A Validation of Passive Microwave Rain-Rate Retrievals from the Chinese FengYun-3B Satellite

摘要

Level 2 rain-rate retrievals from the Microwave Radiation Imager (MWRI) on board the Chinese FengYun (FY)-3B satellite are verified using minute rainfall measurements from a dense automatic weather station (AWS) network over eastern China for the warm seasons (May-September) of 2012 and 2013. First, analyses of minute rainfall are constructed on a 0.05 degrees latitude-longitude grid box through interpolation of quality-controlled gauge reports. Ground truth for the FY-3B rain-rate retrievals is defined as the 5-min mean rate centering at the satellite observation time and over the 0.05 degrees latitude-longitude grid boxes falling into the target field-of-view (FOV) coverage determined with parallax correction. Parallax displacement is about the same as the height of cloud or half of the FY-3B FOV size. Parallax correction is crucial to ensure accurate evaluation and applications of the level 2 precipitation retrievals from FY-3B and other satellites, including the Global Precipitation Mission (GPM) core satellite, and should be implemented before the level 2 retrievals may be used as inputs to the level 3 integrated satellite precipitation analyses. FY-3B level 2 retrievals present good skills in detecting raining pixels and quantifying rain rate as retrievals from other PMW sensors. However, they tend to miss rainfall from warm and low clouds of small scales and underestimate (overestimate) heavy (light) precipitation. In particular, the limited maximum rain rate yields significant underestimation for many heavy rainfall events. Maximum rainfall detected by the FY-3B retrievals for the afternoon orbits is shifted by about 7-8 km toward the leeward direction, most likely caused by the displacement between the heavy rainfall and tallest cloud top.