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摘要: 层析SAR(TomoSAR)成像技术已经成为获取三维SAR点云的关键技术。然而,如果忽略斜距垂向的二次相位,可能会导致目标在高程方向的散焦问题,这是由于层析SAR成像中第三维也可能存在菲涅耳衍射所导致的。该文利用光学成像中的衍射原理解释了SAR成像中的衍射问题同样在第三维存在,并提出采用稀疏匹配滤波方法对第三维进行聚焦。第三维稀疏匹配滤波的关键在于构建稀疏相位补偿因子,进而构建稀疏匹配滤波器。首先根据TomoSAR影像的空间几何基线,构建第三维归一化的稀疏频率;然后,结合波长、距离、孔径等参数,根据菲涅耳积分特性构建频域稀疏匹配滤波器;最后,使用频域稀疏滤波器对稀疏采样的SAR图像进行相位补偿,再利用经典的稀疏成像算法(如压缩感知、似然比检测方法等)进行高程即第三维目标检测。该文采用中国科学院空天信息创新研究院的机载SAR数据,运用该文构建的频域稀疏匹配滤波器对其进行实验,实验结果验证了该文所提的方法能够解决层析SAR在菲涅耳衍射情况下导致的散焦问题,从而改善散焦引起的目标位置和后向散射信息不准确的问题。Abstract: Synthetic Aperture Radar Tomography (TomoSAR) has emerged as the primary technique for generating 3D SAR point clouds. In practice, ignoring the quadratic phase distribution in the elevation dimension causes defocusing artifacts due to inherent Fresnel diffraction in tomographic SAR processing. By comparing with optical diffraction theory, this paper identifies similar diffraction effects in the third dimension of SAR images and introduces a sparse matched filtering technique for tomographic focusing. Our method is based on deriving a sparse phase compensation factor to construct the matched filter. The proposed processing chain includes three key steps. First, a normalized sparse frequency profile in the tomographic dimension is constructed using the spatial geometric baseline of TomoSAR acquisitions.Next, we derive a frequency-domain sparse matched filter based on Fresnel integral properties incorporating system parameters such as wavelength, range, and aperture size. Finally, phase compensation is applied through the designed sparse filter, enabling elevation target detection using established sparse imaging techniques, including compressed sensing and likelihood ratio detection. This study employs airborne SAR data acquired by the Aerospace Information Research Institute, Chinese Academy of Sciences, to validate the proposed frequency-domain sparse matched filter. Experimental results demonstrate that our method effectively reduces tomographic defocusing artifacts caused by Fresnel diffraction, substantially improving the accuracy of both target localization and backscattering coefficient estimation.
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表 1 两组TomoSAR数据参数
Table 1. Two sets of TomoSAR data parameters
参数 符号 机载数据(m) 星载数据(m) 最小基线间隔 ${B_{\min }}$ 0.1071 20 最大基线长度 ${B_{\max }}$ 0.442 400 波长 $\lambda $ 0.0197 0.031 斜距 r 482.0413 603638.971 -
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