Intercomparison of Reflectivity Measurements between GPM DPR and NEXRAD Radars

Hydrologic applications over a large area require radar composite products from multiple radar data. The composite products are often affected by radar measurement differences at the overlapping zones among ground radars (GRs). This systematic difference is caused by radar calibration, range effect, or combination of both and is revealed in the composite map as a linear feature at the equidistance zone. Since the launch of the GPM DPR (Global Precipitation Measurement Dual-frequency Precipitation Radar) in February 2014, NASA has implemented reflectivity measurement comparisons between DPR and NEXRAD GRs to help mitigate the GR calibration issues. NASA developed an algorithm to match reflectivity measurements over different sampling volumes (e.g., DPR vs. GRs) and has recently updated the level 1 DPR algorithm in May 2017 with generating new matchups retrospectively. In this study, we compare the latest two versions of these matchups that are generated using the different DPR level 1 algorithms. We test several factors (e.g., precipitation type, proximity to bright band, and partial beam filling percentage) in matching DPR vs. GR sampling volumes and statistically examine their sensitivity or contribution to the number and agreement of the selected DPR-GR matchups. In addition, we compare the NASA results with those of the GR relative difference estimates over Iowa using a method that represents coincidence in spatial and temporal sampling between GRs. We discuss potential benefits and limitations of the different approaches.