基于极化SAR的周期起伏地表各向异性散射建模和解译

The periodic surfaces have strong anisotropic scattering on the Synthetic Aperture Radar (SAR) images. The cause and mechanism of the anisotropic scattering is critical to reasonable interpretation of the heterogeneous scattering of periodic surface and to further understanding the interactions between underlying surface and canopy. It is meaningful and valuable for scientific research and application to interpret periodic surface by using polarimetric SAR (PolSAR) images. At present, it is difficult to precisely predict the anisotropy scattering of periodic surface by theoretical models, to interpret the polarimetric scattering mechanism of coherent and incoherent scattering by using a self-adaptive model, and to interpret the heterogeneous scattering of vegetation-covered periodic fields. New theoretical model and polarimetric scattering mechanism model will be built by introducing the factors related to observation geometry. Besides, a new scattering mechanism interpretation algorithm of the periodic surface based on target decomposition will be developed. In addition, a new interpretation algorithm of vegetation-covered areas will be explored based on the polarimetric geometrical perturbation. The research can not only improve the interpretation accuracy of the periodic surface, but also weaken their effect on the vegetation monitoring. Last but not least, the developed models and algorithms will improve the application capability of SAR images by providing techniques for the inversion of physical parameters and growth monitoring of crops.

合成孔径雷达(SAR)影像上周期起伏地表具有较强的方向相关异质散射。研究造成各向异性散射成因和其散射机理，不仅有助于合理解释SAR影像上异质散射现象，而且能更好地研究雷达信号与植被层和下垫面相互作用过程，其研究具有重要的科学意义和应用价值。本项目以裸露和有植被覆盖的周期起伏地表为研究对象，针对模型不能完整描述多观测方向下的散射变化、相干和非相干散射导致的极化散射机制解译模糊、周期起伏下垫面造成的植被层散射异质等问题，构建引入观测几何因子的裸露起伏地表理论散射模型和极化分解模型、建立基于目标分解的周期起伏地表散射机制提取算法、发展基于极化几何扰动的植被覆盖周期起伏结构散射解译方法。研究成果不仅可以提高周期起伏地表异质散射解译精度、削弱起伏下垫面对植被监测的影响，也可为SAR定量参数反演、植被生长监测等应用提供核心技术支持，提高极化SAR数据的实际应用水平。

合成孔径雷达(SAR)影像上周期起伏地表具有较强的方向相关异质散射，对SAR影像的解译和定量参数反演都具有较大的影响。本项目利用极化散射研究了各向异性散射成因和其散射机理，并分析了其对定量参数反演和周期起伏地表上植被时序监测的影响。取得的主要研究结果如下：（1）揭示了周期起伏后向散射与雷达视向的关系，发现在雷达视向和起伏地表垄向垂直时，相干散射增加量较大，且对同极化通道影响最大，解释了SAR影像上异质散射成因；（2）利用周期起伏积分方程模型（PIEM）定量模拟了不用雷达视向下的后向散射变化、相干和非相干散射，更好地描述了窄方向下相干散射的快速增加；（3）利用多个极化参数分析了造成的相干散射主导散射机制为奇次散射，并提取了敏感的同极化后向散射和不敏感的交叉极化后向散射特征；（4）以土豆田和成垄小麦为例，分析了垄向引起的相干散射对上层冠层散射造成的影响，发现相干散射会降低冠层随机散射的比重，利用同极化比，交叉极化散射等不敏感特征削弱了起伏下垫面对植被监测的影响，并进一步发展了周期起伏地表下垫面含水量反演方法，提高了异质下垫面定量参数反演的精度。研究方法和结果对粗糙度、含水量、种植模式、植被等引起的相干和非相干散射分离，信号与植被层和下垫面相互作用过程理解等SAR影像解译和定量参数反演都具有重要意义。