运动补偿(MOCO)是机载合成孔径雷达(SAR)获取高质量图像的关键,超高分辨率成像中,如何精确、高效地校正空变运动误差仍是很大的挑战。本文提出了一种改进的多级空变运动补偿方案,兼顾处理的精度和效率。首先,采用一步运动补偿法有效去除运动误差的距离空变分量,避免引起额外的距离徙动校正(RCMC)误差。同时,修正视线方向误差的传统计算方式,保证相位精度的前提下结合距离子带实现无插值的近似距离包络补偿。然后,利用距离子带降低残余方位空变误差的距离空变性和对方位时频关系的影响,显著改善宽波束情况下的聚焦效果,降低孔径依赖补偿算法的运算量。最终分辨率达到0.1 m,具有实际工程应用价值。点目标仿真和实测数据处理验证了所做的研究。
MOtion COmpensation (MOCO) is the key to acquisition of high quality images by the airborne Synthetic Aperture Radar (SAR). In ultra-high resolution imaging, it is still a great challenge to correct space-variant motion errors accurately and efficiently. In this paper, an improved approach for multi-level space-variant MOCO with multi-level processing is proposed, which gives consideration to both precision and efficiency. First, the one-step MOCO algorithm is used to correct the range-variant component of the motion error effectively, avoiding inducing additional Range Cell Migration Correction (RCMC) error. Meanwhile, on the premise that the accuracy of phase correction should be guaranteed, the conventional calculation formula for line-of-sight range displacement is revised, and an approximate range envelope compensation without complex interpolation can be implemented with the subswath. Then, the subswath is used to reduce the range variance of the residual azimuth-variant error, as well as the influence of the error on the azimuth-to-frequency mapping. Consequently, the focusing effect in the case of wide beam is improved observably, and the computational burden of the aperture-dependent compensation algorithm is also reduced. The proposed approach can attain 0.1 m resolution, being useful in engineering practice. Simulations of point targets and processing of test data have validated the present research.
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