Scattering from Rough Surfaces Using the"Shooting and Bouncing Rays" Technique

The “shooting and bouncing rays” (SBR) technique is used to analyze the electromagnetic scattering characters of ocean rough surfaces varying with time. Some numerical results are presented and compared with the method of moments, and some factors, such as the incident angle, polarization and frequency are investigated which influence on electromagnetic scattering characters of ocean rough surfaces.

基于改进SBR技术的地面目标SAR图像快速生成技术

传统的弹跳射线(shooting and bouncing ray,SBR)技术主要适用于自由空间目标的电磁散射计算,当用于地面目标与背景复合场景的电磁散射计算和合成孔径雷达(synthetic aperture radar,SAR)图像建模与仿真时,在小擦地角下其计算误差显著增大。针对此问题,提出了一种基于“四路径”模型的改进SBR技术,其考虑了目标与邻域地面之间的多次反射效应以及目标与远区地面之间的多径散射效应对地面目标散射回波的影响。首先构建一个尺寸略大于目标包围盒的粗糙地面实体模型;然后结合“镜像法”改进射线追踪技术,分析电磁波在目标各部件间、目标同实体地面之间以及同虚拟半空间分界面之间的射线传播过程;最后结合高频渐近方法完成电磁散射计算。利用精确数值法计算结果对所提出技术进行了验证,并将其应用于地面目标的SAR图像高逼真度仿真,同实测SAR图像比对表明了所提技术具有良好的适用性。

New hybridization of PO, SBR, and MoM for scattering by large complex conducting objects

As a marked extension of the traditional MoM-PO （method of moment-physical optics） hybrid method, a new hybridization of PO, SBR, and MoM （MoM-SBR/PO） is presented to calculate the multireflection contribution in the PO region efficiently by introducing the method of SBR based on RDN notion, which avoids the time-consuming iterative procedure and the choice of proper Green＇s function. As compared with the traditional MoM-PO hybrid method, the calculation efficiency of the proposed method is greatly improved, and its validity is verified by numerical results.

基于自适应射线管分裂的多次反射计算方法

传统弹跳射线(shooting and bouncing rays,SBR)方法采取按均匀射线管的方式进行射线追踪,因此,在计算电大尺寸复杂目标多次反射时,需要处理海量射线,计算效率极低,应用上受到很大限制。提出了一种基于复杂目标不规则三角网(triangle irregular network,TIN)模型的自适应射线管分裂算法(adaptive ray tubesplitting algorithm,ARTSA),利用TIN模型信息动态生成非均匀初始射线管,经过与模型三角面元的求交、多边形裁剪和三角化处理,将初始射线管自适应分裂成多个子射线管,利用口面积分(aperture integral,AI)法计算各子射线管的多次反射场,通过相干叠加获得目标多次反射贡献。与传统SBR方法相比,在相同计算精度下,所提算法能极大地减少射线追踪数量,显著提高计算电大尺寸复杂目标多次反射的效率。

一种基于三维射线弹跳法的并行电磁传播预测算法

提出了一种基于三维射线弹跳法的并行电磁波传播预测算法。三维射线弹跳法中每条射线跟踪、每个绕射源都具备可并行性，其并行计算可分为射线并行、绕射源并行2个阶段先后处理。每个阶段都使用管理者／工作者并行模式，管理节点依据各个工作节点的任务量动态分配任务，并收集计算结果，工作节点并行完成射线跟踪或绕射源处理任务。测试结果表明：该算法的加速比趋干线性，可扩展性好，利用128个CPU核求解大规模问题时加速比可达116，并行效率约为90％。

基于弹跳射线技术的三维GTD模型构建方法

传统的基于弹跳射线(shooting and bouncing ray,SBR)技术的散射中心提取方法只考虑了理想点模型,但理想点模型无法描述散射中心的频率依赖特性。对此,提出一种基于弹跳射线技术的三维几何绕射理论(geometrical theory of diffraction,GTD)模型构建方法,在通过传统方法获取的理想点模型的基础上,利用射线管数据正向推算散射中心的频率依赖参数并修正其径向位置,实现了高精度三维GTD模型构建。仿真结果表明,点频、单视角下构建的三维GTD模型不仅能准确重构相同条件下的雷达散射截面(radar cross section,RCS),还能实现宽带RCS外推,能够满足目标宽带散射数据高效压缩和快速重构的应用需求。

A hybrid method of solving near-zone composite eletromagnetic scattering from targets and underlying rough surface

For composite electromagnetic(EM)scattering from rough surface and target above it in near-field condition,modified shooting and bouncing ray(SBR)method and integral equation method(IEM),which are analytic methods combined with two-scale model for rough surface,are proposed to solve the composite near-field scattering problems.And the modified method is verified in effectiveness and accuracy by comparing the simulation results with measured results.Finally,the composite near-fielding scattering characteristics of a slanted plane and rough water surface below are obtained by using the proposed methods,and the dynamic tendency of composite scattering characteristics versus near-fielding distance is analyzed,which may have practical contribution to engineering programs in need of radar targets near-field characteristics under extra-low-altitude conditions.