SIMULATION-BASED ANALYSIS OF THE ERROR CAUSED BY NONUNIFORM BEAM FILLING AND SIGNAL FLUCTUATION IN RAINFALL RATE MEASUREMENT WITH A SPACEBORNE RADAR

We focus on two rainfall measurement algorithms which will be used wit h a spaceborne radar for the Tropical Rainfall Measuring Mission. One is the conventional rainfall measurement algorithm (Z method), which u ses the radar reflectivity factor, and the other is the surface refere nce technique (SRT method), which uses rain attenuation. Non-uniform b eam filling (NUBF) is one source of error in the above methods. This p aper investigates the error caused by NUBF using a computer simulation that employs rain data measured by a ground-based radar. The simulati on shows that the Z method always overestimates the rainfall rate, and the SRT method almost always underestimates the rainfall rate. The si mulation takes into consideration the effect of the signal fluctuation . The results show that the effect of the signal fluctuation is larger than that of the NUBF, in both the Z method and the SRT method. In pa rticular, the signal fluctuation causes serious errors in rainfall rat e estimation by the SRT method in light rain.