Global precipitation measurement (GPM) mission and dual-frequency precipitation radar (DPR)

Abstract

Global precipitation measurement is essential not only for the research of the global change but also for the water resources management. Currently, satellite precipitation measurement is not sufficient for the detailed study of the precipitation and is far from enough for the water resources management which requires very high spatial and temporal resolution. To fill the gap at least partly, the Global Precipitation Measurement (GPM) was proposed jointly by US and Japan. The basic concept of the GPM is to provide three hourly global precipitation maps using eight constellation satellites equipped with microwave radiometers and a core satellite equipped with the Dual-frequency Precipitation Radar (DPR) and a microwave radiometer. The DPR which uses radiowaves of 13 and 35 GHz is now being developed in Japan. The DPR will observe 3D precipitation structure and will provide essential data for microwave rain retrieval. GPM is partly a follow-on mission of the Tropical Rainfall Measuring Mission (TRMM), but the GPM will extend the observation to cold regions where solid precipitation frequently exists. Rain retrieval algorithms that use the DPR data are also being developed. Using two wavelength data, two parameters in the raindrop size distribution could be retrieved, which would result in precise rain retrieval. The retreaval of solid precipitation rate is another challenge. The solid precipitation has another parameter of density which varies significantly. The hydrometeor shape also deviates significantly from a sphere. Several algorithms including a combination with the microwave radiometer would be applied to the DPR.