A rain effect elimination approach using FengYun-3E WindRAD dual-frequency measurements

Satellite scatterometers play a vital role in providing sea surface wind observations and can help to understand air–sea interaction. The wind radar (WindRAD) mounted on FengYun-3E (FY-3E) with Ku and C bands enhances the capacity to measure sea surface vector winds globally. However, the current GMFs (geophysical model functions) do not consider rain effects, which leads to local wind field retrieval biases under rainy conditions, especially for Ku-band measurements. A rain conceptual model, which describes the relationship between Ku-band measured normalized radar cross-section (NRCS) biases and the sea surface wind-induced NRCS and rain rates, has been proposed to simulate the rain effects on Ku-band measurements. This paper estimates the model parameters and validates its rain-correction effectiveness based on the near-simultaneous C- and Ku-band observations of WindRAD. The results show that after correction, the Ku-band wind speed biases relative to C-band wind speeds are significantly reduced under low to medium rain conditions. The root-mean-square differences have been reduced by about 0.2 m s −1 for wind speed and about 1.6° for wind direction, respectively. Although some correction issues require further investigation under low wind and high rain-rate conditions when auxiliary rain-rate collocation is available, the model can still contribute to more accurate sea surface wind fields in rainy areas, which enhances the global-wind-observation abilities of the scatterometer constellation. 目前散射计风场反演采用的地球物理模式函数未考虑降雨影响, 导致降雨条件下反演的风场存在偏差.研究基于风云三号E星WindRAD近同步观测的Ku/C波段数据, 提出了一种降雨概念模型, 描述了降雨引起的Ku波段归一化雷达后向散射截面 (NRCS) 测量偏差与海面风场NRCS及降雨率之间的关系.通过该模型对Ku波段进行降雨影响校正后, 在3-10 m s −1 风速范围内, Ku与C波段间的平均风速偏差接近零;反演风速和风向的均方根误差相较校正前分别降低约0.2 m s −1 和1.6°.该模型可有效改进散射计风场反演算法, 从而在中低降雨条件下提供更准确的海面风场信息, 增强散射计星座的全球风场观测能力.