月地双基SAR成像的快速后向投影算法研究

为了提高对全球变化的大尺度观测能力，月基对地观测的概念应运而生。由于月基单站合成孔径雷达（Synthetic Aperture Radar，SAR）的双程传播会造成回波信噪比衰减，为此针对月地双基SAR工作模式展开研究。考虑到月、地、星复杂的相对运动为成像带来困难，根据月、地、星的几何关系建立平面直角回波模型。同时考虑到月球和卫星运行轨迹的弯曲性，分析模型误差，推导了精确的回波二维频谱表达式。在此基础上提出了一种基于快速后向投影的SAR成像算法，补偿了方位空变的模型误差，利用频域子孔径成像和频谱融合实现成像算法的快速化。通过分析可知月地双基SAR的理论回波信噪比与地月距离的平方成反比，与月基单站SAR相比有显著提升，最后通过X波段SAR仿真数据验证了文章算法处理月地双基SAR成像问题的效性。

Study on fast back projection algorithm for lunar earth bistatic SAR imaging

The concept of lunar based earth observation concept has been proposed in order to improve the large scale observation ability towards global changes. Because the signal to noise ratio of lunar based monostatic synthetic aperture radar （SAR） decreases seriously due to the two way propagation，a novel lunar earth bistatic SAR operating mode was studied. Considering the complex relative movement among lunar，earth and satellite brings difficulty to SAR imaging，a rectangular plane echo model was built according to the geometrical relationship of lunar，earth and satellite. Due to the curves of lunar and satellite orbits，the modeling error was analyzed，and a precise two dimensional frequency domain expression of echo was also deduced. Then a fast back projection based SAR imaging algorithm was designed to compensate the azimuth variant modeling error. The calculation speed was increased by frequency domain sub aperture imaging and spectrum combination. The signal noise ratio of lunar earth bistatic SAR is inversely proportional to the distance between earth and lunar through analysis，simulated X band SAR data sets are used to validate the effectiveness of the proposal to deal with lunar earth bistatic SAR imaging.