Ground Validation of IMERG as a Function of Spatiotemporal Scale

Abstract:

The Integrated Multi-satellitE Retrievals for GPM (IMERG), a global high-resolution gridded precipitation data set, will have widespread uses, ranging from studies on precipitation characteristics to applications in hydrology to evaluation of weather and climate models. These applications typically re-grid the precipitation rates to lower resolutions or average them over specific domains. Such a modification of scale will impact the reliability of IMERG. In this study, the performance of IMERG is evaluated against ground-based measurements as a function of increasing spatial resolution and accumulation periods.

The focus of this study is the Final run of IMERG, which is derived from a constellation of satellites with monthly gauge adjustment. For ground truth, the Multi-Radar Multi-Sensor (MRMS) Stage III product, a radar- and gauge-based operational precipitation product over the US, is used. The analysis is restricted to a region in which MRMS is highly reliable due to good radar coverage, wherein IMERG is compared to MRMS averaged over boxes of increasing size and accumulation, starting from 0.1° at 1 h. TRMM Multisatellite Precipitation Analysis (TMPA) is also included as a benchmark.

In general, IMERG expectedly performs better with increasing spatial and temporal scale, with higher correlations, lower error values and better identification of rain events. IMERG also outperforms TMPA most of the time. These results will serve as a reference for users of IMERG on its reliability over the scales relevant to their studies.