrared temperature was found to agree with other aircraft or conventional data. A similar technique is then developed and applied to METEOSAT digital images. The results indicate that using both infrared channels should lead to a major improvement in the determination of the cirrus cloud temperature and height from satellites.