Database Construction for GPM Constellation Precipitation Retrievals Using Core Satellite Combined Microwave Radar-Radiometer Observations

The Global Precipitation Measurement Mission (GPM) offers the opportunity for a greatly increased understanding of global rainfall and the hydrologic cycle. By employing a constellation of radiometers, coverage and sampling are greatly increased (Hou et al. 2014), while the core satellite acts as a standard, enabling consistent retrievals across constellation members. The combination of GPM core active and passive microwave sensors are used, following techniques developed using the predecessor Tropical Rainfall Measuring Mission (TRMM) satellite, to construct observationally constrained databases of precipitation profiles for use in constellation member retrieval algorithms. The method uses a conservative approach that begins with the operational GPM combined radar-radiometer retrieval algorithm and adjusts its solution while maintaining a match to observed radar reflectivities and radiometer brightness temperature (Tb) in all GMI frequencies. Adjustments include adding a graupel species for convective pixels, cloud ice for improved agreement in the high frequency channels, and drizzle below the sensitivity of the radar. In order to build a robust, statistically representative database for use in a Bayesian retrieval scheme, non-raining pixels must also be proportionally represented. Tbs are modeled in non-raining areas using atmospheric and surface information consistent with the combined retrieval and observed Tbs, and the procedure is performed over all ocean and land surfaces. The resulting profiles include surface characterization, atmospheric information, and hydrometeor profiles, radiometrically consistent with the observed Tb. The profiles can then, using forward radiative transfer, be used to create databases for each of the GPM constellation radiometers. Early results indicate good agreement and high correlations between database simulated and observed Tbs. The database will be implemented within the GPROF algorithm for passive microwave rainfall retrievals applied to radiometers that form the GPM constellation.