Evaluation of Raindrop Size Distribution Parameterization for Fengyun Satellite Precipitation Retrieval over South China

The parameterization of raindrop size distribution (DSD) is critical for the satellite precipitation retrieval algorithms. Utilizing the multiple ground-based two-dimensional video (2DVD) and Particle Size and Velocity (Parsivel) disdrometers data from the Precipitation Validation Network (Guangdong) of the Fengyun satellites during April–September 2024, this study evaluates the uncertainty of DSD parameterization on a dual-frequency (DF) precipitation retrieval algorithm over South China. It is shown that the composite raindrop spectra generally conform to the gamma distribution, with the shape parameter μ on average of 4.5–4.8, which is higher than the fixed μ = 3 used in the Global Precipitation Measurement mission (GPM) Dual-Frequency Precipitation Radar (DPR) algorithms. By varying the μ value in the DSD gamma model, the effects on the retrieved mass-weighted mean diameter (D_m), normalized intercept parameter (N_w), and rain rate are examined. As μ increases from 1 to 6, the underestimation of D_m shifts to overestimation, while for lgN_w and rain rate, it is the opposite. The overestimation of rainfall, especially at the range of 8–32 mm h⁻¹, mainly comes from underestimated D_m and overestimated lgN_w. On the contrary, overestimation of D_m and underestimation of lgN_w mainly lead to underestimated rainfall, especially when rain rate is above 64 mm h⁻¹. Comprehensive analysis shows that the DSD gamma distribution with μ in the range of 4–5 may be more suitable for South China. These results provide valuable reference for optimizing the DSD module of the precipitation retrieval algorithm for the Fengyun-3G (FY-3G) satellite.