并行FDTD方法在海面及其上方漂浮目标复合电磁散射中的应用

利用基于图形处理器(Graphics Processing Unit, GPU)的并行时域有限差分(Finite Difference Time Domain, FDTD)法计算一维粗糙海面及其上方二维漂浮目标的复合电磁散射.采用各向异性完全匹配层(Uniaxial Perfectly Matched Layer, UPML)吸收边界作为截断边界, 为了便于并行程序的设计, 在整个计算区域使用UPML吸收边界差分公式进行迭代.利用异步通信技术来隐藏主机和设备之间的通信时间, 同时使用片上的共享存储器提高读取速度, 进一步对程序进行优化, 得到很好的加速比, 证明了该方法的计算高效性.通过与串行FDTD法以及串行矩量法获得的数值结果进行比较, 验证了该并行方法的正确性, 进而研究了海面上方类似舰船漂浮目标的电磁散射特性, 讨论了入射角、海面风速以及目标吃水深度对双站散射系数的影响.     

分层粗糙面电磁散射的矩量法研究

本文主要采用矩量法(method of moment MOM)研究了分层粗糙面的电磁散射特性,首先给出了该散射问题的积分方程和矩阵方程,然后通过与时域有限差分(finite difference time domain FDTD)计算结果的对比说明了本文所提算法的有效性,最后讨论了分层粗糙面的均方根高度、相关长度以及两层粗糙面之间的距离对双站散射系数的影响。     

高斯介质粗糙面电磁散射的小斜率近似方法

基于小斜率近似方法推导了极坐标系下介质粗糙面的双站散射系数和后向散射系数计算公式.为验证小斜率近似方法的准确性,针对二维高斯介质粗糙面,计算了双站散射系数并将得到的数值结果与实验测量数据和基尔霍夫近似方法计算结果进行了对比分析,结果表明:小斜率近似方法的结果和实验数据吻合较好.同时对不同入射角下散射系数的角分布及粗糙度和均方根斜率对散射系数的影响进行了讨论分析.     

基于图形处理器的时域有限差分算法研究

如何提高时域有限差分算法(FDTD)的运算效率一直是FDTD数值运算研究的核心问题之一.针对近年来图形处理器(GPU)运算能力的高速增长及GPU通用运算概念提出的背景,对GPU加速FDTD运算的潜力与研究现状进行了总结,并对GPU加速FDTD运算的并行实现原理进行了阐述,通过将其与其他典型硬件加速方式进行比较,指出了G...     

粗糙面下方金属目标复合电磁散射的快速算法

为快速有效计算粗糙面下金属目标的复合电磁散射,提出了一种基于前后向迭代算法(FBM)和共轭梯度(CG)法的快速互耦迭代算(CCIA).首先建立目标与粗糙面的耦合积分方程组,并采用矩量法将其离散为矩阵方程.其次针对得到的耦合积分方程,用FBM求解粗糙面表面电流分布,用CG法求解目标表面电流分布,目标和粗糙面的相互作用通过更新两方程的激励项完成.最后,计算了高斯粗糙面下方无限长金属圆柱目标的复合电磁散射系数,当目标尺寸趋于零或目标深度趋于无穷时的结果与单独介质粗糙面相一致,验证了该数值方法的正确性;同时,讨论了不同粗糙面情况下该方法的收敛性,并分析了不同粗糙面媒质、目标尺寸和目标位置对双站散射系数的影响.     

分层粗糙面下方介质目标散射的快速算法

为快速获取分层粗糙面与下方介质目标的复合电磁散射特性,提出了一种基于前后向迭代算法(FBM)和双共轭梯度法(Bi-CG)的快速互耦迭代算法。推导了一维分层粗糙面与下方介质目标(二维散射问题)的耦合边界积分方程组,用FBM求解分层粗糙面的表面积分方程,而用Bi-CG求解目标的表面积分方程,目标和粗糙面的相互耦合作用通过更新两方程的激励项来迭代求解。应用该算法计算了下方存在介质目标时双层介质粗糙面的双站散射系数,与传统矩量法得到的结果相吻合,验证了该算法的正确性;分析了不同极化波入射时该算法的收敛性,讨论了目标尺寸和位置变化对双站散射系数的影响。     

基于GPU加速的地震图像重建技术

针对目前地层层析成像算法中正演算法存在计算量大、计算速度慢的问题,以图像处理器(GPU)为核心,研究并实现了一种基于GPU平台的时域有限差分(FDTD)正演算法。CUDA是一种由NVIDIA推出的GPU通用并行计算架构,也是目前较为成熟的GPU并行运算架构。而FDTD正演算法本身在算法特性上满足并行的要求,二者的结合将极大地加速程序的计算速度。在基于标准Marmousi速度模型的正演模拟中,程序速度提升30倍,而GPU正演图像与CPU正演结果误差小于千分之一。算例表明CUDA可以大大加速目前的FDTD正演算法,并且随着GPU硬件自身的发展和计算架构的不断改进,加速效果还将进一步提升,这将有利于后续波形反演工作的进展。     

二维海面上方金属目标复合散射快速算法研究

为快速获取二维海面上方金属目标的复合散射,通过改进计算分层粗糙面散射的层内波传播展开法(PILE),结合快速计算二维粗糙面散射的稀疏矩阵平面迭代与规范网格法(SMFIA/CAG),以及计算金属目标散射的基于三角屋顶(RWG)基函数的矩量法(MoM),提出了结合稀疏矩阵平面迭代及规范网格法的扩展层内波传播展开法(E-PILE+SMFIA/CAG)。引入锥形入射波以减小人为截断粗糙面所引起的边缘衍射,采用蒙特卡洛(Monte-Carlo)模拟生成具有Pierson-Moskowitz(PM)海浪谱的随机海洋粗糙面。数值分析了海面上方典型导体目标的复合双站散射系数,验证了算法的有效性与收敛性。最后,应用该算法计算了海面上方导弹目标的电磁散射,讨论了目标高度及海面上风速对复合散射系数的影响。     

土壤表面与置于其上组合目标复合电磁散射特性研究

为了满足置于粗糙面之上组合目标测量和检测的需要,该文分别采用Dobson半经验模型和电介质复介电常数公式表示土壤介电常数的实部和虚部,应用指数型分布粗糙面和Monte Carlo方法模拟实际的土壤表面。通过与矩量法得到的计算结果比较,验证了时域有限差分(FDTD)方法计算粗糙面与目标复合散射问题的有效性,进而运用该方法研究了土壤表面与置于其上组合目标的复合散射,得出了复合散射系数的角分布曲线。结果表明:复合散射系数随散射角振荡地变化,在镜反射方向处发生散射增强效应;土壤表面高度起伏均方根越大,复合散射系数越大;相关长度越大,复合散射系数越小;湿度越大,复合散射系数越小;组合目标尺度、介电常数、入射角对复合散射系数影响比较复杂。该文结果可用于求解地、海粗糙面与置于其上任意目标的复合电磁散射问题,与其它数值计算方法相比较,采用时域有限差分方法既可获得较高的准确性,同时又可减少计算时间和内存占用量。     

基于MPI实现粗糙地面电磁散射并行FDTD计算

提出了在由微机互连构成的机群(COW)并行计算系统上应用信息传递的方式实现粗糙地面散射并行FDTD算法.综合考虑了区域分割和负载平衡因素,并详细分析了子区域在普通网格和吸收边界处与相邻子区域的场值的数据传递,提高了二维粗糙地面FDTD并行计算效率.解决了在计算电大尺寸粗糙地面散射时产生的内存不足和计算耗时长等瓶颈问题.理论分析和数值计算结果验证了该算法的正确性;当计算电大尺寸的粗糙地面散射时,并行效率提升明显,即当参与计算的处理器数量达到6个时,并行效率仍然可以保持在90%以上.     

Response of realistic soil for GPR applications with 2-D FDTD

The three-dimensional (3D), wideband, bistatic ground penetrating radar (GPR) scatter response of rough, realistic ground is efficiently and accurately simulated using a hybrid high resolution 3D and large area two-dimensional (2D) finite difference time domain (FDTD) model. The 3D computation carefully models the transmitting and receiving antennas, while the 2D FDTD models wave propagation between the antennas and the scattering by the soil below them. The FDTD soil model considers realistic frequency dependent (dispersive) soil with Gaussian height variations. The modeling results are compared to experiments performed with the Geo-Centers, Inc., Newton, MA, commercially available GPR system used for mine detection. Despite the simplicity of the 2D model, the results of the simulation and the experiment agree quite well     

A Monte-Carlo FDTD Technique for Rough Surface Scattering

A Monte-Carlo finite-difference time-domain (FDTD) technique is developed for wave scattering from randomly rough, one-dimensional surfaces satisfying the Dirichlet boundary condition. Both single-scale Gaussian and multiscale Pierson-Moskowitz surface roughness spectra are considered. Bistatic radar cross sections are calculated as a function of scattering angle for incident angles of 0, 45, 70, and 80 degrees measured from the vertical. The contour path FDTD method is shown to improve accuracy for incident angles greater than 45 degrees. Results compare well with those obtained using a Monte-Carlo integral equation technique     

Short-pulse three-dimensional scattering from moderately rough surfaces: a comparison between narrow-waisted Gaussian beam algorithms and FDTD

In this paper, with reference to short-pulse three-dimensional scattering from moderately rough surfaces, we present a comparison between Gabor-based narrow-waisted Gaussian beam (NW-GB) and finite-difference time-domain (FDTD) algorithms. NW-GB algorithms have recently emerged as an attractive alternative to traditional (ray-optical) high-frequency/short-pulse approximate methods, whereas FDTD algorithms are well-established full-wave tools for electromagnetic wave propagation and scattering. After presentation of relevant background material, results are presented and discussed for realistic parameter configurations, involving dispersive soils and moderately rough surface profiles, of interest in pulsed ground penetrating radar applications. Results indicate a generally satisfying agreement between the two methods, which tends to improve for slightly dispersive soils. Computational aspects are also compared.     

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     

A numerical model for electromagnetic scattering from sea ice

A numerical model for scattering from sea ice based on the finite difference time domain (FDTD) technique is presented. The sea ice medium is modeled as consisting of randomly located spherical brine scatterers with a specified fractional volume, and the medium is modeled both with and without a randomly rough boundary to study the relative effects of volume and surface scattering. A Monte Carlo simulation is used to obtain numerical results for incoherent υυ backscattered normalized radar cross sections (RCSs) in the frequency range from 3 to 9 GHz and for incidence angles from 10° to 50° from normal incidence. The computational intensity of the study necessitates an effective permittivity approach to modeling brine pocket effects and a nonuniform grid for small scale surface roughness. However, comparisons with analytical models show that these approximations should introduce errors no larger than approximately 3 dB. Incoherent υυ cross sections backscattered from sea ice models with a smooth surface show only a small dependence on incidence angle, while results for sea ice models with slightly rough surfaces are found to be dominated by surface scattering at incidence angles less than 30° and by scattering from brine pockets at angles greater than 30°. As the surface roughness increases, surface scattering tends to dominate at all incidence angles. Initial comparisons with measurements taken with artificially grown sea ice are made, and even the simplified sea ice model used in the FDTD simulation is found to provide reasonable agreement with measured data trends. The numerical model developed ran be useful in interpreting measurements when parameters such as surface roughness and scatterer distributions lie outside ranges where analytical models are valid     

Numerical Simulation Bistatic Scattering from Three-Dimensional Conducting Rough Surface with UV Multilevel Partitioning Method Using Pulse Vector Basic Function

Vector wave three-dimensional (3D) conducting rough surface scattering problem solved by a UV method with multilevel partitioning procession (UV-MLP) using pulse vector basic function is developed in this paper, in which pulse vector basic function is more appropriately to be used for truly describe the vector inducted currents’ distribution along 3D PEC rough surface. For a 3D conducting rough surface scattering problem, the scattering structure is partitioned into multilevel blocks. By investigating the rank in the static problem, the impedance matrix for given transmitting and receiving blocks is expressed into products of U and V matrices. The UV method is illustrated by applying to a 3D scattering problem of random conducting rough surface. Finally, numerical simulation results are carried and discussed.