Simulation-based analysis of the error caused by non-uniform beam filling and signal fluctuation in rainfall rate measurement with a spaceborne radar

The Tropical Rainfall Measuring Mission is a United States-Japan joint project for rain measurement using a spaceborne rain radar. The authors investigate the rainfall-rate error caused by the effect of non-uniform beam filling on the radar reflectivity and the surface reference technique simulation which employs rain data measured by a ground-based radar. Complete 3D rain data generated from a radar-based volume scan are used, and these 3D rain data are assumed to be true data. To estimate the mean value of the rain echo power, it is essential to take an average of fluctuating radar signals; to estimate that value correctly, a large number of samples is needed. However, the number of averaging samples is limited because the measurement time at spatially fixed points is limited by the continuous movement of the satellite. Thus, instrument-measured quantities always have some errors. This study takes into consideration the error caused by the limited number of averaging samples