多重散射随机介质中隐藏物体的 强度成像研究

用背散射光强研究了多重散射随机介质中隐藏物体位置的确定,由强度的分布曲线确定出隐藏物体的位置,并实验研究了隐藏物体在多重散射随机介质中不同深度下的强度分布     

积灰光伏板表面散射光强度分布实验研究

针对现有光伏板积灰程度检测方法中存在难以直接对光伏板透射率进行测量和环境光干扰大的问题,提出了一种基于散射光强度的光伏板积灰密度测量方法。该方法使用调制的主动光源,基于角分辨散射(angle-resolved scattering,ARS)测量原理,对积灰光伏板表面散射光强度空间分布进行研究。根据散射光强度的分布规律,建立特定立体角范围的散射光强度与光伏板积灰密度之间的关系。实验结果表明,当探测器放置在光源同侧时,系统线性度更好,散射光强度随着光伏板积灰密度的增加先线性增长,随后增长逐渐放缓,最终趋于一定值。本方法抗环境光干扰能力强,能直观地表征光伏板的积灰状态。     

激光大气散射离轴探测分析

利用Mie散射理论,通过数值计算得到了1.06 μm激光在低空大气中传输时的散射特性;不同尺度参数的粒子的散射光强分布相差极大,随着尺度参数的增加,散射光强越来越集中于前向;复折射率的变化对散射光强影响不大.通过对大气散射的辐照度理论分析和数值计算,得到大气散射的辐照度随离轴距离的增大而近似按反比规律下降的特征;同时,对不同能见度下的散射辐照度进行了数值计算,能见度的不同只影响散射强度的大小,而不影响散射强度的分布.不同散射点的散射光到达探测器所需的时间不同,延迟时间与离轴垂直距离和探测角呈简单的线性关系,这些特征为激光散射离轴探测提供了理论依据和参考.     

部分空间相干光经准均匀介质的散射

基于一阶波恩近似,研究了部分空间相干平面光经准均匀介质的散射特性,得到了远场散射光谱强度和光谱相干度的解析表达式。讨论了入射光的空间相干性和介质特性对散射场光谱强度和光谱相干度的影响。比较了入射光是完全相干光和部分相干光时,散射场光谱强度和相干度的区别。研究结果表明:入射光的空间相干性对散射场光谱强度的分布有重要影响;随着入射光空间相干长度的增大,光谱宽度减小;光谱相干度随着入射光束腰宽度或介质有效半径的增大而减小。当准均匀介质的有效半径和相干长度、入射光的空间相干长度满足一定条件时,散射光是完全相干光。     

水泥路面激光散射特性研究

为了通过激光散射特性识别不同粗糙程度水泥路面, 设计了路面粗糙度测量系统。使用千分表测量水泥路面高度分布, 计算高度均方根与相关长度。根据以上参量采用功率谱频域滤波生成随机粗糙表面以模拟水泥路面, 通过切平面近似将粗糙面离散为大量微面元, 由菲涅耳公式计算本地场, 利用蒙特卡罗方法获取不同偏振光入射条件下粗糙面双向与后向散射光强度统计平均值。基于虚拟仪器技术进行高精度自动化激光散射测量, 并根据实验数据对理论模型进行了验证。结果表明, 双向散射小粗糙度水泥路面散射光强度在镜像方向散射角40°附近具有峰值90lx, 在镜像方向两侧逐步递减, 大粗糙度水泥路面光学特性近似为朗伯体, 散射光强度在各散射角方向变化不大; 后向散射在垂直入射时, 小粗糙度水泥路面散射光强度峰值为103lx, 随散射角增大逐渐递减, 大粗糙度水泥路面具有朗伯体散射特征。此研究结果可为车辆自主驾驶方案路面信息感知提供参考。     

以激光散射立体角分布测量表面横向形貌参数

为了利用光学非接触方法测量表面横向形貌参数,从Beckmann-Kirchhoff标量散射理论出发,分析并得到了高斯粗糙表面激光散射能量的立体角分布特征与轮廓均方根斜率之间的关系.提出了散射光的两个特征值:经度及纬度辐射立体角密度矩,用以提取散射光能量立体角分布情况,并给出了利用数字图像信号在非傍轴远场条件下测量和计算特征值的方法.实验证明:给出的特征参数和测量方法能够得到激光散射立体角分布特征并可用于测量粗糙表面轮廓均方根斜率.     

散射诱导的多色高斯光束远场的光谱移动和光谱开关

在静态散射的框架内,以高斯光束透过表面粗糙的绝缘板的远场谱强度为例,对散射诱导的光谱变化做了研究.前散射光的谱强度相对源光谱可能有红移和蓝移,某些条件下还会产生光谱开关.在影响散射光谱强度的诸参数中,板的厚度相对平均厚度的差值H参数起主要作用.当H=0时,归一化谱强度保持不变.散射诱导的多色高斯光束远场光谱开关属于"奇点光学"效应.     

典型粗糙表面激光后向散射特性实验

对现有的粗糙度比较样块和其他典型粗糙目标进行了后向光散射特性的实验。实验结果表明,当入射光为632.8 nm波长时,随着入射角的增大,不同的被测目标的散射强度变化得比较明显。如果被测目标的表面斜率均方根比较接近,可以发现它们整体的散射光强度变化趋势几乎一样,而且它们的偏振度也相差不大。表面斜率很小的被测目标,相对其他被测目标,其散射光光强明显大很多,其偏振度也是最大的,说明相对光滑的表面探测到的后向散射光强度比相对粗糙表面探测到的散射光强度大得多。文中关于典型粗糙表面后向散射偏振特性的研究结果对于探讨进行目标识别的理论及应用方面有一定的价值。     

蓝宝石晶片中微/纳米缺陷散射特性的仿真

基于广义Lorenz-Mie理论,对蓝宝石晶片中微体缺陷的散射特性进行了仿真,分析了散射光接收位置、缺陷大小、入射光波长对散射光强的影响。结果表明:前向散射方向上的空间散射光强信息量最大,检测结果最准确;缺陷大小对散射光强分布具有显著影响,可以将散射光强分布曲线的特征作为判断缺陷大小的依据;入射光波长越小,测量越准确。     

基于Mie氏散射理论的石墨微球颗粒光散射特性研究

本文应用Mie氏散射理论对石墨微球颗粒光散射的性质进行了理论分析与数值计算,得到了消光特性与入射波长及粒子半径,散射强度与散射角以及散射强度与参数x的关系.结果表明,粒子的半径越小,其消光效果越好;入射波长越小,粒子的前向散射强度越强.因此,通过测量前向散射光的分布可以确定微球体颗粒的半径.     

A numerical simulation of scattering from one-dimensionalinhomogeneous dielectric random surfaces

An efficient numerical solution for the scattering problem of inhomogeneous dielectric rough surfaces is presented. The inhomogeneous dielectric random surface represents a bare soil surface and is considered to be comprised of a large number of randomly positioned dielectric humps of different sizes, shapes, and dielectric constants above an impedance surface. Clods with nonuniform moisture content and rocks are modeled by inhomogeneous dielectric humps and the underlying smooth wet soil surface is modeled by an impedance surface. In this technique, an efficient numerical solution for the constituent dielectric humps over an impedance surface is obtained using Green's function derived by the exact image theory in conjunction with the method of moments. The scattered field from a sample of the rough surface is obtained by summing the scattered fields from all the individual humps of the surface coherently ignoring the effect of multiple scattering between the humps. The statistical behavior of the scattering coefficient σ° is obtained from the calculation of scattered fields of many different realizations of the surface. Numerical results are presented for several different roughnesses and dielectric constants of the random surfaces. The numerical technique is verified by comparing the numerical solution with the solution based on the small perturbation method and the physical optics model for homogeneous rough surfaces. This technique can be used to study the behavior of scattering coefficient and phase difference statistics of rough soil surfaces for which no analytical solution exists     

Full-wave solutions for the scattered radiation fields from rough surfaces with arbitrary slope and frequency

Full-wave solutions are derived for the scattered radiation fields from rough surfaces with arbitrary slope and electromagnetic parameters. These solutions bridge the wide gap that exists between the perturbational solutions for rough surfaces with small slopes and the quasi-optics solutions. Thus it is shown, for example, that for good conducting boundaries the backscattered fields, which are dependent on the polarization of the incident and scattered fields at low frequencies, become independent of polarization at optical frequencies. These solutions are consistent with reciprocity, energy conservation, and duality relations in electromagnetic theory. Since the full-wave solutions account for upward and downward scattering, shadowing and multiple scatter are considered. Applications to periodic structures and random rough surfaces are also presented.     

粗糙平面的激光散射特性研究

为了检测目标的边缘信息,采用激光扫描目标表面、通过回波信号变化来得到目标的边缘信息的方法,利用随机面元模型,分析了刚性随机粗糙平面的激光散射特点,建立了实用化的随机粗糙平面激光散射理论模型,并给出了正入射时几种情况下的激光散射图像,分析了平面目标的激光散射能量计算方法,仿真了光束在平面目标表面做正弦摆动时,光斑在不同位置的反射能量,利用激光信号的强度变化,采用峰(谷)检出法或者过零检出法就可以得到物体的边缘信息。结果表明,通过回波信号的变化,可以得到目标的边缘轮廓。     

Full-wave solutions for the depolarization of the scattered radiation fields by rough surfaces of arbitrary slope

Employing a variable coordinate system associated with the local features of two-dimensionally rough surfaces with arbitrary slope, full-wave solutions are derived for the depolarization of the scattered radiation fields. An outline of the analytical procedures used in the derivations of the solutions are presented. Furthermore, the engineer who is not familiar with them can also use the final result which is expressed as a definite integral whose integrand is given explicitly and in closed form. These full-wave solutions are compared with the quasi-optics solution and the iterative or perturbational solutions for slightly rough surfaces, and they are shown to bridge the wide gap that exists between them. The full-wave solutions are consistent with energy conservation, duality, and reciprocity relationships in electromagnetic theory. These solutions account for upward and downward scattering of the incident waves with respect to the horizontal reference plane, thus shadowing and multiple scattering are considered. Applications to two-dimensionally periodic structures and random rough surfaces are also presented. The fullwave solutions are examined for Brewster, grazing, and specular angles and backscatter. Special consideration is also given to good conducting boundaries.     

Scattering, transmission, and absorption by a rough resistive sheet - E polarization

Motivated by the use of thin conducting textiles in absorbers, the interaction of electromagnetic waves with a rough resistive sheet is examined. Expressions for the fields above and below the sheet are derived in terms of an equivalent current using Gaussian beam illumination. These field expressions are then used with equations derived from the conservation of energy to find the distribution of scattered, transmitted, and absorbed power using an exact numerical solution and the Kirchhoff approximation. As a consequence of the lack of refraction, the Kirchhoff single scattering solution produces strong coherent transmitted intensities at the forward angles with an attendant minimum in the incoherent intensity. A second minimum in the incoherent intensity is observed in the antispecular direction. Fields arising from multiple scattering interactions are observed independent of the Kirchhoff single scatter contributions at these angles for surfaces of large root-mean-square slope. An increase in the absorption in the sheet is also observed as surface roughness is increased. The increase in absorption is believed due to multiple scattering interactions on the surface.     

Electromagnetic scattering interaction between a dielectriccylinder and a slightly rough surface

An electromagnetic scattering solution for the interaction between a dielectric cylinder and a slightly rough surface is presented in this paper. Taking the advantage of a newly developed technique that utilizes the reciprocity theorem, the difficulty in formulating the secondary scattered fields from the composite target reduces to the evaluation of integrals involving the scattered fields from the cylinder and polarization currents of the rough surface induced by a plane wave. Basically, only the current distribution of isolated scatterers are needed to evaluate the interaction in the far-field region. The scattered field from the cylinder is evaluated in the near-field region using a stationary phase approximation along the cylinder axis. Also, the expressions for the polarization current induced within the top rough layer of the rough surface derived from the iterative solution of an integral equation are employed in this paper. A sensitivity analysis is performed for determining the dependency of the scattering interaction on the target parameters such as surface root mean square (RMS) height, dielectric constant, cylinder diameter, and length. It is shown that for nearly vertical cylinders, which is of interest for modeling of vegetation, the cross-polarized backscatter is mainly dominated by the scattering interaction between the cylinder and the rough surface. The accuracy of the theoretical formulation is verified by conducting polarimetric backscatter measurements from a lossy dielectric cylinder above a slightly rough surface. Excellent agreement between the theoretical prediction and experimental results is obtained     

Electromagnetic scattering from slightly rough surfaces withinhomogeneous dielectric profiles

Remote sensing of soil moisture using microwave sensors require accurate and realistic scattering models for rough soil surfaces. In the past, much effort has been devoted to the development of scattering models for either perfectly conducting or homogeneous rough surfaces. In practice, however, the permittivity of most soil surfaces is nonuniform, particularly in depth, for which analytical solution does not exist. The variations in the permittivity of a soil medium can easily be related to its soil moisture profile and soil type using the existing empirical models. In this paper, analytical expressions for the bistatic scattering coefficients of soil surfaces with slightly rough interface and stratified permittivity profile are derived. The scattering formulation is based on a new approach where the perturbation expansion of the volumetric polarization current instead of the tangential fields is used to obtain the scattered field. Basically, the top rough layer is replaced with an equivalent polarization current and, using the volumetric integral equation in conjunction with the dyadic Green's function of the remaining stratified half-space medium, the scattering problem is formulated. Closed-form analytical expressions for the induced polarization currents to any desired order are derived, which are then used to evaluate the bistatic scattered fields up to and including the third order. The analytical solutions for the scattered fields are used to derive the complete second-order expressions for the backscattering coefficients as well as the statistics of phase difference between the scattering matrix elements. The theoretical results are shown to agree well with the backscatter measurements of rough surfaces with known dielectric profiles and roughness statistics     

Depolarization of EM waves by slightly rough surfaces

Depolarization is obtained for the scattering of electromagnetic waves from a slightly rough surface using Rice's theory. In the plane of incidence, depolarization is a second-order effect. The results are applied to backscattering from a slightly rough sea using the Neumann spectrum for a fully developed sea. The expression for the depolarized scattered power is of the form obtained in multiple scattering investigations. Therefore, it can be inferred that depolarization from slightly rough surfaces is due to multiple scattering. For the sea, depolarization increases with wind speed and with the magnitude of the complex dielectric constant of the surface.     

Very high frequency radiowave scattering by a disturbed sea surface Part II: Scattering from an actual sea surface

A two-scale model of rough surfaces is considered which permits theoretical interpretation of the features of very high frequency (VHF) scattering from such surfaces (say, from a sea surface). The scattering surface is assumed to be a superposition of small-scale ripple and large waves (swell). Reflection from the latter may he considered by the Kirchhoff approximation. The spatial spectrum of corrugations is taken into consideration; the calculations based on this model help to give an explanation of the behavior of the scattered intensity as a function of the angle of incidencepsi, and to establish which factors affect this dependence at various values ofpsi- Theoretically predicted dependence of the scattered intensity upon radio wavelengthlambda, depolarization of the scattered signal, and other features of the scattered radiation are in good agreement with the experimental data obtained from direct measurements. Frequency spectra of the backscattered signal were also investigated (experimental measurements were carried out at wavelengths 3.2 cm, 10 cm, 50 cm, 1.5 m, and 4 m). Observed shifts of the central frequency agree with results of other authors (for the range oflambda = 3cm to 200 m). The measured values of the spectrum width appeared approximately twice those theoretically calculated. This may be explained by the influence of dissipative processes and of fluctuations of the skin-deep layer drift velocities. Space correlation of the backscattered signal was also investigated (both theoretically and experimentally). 50 percent decorrelation occurs at distances compared with dimensions of a wave slope.