The Precipitation Retrieval and Profiling Scheme for the Special Sensor Microwave Imager/Sounder

The Special Sensor Microwave Imager/Sounder (SSMIS) of the US Defense Meteorological Satellite Program (DMSP) has been the mainstay of observations used for precipitation retrievals over the last 20 years. The sensor, building upon the heritage of the DMSP Special Sensor Microwave/Imager (SSMI) series that operated between 1987 and 2020, provides precipitation-capable frequencies from 18-183 GHz at resolutions up to 15x13 km. The longevity of the SSMIS and the SSMI satellite series makes these sensors extremely important for the retrieval of precipitation at the climate-scale. The adaptation of the Precipitation Retrieval and Profiling Scheme (PRPS), originally developed for passive microwave sounders, to the SSMIS aims to provide model-free precipitation retrievals that can be incorporated into the Global Interpolated Rainfall Estimation (GIRAFE) product developed by EUMETSATs Satellite Application Facility on Climate Monitoring (CM SAF).

Fundamental to the PRPS is the avoidance of external dynamic data sets, such as model information, to ensure that the retrieval scheme is purely a satellite-based observational product. The scheme relies upon the generation of observational databases, based upon co-temporal and co-located observations made by the satellite sensor(s) and observations of precipitation made by either satellite-based precipitation radar or surface radars. For the PRPS-SSMIS, the databases have been generated using observations from SSMIS sensors on the F16, F17, F18 satellites matched against the precipitation estimates provided by the NASA/JAXA Dual frequency Precipitation Radar (DPR) on the NASA/JAXA Global Precipitation Measurement mission (GPM) core observatory. The orbits of the SSMIS and GPM provide about 20,000 crossing points per satellite between 2016 and 2022, and generate about 30M co-located (<2.5km) and co-temporal (<15mins) entries for the a priori database. The retrieval stage of the PRPS uses this database as a reference against which the satellite observations are made to provide an estimate of the surface precipitation. The PRPS-SSMIS as implemented here, provides instantaneous precipitation estimates across the globe at a spatial resolution of 15x15 km.

This presentation will show some initial results of the scheme which show that the PRPS-SSMIS retrievals are comparable with those generated by NASA’s operational precipitation retrieval scheme, GPROF. At the instantaneous scale the PRPS tends to generate less light precipitation and more heavy precipitation, this can be explained in part by the difference in the resolution of the PRPS-SSMIS (15x15 km) and GPROF-SSMIS (45x74 km). Crucially, the PRPS provide much more information on light precipitation compared with the existing CM SAF SSMIS retrieval scheme (not utilised in the current GIRAFE version because of these detection issues). At the monthly scale, the PRPS generates very similar results to GPROF with all the main precipitation features correctly portrayed.