改进的NLCS星弹双基SAR俯冲前视成像算法

A Spaceborne-missile Bistatic SAR Diving Forward-looking Imaging Algorithm Based on Modified Nonlinear Chirp Scaling

在俯冲阶段由于导弹具有加速度,速度大小和方向会发生急剧变化,其收发瞬时斜距会变复杂,将导致距离-方位向耦合严重和方位空变性问题,若直接进行方位向聚焦压缩,会造成图像畸变。针对这两个难题,采用一种改进的非线性变标(Nonlinear Chirp Scaling,NLCS)算法运用到新型星弹双基系统模型中。首先建立了星弹双基系统模型;接着利用级数反演法推导了二维频谱表达式,在二维频域中通过完成距离压缩和徙动校正来消除距离-方位耦合的影响,再利用改进的NLCS算法对方位向多普勒调频率进行补偿解决方位向空变性问题,完成方位向压缩聚焦,从而得到良好的成像结果。与改进的距离多普勒(Range Doppler,RD)算法相比,该算法减少了1.013×10^(8)浮点运算量(Floating Point Operations per Second,FLOPS),边缘点方位向聚焦效果有了很大的改善,方位向峰值旁瓣比(Peak Sidelobe Ratio,PSLR)、积分旁瓣比(Integrated Sidelobe Ratio,ISLR)、分辨率分别提升了2.41 dB,1.29 dB,1.16 m,证明了该方法的有效性与可行性。

In diving stage,due to the acceleration of the missile,the amplitude and direction of velocity change sharply and the slant range becomes complicated,which leads to serious range-azimuth coupling and the space variance of Doppler phase.If the azimuth focusing compression is carried out directly,the image must be distorted.To address these two challenges,a modified Nonlinear Chirp Scaling(NLCS)algorithm is applied to the new spaceborne-missile bistatic system model.Firstly,the spaceborne-missile bistatic system model is established.Then,a two-dimensional(2D)spectral expression is derived by using the method of series reversion.In the 2D frequency domain,the effects of range-azimuth coupling are eliminated by completing range compression and migration correction,and the modified NLCS algorithm is used to compensate the azimuth frequency modulation rate to solve the space variance of Doppler phase problem,complete azimuthal compression focusing,and get good imaging results.Compared with the improved Range Doppler(RD)algorithm,the proposed algorithm reduces 1.013×10^(8) floating point operations per second(FLOPS),the azimuthal focusing effect of edge points has been greatly improved,and the peak sidelobe ratio(PSLR),integrated sidelobe ratio(ISLR),and resolution are improved by 2.41 dB,1.29 dB,and 1.16 m,respectively,which proves the effectiveness and feasibility of the proposed method.