Effect of Multiple Scattering in GPM Precipitation Radar Measurement

Dual-frequency precipitation radar (DPR) onboard the Global Precipitation Measuring Mission (GPM) core satellite will be operated at two frequencies of 14 GHz and 35 GHz. Because the size of foot print is so large in case of space-borne radar that the effect of multiple scattering may not be negligible, especially for radar signals with 35 GHz wavelength. In this study, the contribution of multiple scattering to the total received signal is quantitatively considered using a radar signal simulator. In this physically-based simulator, scattering properties are calculated for precipitation and cloud particles based on radio wave scattering theory and T-matrix method. Multiple scattering is modeled by a forward Monte-Carlo method. Radar signals from DPR are simulated for warm-rain cloud measurement assuming homogeneous gamma-type drop size distribution (DSD) and liquid water content (LWC) in cloud. Results indicate that the degree of the contribution of multiple scattering depends on path-length from the cloud top and LWC, and that radar signals with 35 GHz wavelength are clearly suffered from multiple scattering effect. The contribution of multiple scattering to the total received signal with 35 GHz wavelength can be estimated well by the ratio of the total signal (14 GHz) to the total signal (35 GHz), which has little dependence on path-length from the cloud top. In this study, the dependence of this relationship on DSD will be also investigated including simulation under more realistic distribution of precipitation particles with snowflakes in stratiform-type cloud.