Passive Microwave Rainfall Error Analysis using High-Resolution X-band Dual-Polarization Radar Observations in Complex Terrain

Accuracy and reliability of hydrological modeling studies heavily depends on the quality and availability of precipitation estimates. Difficulties in representation of high rainfall variability over mountainous areas using ground based sensors makes satellite remote sensing techniques attractive for hydrologic studies in these regions. Even though satellite-based rainfall measurements are quasi global and available at high spatial resolution, these products have significant uncertainties that necessitates the use of error correction procedures based upon more accurate in situ rainfall measurements. Such measurements can be obtained during experimental studies facilitated by research quality sensors such as locally deployed weather radar and in situ weather stations. This study uses such high quality and resolution rainfall estimates derived from dual-polarization X-band radar (XPOL) observations from two field experiments in Mid-Atlantic US East Coast and the Mediterranean to characterize the error of rainfall estimates from passive microwave (PMW) sensors onboard different earth orbiting platforms. The study first conducts an independent error analysis of the XPOL reference rainfall fields using in situ observations from rain gauges and disdrometers. Subsequently, coincident XPOL and PMW rainfall estimates are matched in space and time for a number of convective and stratiform type precipitation events. Specifically, coincident XPOL data are extracted for the PMW overpasses to produce the satellite field-of-view averages for the orbital PMW sensors and produce match-ups of PMW/XPOL rainfall and raindrop size distribution parameters. Both standard and climate versions of GPROF PMW retrievals on SSMIS, AMSU/MHS, GMI, and AMSR2 and the CNR-ISAC PMW products for SSMIS and AMSU/MHS are evaluated based on the produced match-ups. Moreover, version 3 of GPROF is compared to version 4 to evaluate improvements. The error analysis investigates dependences on precipitation type, precipitation vertical structure and microphysics (derived from XPOL).