Calculations of Infrared Laser Beam Scattering from Rough Dielectric Objects

The coherent and incoherent scattering cross sections of Infrared Laser Gaussian beam scattering from arbitrarily shaped convex dielectric objects with rough surfaces are investigated by using plane wave spectrum method and physical optics approximation. In the paper, the infrared laser scattering cross sections of rough sphere are calculated at 10.6 μm , and the influence of the beam size, permittivity, and polarization as well as roughness parameters is analyzed numerically. When the beam size is much larger than the size of object, the results in the paper can reduce to those of an incident plane wave. On the other hand, for the case of roughness statistical parameter close to zero, only the forward scattering has a parent difference compared with the result of gaussian beam scattering from smooth sphere.     

Scattering cross sections for composite rough surfaces using the unified full wave approach

The full wave approach is used to derive a unified formulation for the like and cross polarized scattering cross sections of composite rough surfaces for all angles of incidence. Earlier solutions for electromagnetic scattering by composite random rough surfaces are based on two-scale models of the rough surface. Thus, on applying a hybrid approach physical optics theory is used to account for specular scattering associated with a filtered surface (consisting of the large sonic spectral components of the surface) while perturbation theory is used to account for Bragg scattering associated with the surface consisting of the small scale spectral components. Since the full wave approach accounts for both specular point scattering and Bragg scattering in a self-consistent manner, the two-scale model of the rough surface is not adopted in this work. These unified full wave solutions are compared with the earlier solutions and the simplifying assumptions that are common to all the earlier solutions are examined. It is shown that while the full wave solutions for the like polarized scattering cross sections based on the two-scale model are in reasonably good agreement with the unified full wave solutions, the two solutions for the cross polarized cross sections differ very significantly.     

Wave diffraction by a rough boundary of an arbitrary plane-layeredmedium

The problem of electromagnetic (EM) wave scattering by a slightly rough boundary of an arbitrary layered medium is solved by a small perturbation method. The bistatic amplitude of scattering as well as scattering cross sections for a statistically rough surface are calculated for linear and circular polarized waves. Along with the scattering into the upgoing waves in the homogeneous medium, the scattering cross sections in the downgoing waves into a layered medium are obtained. Analytical results are applied to the modeling of natural layered media (ice and sand layers) remote sensing problems employing global positioning system (GPS) technics     

Scattering by anisotropic models of composite rough surfaces--Full wave solution

Expressions for the scattering cross sections of anisotropic models of composite random rough surfaces are derived using the full wave approach that accounts for specular point scattering and Bragg scattering in a self-consistent manner. Backscatter cross sections are evaluated for vertically and horizontally polarized waves as a function of angle of incidence for cross wind, up wind, and down wind directions. The cross sections are most sensitive to wind direction for angles of incidence around40deg.     

A new unified full wave approach to evaluate the scatter crosssections of composite random rough surfaces

A new unified approach, based on the original full wave solutions, is presented to evaluate the like and cross polarized scattering cross sections of composite (multiple scale) random rough surfaces. The rough surfaces are assumed to be characterized by the Pieson-Moskowitz spectral density function. To account for the surface undulations, the incoherent radar cross sections are obtained by regarding the composite rough surface as an ensemble of pixels of arbitrary orientation     

RF Characteristics of thin dipoles

This paper considers the average bistatic scattering cross section of thin cylindrical dipoles as a function of frequency, bistatic angle, and transmitting and receiving polarization. The averaging is over all orientations of the dipole with all orientations equally likely. Section II is essentially tutorial, approaching the problem of scattering cross section from the equivalent circuit point of view. Using this approach, the maximum scattering cross sections of lossless dipoles in the Rayleigh region and at the first and second resonances are derived. Section III presents a novel method of predicting cross section at the first resonance with the effect of loss included. Numerous measurements indicate that this method is widely applicable. Section IV describes our microwave scattering range and the results of measurements made on dipoles resonant at X band. In Section V the averaging of cross sections is considered. The average bistatic cross sections for resonant half-wave and full-wave dipoles are plotted vs bistatic angle for various transmitting and receiving polarizations. These results, which are new, were obtained using a digital computer. The average cross section for short (Rayleigh region) dipoles is also obtained as a function of bistatic angle for various polarizations. Section VI is a summary of parameters of the West Ford dipoles.     

Tilt modulation of high resolution radar backscatter crosssections: unified full wave approach

The unified full wave approach is used to determine the tilt modulation of the like- and cross-polarized (high-resolution) radar backscatter cross sections for the rough sea surface. Real or synthetic aperture radars (SARs) with small effective footprints (resolution cells) are considered. Since the unified full-wave approach accounts for Bragg scattering as well as specular point scattering in a self-consistent manner, it is not necessary to adopt a two-scale model for the rough sea surface. The sea surface slope probability density function is assumed to be Gaussian. The backscattering cross sections are evaluated for all angles of incidence (normal to grazing). For tilts in the plane of incidence, the modulation of all the cross sections is largest at angles of incidence of 10°. The cross-section modulation due to tilts perpendicular to the plane of incidence critically depends on the incident and scattered polarizations. The effective filtering of the large-scale spectral components of the rough sea surface by the high-resolution radar is accounted for, and the dependence of the cross-section tilt modulation on the size of the effective footprint is determined     

低频太赫兹准目标雷达散射截面的实验研究

以研究太赫兹雷达散射截面的特性为目的,选用所搭建低频太赫兹雷达测试系统,并借助于标准目标法开展了有关太赫兹雷达粗糙铝盘散射截面的实验研究工作.实验结果表明:在小角度散射中太赫兹雷达散射截面随散射角的增大变化比较明显,在散射角超过5后太赫兹雷达散射截面随散射角的变化趋向缓慢,但当散射角超过12后探测信号的强度已衰减到无法测量,在太赫兹雷达散射截面的测试中没有出现微波雷达散射截面的大小随散射角的变化而剧烈振荡的现象;将测试结果与同尺寸微波、激光雷达散射截面的结果进行了对比,得到结论:在0附近太赫兹雷达散射截面的数值比同尺寸微波雷达散射截面的数值要小两个数量级,但比同尺寸激光雷达散射截面的数值要高一个数量级.     

基于积分方程的地下管线电磁散射计算

采用积分方程仿真粗糙地面下方金属和介质管线的电磁散射。由于地下的土壤是分层的,根据面等效原理、边界条件以及目标在分界面上方还是下方,分别列出相应的积分方程,采用矩量法求解积分方程。粗糙地面的建模采用谱快速傅里叶变换(FFT)方法和高斯谱,仿真了粗糙地面下方圆截面和矩形截面的管线。仿真结果表明,本文的分析方法能够计算地下管线的电磁散射。     

Scattering cross sections for composite models of non-Gaussian rough surfaces for which decorrelation implies statistical independence

The full wave approach is used to determine the scattering cross sections for composite models of non-Gaussian rough surfaces. It is assumed in this work that the rough surface heights become statistically independent when they decorrelate, thus no delta function type specular term appears in the expressions for the scattered fields. The broad family of non-Gaussian surfaces considered range in the limit from exponential to Gaussian. It is seen that for small angles of incidence the like polarized cross sections have the same dependence on the specific form of the surface height joint probability density, but for large angles the scattering cross sections for the horizontally polarized waves are much more sensitive to the specific form of the joint probability density. On the other hand the shadow functions are rather insensitive to the specific form of the joint probability density.     

红外波段气溶胶粒子光学特性的数值计算

气溶胶是大气电磁环境中的重要组成部分,气溶胶粒子的光学特性是研究红外遥感、目标探测等激光传输特性的一个关键问题。依据粒子电磁散射理论,利用离散偶极子近似方法对不同形状、不同成分气溶胶粒子的光学特性进行计算,得到气溶胶粒子散射截面、吸收截面及不对称因子等光学特征量在0.71～11μm波段的数值结果。结果显示:入射光波长、气溶胶粒子折射率及气溶胶粒子形状是影响气溶胶粒子光学特性的主要因素。散射截面、吸收截面及不对称因子等光学特征量的数值结果也为研究气溶胶中红外激光的传输特性提供了参考依据和计算方法。     

太赫兹波在烟尘气溶胶中的传播特性

随着太赫兹波技术的发展,对其在各种大气条件下的传播特性的研究是很有必要的。本文利 用扩散限制凝聚模型(DLA 方法)模拟了组成烟尘气溶胶的簇团粒子,并利用广义Mie 理论(GMM)方法 计算了不同基本粒子个数的单个簇团粒子对波长分别为30μm、35μm 和40μm 的太赫兹波的散射特性。 另外本文还利用蒙特卡罗方法模拟计算了浓度较大的烟尘气溶胶对太赫兹波的衰减特性并将结果与波 长为6.2μm 的红外波段的结果进行比较,结果显示,太赫兹波在烟尘气溶胶中传播的衰减要小的多, 这也说明太赫兹波更加适合在烟尘气溶胶中传播。     

Scattering from the perfectly conducting cube

The scattering cross sections in the E-plane, H-plane, and 45°-plane of the perfectly conducting cube illuminated broadside by an incident plane wave are computed using both a uniform high-frequency diffraction solution and magnetic-field integral equations. The computed cross sections are compared with measured cross sections for cube perimeters of 3, 6, 12, and 20 wavelengths. The total scattering cross section versus the perimeter of the cube is also computed and compared to that of the sphere     

Scattering of Solar and Atmospheric Background Radiation from a Target

Light scattering property of environment is very important in theoretical study and application of the remote sensing. What's more, it is valuable for infrared radiation, imaging, and the detection of target and tracking. In this paper, solar and atmospheric background radiation, and their scattering property from target are discussed. BRDF (Biodirectional Reflectance Distribution Function) is a very important quantity that shows the radiation and reflection feature of target. According to electromagnetic radiant and scattering theories, the relationship between laser radar scattering cross section (LRCS) and BRDF is introduced. LOWTRAN model is an effective method of calculating the spectral distribution of solar and atmospheric radiation. Here it is applied to compute solar and atmospheric background radiation scattered from a target. The relative equations are deduced. Thus, the spatial and spectral distribution of scattering light is given. As a special example, for the Lambert's surface, the equations are simplified. As a result, the spatial and spectral distributions scattering radiation of solar and atmospheric background from a rough painted surface are present. The scattering of solar radiation plays a primary role in MIR region, but scattering of atmospheric background radiation is higher in LIR region. At the same time, there is obviously specular reflectance for solar radiation due to coherent scattering from rough surface.     

Computations of scattering cross sections for composite surfaces and the specification of the wavenumber where spectral splitting occurs

The scattering cross sections for composite random rough surfaces are evaluated using the full wave approach. They are compared with earlier solutions based on a combination of perturbation theory which accounts for Bragg scattering, and physical optics which accounts for specular point theory. The full wave solutions which account for both Bragg scattering and specular point scattering in a self-consistent manner are expressed as a weighted sum of two cross sections. The first is associated with a filtered surface, consisting of the larger scale spectral components, and the second is associated with the surface consisting of the smaller scale spectral components. The specification of the surface wavenumber that separates the surface with the larger spectral components from the surface with the smaller spectral components is dealt with in detail. Since the full wave approach is not restricted by the limitations of perturbation theory, it is possible to examine the sensitivity of the computed values for the backscatter cross sections to large variations in the value of the wavenumber where spectral splitting is assumed to occur.     

The scattering behavior of a slightly rough surface moving parallel to its mean plane with uniform velocity

The scattering of plane electromagnetic (EM) waves from a perfectly conducting, slightly rough surface moving in vacuum with uniform and constant velocity is examined by combining the boundary perturbation method and the special, homogeneous Lorentz transform. The direction of motion is assumed to be parallel to both the incidence plane and the mean plane of the moving rough surface. The analysis is confined to first-order scatter. The end result is the determination of the velocity-dependent expressions for the bistatic and backscatter incoherent cross sections per unit area of the scattering surface. The expressions for bistatic geometry are only valid for scattering inside the plane of incidence. A numerical example demonstrates the effect of the motion on the scattering behavior of the rough surface.     

大粗糙度表面激光散射特性实验研究

本文利用激光散射自动测量系统,对经喷丸处理后的钢基粗糙表面及其喷漆表面的后向激光雷达散射截面(LRCS)进行了测量。测量波长分别为λ=633nm和λ=904nm.在λ=904nm,利用粗糙面电磁散射理论的基尔霍夫方法对上述样片进行了理论计算,其中将粗糙表面视为双尺度模型,根据驻留相位法和标量近似法理论计算双尺度模型随机粗糙表面的散射强度角分布,其理论值与实验测量结果有较好的吻合。     

Scattering of electromagnetic waves from a layer with rough front and plane back (small perturbation method by Rice)

Rice's small perturbation method is extended to obtain first- and second-order terms of the field scattered from a rough layer. The first-order terms are utilized to obtain average scattering cross sections. Lossy and lossless layers are considered for horizontal and vertical polarizations.     

Scattering of screened excitons by free carriers in semiconductingquantum well structures

The theoretical treatment of the scattering of excitons by free electrons and holes in a two-dimensional semiconducting quantum-well system is extended to take into account screening by the free carriers. The scattering cross sections are calculated using the Born approximation for elastic scattering of the excitons by the free carriers. For the heavy-hole exciton, the screening by the free carriers reduces the cross section for free-carrier exciton scattering for all values of the energy of relative motion of the free carriers and the excitors. For the light-hole exciton, however, screening can actually lead to an enhancement of the scattering cross section for low values of the energy of relative motion when the density of free carriers is high. This is because screening not only reduces the interaction between the free carriers and the exciton, but also decreases the binding of the exciton, leading to a larger effective radius of the exciton. The results for the scattering cross sections are then applied to calculate the contribution of the exciton linewidth due to elastic scattering of the excitons by free carriers. It is found that this contribution to the exciton linewidth is decreased below its value in the absence of screening for both the heavy- and light-hole excitons