On the detection of cirrus clouds from satellite measurements

A thorough literature review of cloud algorithm validation strategies is presented, with particular emphasis on the problems of detecting cirrus clouds. To further advance our cirrus detection capabilities, a new cloud detection technique is proposed for the Multi-angle Imaging Spectro-Radiometer (MISR), which is scheduled to be on the first platform of the Earth Observing System. Radiative Transfer simulations have been used to develop a Band-Differenced Angular Signature technique. This new technique takes the difference between two solar spectral reflectances as a function of view angle. The resulting angular signature is used to discriminate between high- and low-level clouds and surface reflectance anomalies. This technique, coupled with a Predetermined Clear Sky Threshold developed in this study for MISR, can detect cirrus clouds of visible optical thickness $>$0.5 without any a priori knowledge of atmospheric conditions. Other techniques that can be used with MISR (i.e. stereo) are also discussed.