The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, th...The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, the multigrid method is extended to the application of solving integral equations which appear in electromagnetic scattering problems. The diakoptic theory is used for this purpose. Compared with other methods, the numerical results show that the multigrid method is powerful to solve electromagnetic scattering problems and can be used to compute electromagnetic scattering problems with electrically large bodies and complex structures.展开更多
In this paper, a theoretical model of multi-level, non-spherical scatterers is developed for fully polarimetric scattering from tree canopy in SAR imaging at C band. The amplitude functions of non-spherical particles ...In this paper, a theoretical model of multi-level, non-spherical scatterers is developed for fully polarimetric scattering from tree canopy in SAR imaging at C band. The amplitude functions of non-spherical particles with randomly spatial orientation are derived by the generalized Rayleigh-Gans (GRG) approximation. The non-diagonal extinction matrix and the Mueller matrix solution are constructed. Numerical solutions of polarimetric scattering of four Stokes parameters from random, non-spherical scatterers are obtained. To physically identify polarimetric scattering of the Mueller matrix solution, the coherency matrix and its eigen-analysis are discussed. Functional dependence of the coherency matrix and entropy upon various parameters are obtained. As an application, the analysis of AirSAR images at P, L, C bands is discussed.展开更多
电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人...电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人机(unmanned aerial vehicle, UAV)群组成的传播链路中信号强度计算方法。利用30~70 MHz甚高频(very high frequency, VHF)信号研究人工等离子体云团与UAV群的复合散射特性,得出如下结论:接收功率随着信号频率增加呈下降趋势;当机群由N架UAV构成时,阵因子迭加使机群雷达散射截面(radar cross section, RCS)出现一定的起伏,同相迭加时,接收功率可比单个UAV高约20lg N dB;利用人工等离子体云团散射可实现VHF频段用于对米级尺度RCS目标进行超视距探测,有助于解决紧急情况下电离层扰动对高频探测的不利影响。展开更多
多尺度非均匀背景为不同尺度和形状且在空间上分布不均匀的粗糙结构。本文针对多尺度非均匀粗糙背景散射特性快速计算问题,提出了基于散射中心方法的参数化表征模型。多尺度非均匀背景的散射场一般由地表大尺度表面所产生的镜反射分量...多尺度非均匀背景为不同尺度和形状且在空间上分布不均匀的粗糙结构。本文针对多尺度非均匀粗糙背景散射特性快速计算问题,提出了基于散射中心方法的参数化表征模型。多尺度非均匀背景的散射场一般由地表大尺度表面所产生的镜反射分量、大尺度表面几何不连续处所产生的绕射分量和地表小尺度粗糙面引起的漫散射分量共同组成。传统雷达目标散射中心建模采用分布型、局部型和滑动型散射中心模型(scattering center model, SCM)表征目标的反射和绕射散射;但是,传统散射中心表征形式仅能描述大尺度光滑表面、几何不连续处的散射场,无法描述小尺度粗糙面的散射效应。本文结合粗糙面的相干-非相干散射理论,在大尺度地形散射中心表征模型的基础上,利用相干模型修正小尺度粗糙面对大尺度表面散射场幅度的影响;利用双向反射分布函数(bidirectional reflectance distribution function, BRDF)建立非相干散射的参数化表征形式。对两种非均匀多尺度背景的散射特性进行参数化表征,并采用商业软件高频求解器对计算结果的精度和效率进行了校验,证明了粗糙背景散射中心参数化建模方法的可行性。展开更多
文摘The multi-grid method has been known as an efficient iterative method for the linear systems and nonlinear systems that arise from finite difference approximations for partial differential equations. In this paper, the multigrid method is extended to the application of solving integral equations which appear in electromagnetic scattering problems. The diakoptic theory is used for this purpose. Compared with other methods, the numerical results show that the multigrid method is powerful to solve electromagnetic scattering problems and can be used to compute electromagnetic scattering problems with electrically large bodies and complex structures.
文摘In this paper, a theoretical model of multi-level, non-spherical scatterers is developed for fully polarimetric scattering from tree canopy in SAR imaging at C band. The amplitude functions of non-spherical particles with randomly spatial orientation are derived by the generalized Rayleigh-Gans (GRG) approximation. The non-diagonal extinction matrix and the Mueller matrix solution are constructed. Numerical solutions of polarimetric scattering of four Stokes parameters from random, non-spherical scatterers are obtained. To physically identify polarimetric scattering of the Mueller matrix solution, the coherency matrix and its eigen-analysis are discussed. Functional dependence of the coherency matrix and entropy upon various parameters are obtained. As an application, the analysis of AirSAR images at P, L, C bands is discussed.
文摘电离层中释放的金属蒸气产生人工等离子体云团,其可显著改变无线电波传播。本文利用几何绕射理论(geometrical theory of diffraction, GTD)和有限元法(finite element method, FEM)相结合的方法,给出了经由天线、人工等离子云团和无人机(unmanned aerial vehicle, UAV)群组成的传播链路中信号强度计算方法。利用30~70 MHz甚高频(very high frequency, VHF)信号研究人工等离子体云团与UAV群的复合散射特性,得出如下结论:接收功率随着信号频率增加呈下降趋势;当机群由N架UAV构成时,阵因子迭加使机群雷达散射截面(radar cross section, RCS)出现一定的起伏,同相迭加时,接收功率可比单个UAV高约20lg N dB;利用人工等离子体云团散射可实现VHF频段用于对米级尺度RCS目标进行超视距探测,有助于解决紧急情况下电离层扰动对高频探测的不利影响。
文摘多尺度非均匀背景为不同尺度和形状且在空间上分布不均匀的粗糙结构。本文针对多尺度非均匀粗糙背景散射特性快速计算问题,提出了基于散射中心方法的参数化表征模型。多尺度非均匀背景的散射场一般由地表大尺度表面所产生的镜反射分量、大尺度表面几何不连续处所产生的绕射分量和地表小尺度粗糙面引起的漫散射分量共同组成。传统雷达目标散射中心建模采用分布型、局部型和滑动型散射中心模型(scattering center model, SCM)表征目标的反射和绕射散射;但是,传统散射中心表征形式仅能描述大尺度光滑表面、几何不连续处的散射场,无法描述小尺度粗糙面的散射效应。本文结合粗糙面的相干-非相干散射理论,在大尺度地形散射中心表征模型的基础上,利用相干模型修正小尺度粗糙面对大尺度表面散射场幅度的影响;利用双向反射分布函数(bidirectional reflectance distribution function, BRDF)建立非相干散射的参数化表征形式。对两种非均匀多尺度背景的散射特性进行参数化表征,并采用商业软件高频求解器对计算结果的精度和效率进行了校验,证明了粗糙背景散射中心参数化建模方法的可行性。
