The combined use of coincident active and passive microwave sensor data provides complementary information about the macro and microphysical processes of precipitating clouds which can be used to reduce uncertainties in combined radar/radiometer retrieval algorithms. In simple terms, the combined algorithms use the radiometer signal as a constraint on the attenuation seen by the radar.

The combined retrievals produce a hydrometeor profile, particle size distribution and surface parameters for which brightness temperatures and reflectivities are consistent with the actual satellite measurements. These combined products can be repackaged for use as retrieval Bayesian databases for multiple radiometers. For the theoretical and mathematical details of the combined radar/radiometer algorithm please review its Algorithm Theoretical Basis Document (ATBD) found at the Precipitation Processing System website.