非均匀散射层矢量辐射传输(VRT)方程高阶散射解的迭代法

将散射介质层在z轴方向划分成薄层，用薄层的一阶散射强度、Fourier变换和迭代方法求解散射介质整层的矢量辐射传输(VRT)方程的高阶散射解.该方法将一阶散射与高阶散射迭代结合起来，计算公式简明，可计算高阶迭代解，计算时间少.计算结果与一层均匀散射介质的VRT方程一阶Mueller矩阵解、半空间均匀散射介质二阶Mueller矩阵解、以及离散坐标-特征值特征矢量法的VRT热辐射的数值解作了全面的比较.提出并讨论了非均匀散射层主动与被动VRT方程的高阶解.本计算程序可以通用于非球形粒子多层结构及非均匀介质的散射和热辐射计算. 关键词： VRT方程 分层 迭代解     

非均匀随机散射介质层的多次散射和热辐射的分层迭代解

为纳入矢量辐射传输方程的多次散射，将非均匀平行分层分布的随机散射介质划分成多个薄 层，利用各薄层的低阶Mueller矩阵解推导出整层的高阶散射迭代解.用这一方法计算了具有 占空比、粒子大小和温度廓线非均匀分布的平行分层随机密集球形粒子积雪层的极化热辐射 .数值结果与一层均匀随机散射层的离散坐标-特征值方法作了比较，讨论了多次散射和热辐 射与散射层各特征参数的关系，与积雪层微波遥感数据进行了对比. 关键词： VRT方程 平行分层 高阶散射解 迭代解     

大尺度分层介质粗糙面电磁散射的特性研究

首先建立大尺度分层介质粗糙面散射的物理模型, 基于Stratton-Chu积分方程和Kirchhoff近似导出了粗糙面散射场的计算公式. 采用高斯随机粗糙面来模拟实际的分层介质粗糙面, 通过数值计算得到了正下视单站雷达接收到的后向散射回波. 理论推导了散射场强度与表面粗糙度之间的定量关系, 并从数值仿真的角度分析了表面和次表面的粗糙度对散射回波的影响, 给出了散射场随粗糙度变化的曲线. 最后考察了分层介质的电特性参数(介电常数和电导率)对分层粗糙面散射场的影响, 并对计算结果做出了分析.     

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.     

光学薄膜的分层界面散射模型

提出了一种计算光学介质膜系表面总积分散射(TIS)的理论模型。该模型认为,介质膜系粗糙的膜层界面和表面为微观结构不均匀的微薄过渡区;过渡区可用折射率为不同常量的层数足够多的均匀子层来代替,同时这些均匀子层的折射率变化满足指数函数的分布规律。利用矩阵法对积分散射的表达式进行了推导。对于电子束蒸发方法在K9玻璃上沉积的ZrO2单层膜,分层界面散射模型对积分散射的理论计算值要比非相关表面散射模型的计算值更加符合总积分散射仪的实验测量结果。     

多波长发光二极管光源雷达系统与近地面低层大气气溶胶探测

设计并研制了一台多波长发光二极管(LED)光源雷达系统,用于探测近地面低层大气气溶胶特性.介绍了LED光源雷达系统的组成及工作原理,计算分析了系统几何重叠因子,从而确定了LED光源雷达系统的最低探测高度为60 m.研究了LED光源雷达散射回波信号的数据反演方法,根据LED光源雷达适合近距离探测的特点,采用了Fernald前向积分反演算法,并以地面能见度仪数据为基础,确定了气溶胶消光系数的边界值.利用所设计的475, 530和625 nm三个波长的LED光源雷达系统,分别在轻度污染、中度污染和重度污染天气情况下,对西安夜晚城区上空低层大气气溶胶进行了探测,获得了近300 m高度内三个波长的大气气溶胶消光系数高度分布曲线,并对近地面低层大气气溶胶的垂直分布与变化特征进行了探讨.     

非球形粒子散射光的去偏振特性研究

目标对入射偏振光的散射特性反映了目标的属性信息。在Rayleigh散射理论的基础上，通过单层非球形粒子对入射偏振光的散射数学模型，应用矢量传输方程来计算非球形粒子散射的Mueller矩阵元，求解散射介质的偏振度，讨论在不同介质层厚度、粒子半径和探测角的条件下，非球形粒子散射光去偏振度的变化特性，给出了模拟仿真结果。该方法为研究目标的内部结构、厚度和粗糙度等特征以及目标的探测和识别提供了一种新的途径。     

Mie理论递推公式计算散射相位函数

在激光雷达探测中,关于多次散射雷达回波的研究,散射相位函数是个非常重要的物理量。本文利用Mie理论的递推公式,对单一粒径介质的散射相位函数进行了计算,计算结果与散射理论中前、后向散射峰值大小随粒子半径的增大而增大相一致。同时,对非单一粒径介质的散射相位函数进行了计算,可用于大气、雾和云等气溶胶多次散射的研究。     

大尺度分层介质电特性参数的反演方法研究

针对大尺度分层介质电磁场散射回波数据, 提出了一种用于分层介质特性参数反演的新方法, 实现了分层介质的介电常数、电导率和介质厚度的同时反演. 方法首先将这些参数的反演转化为最优化问题进行求解, 然后应用模拟退火算法搜索最优解, 充分利用算法的全局寻优能力, 同时改善了算法的搜索控制策略, 使算法在最优解的搜索过程中可以自适应地调整搜索步长, 提高了算法的搜索效率. 结果表明, 本文方法可以实现大尺度分层介质特性参数的准确反演, 且具有较强的抗噪声能力. 该方法可以应用于火星/月球 雷达探测回波数据的反演以及地下分层结构特性的分析. 关键词： 电磁散射 分层介质 模拟退火算法 最优化     

包覆微米碳颗粒的光散射特性

利用分层介质球光散射理论公式,计算分析了包覆水和黄铜介质层对碳微粒的微分散射特性的影响,比较了包覆前后散射的极化特性。在计算中为保持收敛性,对Bessel函数采用了递推求解,并对求和项数进行了限定。结果表明,在包覆前后,单粒子的微分散射截面发生了变化,而包覆层的影响与其厚度和光在其中的趋肤深度有关;厚度小于趋肤深度的包覆层对粒子的前后向散射的极化特性没有影响,而在其它方向上却影响较大。     

The scattering of electromagnetic waves in fractal media

The scattering of electromagnetic waves in fractal media is studied. The fractal dimension is naturally involved in the formulation of two physical problems studied in this paper. The general theory of multiple scattering of electromagnetic wave in fractal media is developed by modifying Twersky's theory. Statistical quantities, such as the average field and average intensity of the multiple scattered wave, are studied for a wave propagating in a fractal medium. The scattering cross section of the medium is deduced. The backscattering of electromagnetic waves is also studied. The results showing the range of dependence of the backscattered signals are in agreement with numerical simulations by Rastogi and Scheucher (1990). It also suggests a method of measuring the fractal dimension of the fractal embedded media using radar sounding. The theory developed in this paper can also be used for problems related to multiple scattering of other kinds of waves, such as acoustic waves, elastic waves etc, in fractal media.     

The scattering of electromagnetic waves in fractal media

Abstract

The scattering of electromagnetic waves in fractal media is studied. The fractal dimension is naturally involved in the formulation of two physical problems studied in this paper. The general theory of multiple scattering of electromagnetic wave in fractal media is developed by modifying Twersky's theory. Statistical quantities, such as the average field and average intensity of the multiple scattered wave, are studied for a wave propagating in a fractal medium. The scattering cross section of the medium is deduced. The backscattering of electromagnetic waves is also studied. The results showing the range of dependence of the backscattered signals are in agreement with numerical simulations by Rastogi and Scheucher (1990). It also suggests a method of measuring the fractal dimension of the fractal embedded media using radar sounding. The theory developed in this paper can also be used for problems related to multiple scattering of other kinds of waves, such as acoustic waves, elastic waves etc, in fractal media.     

热防护层覆盖弹体目标雷达散射截面的修正的等效电流近似法和图形计算电磁学法分析

将修正的等效电流近似法与图形计算电磁学法相结合引入到热防护层覆盖弹体目标的电磁散射问题的研究中.应用修正的等效电流近似法对介质和有耗表面进行散射计算,结合图形计算电磁学法,借助于计算机显示技术,将三维目标图形在计算机屏幕上投影,由图形加速卡完成遮挡和消隐工作,利用图形计算电磁学的积分公式,把三维空间的计算转化为二维空间的计算,大大降低了计算时间和复杂度.计算结果表明:当入射波频率较低时,热防护层的厚度不会影响弹体雷达截面值的大小,当频率升高,随着热防护层厚度的增加,弹体雷达截面值不断减小,说明热防护涂层为有耗介质,介电常数的虚部越大其消耗能量的能力越强,弹体雷达截面变化越明显;当热防护层中存在孔隙,热防护层厚度一定,孔隙率越大,雷达截面值越大,孔隙率为零时,雷达截面值最小.当孔隙率相同,热防护层越薄,其雷达截面值越大;当弹体在高空中出现脱粘现象,对弹体的雷达截面值影响不大.     

电阻加载半椭圆偶极子天线的设计与研究

针对实际工程应用中安装在探测车底部的表层穿透雷达的需求,设计了一种基于电阻加载技术的超宽带低背腔半椭圆偶极子天线。该天线由一对半椭圆臂组成并通过分布式连续电阻加载有效地改善了输入阻抗特性,展宽了天线的工作带宽。结合应用环境,评估了天线离地高度以及载体探测车对天线性能的影响,在理论分析的基础上设计并制作了一副天线样机,安装在探测车上,在外场进行了实验。仿真和实测结果表明,所设计的天线具有较低的电压驻波比和良好的辐射特性以及较小的振铃,能够满足车载表层穿透雷达的需求。     

Effects on RCS of a perfect electromagnetic conductor sphere in the presence of anisotropic plasma layer

Effects on RCS of perfect electromagnetic conductor (PEMC) sphere by coating with anisotropic plasma layer are studied in this paper. The incident, scattered and transmitted electromagnetic fields are expanded in term of spherical vector wave functions using extended classical theory of scattering. Co and cross-polarized scattered field coefficients are obtained at the interface of free space-anisotropic plasma and at anisotropic plasma-PEMC sphere core by scattering matrices method. The presented analytical expressions are general for any perfect conducting sphere (PMC, PEC, or PEMC) with general anisotropic/isotropic material coatings that include plasma and metamaterials. The behavior of the forward and backscattered radar cross section of PEMC sphere with the variation of the magnetic field strength, incident frequency, plasma density, and effective collision frequency for the co-polarized and the cross polarized fields are investigated. It is also observed from the obtained results that anisotropic layer on PEMC sphere shows reciprocal behavior as compared to isotopic plasma layer on PEMC sphere. The comparisons of the numerical results of the presented analytical expressions with available results of some special cases show the correctness of the analysis.     

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.     

Scattering of a Generic Two-Dimensional Field by Cylindrical Structures in the Presence of a Plane Interface

A new method for treating the scattering of a two-dimensional electromagnetic field, expressed by means of its plane-wave spectrum, by an arbitrary configuration of circular cylinders in the presence of a plane interface between two different media, is presented. The proposed method allows us to solve the problem for both polarizations and to calculate the scattered field both in the near and in the far zone. Numerical results relevant to vacuum-dielectric interfaces are presented and compared with previous known results.     

二维分数布朗运动(FBM)随机粗糙面电磁散射的基尔霍夫近似

采用二维FBM分形函数来模拟二维实际粗糙面,利用基尔霍夫近似给出了FBM粗糙面的电磁散射场和散射截面的计算公式.数值计算并分析了散射截面与分维、特征长度及入射频率的关系,并与高斯相关分布和指数相关分布粗糙面的散射结果做了比较 关键词： FBM粗糙面 分形 电磁散射 基尔霍夫近似     

不同土壤类型的粗糙地面与其下方埋藏目标复合电磁散射研究

利用MOM研究了不同土壤类型的一维有耗介质粗糙地面与其下方二维埋藏目标的复合电磁散射问题,在数值计算中,引入了锥形入射波以减少粗糙面模拟中由于人为截断所引起的计算误差.当给定入射波频率、土壤成分及土壤温度和土壤湿度后,可以根据相关模型计算出土壤的相对介电常数.数值结果以二维无限长导体圆柱为例,利用 Monte Carlo方法统计计算了双站复合散射截面随土壤类型、土壤湿度、入射波频率及均方根高度等的变化情况,并做了详细分析及讨论.该研究结果对于探地雷达在民用、军事、工业等多领域的应用具有一定的理论指导价值. 关键词： 粗糙地面 土壤类型 相对介电常数 四成分模型