二维有耗介质目标重建的迭代——共轭梯度方法

本文提出了一种由已知的散射场数据重建二维非均匀有耗目标的复介电常数的迭代算法。连续采用外个方向的ＴＭ平面波照射目标，并分别采集目标区域外的散射场数据。本文利用矩量法将积分方程变成矩阵方程。我们以Ｂｏｎ近为初始值，通过多次迭代，实现目标特性的重建。通常，逆问题多是不适定的。     

二维有耗介质目标重建的Newton迭代方法

本文给出了一种由已知的散射场数据重建二维非均匀有耗目标的复介电常数的迭代算法。由积分方程出发，利用点匹配技术导出了依赖于未知参数的解析逆散射公式。由此可以以解析的形式计算场量对未知参数的导数（Jacobian和Hessian矩阵）。本文采用Newton优化方法迭代求解逆散射问题，具有二次收敛特性。为了克服逆散射中解的不适定性，连续采用多个方向的TM波照射目标，并采集目标区域外的散射场数据，以及采用共轭梯度法（CGM）求解逆问题，数值结果表明了本文所提方法的可行性和灵活性。     

二维有耗介质目标重建的Newtoin迭代方法

本文给出了一种由已知的散射场数据重建二线非均匀有耗目标的复介电常数的迭代算法。由积分方程出发，利用点匹配技术导出了依赖于未知参数的解析逆散射公式。由此可以以解析的形式计算场量对未知参数的导数（Jacobian和Hessian矩阵）。本文采用Newton优化方法迭代末解道散射问题，具有二次收敛特性。为了克服逆散射中解的不适定性，连续采用多个方向的TM波照射目标，并采集目标区域外的散射场数据，以及采用共轭梯度法（CGM）求解逆问题．数值结果表明了本文所提方法的可行性和灵活性。     

埋于介质体中二维导体目标成象的迭代方法

本文应用一种迭代方法实现了埋于二维均匀介质体中理想导体目标几何构形的重建。在导出介质体与导体混合目标散射边界积分方程的基础上，利用Ｎｅｗｔｏｎ－Ｋａｎｔｏｒｏｖｉｃｈ方法和矩量法建立逆散射基本方程。为克服病态问题，连续采用多方面ＴＭ平面波照射目标以获取足够的信息，并通过迭代方法求解。最后、给出的一些散射目标的重建结果表明本方法的可行性，同时研究了噪声对重建结果的影响。     

IPO—MoM混合法分析开槽电大目标的电磁散射

本文利用迭代物理光学法（ＩＰＯ）与数值方法相结合的混合方法计算二维开槽民大目标的电磁散射,首先根据等效原理将散射场进行分解,分别采用ＩＰＯ法和矩量法（ＭｏＭ）计算槽缝填充的电大目标和槽缝的散射,并在口径处应用广义网络原理处理耦合问题,数据结果表明本文方法是准确和高效的。     

IPO-MoM混合法分析开槽电大目标的电磁散射

本文利用迭代物理光学法（ＩＰＯ）与数值方法相结合的混合方法计算二维开槽民大目标的电磁散射,首先根据等效原理将散射场进行分解,分别采用ＩＰＯ法和矩量法（ＭｏＭ）计算槽缝填充的电大目标和槽缝的散射,并在口径处应用广义网络原理处理耦合问题,数据结果表明本文方法是准确和高效的。     

快速多极子和遗传算法在电磁成像中的应用

从电磁场的积分方程出发,利用快速多极子（ＦＭＭ）加速矩量法（ＭｏＭ）计算导体柱电磁散射的过程;以散射场的测量值与计算值的平均偏差为目标函数,以导体柱截面形状参数为优化变量,利用遗传算法（ＧＡ）进行优化迭代,来重构目标导体柱的电磁影像。对美国空军ＲＯＭＥ实验室提供的实际数据（Ｉｐｓｗｉｃｈ数据）进行了电磁成像;并给出了对较大导体柱电磁成像的例子。     

微波断层成像全局优化重建方法

本文提出了一种类似于禁忌搜索（TABU search)、但不设禁忌列表（TABUlist)的全局优化方法重建微波断层图像。微波断层成像是将微波作为入射波照射介质目标物，根据目标物周围接收器检测到的散射数据重建目标物截面的复介电率图像。它属于非线性、非适应性的逆散射问题，因而难于求其解。本文应用矩量法将积分方程转化为矩阵方程，根据最小二乘准则，视重建过程为最小化目标函数的过程迭代求解。简单 模型的数值模拟结果证明了这种方法的可行性和有效性。     

三维大纵横比目标散射的快速精确求解

采用积分方程法严格求解三维大纵横比目标的电磁散射。在积分方程法的迭代求解中用快速我极子法（ＦＭＭ）加速矩阵与矢量的相乘计算,同时运用快速傅里叶变换（ＦＦＴ）进一步提高快速多极子方法中的转换预计算,数值结果表明：这种快速多极子法－快速傅立叶变换方法（ＦＭＭ－ＦＦＴ）特别适合于三维大纵横比目标的散射求解。     

电大尺寸多柱体电磁散射问题的一种快速混合算法--MEI+FMM

本文提出了一种改进的快速迭代ＭＥＩ（不变性测试方程）算法用于分析电气大尺寸多柱体的散射问题,在此算法中我们首次将快速多极子技术（ＦＭＭ）用于加速多柱体之间多次散射场的计算。应用本算法计算了柱体周长为几千波长的多柱体散射场。实际计算结果显示,一方法与原有的直接计算方法具有几乎同样的精度,而速度提高了两个数量级。     

Polarimetric discriminators for SAR images

A method is developed for optimizing the degree of polarization of a partially polarized wave reflected by a nonstationary scattering object. The method permits, for a scattered wave and a given target characterized by its Mueller matrix, analytic computation of the maximum and minimum values of the degree of polarization, and the corresponding transmitted polarizations. A procedure for the optimization of the scattered wave intensity is also proposed. The degree of polarization and the total scattered intensity extrema are then analyzed experimentally on JPL data. It is shown that several entities such as the received intensity extrema, the coefficient of variation, the fractional polarization and the span, which are currently used for target discrimination, can be deduced from combinations of the maximum and minimum values of the degree of polarization and the scattered wave intensity. Finally, a classification of the San Francisco image, based on these indices, is conducted for a better understanding of the specific physical meaning of each index     

Electromagnetic Modeling for Microwave Imaging of Cylindrical Buried Inhomogeneities

Many diagnostic techniques in geophysics and civil engineering are based on the interaction of electromagnetic waves with objects buried in homogeneous or stratified media. Most of the investigations are concerned with the detection of buried objects, but a few papers have dealt with the problem of identifying the objects. The proposed method is based on the integral representation for a plane wave incident on a lossy half-space containing a cylindrical object of arbitrary cross section and electrical properties. The induced current distribution in the object is obtained from the backscattered field measurement in amplitude and phase. In order to improve the spatial resolution of the image, the scattered field is measured for different plane wave incidence and frequencies. Results of numerical simulations concerning the shape and size of the object for different values of soil electromagnetic parameters are presented in this paper.     

Near-field imaging for conducting objects

A spherical back-projection algorithm is proposed to reconstruct near-field microwave images of conducting objects. In this imaging scheme, the object is mounted on a rotating pedestal and its backscattered near field is measured at discrete-frequency steps. Implementation of the method consists of first estimating the spherical projection (or range profile) at each aspect by inverse Fourier transforming the range-corrected scattered near field, and then coherently spherically back-projecting the range profiles into the image plane. The images are interpreted and predicted based on the procedure of the spherical back-projection method, and numerical and experimental results are presented to verify the effectiveness of the proposed algorithm     

数字全息干涉位移场分离研究

提出了一种基于窗口傅里叶脊的离面与面内位移分 离方法,应用于数字全息的多分量干涉相位场 分离。首先,物光束对称照射待测物体, 参考光束直接照射CCD靶面,由CCD相机记录物体变形前后的两幅离轴数字全息图;然后,采 用菲涅尔衍射积分法再现物体变形前后的复物光场,再由两幅复物光场共轭相 乘构建干涉场,利用幅度区分准则和窗口傅里叶变换处理复干涉场,通过窗口傅里叶脊值的 搜索,提取不 同灵敏度矢量物光对应的干涉相位分量;再对干涉相位场进行简单数值运算,将面内与离面 位移场分离出 来。最后,对周边固定、点加载、绕轴向旋转的Al制圆盘三维位移场进行实际测量。实验结 果验证了本文方法的有效性。     

基于紧支撑径向基函数与共轭梯度法的大规模散乱数据快速曲面插值

该文提出一种快速大规模散乱数据的曲面插值算法。在此算法中,首先采用紧支撑径向基函数(CSRBF)作为插值基函数,采用CSRBF的优点是保证构成的系数方程组是对称正定而且系数是稀疏的。这样可保证系数方程组一定可解而且可以减少内存的开销。其次采用共轭梯度法求解大规模系数方程组。该算法在系数方程组的系数矩阵A:NN是对称正定的情况下,最多迭代N步就可以求得方程组的解,实验结果表明该算法的快速性,特别适合大规模散乱数据的曲面的插值。     

Microwave imaging-Location and shape reconstruction frommultifrequency scattering data

The problem of determining the shape and location of an object embedded in a homogeneous dissipative medium from measurements of the field scattered by the object is considered in this paper. The object is assumed to be an infinite cylinder of known cross section illuminated by a TM plane wave and the scattered field is measured on a line segment perpendicular to the direction of incidence. Measurement data are carried out at three different frequencies for a homogeneous cylinder of known dielectric constant. The location and contour shape are determined using two different reconstruction algorithms, a Newton-Kantorovich (NK) method and the modified gradient (MG) method whose effectiveness and robustness are compared. Both methods are based on domain integral representations of the field in the body. They involve an iterative minimization of the defect between an integral representation of the field measured on the line and the actual measured data. The NK method involves a linearization of the nonlinear relation between the field and the contrast, as well as the solution of a direct scattering problem at each iteration. The MG method seeks the simultaneous reconstruction of the field and the characteristic function of the support of the scatterer without solving a direct problem at each step. Both methods employed the same initial guess and the a priori information that the characteristic function is nonnegative     

A Novel Method to Analyze Electromagnetic Scattering of Complex Objects

The finite-difference time-domain (FD-TD) method is proposed as a means of accurately computing electromagnetic scattering by arbitrary-shaped extremely complex metal or dielectric objects excited by an external plane wave. In the proposed method, one first uses the FD-TD method to compute the near total fields within a rectangular volume which fully encloses the object. Then, an electromagnetic-field equivalence principle is invoked at a virtual surface of this rectangular volume to transform the tangential near scattered fields to the far field. To verify the feasibility of this method, the surface currents, near scattered fields, far scattered fields, and radar cross section of two canonical two-dimensional objects are presented. For these cases, it is shown that the FD-TD method provides magnitude of current and field predictions which are within ± 2.5 percent and further phase values within ± 30 of values predicted by the method of moments ( MOM) at virtually every point including in shadow regions.     

基于PC-MSPCNN模型和SLIC的彩色图像分割方法

针对简单线性迭代聚类(SLIC)方法对图像边缘细节处理效果不佳的问题,提出一种参数可控、改进的简化脉冲耦合神经网络模型(PC-MSPCNN)与SLIC结合的彩色图像分割方法。该方法首先改进MSPCNN模型的加权矩阵和连接系数,并增设辅助参数,以提高分割准确度。随后将彩色图像输入至PC-MSPCNN模型中,依据改进模型中输出Y值的分布划分物体的边缘,使分割结果更好地贴合物体的边缘,利用所提出的相似性准则合并散布的碎片,减小后续处理的复杂度;其次,在SLIC度量相似距离的基础上引入PC-MSPCNN中RGB三个通道的内部活动项U值,完成对图像剩余部分的加权融合聚类,改进聚类效果。实验结果表明,本文方法能更精确地贴合图像中物体的边界,大幅减少碎片,有效提高图像的边缘贴合度。     

“Blind” shape reconstruction from experimental data

A method for reconstructing the shape of a bounded impenetrable object from measured scattered field data is presented. The reconstruction algorithm is, in principle, the same as that used before for reconstructing the conductivity of a penetrable object and uses the fact that for high conductivity the skin depth of the scatterer is small, in which case the only meaningful information produced by the algorithm is the boundary of the scatterer. A striking increase in efficiency is achieved by incorporating into the algorithm the fact that for large conductivity, the contrast is dominated by a large positive imaginary part. This fact together with the knowledge that the scatterer is constrained in some test domain constitute the only a priori information about the scatterer that is used. There are no other implicit assumptions about the location, connectivity, convexity, or boundary conditions. The method is shown to successfully reconstruct the shape of an object from experimental scattered field data in a “blind” test     

A homomorphic filtering method for imaging strongly scatteringpenetrable objects

This paper describes a new method for determining the structure of strongly scattering penetrable objects having permittivity fluctuations with scales comparable to the illuminating wavelength. We are concerned with the case when small wavelength or weakly scattering approximations, such as the Born or distorted wave Born approximations, or slowly varying approximations such as the Rytov approximation, are not valid. The problem is formulated as one of recovering, in principle, a quantitative image of the object's permittivity distribution function from a set of perturbed images. Each perturbed image is obtained by backpropagating the scattered field measured around the object for different illumination directions. These backpropagated images are filtered in the differential cepstral domain to recover the object permittivity distribution, and we show reconstructions from both simulated and real microwave scattered data