AN IMPROVED CLOUD RETRIEVAL ALGORITHM USING HIRS2-MSU RADIANCE MEASUREMENTS

Cloud-top heights and cloud amounts are produced as part of the operat ional processing of polar-satellite data at the National Environmental Satellite Data and Information Service (NESDIS). These products were compared with similar products from the air force's real-time nephanal ysis (RTNEPH), from the International Satellite Cloud Climatology Proj ect, and from NASA Goddard's processing of satellite data. It was foun d that the amount of high-level cloud was too small in the NESDIS resu lts, while the amount of low-level cloud was too large. An examination of the NESDIS algorithm revealed that the differences in cloud distri butions were caused by the selection of channels used for the cloud re trievals. Cloud retrievals are most accurate at the levels at which th e channels that are used are most sensitive. In addition, it was found that no one pair of channels was best at all levels. A new procedure was developed that varied the channels as a function of an initial est imate of the cloud height. This procedure produced improved cloud retr ievals that were then compared with the RTNEPH results. The comparison showed that the two methods provide similar retrievals of cloud heigh t and amount.