Four-port scattering matrix for dual-polarized wave transmissionand reflection network

Co-directional and bi-directional, co-polarized and cross-polarized characteristics of a lossless, matched four-port transmission network have been examined. For example, an arbitrary-inclined dielectric plate in a circular or square waveguide supporting dual-orthogonal linearly polarized modes has been analyzed, and a coordinate system is defined to apply for co-directional and bi-directional propagating circularly polarized waves. The matrix elements are polarization state and network dependent. Instead of using the terms network reciprocity and matrix symmetry, the matrix elements are discussed in terms of ratios to describe co-directional, bi-directional, co-polarized, cross-polarized, and polarization discrimination properties. Some of the ratios are equal to 1∠0° and others 1∠180°. Applications of this analysis are described. If the properties of the four-port network are frequency dependent and integrated over a bandwidth, and/or time dependent and integrated temporally, the scattering matrix formulation is not valid due to the presence of a randomly polarized component; in these cases a Mueller matrix is used to characterize the network     

一种基于表面散射相似度的SAR图像极化增强方法

针对传统极化增强在多类目标增强和极化信息保持方面存在的不足,该文基于表面散射的相似度提出了一种新的极化增强方法。该方法根据目标表面散射的相似度,对不同散射类型的目标相干矩阵乘以不同实系数,从而增大了表面散射的目标与其它散射的目标的对比差异。同时由于该方法将表征目标的相干矩阵作为整体进行运算,因而保持了目标的极化信息。最后利用NASA SIR-C/X-SAR实测极化数据验证了该方法的有效性。     

On the basic principles of radar polarimetry: the targetcharacteristic polarization state theory of Kennaugh, Huynen'spolarization fork concept, and its extension to the partially polarizedcase

Basic principles of radar polarimetry are introduced. The target characteristic polarization state theory is developed first for the coherent case using the three stage, the basis transformation, and the power (Mueller) matrix optimization procedures. Kennaugh's and Huynen's theories of radar target polarimetry are verified for the monostatic reciprocal case. It is shown that there exist, in total, five unique pairs of characteristic polarization states for the symmetric scattering matrix of which two pairs, the cross-polarization null and copolarization max pairs, are identical, whereas the cross-pol max and the cross-pol saddlepoint pairs are distinct. The theory is verified by an example for which next to the polarization fork the copolarized and cross-polarized power density plots are also presented. The partially polarized case for completely polarized wave incidence is presented and compared with the results for the coherent and the partially coherent cases, the latter of which is still unresolved     

Numerical eigenanalysis of the coherency matrix for a layer ofrandom nonspherical scatterers

By using the first-order iterative solution of vector radiative transfer in small albedo for a layer of nonuniformly-oriented, random, nonspherical scatterers, the Mueller matrix and coherency matrix are obtained. Eigenanalysis of the coherency matrix is numerically calculated. The eigenanalysis of the coherency matrix is proposed as a better method for identifying physical scattering mechanisms than direct inspection of the Mueller matrix. The functional dependence of polarimetric scattering is also discussed     

Retrievals of underlying surface roughness and moisture from polarimetric pulse echoes in the specular direction through stratified vegetation canopy

The time-dependent Mueller matrix solution of vector radiative transfer for stratified random media of nonspherical scatterers is presented. Copolarized and cross-polarized bistatic scattering for a polarized pulse incidence are numerically simulated. Numerical results well demonstrate volumetric and surface scattering mechanism and depict the fraction distribution of random scatterers of stratified random media. The peak tails in polarized echoes due to wave reflections from the underlying surface can be identified. Its copolarized peaks in the specular direction are employed for simultaneous retrievals of the underlying surface roughness and moisture with the presence of stratified vegetation canopy.     

Temporal Mueller matrix solution for polarimetric scattering from inhomogeneous random media of nonspherical scatterers

Polarimetric scattering from inhomogeneous random media of nonspherical scatterers under a pulse incidence is studied. The time-dependent Mueller matrix solution of vector radiative transfer for layering random media is derived. Copolarized and cross-polarized bistatic and back- scattering are numerically calculated. The shape and intensity of polarized echoes well depict the inhomogeneous fraction profile of random scatterers. Its functional dependence upon the fraction profile, layering thickness, and other parameters are discussed. This technique is applicable to reconstruction of inhomogeneous fraction profile and inversion of the media thickness.     

基于极化似然比的极化SAR影像变化检测

由于数据获取困难等问题,目前SAR影像变化检测方法多基于幅度,而较少引入极化信息.针对此方面的不足,以极化SAR数据为研究对象,在分析多极化SAR影像极化特征及其分布模型的基础上,构建极化似然比检验模型,以此进行不同时相的多极化SAR数据地表地物变化程度分析,通过设定恒虚警率确定变化区域,最后考虑地物空间信息剔出斑点噪声引起的孤立检测结果.利用多极化SAR数据进行算法的验证,并与图像比值法进行比较,实验表明:基于极化似然比方法可以有效区分地物的变化情况,且变化检测精度要优于图像比值法.     

Polarimetric observations and theory of millimeter-wave backscatterfrom snow cover

Polarimetric radar measurements carried out at 95 and 225 GHz are presented for fresh and refrozen snow cover. These data indicate that the Mueller matrix for snow cover consisting of spherical ice particles has a relatively simple form, with 10 of the 16 elements approximately zero. Measurements of new-fallen snow consisting of predominantly nonspherical snow crystals are also presented. The anisotropic structure of such snow cover results in a more complex Mueller matrix, fitting the general form for natural surfaces. An analytic expression for the Mueller matrix of isotropic snow cover is derived by computing the response of a semi-infinite layer of scatterers that are insensitive to the orientation of the incident polarization. This matrix is shown to accurately predict the polarimetric response of the snow cover comprised of spherical ice particles based solely on copolarized and cross-polarized radar cross-section measurements     

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。     

均匀取向箔条云的RCS极值研究

箔条云的雷达回波为部分极化波,其散射波的极化度和RCS极值问题对于极化滤波、极化对比增强的效果具有重要的决定作用.首先用Mueller矩阵采表征了箔条云的变极化效应,基于Mueller矩阵对均匀取向箔条云散射波的极化程度、共极化和交叉极化的RCS极值进行了研究.研究发现,散射波的总能量不随发射极化改变,当发射波为线极化时,散射波的极化度最大,共极化RCS最大,交叉极化RCS最小,当发射波为圆极化时,散射波为完全未极化波,此时用任意的极化接收,平均功率是相同的.     

An entropy based classification scheme for land applications ofpolarimetric SAR

The authors outline a new scheme for parameterizing polarimetric scattering problems, which has application in the quantitative analysis of polarimetric SAR data. The method relies on an eigenvalue analysis of the coherency matrix and employs a three-level Bernoulli statistical model to generate estimates of the average target scattering matrix parameters from the data. The scattering entropy is a key parameter is determining the randomness in this model and is seen as a fundamental parameter in assessing the importance of polarimetry in remote sensing problems. The authors show application of the method to some important classical random media scattering problems and apply it to POLSAR data from the NASA/JPL AIRSAR data base     

Unsupervised classification of multifrequency and fullypolarimetric SAR images based on the H/A/Alpha-Wishart classifier

Introduces a new classification scheme for dual frequency polarimetric SAR data sets. A (6×6) polarimetric coherency matrix is defined to simultaneously take into account the full polarimetric information from both images. This matrix is composed of the two coherency matrices and their cross-correlation. A decomposition theorem is applied to both images to obtain 64 initial clusters based on their scattering characteristics. The data sets are then classified by an iterative algorithm based on a complex Wishart density function of the 6×6 matrix. A class number reduction technique is then applied on the 64 resulting clusters to improve the efficiency of the interpretation and representation of each class. An alternative technique is also proposed which introduces the polarimetric cross-correlation information to refine the results of classification to a small number of clusters using the conditional probability of the cross-correlation matrix. These classification schemes are applied to full polarimetric P, L, and C-band SAR images of the Nezer Forest, France, acquired by the NASA/JPL AIRSAR sensor in 1989     

Interpretation of the Polarimetric Co-Polarization Phase Tern in Radar Images Obtained with the JPL Airborne L-Band SAR System

The utilization of both polarimetric amplitude and relative phase terms of the polarization scattering matrix [S] given for each pixel, is pursued for polarimetric SAR imagery interpretation. The existing amplitude-only backscattering approaches hitherto used are extended and modified to accommodate the interpretation of information contained in the amplitude and/or phase terms. Both a vector radiative transfer model for surface versus volume scattering from rough terrain with and without vegetation canopy and a high-frequency electrical curvature model for perfectly conducting surfaces are examined to come up with theoretical models that out-perform other hitherto known approaches. The developed models agree with the excellent polarimetric SAR imagery recently obtained with the JPL CV-990 dual-polarization L-band (1.225 GHz) SAR system. Recommendations are made on how to further perfect the system for integration in the SIR-C and other future polarimetric SIR-SAR systems.     

The theory of polarization diversity systems: the partiallypolarized case

A detailed consideration is presented of copolarized and cross-polarized radar response for partially polarized scattering. A technique using an adjustable polarization basis is used where appropriate. Conditions for maximum and minimum copolarized and cross-polarized power return are obtained. Necessary and sufficient conditions for the realization of the polarization fork are presented     

Target decomposition theorems in radar scattering

By converting the coherent scattering matrix into a target vector, the concept of a coherency matrix may be introduced for characterising statistical scattering problems involving polarised waves. This technique is compared with the more conventional Mueller matrix formalism and a unique decomposition theorem developed for modelling dynamic scattering problems.     

利用极化方位角特征的高分辨极化SAR目标增强研究

针对高分辨极化SAR目标增强问题,提出一种利用极化方位角特征的增强方法.首先,利用圆极化法提取极化SAR图像像素点的极化方位角特征;其次,通过"方位角归零化"获得像素点在零度极化方位角下的散射矩阵值.对比归零化前、后目标及杂波区域内部像素点极化特性聚集程度的差异,阐述了利用极化方位角特征进行目标增强的原理;再次,统计获得目标及杂波区域的平均极化特性,采用非线性最优化方法实现了目标增强;最后,基于ADTS全极化SAR实测数据验证了本文方法具有优良的目标增强性能.     

Fully polarimetric bistatic radar scattering behavior of forestedhills

The bistatic radar scattering measurements of forested hills were performed at grazing incidence and at azimuth scattering angles from 28° to 66° from the forward scatter plane. Using pulse-to-pulse switching between orthogonal transmitted polarizations, the radar simultaneously measures two orthogonally polarized components of the scattered wave to obtain full polarimetric information about the scattering process. These are the first fully polarimetric terrain clutter measurements to be conducted at large bistatic angles. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to examine the polarization sensitivity of the bistatic clutter. It is found that the polarization state of the EM wave scattered out of the plane of incidence strongly depends on the polarization orientation of the incident electric field. Unlike the monostatic case, these two incident wave polarization states are found to produce substantially different scattered wave behavior when trees are viewed at large bistatic angles. Scattered fields resulting from vertically oriented incident fields are found to be highly polarized and to produce bistatic clutter power levels that are strongly dependent on the polarization of the receiving antenna. In contrast, horizontally oriented incident fields are found to produce weakly polarized scattered waves with bistatic clutter power levels that are insensitive to the polarization of the receiving antenna     

Polarimetric backscatter measurements of deciduous and coniferoustrees at 225 GHz

Polarimetric radar measurements of foliage made in the 220-GHz transmission window are described. A noncoherent, 60-W-peak-power polarimetric radar was used to measure the target Mueller matrix directly by measuring the scattered polarization state for either four or six incident polarizations. Measurements of deciduous trees indicate that waves scattered from erectophil trees (vertically oriented leaves) are more highly polarized than waves scattered from planophil trees (horizontally oriented leaves) for near-grazing incidence angles. White pine trees, which have thin needles, where the least polarized of all trees studied. A comparison of the Mueller matrices of 11 independent footprints taken from seven white pine trees showed a high degree of consistency between measurements     

穆勒矩阵图像的获取及处理

随着成像技术的发展,偏振信息在成像技术中的应用逐渐受到广泛的重视。偏振信息的提取方式就显得尤为重要。穆勒矩阵作为表示光照射到物体前后偏振态变化的系数矩阵,其不仅与物质本身息息相关,而且含有大量的偏振信息。此外由于穆勒矩阵含有16个元素,且每一个元素含有的信息都不尽相同,充分利用这些信息能够在目标识别、目标信息增强方面以及目标与背景分离的应用中起较好的促进作用。通过提出一种穆勒矩阵图像的获取方式,并对穆勒矩阵的信息加以初步的处理,最后与偏振度的信息加以对比,充分体现出穆勒矩阵图像在偏振成像应用中所具有的价值。结论表明通过穆勒矩阵图像处理后得到的图像比偏振度图像信息更加完整,能够对后期的模式识别处理提供良好的基础。     

Calculation of Mueller matrices and polarization signatures for aslab of random medium using vector radiative transfer

The Mueller matrix which characterizes a slab of random medium containing spherical particles is calculated by using the vector radiative transfer theory. The vector radiative transfer equation is solved for arbitrarily polarized incident waves. The background refractive index of the slab is allowed to be different from the surrounding media. The scattering specific intensities for four independent polarized incident waves are calculated and used to construct the Mueller matrix, which contains multiple scattering due to the randomly distributed particles governed by the vector radiative transfer theory. The calculated are found to be symmetrical, and there are eight nonvanishing matrix elements. Polarization signatures are obtained in the backscattering direction from the Mueller matrix of the reflection side