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.