Evaluation of Germany's network radar composite rain producs with GPM near surface precipitation estimations

The Global Precipitation Measurement core satellite (GPM) has been collecting high quality precipitation data since 2014 over the globe with its Dual-frequency Precipitation Radar (DPR; Ku-band and Ka-band). Specificly over Germany, GPM provides data with typically two daily overpasses. Thus providing a unique opportunity to have a satellite based standard for estimation of precipitation in order to compare and evaluate ground-based radar network counterpart products. The German national weather service (DWD, Deutscher Wetterdienst) provides precipitation observations from its operational radar network RADOLAN as a composite products derived from 17 dual-pol C-band radars. The RADOLAN (RY) regular products are Germany-wide composites of precipitation estimates based on a set of precipitation type dependent Z-R relationships derived for liquid hydrometeors applied to radar reflectivity after clutter- and beam blockage-corrections. In this contribution we focus to compare three years of GPM DPR and RADOLAN precipitation products. This allows us to evaluate at which extend these two Near Surface products are consistent when observed from different geometries and obtained by independent instruements and retrieval methods. We quantify the uncertainties when directly comparing the DPR near surface product with RY. It is shown that a direct comparisons might not take into account a set of uncertainties originated from the scans geometry from DPR and RADOLAN, precipitation types, and sampling volumes. Therefore we suggest an adjusted DPR product, which is extracted from the DPR vertical profiles and adapted to fit the specific RY measurement configuration e.g. scans height and beam width. This allows a much more detailed classification of the hydrometoer phases per measuring volume, which we define as non-uniform phase beam filling (NPBF). The NPBF gives information about the ratio of liquid, solid or mixed hydrometeors in a given volume. Orographic, synoptic, microphysical influences as well as NPBF effects are examined and their uncertainties introduced on a direct comparison of satellite with ground-based producs are put into consideration. The adaptation of the DPR precipitation products to the specific scan geometry of the individual ground radars improves the correlation and reduce the RMSE.