Comparing GPM Satellite to Ground Platform Measurements: Case Studies from the NASA GPM Wallops Precipitation Science Research Facility

NASA’s Global Precipitation Measurement (GPM) satellite mission aims to advance our understanding of precipitation measurement from space, thereby improving weather forecasting, and climate modeling. Ground validation of GPM provides critical feedback to algorithm developers for enhanced understanding of measurement uncertainty and retrieval errors. Observations from the space-borne first generation Dual-frequency Precipitation Radar (DPR) and passive microwave imager (GMI) are being validated through statistical and physical approaches via comparison to research quality ground platform measurements from scanning and profiling radars, disdrometers, and rain gauges. Knowledge of the horizontal and vertical distribution of precipitation within the atmospheric column is crucial to bridge the gap between space and ground platforms. To do this, the System for Integrating Multi-platform data to Build the Atmospheric column (SIMBA – see Wingo et al. (2016) – AGU Conference) is employed to combine measurements from space and ground platforms into a common grid and build an atmospheric column product. This framework facilitates the analysis and comparison of multi-platform observations.

Two GPM overpass cases focused over the NASA GPM Wallops Precipitation Science Research Facility will be presented utilizing the SIMBA framework. A widespread convective and stratiform case from 28 June 2016 and widespread stratiform event from 21 May 2015 will be analyzed for this initial study. Both of these cases were chosen due to excellent GPM satellite and ground instrument coverage from overpass events with close nadir distance (< 60 km). These two differing rain environments will provide insight on the vertical and horizontal variability of rainfall within the atmospheric column in conjunction with GPM coverage. Data will be considered from an array of instruments: NASA’s S-Band Dual-Polarimetric Radar (NPOL), NASA’s Ka/Ku-Band Dual-Polarization Dual-frequency Doppler Radar (D3R), NASA’s K-Band Micro Rain Radar (MRR), NOAA’s S-Band Weather Surveillance Radars 1988 Doppler (WSR-88D), GPM multi-channel Microwave Imager (GMI), GPM Ka/Ku-Band Dual-Precipitation Radar (DPR), 2-Dimensional Video Disdrometers (2DVD), Particle Size and Velocity (PARSIVEL) disdrometers, and surface rain gauges. The goal of the study is to compare GPM derived radar reflectivity (Z), rain rate (R), and gamma drop-size distribution (DSD) parameters (Nw, Dm) to ground measurements in a spatially defined atmospheric column. The grid resolution will be on the order of 250 to 500 meters in the horizontal and vertical. Special attention will be focused on parameter comparison between DPR Ku/Ka band single frequency, dual-frequency, and combined DPR/GMI algorithms to ground observations for analysis of non-uniform beam filling (NUBF) on the sub-grid scale satellite footprint.