地球同步轨道合成孔径雷达欠相关机理与抑制技术研究

Geosynchronous Synthetic Aperture Radar (GEO SAR) has an extremely long synthetic aperture time (up to 1000-second order) and extensive coverage (over 1000 km), but it is impacted seriously by multiple decorrelations: the signal propagation is affected obviously by the spatial-temporal varying atmosphere, leading to two dimensional spatial-temporal atmosphere interfering (named Atmospheric Phase Screen, APS); meantime, the scattering characteristics of targets will change during the integration time and result in serious clutter decorrelation, which will degrade Signal-to-Clutter Ratio (SCR) and cause defocusing and performance degradation in SAR differential interferometry processing. Aimed at spatial-temporal atmosphere interfering and the clutter decorrelation, this project conducts theoretical analysis, physical modeling and quantitative impacts analysis and etc. There are 4 key issues involved: 1) the retrieval and compensation of spatial-temporal high resolution APS based on the iterative processing of subapertures, and the high resolution image products after compensation; 2) physical modeling of clutter decorrelation based on the Billingsley intrinsic clutter motion model and the quantitative impacts analysis using the simulation data from the dynamic forest simulation software, along with the system designing approach constraint by clutter decorrelation; 3) the moderate coherence permanent scatterers (PS) enhancement techniques in the scene of deteriorated coherence by virtue of the selection of moderate coherence PS with the joint use of amplitude and phase and then the adaptive spatial filtering for suppress of the phase random noise and improvement of the quality of PS; 4) verifications of the proposed methods of the APS estimation and the PS enhancement based on ground-based SAR experiments. These achievements will lay the strong theoretical and technical foundation for the future launch of the first GEO SAR satellite in China.

GEOSAR合成孔径时间长、覆盖范围广，多时空尺度的大气传播效应影响大，造成信号相位扰动（即大气相位屏），造成大气去相关；目标散射特性随时间起伏，造成杂波去相关。因此，GEOSAR面临严重的去相关问题，导致大相位误差，造成图像散焦和差分干涉性能下降。本项目针对时空变大气层扰动与目标时变散射特性的去相关机理分析与建模、定量影响分析等开展研究，提出基于迭代子孔径处理的高时空分辨率二维大气相位屏反演和补偿算法，实现高分辨率成像；提出基于Billingsley杂波运动模型的杂波去相关建模方法，结合动态森林场景SAR遥感数据仿真，完成定量影响分析，给出杂波去相关约束下的系统设计方法；提出欠相关区域永久散射体（PS）增强技术，联合幅度-相位实现欠相关区域内中等相关性PS点的选取，并利用空间自适应滤波抑制相位噪声，提高PS点质量；最后结合地基SAR实验，验证大气相位屏估计算法与PS增强技术。

GEO SAR合成孔径时间长、覆盖范围广，多时空尺度的大气传播效应影响大，造成信号相位扰动（即大气相位屏），造成大气去相关；目标散射特性随时间起伏，造成杂波去相关。因此，GEO SAR面临严重的去相关问题，导致大相位误差，造成图像散焦和差分干涉性能下降。本项目针对时空变大气相位屏反演与补偿、目标时变散射特性的去相关机理分析与建模等主要技术难点开展研究，并提出了欠相关区域永久散射体（PS）增强技术，结合地基SAR实验，验证大气相位屏反演与补偿算法和PS增强技术。主要研究成果如下：.一、提出了高时空分辨率二维大气相位屏的反演和补偿方法。建立了GEO SAR时空变大气传播效应影响下的信号模型，定量分析了二维时变-空变大气层影响的机理和程度；研究了基于迭代子孔径的二维大气相位屏提取方法，补偿大气扰动相位，实现了高分辨率成像。.二、进行了目标时变散射特性去相关效应的机理分析与性能评估。采用Billingsley杂波运动模型，建立了目标时变散射特性去相关条件下GEO SAR信杂比与系统参数和外界环境的关系，定量分析了多种杂波去相关对系统性能的影响。.三、提出了欠相关区域永久散射体（PS）增强技术。首先联合幅度-相位信息，完成中等相关性永久散射体（PS点）的选取，然后基于空间自适应滤波完成噪声相位抑制，提高PS点质量，改善差分干涉性能。.四、进行了基于地基SAR雷达系统的实验验证。采用由北京理工大学设计和研制的地基SAR雷达系统设计了地基SAR成像实验，验证了在大气效应影响下的干涉SAR成像和形变测量的影响分析及补偿方法，并验证了长时间序列PS差分干涉技术的有效性。.本项目在GEO SAR信息获取与成像理论研究的基础上，针对长孔径积累时间下多重去相关效应的难题，突破高时空分辨率二维大气相位屏反演、及目标时变散射特性去相关机理建模等关键难点，为实现GEO SAR成像/差分干涉处理提供了基础理论支撑。