海洋降雨的星载合成孔径雷达遥感探测研究

Rainfall has significant impact on local weather, as well as on the transfer of heat, mass and kinetic energy between ocean and atmosphere. The oceanic rainfall may be too far from shore to be detected by observation stations or ground-based weather radars. It is can be detected by space borne precipitation radar and microwave radiometer with low resolution. However, it can be easily detected by space-borne Synthetic Aperture Radar (SAR) with high resolution over global ocean. In this proposal, the microwave backscattering mechanism of oceanic rainfall and its applications on sea surface wind field retrieval for typhoon, correction of microwave scattering by rain and rain rate quantitative retrieval will be investigated to the operating application requirements of sea surface wind and rain rate with high resolution, the problem of non-applicable Bragg scattering model in heavy rain and the non-quantitative coherent scattering model of rain-generated stalks. The work in this proposal will be done by developing oceanic rainfall backscattering model by composing of Two-Scale scattering model for ocean surface, empirical model of scattering and absorption for rain drops and the coherent scattering model of rain-generated stalks. The uncertain coefficients in the model will be given by using empirical fitting of satellite SAR data with multi-polarization, weather radar measured rain rate data and buoy measured wind and wave data. The work of this proposal will has scientific and application significance in sea surface wind and rain rate retrievals from SAR with high resolution, especial in the operating application for the Chinese GF-3 satellite SAR data.

降雨可强烈影响当地天气、海洋与大气之间的热量、质量和动能传输。海洋降雨有时由于离岸太远而无法被观测站和岸基天气雷达所探测，但可被星载降水雷达和微波辐射计以低分辨率探测，而星载合成孔径雷达（SAR）可对其实现高分辨率的全球探测。本项目针对SAR高分辨率海面风场和降雨探测的业务化应用需求，以及海面波布拉格散射在强降雨条件下的不适用性和溅射体相干散射模型的非定量化问题，拟采用海面微波散射的双尺度模型、雨滴的散射与吸收的经验模型及雨滴溅射体相干散射模型联合建模，并利用多极化SAR卫星数据、天气雷达降雨率和风、浪浮标观测数据确定经验系数的方法，开展海洋降雨的微波后向散射机理及其在台风海面风场反演中的降雨影响校正、降雨率定量探测等方面的SAR海洋遥感研究。本项目的研究成果预期对SAR高分辨率海面风场和海洋降雨率定量探测具有重要的科学意义和应用价值，尤其适用于中国GF-3卫星SAR数据的业务化应用。

降雨可强烈影响当地天气、海洋与大气之间的热量、质量和动能传输。海洋降雨有时由于离岸太远而无法被观测站和岸基天气雷达所探测，但可被星载降水雷达和微波辐射计以低分辨率探测，而星载合成孔径雷达（SAR）可对其实现高分辨率的全球探测。. 本项目针对SAR高分辨率海面风场和降雨探测的业务化应用需求，以及海面波布拉格散射在强降雨条件下的不适用性和溅射体相干散射模型的非定量化问题，采用海面微波散射的双尺度模型、雨滴的散射与吸收的经验模型及雨滴溅射体相干散射模型联合建立了海洋降雨微波散射模型，并利用多极化SAR卫星数据、天气雷达降雨率和风、浪浮标观测数据确定经验系数的方法，完成了海洋降雨的微波后向散射机理及其在台风海面风场反演中的降雨影响校正、降雨率定量探测方法等方面的SAR海洋遥感研究。. 研究主要结果为：（1）复合布拉格散射模型小入射角的最优设置值为18°。（2）利用复合布拉格散射模型对46景RADARSAT-2卫星C波段SAR数据进行了海面风速反演试验，VV极化SAR反演的海面风速均方根误差为1.5 m/s，HH极化SAR反演的海面风速均方根误差为1.7 m/s。（3）利用海洋降雨雨团足印的特性可确定SAR影像观测范围内的海面风向。（4）利用本项目提出的海面风速双极化SAR反演方法，台风示例数据海面风速反演均方根误差为1.7 m/s，海面风向均方根误差为12°。（5）以4景台风条件下的RADARSAT-2卫星SAR数据作为示例，协同准同步的微波辐射计降雨率数据，利用本项目的降雨率散射计算模型进行海面风速反演的降雨影响校正，3个处于降雨区的浮标实测值检验显示：未经降雨影响校正的反演均方根误差RMSE为2.0 m/s；经降雨影响校正后，其反演均方根误差RMSE为1.1 m/s。（6）以海面风场作为本项目建立的海上降雨散射模型的已知输入，示例SAR数据研究表明其可定量反演获得海上降雨率。. 本项目的研究成果对SAR高分辨率海面风场和海洋降雨率定量探测具有重要的科学意义和应用价值，尤其适用于中国GF-3卫星和1m-CSAR卫星SAR数据的业务化应用。