差分层析SAR四维成像技术研究

Differential SAR tomography (D-TomoSAR) has the 4-D (spatial and temporal dimension) imaging ability, which makes it greatly potential for earth observation. At present, D-TomoSAR is usually constituted by repeat-pass missions of single-antenna SAR. Two problems will be resulted by this kind of acquisition method: the 2-D data set sparse distribution characteristic in baseline-time plane and the inevitable phase error associated with atmospheric disturbance for the years-long temporal span of SAR observation. The former may cause ill-posed trouble during signal reconstruction. The latter may decrease SNR of the data. Both can significantly degrade the performance of D-TomoSAR if not properly dealt with. Besides, current researchs on temporal deformation estimation are more concentrated on linear motion, whereas more attention should be focused on nonlinear motion which often happens realistically. Taking all the aforementioned aspects into account, this project firstly studies techniques to suppress phase error based on its space-time distribution characteristic. Then according to D-TomoSAR signal's natural property of sparse representation, the sparse reconstruction approaches are investigated in the framework of Compressive Sensing(CS) and Frequency Modulaiton(FM) signal theories to estimate the scatters' position and deformation information. Furthermore, it will be often found in this report that many issues are interpreted from the aspect of radar signal processing. We hope the integration of the two research fields will promote the development and practicality of D-TomoSAR.

D-TomoSAR技术能够对观测对象实现四维（空间－时间）成像，在对地观测领域具有巨大的应用潜力。当前D-TomoSAR系统主要由单雷达重轨飞行构建，存在两个难题：（1）观测数据在垂直基线－观测时刻二维上分布稀疏，即小样本问题；（2）由大气扰动等时间去相关等因素在SAR 单视复图像中引入的相位噪声问题。前者会在信号重构中导致病态问题，后者会降低观测数据的信噪比，二者解决不好将会影响信号估计精度，降低对目标位置和形变的解析能力。此外，目前在形变估计方面的研究还主要针对线性形变，对非线性形变问题的研究不够深入。本项目首先根据相位噪声的空－时特性，研究高精度的相位噪声抑制方法；再根据D-TomoSAR信号的稀疏表示特性，在CS理论和FM信号估计理论指导下，研究目标位置和形变函数的精确估计方法。项目研究将充分借鉴雷达信号处理领域的研究成果，尝试通过学科交叉促进D-TomoSAR技术的实用化进程。

差分层析合成孔径雷达（D-TomoSAR） 技术能够对观测对象实现四维（空间－时间）成像，在对地观测领域具有巨大的应用潜力。当前D-TomoSAR 系统主要由单雷达重轨飞行构建，存在两个难题：（1）观测数据在垂直基线－观测时刻二维上分布稀疏，即小样本问题；（2）由大气扰动等时间去相关等因素在SAR 单视复图像中引入的相位噪声问题。前者会在信号重构中导致病态问题，后者会降低观测数据的信噪比，二者解决不好将会影响信号估计精度，降低对目标位置和形变的解析能力。此外，目前在形变估计方面的研究还主要针对线性形变，对非线性形变问题的研究不够深入。.针对上述问题，根据D-TomoSAR 信号稀疏表示特性，在压缩感知理论和调频信号估计理论指导下，研究了D-TomoSAR 的信号估计技术，包括：基于相位梯度算法的大气扰动相位噪声抑制方法、基于压缩感知方法的D-TomoSAR 聚焦方法以及非线性形变估计方法等。.本课题通过数值仿真、内/外场试验和实测数据处理等手段，验证了所研究方法的性能，对D-TomoSAR的实用化进程具有一定的推动作用。