基于二阶Keystone变换的双站前视SAR成像算法

Focusing Bistatic Forward-looking SAR Data Based on Second-order Keystone Transform

由于回波信号具有剧烈的二维耦合和距离徙动特性,相比传统的单站合成孔径雷达(SAR)而言,双站SAR数据的成像处理更具有挑战性,双站前视SAR则更是如此。由于没有解决距离徙动的空变性和高阶距离-方位耦合,导致目前现存的成像算法效果较差,成像范围也受到较大限制。针对上述问题,文中提出了一种基于二阶Keystone变换(KT)和改进的非线性调频变标(NLCS)方法的成像算法。首先,利用线性距离徙动矫正去除线性距离徙动和多普勒中心频率;然后,采用二阶KT来补偿距离弯曲;最后,采用改进的非线性调频变标方法用于均衡不同点目标方位空变的多普勒调频率。仿真结果证明了该算法的有效性。

Bistatic synthetic aperture radar（BSAR） data is more complicated to focus than that of the traditional monostatic SAR due to its strong 2-D coupling of echo signal,especially for bistatic forward-looking SAR（BFSAR）. Although several algorithms have been proposed,they failed to take the spatial variance of range cell migration（RCM） into account. Moreover,residual RCM caused by higher order coupling have limited the imaging block size. In this paper,an algorithm based on second-order keystone transform（KT） and a modified nonlinear chirp scaling（NLCS） is derived to deal with the above problems. First,linear range walk correction（LRWC） is performed to remove both the linear RCM and Doppler centroid. Then,a second-order KT is used to compensate for the range curvature. Finally,a modified NLCS is utilized to equalize the azimuth-variant Doppler frequency modulation（FM） rates of different targets. Simulation results verify the proposed algorithm well.