Polarimetric scattering from two-layered two-dimensional random rough surfaces with and without buried objects

A three-dimensional polarimetric analysis of the two-layered rough ground with and without buried objects is investigated here. A rigorous electromagnetic surface integral-equation-based model is used in this analysis. The statistical average of the polarimetric scattering matrix elements is computed based on the Monte Carlo simulations for both the vertically and horizontally polarized incident waves. The results show a significant impact on the scattered intensities due to the two-layer nature of the ground. However, these intensities show almost no difference between the ground signature with or without the object. On the other hand, the statistical average of the covariance matrix elements shows a distinct difference between these two signatures despite the small size of the buried object.     

Polarimetric radar backscattering from reciprocal random targets

Radar backscattering from reciprocal random targets is studied employing a covariance matrix approach. Polarization signatures for backscattered power and correlation observables are derived. Optimal polarization for the power return in two orthogonally polarized radar channels can be determined. Polarizations which extremize mean copolar power can be proved to reduce the correlation of the backscattered wave components exactly to zero. In the case of cross-polar optimal polarizations, a particular correlation difference rather than individual interchannel correlations tends to zero. The utilization of these necessary conditions for the power extrema, furthermore, allows the introduction of an efficient numerical algorithm to compute optimal polarization states for a given target covariance matrix. The presented polarimetric concept is demonstrated to generalize the well-established theory of characteristic polarizations. Analysis of chaff radar data illustrates the efficiency of the outlined approach     

NUMERICAL SIMULATIONS OF POLARIZED SCATTERING FROM RANDOM CLUSTERS OF SPATIALLY-ORENTED, NON-SPHERICAL SCATTERS

Employing multiple scattering formulation of T-matrix method, numerical simulations are developed and applied to polarized scattering from random clusters of spatially-oriented, non-spherical particles. Polarized scattering is numerically presented for the functional dependence on particle shape, size, spatial distribution and orientation, and other physical parameters. Numerical calculations of backscattering from randomly clustered particles are well compared with that from independent particles and clusters. It can be seen that spatial distribution and orientation of non-spherical particles can have significant effect on scattering.     

Polarimetric scattering from natural surfaces at 225 GHz

Polarimetric radar measurement at 225 GHz which demonstrate that the normalized Mueller matrix may be approximated in terms of a single parameter are presented. The depolarization ratio, defined as the ratio of cross-polarized to co-polarized normalized radar cross section, is shown to accurately predict backscatter from vegetation (trees and grass), as well as scattering from terrain at low incidence angles (snowcover and sand). The depolarization ratio also predicts the standard deviation of the scattered field ellipse parameters     

Multiple scattering effect on backscattering from a random medium

The backscattering from a random medium is analytically studied. The result gives a mathematical foundation to the cumulative forward-scatter single-backscatter (CFSB) approximation proposed by de Wolf. The multiple scattering effects on backscattering of a plane wave incidence are examined for both Fresnel and Fraunhofer scatterings with various correlation functions of turbulence. As a result, it is found that the multiple scattering effect on the backscattering is sensitive to the statistical properties of the fluctuating medium.     

Numerical computation of scattering from a perfectly conducting random surface

A one-dimensionally rough random surface with known statistical properties was generated by digital computer. This surface was divided into many segments of equal length. The moments method was applied to each surface segment assuming perfect conductivity to compute the induced surface current and subsequently the backscattered field due to an impinging plane wave. The return power was then calculated and averaged over different segments. Unlike numerical computations of scattering from deterministic surfaces, problems of stability (as defined by Blackman and Turkey [11]) and convergence of the solution exist for random surface scattering. It is shown that the stability of the numerically computed estimate of the backscattered average power depends onN, the total number of disjoint surface segments averaged;Delta x, the spacing between surface current points;D, the width of each surface segment; andg, the width of the window function. Relations are obtained which help to make an appropriate choice of these parameters. In general, choices ofDelta x, D, andgare quite sensitive to the incident wavelength and the angular scattering properties of the surface.     

Monte Carlo simulation of scattering from a layer of verticalcylinders

Electromagnetic scattering by a collection of randomly distributed vertical cylinders over a half-space dielectric is considered, using two approaches. In the first approach, a Monte Carlo simulation that takes into account scattering terms up to second order is used. Closed-form expressions for the second-order scattering terms are derived for cylinders that are in each other's near field. The second approach is based on the radiative transfer equations, which are solved by an iterative method up to and including the second-order terms. Radar backscatter measurements at X-band for a collection of metallic cylinders over a conducting ground plane are compared with the Monte Carlo and radiative transfer solutions. The data were acquired polarimetrically from 144 independent spots of the cylinder layer at incidence angles ranging from 20° to 60°. The simulation results agree well with the measured data and are used to check the validity of the radiative transfer results for a medium with large particles. It is shown that both the phase function computed for the cylinders and the extinction matrix of the layer are overestimated in the radiative transfer solution     

Adaptive model-based scattering decomposition of Polarimetric SAR Interferometry

In this paper, a new decomposition method is proposed to solve the problems that vegetation component is overestimated and is not sensitive to directional scattering features with traditional polarimetric Synthetic Aperture Radar （SAR） decomposition. It uses a Polarimetric Interferometric Similarity Parameter （PISP） calculated from Polarimetric SAR Interferometry （PolInSAR） datasets to the scattering decomposition. The PISP is proposed to reveal the geometric sensitivity of SAR inter- ferometry. It is defined by three optimized mechanisms obtained from PolInSAR datasets, therefore, it not only relates to the coherent scattering mechanism closely, but also sufficiently uses the phase and amplitude information. The PISP of building is high, and forest＇s PISP is low. The proposed method uses the PISP as a judge condition to select different vegetation model adaptively. The decomposition results show the proposed method can effectively solve the vegetation ingredients overestimation problem. In addition, it is sensitive to the directional scattering.     

Parallel analysis of electromagnetic scattering from random rough surfaces

An efficient approach for simulation of random rough surface scattering is developed based on using a single integral equation formulation and a multilevel sparse-matrix canonical-grid method. Merits of the scheme are demonstrated using two wind-driven ocean surfaces, one which is very rough and the other large in size.     

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。     

Polarimetric signatures of a layer of random nonspherical discretescatterers overlying a homogeneous half-space based on first- andsecond-order vector radiative transfer theory [geophysical radar remotesensing]

Complete polarimetric signatures of a layer of random, nonspherical discrete scatterers overlying a homogeneous half space are studied with the first- and second-order solutions of the vector radiative transfer theory. The vector radiative transfer equation contains a general nondiagonal extinction matrix and a phase matrix that are averaged over particle orientations. The nondiagonal extinction matrix accounts for the difference in propagation constants and the difference in attenuation rates between the two characteristic polarisations. The Mueller matrix based on the first-order and second-order multiple scattering solutions of the vector radiative transfer equation is calculated. The copolarized and depolarized returns are also calculated     

Raman scattering study of a GaAsN epitaxial layer

Raman scattering study of a dilute GaAsN epitaxy layer was carried out at variable temperature and pressure. The localization due to the presence of the N atoms is responsible for the small correlation length in the GaAsN alloy, which is also evident from the broadening and asymmetry of the LO mode of the GaAs-like Raman band. The temperature dependence of the correlation length was analyzed. Nitrogen-induced localization also has a strong influence on the pressure dependence of the Born's effective dynamic charge e*.     

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     

Finite-difference time-domain simulation of scattering from objectsin continuous random media

A three-dimensional (3D) finite-difference time-domain (FDTD) scheme is introduced to model the scattering from objects in continuous random media. FDTD techniques have been previously applied to scattering from random rough surfaces and randomly placed objects in a homogeneous background, but little has been done to simulate continuous random media with embedded objects where volumetric scattering effects are important. In this work, Monte Carlo analysis is used in conjunction with FDTD to study the scattering from perfectly electrically conducting (PEC) objects embedded in continuous random media. The random medium models under consideration are chosen to be inhomogeneous soils with a spatially fluctuating random permittivities and prescribed correlation functions. The ability of frequency averaging techniques to discriminate objects in this scenarion is also briefly investigated. The simulation scheme described in this work can be adapted and used to help in interpreting the scattered field data from targets in random environments such as geophysical media, biological media, or atmospheric turbulence     

Experimental studies of bistatic scattering from two-dimensionalconducting random rough surfaces

Despite the recent development of analytical and numerical techniques for problems of scattering from two-dimensional rough surfaces, very few experimental studies were available for verification. The authors present the results of millimeter-wave experiments on scattering from two-dimensional conducting random rough surfaces with Gaussian surface roughness statistics. Machine-fabricated rough surfaces with controlled roughness statistics were examined. Special attention was paid to surfaces with large rms slopes (ranging from 0.35 to 1.00) for which enhanced backscattering is expected to take place. Experimentally, such enhancement was indeed observed in both the copolarized and cross-polarized returns. In addition, it was noticed that at moderate angles of incidence, the scattering profile as a function of observation angle is fairly independent of the incident polarization and operating frequency. This independence justifies the use of the geometric optics approximation embodied in the Kirchhoff formulation for surfaces with large surface radius of curvature. When compared with the experimental data, this analytical technique demonstrates good agreement with the experimental data     

Polarimetric processing of coherent random noise radar data forburied object detection

Random noise polarimetry is a new radar technique for high-resolution probing of subsurface objects and interfaces. The University of Nebraska has developed a polarimetric random noise radar system based on the heterodyne correlation technique. Simulation studies and performance tests on the system confirm its ability to respond to phase differences in the received signals. In addition to polarimetric processing capability and the simplified system design, random noise radar also possesses other desirable features, such as immunity from radio frequency interference. The paper discusses the theoretical foundations of random noise polarimetry, and presents examples out of the entire data set collected that demonstrate the usefulness of the image processing and Stokes matrix presentation to enhance target detection using the coherent random noise radar     

Bistatic scattering of radiowaves by a melting layer ofprecipitation

This paper addresses bistatic scattering of radiowaves by the melting layer of precipitation. The bistatic radar reflectivities are formulated and can be computed at 1-100 GHz by applying the Mie theory for five raindrop-size distributions at rain rates below 12.5 mm/h. Examples computed at 35 GHz are presented. This original bistatic scatter calculation is not only of substantial guidance into bistatic scattering of radiowaves by the real melting layer of precipitation, but also should be appropriate for considering the interference problems including the melting layer effects for engineering purposes     

二维fBm随机分形界面的电磁散射特性

应用二维fBm（分形布朗运动）模拟了这种既非完全周期的也非完全随机的实际粗糙界面，用Kirchhoff方法计算了电磁波在随机分形界面的散射特性。数值结果表明随着分形维数的增加，散射场中非相关分量逐渐增大，旁瓣增多并在镜面方向周围不断展宽。     

一层随机分布的异向材料小椭球粒子的极化散射特征

该文推导了异向材料(Metamaterial)小椭球粒子的复散射振幅函数。构造了一层随机取向的异向材料小椭球粒子全极化散射的Mueller矩阵解。计算和比较了异向材料粒子和通常介质粒子的散射特性、同极化后向散射系数hh, vv, 以及hh－vv 随频率的变化。计算了任一椭圆极化入射下一层非均匀取向的随机分布异向材料粒子的同极化和交叉极化后向散射系数,以及随机粒子产生散射场去极化的极化度。解释了异向材料的媒质参数对粒子散射特性的影响和一层粒子的散射机理。结果表明：与通常介质粒子比较,异向材料粒子的散射产生了特征方向性的增强,全极化散射呈现非对称模式,并且由于异向材料的 和与频率的特殊关系,一层异向材料粒子的hh－vv 随频率有显著的复杂变化。