雪层覆盖地面电磁散射的矩量法

为实现分层介质粗糙面电磁散射的矩量法研究,给出一种分层介质粗糙面电磁积分方程的区域分解方法.将格林定理应用于粗糙面所分的各子空间,结合波动方程和格林函数推导分层粗糙面的电磁积分方程,利用矩量法对其进行离散,数值计算得到雪层覆盖地面散射系数的角分布曲线,其中,粗糙表面由一维带限Weierstrass分形谱和Monte Carlo方法模拟.通过与时域有限差分法数值结果的比对,验证该方法的准确性,并分析散射系数随雪和地面参数、介质参数以及入射波参数的变化,获得了较完整的散射特征.     

车载探地雷达信号在分层介质中的散射特性

建立了多层分层介质散射的物理模型,基于雷达方程和斯涅尔定律给出了多层分层介质散射场强度计算公式.分析研究了分层介质的电特性参数(介电常数和损耗正切)对雷达系统的探测距离和散射场的影响.以安装于探测车上的探地雷达系统为应用背景,利用时域有限差分方法对整个车载探地雷达系统进行了建模和仿真计算,对接收到的散射回波信号进行了研究.最后将系统数值模拟结果和解析计算结果进行了对比,并对结果做出了分析.     

具有二维fBm特征的分层介质粗糙面电磁散射的特性研究

运用微扰法研究了平面波入射分层介质粗糙面的电磁散射,推出了不同极化状态下的双站散射系数公式.采用二维fBm分形粗糙面来模拟实际的分层介质粗糙面,结合二维fBm分形粗糙面的功率谱导出了平面波入射二维fBm分形分层介质粗糙面的散射系数计算公式.通过数值计算得到了HH极化下双站散射系数随散射角的变化曲线,讨论了分维、底层介质介电常数、中间介质介电常数和厚度及入射波频率对双站散射系数的影响,得到了二维fBm分形分层介质粗糙面散射系数的分维特征、基本特征、分区特征和随频率变化的特征. 关键词： 电磁散射 二维fBm分形粗糙面 分层介质 微扰法     

随机Gauss粗糙面上三维导体目标散射差场的随机泛函解析计算方法

提出一种解析的随机泛函方法(SFA),计算导体Gauss粗糙面上三维导体目标的复合电磁散射.推导粗糙面的随机Green函数,用一种新的四路径模型描述面体复合散射机理,用SFA求解双站差场雷达散射截面.以导体球目标为算例,与其他数值计算方法比较后验证了SFA的有效性与准确性,同时讨论了粗糙度、体目标尺寸以及距离粗糙面高度等参量变化对结果的影响,给出复杂形状体目标的双站差场雷达散射截面的空间角分布. 关键词： 随机泛函方法 粗糙面随机Green函数 差场雷达散射截面 面体复合散射     

基于微面斜率法的粗糙表面半透明介质层光谱散射特性分析

对具有一维高斯分布粗糙表面的半透明介质层光谱散射,基于微面斜率法建立了考虑遮蔽效应的粗糙表面光谱辐射传递概率模型,采用蒙特卡罗法模拟光谱辐射能束在粗糙表面、半透明介质层介质与镜反射基底之间的多次反射、折射和吸收等传递过程。通过数值模拟,分析了介质层表面粗糙度、光谱光学厚度、折射率和基底反射率对介质层双向反射分布函数(BRDF)的影响。结果表明,表面粗糙程度不同时,反射峰值随入射角度呈现不同的变化趋势;表面粗糙度增加或折射率增大都将导致漫反射份额增大;介质层光谱光学厚度和基底反射率主要影响BRDF的数值大小,而对BRDF的分布形态影响很小。     

高斯分层介质粗糙面光波透射问题的微扰法研究

运用微扰法研究平面波入射分层介质粗糙面的光波透射问题,推出了不同极化状态的透射光波散射系数公式。采用高斯粗糙面来模拟实际的分层介质粗糙面,结合高斯粗糙面的功率谱导出了平面波入射高斯分层介质粗糙面的透射系数计算公式。通过数值计算得到HH极化透射系数随透射光波散射角变化的曲线,讨论底层介质介电常数、中间介质介电常数和厚度、粗糙面参数及入射光波长对透射系数的影响。数值计算结果表明：底层介质介电常数、中间介质介电常数和厚度、粗糙面参数及入射光波长对透射系数的影响是非常复杂的。     

余弦粗糙面辐射特性数值模拟研究

提出一种基于几何光学法的精确计算粗糙表面的辐射特性的研究方法，研究了半球漫入射一维余弦粗糙面情况下，离散网格数目和方向离散数目对计算精度的影响，分析了粗糙面的粗糙度和相对尺度，及一次、多次散射分别对出射方向辐射强度的影响，解释了不同粗糙面中的散射增强现象。     

微高斯分层介质粗糙面光波透射

应用微扰法研究三层介质构成的微粗糙面光透射问题,推导出不同极化状态透射系数的公式.采用高斯粗糙面模拟实际的分层介质粗糙面,通过数值计算得到底层介质介电常数、中间层介质介电常数和厚度、粗糙面参数和入射光波长对HH极化透射系数的影响.     

粗糙表面涂覆目标的太赫兹波散射特性研究

对具有涂覆层目标的太赫兹波段粗糙表面的散射特性进行了研究. 考虑到表面粗糙度的影响, 可先对反射系数进行修正, 再利用反射系数对等效电磁流进行修正, 得到粗糙涂覆表面的等效电磁流, 然后在物理光学方程的基础上得到粗糙表面涂覆目标的雷达散射截面; 最后进行图形电磁学可视化计算, 并采用Visual C++对模型进行OpenGL显示, 提取像素面元的有效信息对所得理论进行了仿真分析, 研究了不同入射角度、不同频率、不同介质、不同粗糙度和不同涂层厚度下的太赫兹波电磁散射特性, 得到了一些有参考价值的结论.     

小斜率近似在粗糙面激光散射BRDF计算中的应用

基于小斜率近似法建立了粗糙面激光散射双向反射分布函数的数学模型,采用该模型计算了粗糙度参量已知的合金铝样片的双向反射分布函数值,计算结果与实测结果吻合良好,验证了模型的正确性.研究了粗糙度参量和样片光学常量对双向反射分布函数的影响,结果表明,粗糙面激光散射的双向反射分布函数与表面高度起伏均方根、自相关长度及样片光学常量相关.当入射波长一定时,高度起伏均方根越大,或者自相关长度越小,粗糙面粗糙度越大,入射激光的漫反射特性越强,双向反射分布函数峰值越小且分布越分散;当粗糙度一定时,样片光学常量对双向反射分布函数影响较大,粗糙面对入射激光复折射率的虚部越大,样片双向反射分布函数的峰值越小,当粗糙度参量增大时,样片光学参量对双向反射分布函数的影响逐步减弱.     

Wave diffraction by rough interfaces in an arbitrary plane-layered medium

Abstract

The problem of electromagnetic wave scattering by a slightly rough interface in an arbitrarily layered medium is solved by a small-perturbation method. The bistatic amplitude of scattering as well as the scattering cross sections for statistically rough surfaces are calculated for linear polarized waves. Along with scattering into up-going waves in a homogeneous medium and scattering cross sections in down-going waves into a layered medium, scattering amplitudes from a rough interface in the arbitrarily layered medium are obtained.     

Investigation on electromagnetic scattering from rough soil surface of layered medium using the small perturbation method

Electromagnetic scattering from a rough surface of layered medium is investigated, and the formulae of the scattering coefficients for different polarizations are derived using the small perturbation method. A rough surface with exponential correlation function is presented for describing a rough soil surface of layered medium, the formula of its scattering coefficient is derived by considering the spectrum of the rough surface with exponential correlation function; the curves of the bistatic scattering coefficient of HH polarization with variation of the scattering angle are obtained by numerical calculation. The influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the roughness surface parameters and the frequency of the incident wave on the blstatic scattering coefficient is discussed. Numerical results show that the influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the rms and the correlation length of the rough surface, and the frequency of the incident wave on the bistatic scattering coefficient is very complex.     

一维带限Weierstrass分形分层地面与矩形截面导体柱复合电磁散射FDTD研究

运用时域有限差分方法研究一维带限分形分层粗糙地面与矩形截面导体柱的复合电磁散射,计算复合电磁散射的双站散射系数,得到复合散射系数随散射角的变化,讨论粗糙面高度起伏均方根、分维、中间层介质、下层介质及矩形截面导体柱的参数等对复合散射系数的影响.     

Electromagnetic Wave Transmission from Slightly Gaussian Rough Surface of Layered Medium

The electromagnetic wave transmission from the slightly rough surface of three-layered medium is studied, and formulae of the transmission coefficients for different polarizations are derived using the small perturbation method. A Gaussian rough surface is presented for describing rough surface of the layered medium, the influence of permittivity of the layered medium, the mean layer thickness of the intermediate medium, the roughness surface parameters and the incident frequency on the transmission coefficient of HH polarization are obtained and discussed with numerical implementation.     

指数型分层介质粗糙面光透射问题的微扰法

运用微扰法研究了平面波入射分层介质粗糙面的光透射问题,推出了不同极化状态的透射系数公式.采用指数型粗糙面模拟实际的分层介质粗糙面,结合其功率谱导出了平面波入射时的透射系数计算公式.通过数值计算得到了HH极化情形透射系数随透射光散射角变化的曲线.数值计算结果表明,底层介质介电常量对透射系数几乎没有影响;中间介质介电常量影响透射系数的大小及透射系数角分布曲线;中间介质厚度增大为原来的二倍时,曲线振荡的周期减小为原来的二分之一;粗糙面高度起伏均方根影响透射系数的大小、曲线振荡的振幅;粗糙面高度起伏相关长度既影响透射系数的大小、同时影响曲线的振荡行为;透射系数随入射波长的增大而振荡减小.     

Research on synthetic aperture radar imaging technology of one-dimensional layered rough surfaces

A quick and exact imaging method for one-dimensional layered rough surfaces is proposed in this paper to study the scattering characteristics of a layered medium that exists widely in nature.The boundary integral equations of layered rough surfaces are solved by using the propagation-inside-layer expansion combined with the forward and backward spectral acceleration method(PILE+FB-SA),and the back scattering data are obtained.Then,a conventional synthetic aperture radar(SAR) imaging procedure called back projection method is used to generate a two-dimensional(2D) image of the layered rough surfaces.Combined with the relative dielectric permittivity of realistic soil,the random rough surfaces with Gauss spectrum are used to simulate the layered medium with rough interfaces.Since the back scattering data are computed by using the fast numerical method,this method can be used to study layered rough surfaces with any parameter,which has a great application value in the detection and remote sensing areas.     

Analysis of one-dimensional rough surface scattering based on bidirectional reflectance distribution function model

Through in-depth analysis of the scattering properties of a one-dimensional random rough surface, a method to calculate the spatial bidirectional reflectance distribution function (BRDF) characteristics of a randomly rough surface is proposed. The scattering characteristics of an electrically large rough surface can be substituted by combination of subsection electromagnetic fields. The radar cross-section (RCS), which is transformed from the BRDF, is compared with numerical results from the Method of Moment (MoM). The agreement of the results verifies that this method could calculate the electromagnetic scattering field efficiently and straightforwardly. Moreover, the resulting combined fields from the BRDF of subsections in the rough surface show a good match with the entire scattering field of a whole surface, which indicates that a large electrically rough surface could be feasibly and effectively substituted with the combination of scattering elements using the BRDF method and the statistical method.