如何从雷达干涉时间序列影像中获取更全面的相干目标集合,进行变形时间序列分析是当前研究的难点和热点。本文提出了改进的相干目标法,可获取更为全面且可信度高的相干目标集合,进而提高地表形变监测的时空分辨率和精度。根据雷达影像中同类型地物散射分布相近的特点,采用非参数同分布检验算法提取后向散射特性相近的同质点开展空间非局部滤波,提高干涉图的质量。与此同时,利用多尺度的极大似然条纹频率估计算法分离差分干涉图中的系统性相位,并基于同质点进行自适应相干性估计,获取相干性的平稳估计量,从而获取更多的相干点目标。利用20景TerraSAR-X条带模式时间序列影像,分别利用传统的及改进后的相干目标法对香港填海区域地表形变信息进行时序分析。对试验数据的分析结果表明,本文提出的改进方法在具有稀疏植被的填海区可有效增加相干目标点的提取,得到更为可信的沉降结果。
How to obtain a more comprehensive collection of coherent points from interferometric datasets and analyze deformation time-series is the difficult and hot spot in current research. An improved coherent targets technology is proposed, which can obtain a more comprehensive and reliable collection of coherent points and improve temporal-spatial resolution and precision of deformation signal. Based on similar backscattering properties of the same ground object, non-parametric hypothesis test is used to extract the homogeneous pixels and nonlocal filter is applied to improve the quality of interferogram. Meanwhile, the systematic phase is removed based on multi-resolution maximum likelihood estimation (MLE) of fringes algorithm, then the coherence of homogeneous pixels is estimated stationarily. Thereby more coherent points can be obtained. 20 TerraSAR-X stripmap images are exploited by the conventional CT and the proposed method to investigate the ground deformation of the reclaimed lands in Hong Kong. Experimental results show that this method can effectively improve the density of coherent points in the reclaimed lands with sparse vegetation and obtain a more reliable result.
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