This document provides a basic set of documentation for the data products available from the GPM Ground Validation System (GVS) Validation Network (VN). In the GPM era the VN performs a direct match-up of GPM’s space-based Dual-frequency Precipitation Radar (DPR) data with ground radar data from the U.S. network of NOAA Weather Surveillance Radar-1988 Doppler (WSR-88D, or “NEXRAD”). Ground radar networks from international partners are also part of the VN. The VN match-up will help evaluate the reflectance attenuation correction algorithms of the DPR and will identify biases between ground observations and satellite retrievals as they occur in different meteorological regimes. Volume 2 of the Validation Network Data User’s Guide describes the GPM core and constellation VN data set. 

An earlier version  of the VN capability performed a match-up of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data with ground-based radar (GR) measurements from a subset of the WSR-88D sites now included in the GPM-era VN operational radar data network. Legacy TRMM data and their matching GR observations will continue to be part of the VN operations in the GPM era.  Refer to Volume 1 of the Validation Network Data User’s Guide for a description of the legacy TRMM-specific VN data set.