Effects of Degraded Sensor Resolution upon Passive Microwave Precipitation Retrievals of Tropical Rainfall

Abstract

Based on the fundamental relationship involving the interaction of microwave radiation with precipitation, microwave-based satellite precipitation estimates hold the most promise for quantitative rain estimation from space. At present, the low-resolution channels onboard the DMSP Special Sensor Microwave Imager (SSM/I) are sampled with a spatial resolution several times larger than the scale at which rainfall is generated in typical convective rainbands. Aircraft-based instruments can provide views of the detailed microwave radiometric characteristics of precipitating clouds. In this manuscript, the authors present coincident finescale (1?3-km resolution) collocated aircraft radiometric and aircraft precipitation radar measurements collected during the 1993 Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment in the western Pacific Ocean. By intentionally degrading the resolution of the aircraft datasets from their native resolution to that of current and future spaceborne sensors, the impact of sensor resolution upon a combined radiometer?radar vertical profiling rain-retrieval algorithm (developed and utilized for the Precipitation Intercomparison Program 2) was examined. Retrieved values of the columnar graupel content were more influenced by the addition of the radar profile than was the columnar rain content. The retrieved values of columnar graupel were also significantly smaller than previously published results for land-based rainfall. The results show that the general trend of the rain structure is maintained but finescale details are lost once the observations are reduced to resolutions of 15 km.