Infrared Low-Cloud Detection

Traditional infrared cloud retrieval algorithms, such as the Chahine method or the CO2 Slicing technique (Chahine 1974, Smith 1968), rely on recognizing the temperature difference between the ground and the cloud tops. For a low-cloud, however, the temperature difference is small, making it indistinguishable from the surface. As part of our work for the Atmospheric Infrared Sounder (AIRS), to be flown on the EOS-PM platform, we are developing an improved technique for the detection of low-clouds. It is based upon observations of the depth of narrow water vapor lines in an atmospheric window region. Compared to traditional methods, there is an extra factor (the water vapor amount) making the signal from a cloudy column different than that from a clear column, which increases our sensitivity to low-clouds.