共查询到19条相似文献,搜索用时 175 毫秒
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利用建立在多次散射基础上的Dyson方程和Bethe-Salpeter方程,讨论了在考虑随机分布的散射间的对相关而忽略高阶相关的情况下标量波声波场的传播问题。认为在波传播方向散射体的相关性具有马尔科夫近似,同时运用前向散射近似,得到了在相关性离散随机介质中的等效传播常数,吸收截面和互相干函数的解析解。 相似文献
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该文针对传统极化合成孔径雷达(PolSAR)分解方法过高估计植被成分的问题,提出一种基于极化干涉相似性参数(PISP)的极化干涉分解方法。利用极化干涉合成孔径雷达(PolInSAR)的3组最优相干散射机制定义的PISP具有对地表散射体空间分布敏感的特性和旋转不变性。该文基于PISP的物理意义对植被模型进行改进,使利用该模型分解相干矩阵得到的不同地物体散射功率具有自适应性。最后利用欧空局(DLR)E-SAR获取的L波段全极化干涉数据验证该分解方法的有效性,实验结果表明,该算法得到的分解结果能有效区分植被和建筑物。 相似文献
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重点研究了具有极化特征的植被相干散射模型及参数反演算法。基于目标分解理论,推导了植被及地表回波的极化干涉相干系数与植被高度、衰减系数、地形相位等参数之间的数学关系,以衰减系数作为极化分量的函数,建立了具有明显极化特征的植被及地表相干散射模型。在此基础上,以全极化干涉相干系数作为输入参量,考虑模型对极化的依赖性,采用三阶段法对植被的物理参量进行反演,获得了地形相位和植被高度。在环境可控的微波暗室内构建了极化干涉半实物合成孔径雷达系统对模型进行实验验证,获取了南洋杉和土壤所构成场景的极化干涉回波数据,实验结果表明:采用该模型在场景的地体幅度比小于-10dB的情况下,植被反演高度与实际高度的误差仅为0.03m,说明了模型的有效性。 相似文献
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多入多出(MIMO)传输技术是第四代移动通信系统的关键技术之一,而小尺寸间隔下天线阵元间的互耦效应则是有可能影响MIMO系统性能的一个重要因素。文中首先研究分析了一种接近实际电波传输环境的、收发端皆存在散射体的双散射MIMO信道传输模型,然后将天线互耦效应引入此MIMO传输系统;接下来通过建立多天线系统等效互耦效应网络模型,推导了互耦效应影响下空间相关系数和信道容量表达式;最后通过计算机仿真研究了双散射环境下天线阵元互耦对MIMO系统信道容量的影响。仿真实验表明:双散射环境下,互耦效应将降低MIMO系统信道容量。 相似文献
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本文研究了单壁碳纳米管在THz 波段的散射特性。首先,建立了金属性碳纳米管散射体模型。通过严格的级数展开,给出了单壁碳纳米管散射场和透射场的表达式。其次,以TM 波为例,分别在平面波正入射及斜入射的条件下,研究其散射场及散射宽度的特性。通过散射场、感应电流、散射宽度,有效地描述了碳纳米管在THz 的散射特性。研究结果对利用碳纳米管进行THz 的探测具有一定意义。 相似文献
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Sarabandi K. Dehmollaian M. Mosallaei H. 《Geoscience and Remote Sensing, IEEE Transactions on》2006,44(8):2072-2082
A hybrid target-foliage model is developed to investigate the scattering behavior of hard targets embedded inside a forest canopy. The proposed model is composed of two existing electromagnetic-scattering models, one for the foliage and the other for the hard targets that are coupled in a computationally efficient manner. The connection between these two models, which accounts for the interaction between the foliage scatterers and the target, is accomplished through the application of Huygens' principle. Wave penetration through the forest canopy and near-field and far-field scattering from its constituents is calculated using a coherent single-scattering theory, which makes use of realistic tree structures. Defining a Huygens' surface enclosing the hard target and calculating the illuminating field (the scattered fields from the nearby vegetation scatterers and reduced incident field), the interaction between the foliage and the hard target is accounted for. Computing the scattered field from target on the Huygens' surface and using a reciprocity theorem target-foliage interaction is captured very efficiently. Calculation of scattering from a hard target is carried out using a finite-difference time-domain (FDTD) technique. For a typical vehicle dimensions, the required time and memory for the FDTD computation and exact field calculation inside the foliage limits the simulation frequency to upper very high frequency (VHF) band. 相似文献
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The use of cellular or foamed plastics in various microwave applications, such as supports at radar ranges, makes it desirable to know the back scattering properties of such materials. Since the cell structure is of a random nature with some predictable average properties such as cell size and density, it is modeled by an aggregate of randomly distributed spherical shells. Assemblies of scatterers will in general have a coherent and an incoherent scatter. Coherent scattering comes primarily from sudden particle density changes such as that at the boundaries of a particle system. Since coherent scattering comes only from the boundaries of a constant density material, it can sometimes be reduced by appropriate shaping. Incoherent scattering is the result of the contribution of all the particles in the system, i.e, a volume or an interior effect. It represents the irreducible scattering contribution to the total back scatter. As such it can be looked upon as the minimum cross section that can be obtained from a foam structure provided all coherent scatter has been removed. The magnitude of the incoherent scattering is illustrated by calculating radar cross sections for a cylinder made of styrofoam. Since the compressive strength of styrofoam is known, the maximum load that a styrofoam structure can support and the minimum achievable cross section from it can be easily calculated. 相似文献
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A coherent scattering model for tree canopies is employed in order to characterize the sensitivity of an interferometric SAR (INSAR) response to the physical parameters of forest stands. The concept of an equivalent scatterer for a collection of scatterers within a pixel, representing the vegetation particles of tree structures, is used for identifying the scattering phase center of the pixel whose height is measured by an INSAR. Combining the recently developed coherent scattering model for tree canopies and the INSAR Δk-radar-equivalence algorithm, accurate statistics of the scattering phase-center location of forest stands are obtained numerically for the first time. The scattering model is based on a Monte Carlo simulation of scattering from fractal-generated tree structures, and therefore is capable of preserving the absolute phase of the backscatter. The model can also account for coherent effects due to the relative position of individual scatterers and the inhomogeneous extinction experienced by a coherent wave propagating through the random collection of vegetation particles. The location of the scattering phase center and the correlation coefficient are computed using the Δk-radar equivalence simply by simulating the backscatter response at two slightly different frequencies. The model is successfully validated using the measured data acquired by JPL TOPSAR over a selected pine stand in Raco, MI. A sensitivity analysis is performed to characterize the response of coniferous and deciduous forest stands to a multifrequency and multipolarization INSAR in order to determine an optimum system configuration for remote sensing of forest parameters 相似文献
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A microwave scattering formulation is presented for grassland and other short vegetation canopies. The fact that the constituent elements of these targets can be as large as the vegetation layer make this formulation problematic. For example, a grass element may extend from the soil surface to the top of the canopy, and thus the upper portion of the element can be illuminated with far greater energy than the bottom. By modeling the long, thin elements of this type of vegetation as line dipole elements, this nonuniform illumination can be accounted for. Additionally, the stature and structure of grass plants can result in situations where the average inner-product of coherent terms are significant at lower frequencies. As a result, the backscattering coefficient cannot be modeled simply as the incoherent addition of the power from each element and scattering mechanism. To determine these coherent terms, a coherent model that considers scattered fields, and not power, is provided. This formulation is then used to provide a solution to the multiple coherent scattering terms, terms which include the correlation of the scattering between both dissimilar constituent elements and dissimilar scattering mechanisms. Finally, a major component of the grass family are cultural grasses, such as wheat and barley. This vegetation is often planted in row structures, a periodic organization that can likewise result in significant coherent scattering effects, depending on the frequency and illumination pattern. Therefore, a formulation is also provided that accounts for the unique scattering of these structures 相似文献
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Fano共振效应拥有独特的局域场增强效果,在表面增强相干反斯托克斯拉曼散射中,不同波长局域场增强空间位置相同的结构结合Fano共振效应,可以实现混合频率共振模式,使得表面增强相干反斯托克斯拉曼散射总的增强因子得到大幅度提高。采用FDTD软件系统研究了对称的交叉蝴蝶结Au纳米结构的Fano共振效应,该效应使得交叉蝴蝶结结构中心位置附近的电场强度得到大幅度的增强,把该结构应用到表面增强相干反斯托克斯拉曼散射中,可以使表面增强相干反斯托克斯拉曼散射信号的增强因子高达1013,达到单分子检测的水平。 相似文献
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Saatchi S.S. McDonald K.C. 《Geoscience and Remote Sensing, IEEE Transactions on》1997,35(4):1032-1044
In modeling forest canopies, several scattering mechanisms are taken into account, (1) volume scattering; (2) surface-volume interaction; (3) surface scattering from forest floor. Depending on the structural and dielectric characteristics of forest canopies, the relative contribution of each mechanism in the total backscatter signal of an imaging radar can vary. In this paper, two commonly used first-order discrete scattering models, distorted Born approximation (DBA) and radiative transfer (RT) are used to simulate the backscattered power received by polarimetric radars at P-, L-, and C-bands over coniferous and deciduous forests. The difference between the two models resides on the coherent effect in the surface-volume interaction terms. To demonstrate this point, the models are first compared based on their underlying theoretical assumptions and then according to simulation results over coniferous and deciduous forests. It is shown that by using the same scattering functions for various components of trees (i.e. leaf, branch, stem), the radiative transfer and distorted Born models are equivalent, except in low frequencies, where surface-volume interaction terms may become important, and the coherent contribution may be significant. In this case, the difference between the two models can reach up to 3 dB in both co-polarized and cross-polarized channels, which can influence the performance of retrieval algorithms 相似文献
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Radar polarimetry: analysis tools and applications 总被引:3,自引:0,他引:3
Evans D.L. Farr T.G. van Zyl J.J. Zebker H.A. 《Geoscience and Remote Sensing, IEEE Transactions on》1988,26(6):774-789
The authors have developed several techniques to analyze polarimetric radar data from the NASA/JPL airborne SAR for Earth science applications. The techniques determine the heterogeneity of scatterers with subregions, optimize the return power from these areas, and identify probable scattering mechanisms for each pixel in a radar image. These techniques are applied to the discrimination and characterization of geologic surfaces and vegetation cover, and it is found that their utility varies depending on the terrain type. It is concluded that there are several classes of problems amenable to single-frequency polarimetric data analysis, including characterization of surface roughness and vegetation structure, and estimation of vegetation density. Polarimetric radar remote sensing can thus be a useful tool for monitoring a set of Earth science parameters 相似文献
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本文按分形几何的自相似原理构造出一种具有自相似分布结构的随机粒子模型,求得了其数密度相关函数孔子。这种模型有确定的构造方法,在结构上具有自相似性,并可按其结构特征求得其相关函数,因而便于应用于随机介质与波的相互作用的研究和计算机模拟。本文应用此模型分析了雷达回波功率与距离的关系。结果与Rastogi等人(1990)的数值模拟结果完全一致。 相似文献
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《Microwave Theory and Techniques》1979,27(11):883-890
A method is established which gives the internal field of a radial waveguide in the presence of annular-type slots on the conducting walls or metallic scatterers inside the guide. The exciting field can have a general form, and the dielectric constant of the region could be lossy or lossless. To obtain a solution, the induced currents (magnetic current in case of slot-type discontinuity) over the scattering bodies are expanded into a finite series of suitable basis functions with unknown coefficients. The total number of these functions is directly related to the electrical dimensions of the scatterers. The complex coefficients are then obtained by employing the appropriate Green's functions and an application of the boundary conditions over the scattering bodies. The method is then applied to the probIem of coupling between two radials waveguides by annular slots on the common boundary. It is shown that in general, higher order modes have significant effect on the solution, and for a precise evaluation of the field their contribution must also be included. 相似文献