Evolving improvements to TRMM ground validation rainfall estimates

Abstract The primary function of the TRMM Ground Validation (GV) Program is to create GV rainfall products that provide basic validation of satellite-derived precipitation measurements for select primary sites. Since the successful 1997 launch of the TRMM satellite, GV rainfall estimates have demonstrated systematic improvements directly related to improved radar and rain gauge data, modified science techniques, and software revisions. Improved rainfall estimates have resulted in higher quality GV rainfall products and subsequently, much improved evaluation products for the satellite-based precipitation estimates from TRMM. Early improvements in TRMM GV rainfall products involve replacing a default radar reflectivity (Z e ) — rain rate (R) relationship with convective and stratiform relationships independently derived using bulk-adjusted, quality-controlled rain gauge data. Upon the development of an automated gauge quality control procedure, poorly correlated gauge-radar data in the bulk-adjustment process are ignored and Z e -R relationships are again refined. These Z e R relationships, applied to base scan reflectivity data to produce GV rain maps, are further modified as improvements to intermediate radar and gauge products result in more realistic and internally consistent rainfall statistics. Additionally, improvements to radar and gauge data from the primary GV sites further increase the reliability of rainfall products. Rainfall accumulation statistics for each primary site are presented, demonstrating the evolving improvement in radar rainfall estimation for each successive generation of products. Current generations of GV rainfall products, based on more robust data and science techniques, have removed known biases in radar rainfall estimates. Increased confidence in GV rainfall products results in more meaningful comparisons with satellite-derived precipitation estimates from TRMM.