Comparative Experiments on Separation Performance of Overlapping Scatterers with Several Tomography Imaging Methods
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摘要: 层析技术因具有解译城区SAR影像上复杂叠掩场景的能力而备受关注。层析成像包含两个部分:估计散射体在高程向的分布和确定散射体在混叠像元内的真实数目。该文以中科院空天院峨眉数据的机载阵列干涉系统参数为基础,选取了若干代表性的方法,包括OMP, SLIM和MUSIC等层析谱估计方法以及BIC和GLRT等模型定阶方法,进行了模拟叠掩目标的层析反演实验,使用了克拉默-拉奥界和重建成功率来评估实验结果。实验表明:在机载阵列数很有限的条件下,(1)使用2阶统计量反演的高程估计量的方差比单个观测矢量反演结果的方差更小;(2)叠掩散射体间的幅度比、相位差和散射间距会影响层析算法解叠掩的成功率;(3)叠掩散射体间的相位差会使层析算法的高程估计发生偏差。Abstract: The tomographic technique has attracted much attention because of its ability to separate overlapping scatterers in urban Synthetic Aperture Radar (SAR) images. The general method of SAR Tomography (TomSAR) imaging combines the following two aspects: estimating the distribution of the scatterers in the elevation direction and determining the number of strong scatterers in an overlapped pixel. This study applied several sophisticated spectrum estimations (e.g., Orthogonal Matching Pursuit, Sparse Learning via Iterative Minimization and Multiple Signal Classification) and model order selection approaches (e.g., Bayesian information criterion and generalized likelihood ratio test) with highly technical potential to recover the simulated overlapping scatterers. This simulation experiment is based on the parameters of the AIRCAS X-band TomoSAR data from Emei, Sichuan, China. The Cramér-Rao Lower Bound (CRLB) and recovery probability are used to evaluate the performances of different methods for the separation of overlapped scatterers. The experimental results revealed the following: (1) the standard deviation of estimation using second-order statistics is smaller than that of a single observation vector, especially when the number of acquisitions is very limited; (2) the amplitude ratio, phase difference, and elevation spacing between overlapping scatterers will have a significant impact on the different kinds of algorithms; and (3) the phase difference between overlapping scatterers will make the phase center estimation of greedy algorithm or spectrum estimation algorithm biased.
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表 1 峨眉数据的参数
Table 1. Parameters of Emei data
参数 数值 波长 $\lambda $ 0.031 m 斜距 r 1629 m 入射角 $ \theta $ $ {47}^{\circ } $ 基线 b 0.2$ \times $11 m 瑞利分辨率 ${\rho _s}$ 23.78 m -
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