Observing precipitation by means of water vapor absorption lines: A first check of the retrieval capabilities of the 183-WSL rain retrieval method

A new approach is described to infer rain rates by using the opaque channels of the Advanced Microwave Sounding Unit-B (AMSU-B) sensor on board of the NOAA satellites. The retrieval scheme of the 183-WSL (Water Strong Lines at 183.31 GHz) algorithm consists of two main modules. First, some thresholds act to discriminate between rainy and non-rainy pixels (183-WSLW). This is necessary to prevent false alarms mainly caused by the strong absorption of the condensed cloud droplets developing during light precipitation formation. Cloud droplets, especially when they feed precipitation formation mechanisms, can sensibly grow as a consequence of intense condensation in the surrounding regions of rainy clouds. Secondly, on the basis of different extinction of radiation, rain types are classified as convective (183-WSLC module) or stratiform (183-WSLS module) typologies.