陕北地区地物电磁散射与地物参数反演研究

Based on the application requirements of electromagnetic scattering from the land surface, the composite scattering from the land surface with target and inverse electromagnetic scattering for Northern Shaanxi region, the statistical characteristics of time domain and frequency domain of the scattering field from land surface and the composite scattering field from land surface with target, the theory, the algorithm, verification of typical land parametric inversion and parametric inversion of target near the land surface are investigated, using the electromagnetic theory such as the theory of scattering and inversion scattering, analysis and calculation methods; the calculation model of electromagnetic scattering from land surface is built according to statistical method such as the Monte Carlo Method, the time and the space distribution of scattering field, the characteristics of angle distribution, amplitude and fractal of scattering coefficient are obtained using approximate analytical methods such as the Two-Scale Method, the Small Slope Approximation and the Full Wave Method and numerical method such as the Finite Difference Time Domain and the Method of Moment; the calculation model of composite scattering field from land surface with target above it, target placed on it, the buried target and partly buried target, the characteristics of composite electromagnetic scattering are obtained using approximate analytical methods such as the Geometrical Theory of Diffraction, the Physical Optics and the Low and High Frequency Hybrid Method and numerical method such as the Alternating-Directions-Implicit Finite Difference Time Domain and Fast Iteration Algorithm Based on the Method of Moment; According to the observational information and prior to the physical model, the land surface parameter, the geometric and electromagnetic parameter of target near the land surface is inversed using Genetic Algorithm, Neural Network and the Born Iteration.

基于陕北地区地物电磁散射及其与目标复合散射、电磁逆散射应用需求，运用粗糙表面散射与逆散射理论等电磁场理论和分析、计算方法，研究地物散射场、地物与目标复合散射场时域、频域统计特征，典型地物参数、地物附近目标参数反演理论、算法、检验；根据蒙特卡罗等统计方法，建立有关地物背景电磁散射计算模型，应用双尺度方法、小斜率近似、全波法等近似解析方法和时域有限差分方法、时域多分辨方法、矩量法等数值方法得出散射场的时间、空间分布，散射系数的角分布特征、幅值特征等；给出地物背景与其上方、置于其上、部分埋藏及下方埋藏目标复合散射场的计算模型，应用几何绕射理论、物理光学、高低频混合方法等近似解析方法和交替方向隐式的时域有限差分方法、基于矩量法的快速迭代算法等数值方法得到复合电磁散射特征；根据观测信息和前向物理模型，应用遗传算法、神经网络、Born迭代等方法，反演地物参数及地物背景中目标的几何与电磁参数。

推导了瑞利分布、对数正态分布的功率谱密度函数，编写了典型地物（土壤、沙漠）表面建模程序；用高斯谱、指数谱、分形函数、瑞利分布、对数正态分布等功率谱密度函数对土壤表面、沙漠表面等地物表面、分层介质地物表面电磁散射、地物表面、分层介质地物表面与上方目标、埋藏目标及部分埋藏目标的复合散射进行了建模。.运用二阶小斜率近似、时域有限差分法、矩量法等研究了土壤表面、沙漠表面的电磁散射特性，编写了数值计算程序，得出了散射系数随散射角和入射波频率变化的曲线，分析了土壤表面、沙漠表面粗糙度参数、介质介电参数对电磁散射特性的影响；运用瞬态时域有限差分法研究了指数型粗糙地面、分形地面的宽带电磁散射特性，得出了后向散射系数的频率响应曲线，分析了后向散射系数随地面粗糙度参数、分形维数、土壤湿度、电磁波入射角等的变化规律。.运用二阶小斜率近似、矩量法、时域有限差分法等研究了分层介质土壤、沙漠表面等的电磁散射特性，得出了散射系数随散射角和入射波频率变化的曲线，讨论了分层土壤、沙漠表面粗糙度参数、介质介电参数、介质层厚度等对分层地物表面电磁散射特性的影响。.运用时域有限差分法、矩量法研究了粗糙地面、分形地面与上方目标、部分埋藏目标及下方埋藏目标的复合电磁散射特性，分析了地物表面粗糙度参数、地物介电参数、目标几何参数、目标介电参数对复合散射系数的影响规律。.运用时域有限差分方法、矩量法与基尔霍夫近似的混合算法等研究了指数型分层地面、分形分层地面与上方目标、部分埋藏目标及下方埋藏目标的复合散射特性，讨论了分层地物表面粗糙度参数、介质介电参数、目标几何参数、目标介电参数等对复合散射系数的影响；运用瞬态时域有限差分方法研究了指数型分层地面、分形分层地面的前向、后向宽带电磁散射特性，研究了分层地面与上方、部分埋藏目标及埋藏目标的宽带复合电磁散射特性，得出了散射系数、复合散射系数的频率响应曲线，讨论了前向、后向散射系数随粗糙度参数、分形维数、土壤湿度、目标几何参数及介电参数等的变化规律。.基于电磁逆散射理论，利用遗传算法、神经网络等研究了地物参数的反演问题。