降雨对C波段散射计测风的影响及其校正

传统观点认为C波段散射计工作波长大于雨滴直径,受降雨散射衰减的影响很小, 因此往往忽略降雨对C波段散射计测风的影响.本文基于降雨引起C波段散射计信号的衰减、 后向体散射及雨滴落入海面后的扰动作用,推导了降雨条件下的雷达方程, 构建了2010年全年的ASCAT散射计、降雨雷达和欧洲中期天气预报中心数值预报的匹配数据集, 定量分析了降雨对C波段散射计测风的影响,发现其信号衰减随降雨强度和入射角的增大而增强; 后向体散射和雨表面扰动作用随降雨强度的增大而增强、随入射角的增大而减小, 其中雨表面扰动作用对散射计测风的影响大于后向体散射.另外, 利用降雨条件下的雷达方程和匹配数据集,本文建立了降雨条件下的C波段主动微波辐射传输模型, 实验表明,该模型能够改善降雨条件下C波段散射计测风的精度.

Rain effect on C-band scatterometer wind measurement and its correction

It is viewed traditionally that the attenuation and scattering of rain have no effect on C-band scatterometer because its wavelength is greater than the diameter of raindrops, so rain effects on C-band scatterometer wind measurement are often ignored. According to the attenuation and the volume backscatter of the scatterometer signal by raindrops and the perturbation of the water surface by rain, in this paper, we derive the radar equation of the rainfall, collect the data from ASCAT backscatter, rain data from PR and wind field from the European Centre for Medium-Rang Weather Foremasts in 2010, and quantitatively analyze the influence of rainfall on the normalized radar backscattering cross section of the C-band scatterometer. Our results show that the attenuation increases as the rain rate and the incidence angle increase, the volume backscatter and the perturbation of the water surface increase with the increase of rain rate and decrease with the increase of incidence angle, and the influence of the perturbation on the wind measurement of the scattermeter is greater than the volume backscatter. In addition, we establish the C-band active microwave radiative transfer model for the rainfall by the radar equation and the collected data. The experimental results indicate that the new model can improve the C-band scatterometer wind measurement accuracy under rainfall conditions.