A further study of the IEM surface scattering model

The objective of this study is to develop a surface scattering model including multiple scattering based on extending an existing integral-equation-based surface scattering model (IEM). This is done by removing a simplifying assumption in the spectral representation of the Green's function used in the scattered field expression of the IEM surface scattering model. It is noted that while this simplifying assumption is valid and useful in single scattering calculation, it is a hindrance to separating and identifying terms responsible for surface multiple scattering. Furthermore, it is demonstrated that the removal of this assumption permits multiple surface scattering calculations to be carried out and shown to agree with controlled laboratory measurements acquired from known surfaces     

Full-wave analysis of microwave scattering from short vegetation: an investigation on the effect of multiple scattering

A full-wave solution for polarimetric scattering from a cluster of randomly oriented three-dimensional lossy dielectric structures above an impedance surface is presented to investigate the importance of multiple scattering. The problem is formulated using an integral equation in conjunction with the exact image representation of dyadic Green's function for the half-space problem. Then, the integral equation is solved for the induced equivalent polarization currents using the method of moments. The accuracy of the numerical code is verified using other existing numerical results and experimental observations. The model is then used to examine the effect of multiple scattering among a cluster of relatively short stems and is shown that multiple scattering significantly affects the cross-polarized backscatter whereas it has a moderate effect on the copolarized backscattering depending on the stem density.     

Note on the scattering of waves by rough surfaces

A calculation of back scattering from a rough surface using Huygen's principle is carried out along the lines introduced by Davies. Davies original equation is extended to include a contribution from the component of the surface normal which is parallel to the average surface. The effect of this component is to multiply the usual expression for incoherent backscatter by a factor of1/ cos^{4} PsiwherePsiis the angle between the radar line of sight and the normal to the average surface.     

A reappraisal of the validity of the IEM model for backscattering from rough surfaces

An integral equation method (IEM) surface scattering model was examined in terms of its applicability to laboratory measurement and numerical simulations. New expressions for both single scattering and multiple scattering were obtained by rederiving the scattering coefficient to keep all the phase terms in the spectral representation of the Green's function. After quite intricate mathematical manipulations, a fairly compact form is obtained for the scattering coefficients. In addition, the Fresnel reflection coefficients used in the model were replaced by a transition function that takes surface roughness and permittivity into account. The results of comparisons with both the numerical simulations and measurements for the backscattering case indicate that the IEM is improved, becoming more accurate and practical to use.     

基于改进圆模型的到达角度和时间估计

为提高对到达角度(AOA)和到达时间(TOA)估计的准确性,引入了"有效散射体"和"反射概率"两个有明确物理意义的概念,在单反射圆模型的基础工提出一种改进圆模型,推导出AOA和TOA的分布表达式.仿真结果与实测数据对比表明,相对单反射圆模型而言,改进圆模型的AOA和TOA的估计值与实测结果吻合得更好.     

Effects of multiple scattering and Fresnel diffraction on random volume scattering

A wave incident on a volume of random fluctuations of medium parameters will be scattered in all directions. Two kinds of effects on random volume scattering are considered: 1) multiple scattering effect, and 2) Fresnel diffraction effect. The cumulative forward scattering is known to be responsible for the scintillation phenomenon. When strong, such cumulative or multiple scattering can drive the signal statistics into the saturated regime in which the complex amplitudes behave as a complex Gaussian process. These cumulative scattering effects on signals of a bistatic radar are investigated. Additionally, to allow for the possibility that the size of the irregularity is comparable or larger than the first Fresnel zone, Fresnel diffraction instead of Fraunhofer diffraction is considered. A generalized formula for calculating average scattered power, taking both multiple scattering and Fresnel diffraction into account, is derived. It shows that the Fresnel diffraction pattern appearing around the forward direction tends to be smeared out by multiple scattering. Also, both multiple scattering and Fresnel diffraction effects weaken and broaden the forward-scattered beam, and reduce the backscattered power when compared with the single scattering and Fraunhofer diffraction cases respectively. Under certain conditions, the enhancement effect of the backward scattered power is confirmed.     

Note on interpolational basis functions in the method of moments[EM scattering]

Efficient basis sets for the method of moments may be obtained using quasi-localized bandlimited interpolational functions that, broadly speaking, are defined relative to a mean sampling rate that is adjusted to curvature and proximity to edges, thus reflecting the local spatial-frequency bandwidth. Computed scattering data in a number of structures, including perfectly conducting circular and elliptical two-dimensional cylinders as well as a flat infinite strip, indicate that reasonable accuracy can be obtained with an average rate of between 2.5 and 3 basis functions per wavelength. Average sampling rates need not correspond strictly to the bandwidth of the basis functions, and there is considerable latitude with respect to random variation of sampling intervals. Although each basis function typically extends over several sample points, required integrals can be obtained speedily by the use of standard sampling-theoretical methods     

LAI inversion using a back-propagation neural network trained witha multiple scattering model

Standard regression methods applied to canopies within a single homogeneous soil type yield good results for estimating leaf area index (LAI) but perform unacceptably when applied across soil boundaries. In contrast, the neural network reported generally yielded absolute percentage errors of <30%. The network was applied, without retraining, to a sample of Landsat TM data for an agriculture/forestry study site     

Effect of multiple scattering on line-of-sight propagation

This paper deals with the effect of small random variations in the atmosphere's refractive index upon electromagnetic waves propagated along a line-of-sight path. These fluctuations are considered to be due only to the turbulent character of the medium, and the effect of the earth and other bodies is taken to be negligible. Previous analyses of this problem have utilized the first Born or single-scattering approximation. This method, however, assumes that each part of the scattering region is illuminated by the incident wave, i.e., that any incident wave is scattered at most once. The applicability of this approximation in the microwave region is questionable since the mean free path for scattering at high frequencies decreases as the square of the frequency. If at microwave frequencies the transmission distance is large compared to the mean free path length multiple-scattering effects are of importance. It is these effects which are considered here. Multiple-scattering analysis is used to determine expressions for the mean value, mean-square value, and variance of the field at a single receiver. Also determined is the correlation function for zero time difference for the fields at two spaced receivers, as well as the mean value, mean square, and variance of the difference of the fields at two spaced receivers.     

High-frequency scattering by multiple spheres

Use is made of simple geometrical optics to obtain back-scattering cross sections of arrays of identical spheres, both for broadside and end illumination. Experimental data are given for two- and three-sphere arrays for all angles of illumination and for various spacings of spheres. It is shown that a reasonable knowledge of the general behavior of the cross sections may be obtained even from simple geometrical considerations.     

缝隙及其与边缘的相互作用对目标散射的影响

随着雷达散射截面 ( RCS)减缩技术的发展 ,缝隙对目标散射行为的影响已经日益突出。文中分析了有限目标上缝隙自身的散射 ,及缝隙与边缘的相互作用对目标散射的影响     

基于扩展球谐函数的多次散射理论分析

粒子的单次散射在一定程度上描述了光的传播特征。但在实际情况中,单次散射不足以描述传播过程的全貌。因此,我们必须考虑粒子的多次散射效应,以得到对光传播问题的一个完整描述。在本文中,我们首先建立散射传输方程,在求解散射传输方程中引入了辅助函数,然后再利用球谐函数对辅助函数进行扩展,导出了多次散射方程的解。     

一种顾及表面间多次散射的热辐射方向性模型

利用辐射换热角系数描述了非同温异质表面间的多次散射效应,据此建立热辐射方向性模型,并对模型的数值计算进行了讨论.将模型应用于行结构目标,结合孔隙率模型模拟其方向亮温(Directional Brightness Tempera-ture,DBT)变化规律.结果表明,模拟得到的规律与地面观测结果具有较高的一致性,平均偏差在0.5 K以内.同时发现,多次散射效应增强了目标DBT,但对DBT的变化幅度又起平滑作用;目标组分的温差、几何结构、发射率均可导致DBT发生变化,温差越大,表面越凹,发射率越小,DBT随观测角度变化的程度越剧烈;模型可以解释热辐射中的"热点效应",认为"热点"的产生主要与组分温度空间分布有关.模型对于研究发射率方向性,城市热红外遥感反演及热红外邻近像元影响等问题可提供参考或思路.     

Distortion in diffraction tomography caused by multiple scattering

In this paper, we have first presented a new computational procedure for the calculation of the "true" forward scattered fields of a multicomponent object. By "true" we mean fields that are not limited by the first-order approximations, such as those used in the first-order Born and Rytov calculations. Although the results shown will only include the second-order fields for a multicomponent object, the computational procedure can easily be generalized for higher order scattering effects. Using this procedure we have shown by computer simulation that even when each component of a two-component object is weakly scattering, the multiple scattering effects become important when the components are blocking each other. We have further shown that when strongly scattering components that are large compared to a wavelength are not blocking each other, the scattering effects can be ignored. Both these conclusions agree with intuitive reasoning. Since all the currently available diffraction tomography algorithms are based on the assumption that the object satisfies the first-order scattering assumption, it is interesting to test them under conditions when this assumption is violated. We have used the scattered fields obtained with the new computational procedure to test these algorithms, and shown the resulting artifacts. Our main conclusion drawn from this computer simulation study is that even when object inhomogeneities are as small as 5 percent of the background, multiple scattering can introduce severe distortions in multicomponent objects.     

Effects of multiple scattering in optical-fibre transmission line

The authors estimate the magnitude of secondary forward scattering and its dependence on line length and absorption loss. They show that, for pulsed signals, the ratio of the direct signal to the background is increased in the proportion of the peak to mean power in comparison with c.w. behaviour.     

FM-CW制式陆基微波散射计与IEM模型联合反演地表土壤湿度研究

本文利用FM-CW制式的陆基微波散射计对裸土进行了后向散射系数的测量,利用IEM模型对土壤的湿度及表面粗糙度进行了反演,并将反演结果与实地测量结果进行了比较研究.研究表明,通过多角度微波后向散射测量可以较为准确的确定表层土壤的湿度,而用光学方法进行的地表粗糙度的实地测量结果与反演结果相差较大,反映了微波频段的电磁波对地表具有的穿透作用.文中还对测量中存在的误差进行了较为详细的分析.     

光学表面散射模型探索

文章讨论了光散射模型和表面粗糙度的统计特征。由数值解得到：入射角在决定散射曲线的行为中起着重要的作用。     

F-近似下颗粒的多重散射计算公式的改进

利用多重散射基础理论和修正的Fraunhofer近似及其相位函数,我们对过去F一近似下得到的颗粒的多重散射计算公式进行了改进.与理论值的相对误差的计算表明,我们的公式的准确性较原公式有了较大程度的提高.此外,我们也发现,随着光学厚度增加,多重散射光强的角分布的震荡减弱.     

粒子散射的几何光学模型中的多值散射角函数计算

对大颗粒散射特性分析通常采用物理意义清晰的几何光学近似模型(GOM)计算散射光强。本文分析了GOM,针对散射角的多值问题,提出一种基于MATLAB的遍历取值的求解方法,给出了球形大气泡粒子单一阶数散射光强和总散射光强分布图,并与Mie理论和Debye理论光强计算进行了比对,计算结果与Mie理论和Debye理论光强计算吻合很好,验证了算法的正确性。     

自由空间中偶极子云团极化散射特性研究：相干散射模型

根据相干散射模型,求得了偶极子云团的极化散射矩阵,并导出了偶极子云团散射截面的精确计算公式,它们能够反映出由于偶极子云团空间分布的变化而造成的散射截面起伏规律,原则上适用于一切偶极子云团（包括在大气层内抛撒的情形）散射截面的计算问题。