【作者】 熊涛；

【导师】 杨健；

【作者基本信息】 清华大学 ， 信息与通信工程， 2009， 博士

【摘要】 极化干涉合成孔径雷达(PolInSAR)是一种先进的SAR系统。由于引入了电磁波的极化方式,极化SAR干涉测量比起传统的干涉测量具有更加广泛的应用。虽然自从11年前第一篇关于极化SAR干涉测量的文章发表以来,国际上很多研究人员在这方面做了大量的工作,但仍存在一些理论与实际问题需要我们去解决。为了推动极化干涉SAR技术的发展,本文专注于其中的一些关键技术,包括图像配准、数据降噪、相位解缠以及树高反演。本文的主要创新点如下。1)提出了基于相似性参数的极化干涉图像配准方法,利用相干的极化散射矢量的相关系数定义了新的匹配度量,并从理论上分析了方法的性能。实验表明,与仅利用干涉信息的方法相比,新方法提高了像素级和亚像素级配准的稳健性和准确性,减小了误匹配造成的噪声,为获取准确的干涉信息奠定了基础。2)在利用极化信息对干涉数据进行降噪的问题中,提出了一种基于幅度最优化的方法,通过寻找最优极化通道来优化干涉信号的幅度,从而改善相位质量。建立数学模型并推导出解析解,利用相似性参数做出了合理的物理解释。并讨论了输入为多视数据的情况,扩展为基于强度最优化的方法。实验表明新方法较传统方法在性能上有明显提高,特别在弱信号区域尤为显著。3)对于干涉数据滤波问题,提出了模糊干涉滤波器和基于幅度最优化的干涉滤波器。两者均考虑了复信号幅度与相位的关系。前者利用邻域信息对弱信号插值增强,并利用加权中值滤波器进行相位滤波。后者则直接将幅度最优化的模型引入,求取最优的滤波器系数。实验表明,两个滤波器在降噪性能上较传统方法均有提高,后者可以利用较小的邻域信息获取更好的输出相位。4)针对地形起伏剧烈时相位难以精确解缠的问题,提出了基于相位分割和基于参考面的变相位技术。前者将相位解缠视为图像分割问题,将相位合理的分割和拼接,后者则将其视为“去地形效应”,构造参考面来降低解缠的难度。实验表明,两种技术相结合,能够更为准确的恢复复杂地形对应的相位面。5)对于树高反演问题,提出了一种体相干估计的方法,通过求解干涉复相干的辐角范围,得到了体相干最优估计的近似解析解,提高了树高反演的准确程度。实验验证了该方法较传统估计方法的优越性。更多还原

【Abstract】 Polarimetric interferometric synthetic aperture radar (PolInSAR) is an advanced SAR system. Since polarizations of electromagnetic waves are employed, polarimetric SAR interferometry has more extensive applications than traditional SAR interferometry. Although some researchers have done much work since the first paper on polarimetric SAR interferometry was published 11 years ago, we still need to solve some problems in theory. For developing the applications of a PolInSAR, this thesis focuses on some key techniques, including image registration, data denoising, phase unwrapping, and tree height estimation. The following innovations are obtained in this thesis.1) An image registration method for PolInSAR images based on the similarity parameter is proposed: a new registration measurement is defined by the correlation coefficient between the coherent polarimetric scattering vectors, and the method performance is analyzed theoretically. It is proved to have better robustness and accuracy than traditional methods using only interferometric information. The noise caused by mis-registration is reduced and it is beneficial to the later interferogram extraction.2) A denoising method for InSAR data based on the amplitude- optimization (AO) principle using polarimetric information is proposed. By searching the optimal polarimetric channel to maximize the amplitude of the InSAR signals, the phase between them is improved. The mathematical model is built and solved analytically. A physical explanation is supported by the similarity parameter. As an extension, an intensity-optimization (IO) based method is proposed for multi-look input data. The performance of the proposed method is better than those of the coherence-optimization based methods, especially in weak signal areas.3) Two filters, the fuzzy filter and the AO based filter, are proposed for InSAR data filtering. Both of them make use of the relationship between the amplitude and phase of the complex signal. In the fuzzy filter, neighborhood information is used to improve weak signals by interpolation, and then the phase is processed by weighted median filter. In the AO based filter, the AO model is introduced to obtain the optimal filter coefficients. They are proved to have better denoising ability than traditional methods. Particularly, the latter filter uses the neighborhood information with the highest efficiency.4) Two phase-changing techniques, based on the phase segmentation and the referenced surface respectively, are proposed to overcome the difficulty caused by steep topography. The former regards the phase unwrapping as an image segmentation problem, segmenting and combining the phase reasonably. The latter regards it as“topography effect removal”problem, constructing a referenced surface to simplify phase unwrapping. Experiments demonstrate that combining the two techniques can improve the effectiveness and accuracy for complicated topography inversion.5) In the tree height inversion problem, a volume coherence estimation method is proposed. By considering the argument range of the coherence, an approximate analytical solution of the best volume coherence estimation is obtained. Experimental results show that this method can be used to improve the accuracy of the tree height inversion, demonstrating its advantage over conventional estimation methods.更多还原