随机粗糙面上目标散射差值计算的快速互耦迭代方法

用粗糙面上方有目标和无目标时空间散射场的差值计算的雷达散射截面,称为差场雷达散射截面.本文推导TE波入射下电场积分方程(EFIE),直接求解散射差场.本文提出目标与粗糙面之间的互耦迭代的计算方法,散射场纳入了目标与粗糙面之间复杂的相互作用,给出了迭代过程中纳入的粗糙面长度的选择.用Monte-Carlo方法,计算了P-M谱粗糙海面上方二维圆柱和方柱的散射,说明目标的几何结构对散射方向图的影响.     

数值模拟低掠角入射海面与船目标的双站散射

为研究风驱粗糙海面上有船目标时的双站散射,提出了一种结合广义前后的迭代方法（GFBM）与谱加速算法（SAA）快速求解双站散射的Monte Carlo数值方法,计算了在TE、TM锥形波低掠角入射在一维Pierson-Moskowitz谱粗糙导体海面以及船目标存在时的双站散射,数值模拟了在低掠角入射条件下,包含多次散射传播的粗糙海面与目标的双站散射与极化、频率、视角和海面风速等参数的关系。     

激光束海面散射回波建模与仿真

海面散射回波是激光探测系统探测低空掠海目标时的主要干扰,基于Pierson-Moscowitz海浪谱建立了不同风速下粗糙海面的几何模型,并将其作为海面的高度场。在对海面进行面元分割的基础上,根据Cox-Munk关于海浪坡度的统计模型计算了面元的反射回波,建立了粗糙海面的光散射模型,利用该模型对一种圆锥视场入射激光束的散射光分布及探测器接收功率进行了仿真计算。研究结果表明,粗糙海面的散射光分布与入射角度及风速相关,圆锥视场入射激光束的散射光主要分布在入射光束镜像方向周围的立体空间,风速越小,散射光分布越集中;风速越大,散射光分布越分散,为粗糙海面激光束散射特性分析及散射回波计算提供了重要理论依据。     

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。     

海面上方低空突防飞机雷达散射特性研究

为更好地研究海面上方低空突防飞机的雷达散射特性,基于迭代物理光学法（AIPO）和等效电流法（MEC）,提出了计算电大尺寸二维导体海面上方低飞目标的AIPO＋MEC算法,应用AIPO计算海面与目标之间的相互作用,用MEC计算棱边绕射。通过计算海面上金属立方体的双站散射系数,与已有数值算法结果相比较,验证了算法的正确性。用PM谱粗糙面模拟实际海面,应用该算法计算了海面上方三种典型隐身飞机模型的后向散射系数,并与自由空间中飞机模型的散射系数和平面上方飞机模型的散射系数进行了比较。结果表明,由于海面散射以及海面与飞机之间的相互作用,后向散射系数增大,且下方为海面时的散射系数角度性分布的散射比下方为平面时更为平缓。这对现代战争中海面上方低空目标探测和雷达设计具有一定的理论指导意义。     

复杂目标电磁散射特性仿真与实验

对两种形状较为复杂的军用目标缩比模型的电磁散射特性进行了仿真计算和实验,研究了复杂金属目标的电磁散射时域算法,提出了解决MOO算法求解目标瞬态散射稳定性的方法.给出了一种实验测量模型与数据处理方案.将仿真和实验得到的时域散射场数据解卷积分别与利用MOM计算的目标频域散射场数据进行比较,结果表明:在一定的频域范围内仿真与实验结果较好地保持了一致,从而验证了算法的有效性和实验正确性.     

粗糙海面上三维金属目标的电磁散射特性分析

该文采用矩量法(MoM)计算粗糙海面上三维金属目标的电磁散射特性。计算了位于半空间媒质中的电偶极子和磁偶极子的矢量位并矢格林函数和标量位格林函数,并将其应用于矩量法中。把海水视为下半空间媒质,粗糙海面为位于上半空间中的介质表面。通过建立介质和金属混合目标的积分方程,并采用迭代方法求解矩阵方程以得到该模型的散射特性,数值结果验证了本文方法的有效性。     

粗糙海面三维目标电磁散射的快速估算方法

本文使用物理光学法(PO)与区域投影法(AP),结合计算机图形学技术,将两面角反射器的计算原理应用于目标与海面之间的多次散射计算.给出了一种快速判定三维空间内三角形面元是否相交的方法以加速射线追踪.针对Pierson-Moscowitz谱生成的海面,考虑海水的介电特性与海况的影响,计算了不同海况下的三维目标散射特性.并同文献结果进行了比较,表明本文的方法具有较好的准确性.     

BRT-MOM-ILDC方法分析海上无人机群目标全极化散射特性

随着海面低慢小群目标威胁性的不断增强,其雷达回波的有效探测受到了世界各国的广泛重视。海杂波影响分析和对目标上精细结构建模这两个问题是海上低慢小目标雷达散射特性仿真研究的重点内容,因此,本文以海上无人机群为分析目标,针对其飞行高度低、受杂波影响大、局部结构反射截面积小的目标特性,综合采用高频双向射线追踪方法（BRT）、多层快速多极子加速的矩量法（MOM）和边缘区域的增量长度绕射理论方法（ILDC）分区域实现可靠的电磁散射建模。该方法将目标区域分为高频电大区域、低频精细区域和棱边区域进行理论分析与计算,采用多路径方法对目标间、目标与海面的耦合作用进行有效的补充,实现全极化海面目标的散射特性高效计算和快速成像。结果分析表明,采用本文方法可以快速的获取全极化的目标散射回波和雷达图像,从而为目标识别提供大量样本信息。      

海面上舰船目标的紫外散射特性研究

基于粗糙面双向反射分布函数(BRDF)模型,考虑海面的影响,设计了海面舰船目标的紫外光散射亮度计算流程,讨论分析了海面上舰船目标对海天背景紫外辐射的散射特性。运用大气传输软件MODTRAN,计算了0.3～0.4mm波段太阳、天空背景的紫外辐射特性;根据粗糙面散射理论,分别对海面和目标表面进行BRDF建模,并讨论了面元的光散射特性;设计了海面舰船目标的紫外光散射亮度计算流程,并利用此流程计算分析了某舰船模型的紫外光散射亮度。结果显示探测时间、探测方位、舰船表面蒙皮材料、舰船形状、海面散射等因素,都对舰船目标的紫外光散射特性产生影响,为完善舰船目标紫外辐射特性数据库提供有效依据。     

三维随机粗糙海面与舰船的复合电磁特性的高频方法分析研究

3维随机粗糙海面与其上方复杂目标复合电磁(EM)散射特性的建模与分析在微波遥感、目标识别、雷达成像、导弹制导等领域中有着重要的研究价值。该文主要研究了基于高频算法的随机粗糙海面及舰船的复合电磁散射特性,开发了PO-IPO混合方法,为3维随机粗糙海面与复杂目标一体化高效求解提供了新思路。文中分别使用了物理光学方法(PO)、迭代物理光学方法(IPO)、PO-PO以及PO-IPO混合方法对海面及舰船进行了建模与仿真,其中,引入锥形波来代替平面波作为发射源,锥形波可以更好地抑制粗糙面在边缘位置被突然截断而形成的电磁反射和边缘绕射等效应。从数值仿真结果中可以看出,PO-IPO混合方法可将复杂物体本身面元间以及粗糙海面与物体间的耦合作用考虑在内,因此PO-IPO可以作为一种有效的途径来快速获取随机粗糙海面及舰船的复合电磁散射特性。      

基于天线方向图与近场SBR的海面舰船复合散射研究

针对弹目交互场景中近场电磁散射仿真问题,提出了一种基于近场弹跳射线(shooting and bouncing ray,SBR)法并考虑天线方向图影响的海面舰船复合散射计算模型.根据天线方向图和海面舰船一体化几何模型,给出满足物理光学远场计算条件的面元所接收到的电场强度,通过SBR法得出所有面元的散射场,最后由矢量叠加...     

基于水体退化函数补偿方法的水下傅里叶单像素成像

水下光学成像的探测环境相对复杂。前向散射、后向散射和吸收极大地降低了水下光学成像的成像质量。单像素成像因其较高的抗噪声性而被认为是一种适合于水下光学成像的技术。对于水下单像素成像系统,目前存在的问题是需要采用结构光进行照明,当散斑在水下传播时,前向散射会使预先生成的散斑发生畸变。因此,重建结果的分辨率降低,重建结果模糊不清。为了减小前向散射对单像素成像系统的影响,对傅里叶单像素成像的重建过程进行改进。在空间谱域傅里叶单像素成像系统的水下退化函数进行估计,然后根据估计的退化函数实现目标空间谱反演。最后利用傅里叶变换对反演后的目标空间谱进行变换,最终获得目标的强度图像。理论分析和实验结果证明了该方法的有效性。利用该方法,能够有效地减小前向散射对成像质量的影响,提高了水下傅里叶单像元成像的重建结果质量。     

考虑海谱分布的动态分形海面的电磁散射

本文采用考虑了Pierson-Moskowitz谱的归一化带限Weierstrass分形函数来模拟动态分形海面.利用基尔霍夫近似研究了该粗糙面的电磁散射,讨论了后向散射截面随入射角的变化,给出了后向散射截面时间序列的分维与分形海面分维间的关系.计算了散射场幅值,结果表明该分形海面散射场幅值分布服从K-分布.     

Color correction and restoration based on multi-scale recursive network for underwater optical image

Underwater image processing has played an important role in various fields such as submarine terrain scanning, submarine communication cable laying, underwater vehicles, underwater search and rescue. However, there are many difficulties in the process of acquiring underwater images. Specifically, the water body will selectively absorb part of the light when light travels through the water, resulting in color degradation of underwater images. At the same time, due to the influence of floating substances in the water, the light has a certain degree of scattering, which will bring serious problems such as blurred details and low contrast to underwater images. Therefore, using image processing technology to restore the real appearance of underwater images has a high practical value. In order to solve the above problems, we combine the color correction method with the deblurring network to improve the quality of underwater images in this paper. Firstly, aiming at the problem of insufficient number and diversity of underwater image samples, a network combined with depth image reconstruction and underwater image generation is proposed to simulate underwater images based on the style transfer method. Secondly, for the problem of color distortion, we propose a dynamic threshold color correction method based on image global information combined with the loss law of light propagation in water. Finally, in order to solve the problem of image blurring caused by scattering and further improve the overall image clarity, the color-corrected image is reconstructed by a multi-scale recursive convolutional neural network. Experiment results show that we can obtain images closer to underwater style with shorter training time. Compared with several latest underwater image processing methods, the proposed method has obvious advantages in multiple underwater scenes. Simultaneously, we can restore the color information, remove blurring and boost detail for underwater images.     

An improved near- to far-zone transformation for thefinite-difference time-domain method

Near- to far-zone transformation for the finite-difference time-domain (FDTD) method can be performed by integration of the equivalent electric and magnetic currents originating from scattered electric and magnetic fields on a surface enclosing the object. Normally, when calculating the surface integrals, either the electric or magnetic fields are averaged since the electric and magnetic fields are spatially shifted in the FDTD grid. It is shown that this interpolation is unnecessary and also less accurate than if an integration is performed on two different surfaces. It is also shown that the accuracy of the far-zone transformation can be further improved if the phase is compensated with respect to a second-order dispersion corrected wavenumber. For validation, scattering results for an empty volume, a circular disk, and a sphere are compared with analytical solutions     

A study of VLF antennas immersed in sea water: theoretical,numerical, and experimental results

The problem of receiving VLF electromagnetic fields with an underwater electric antenna is of great interest, especially for military-application purposes. In this study, a simple and closed-form expression for the E field in sea water is derived from two physical models, which agree but are different: the surface-wave theory and the Fresnel formulas. Three configurations of immersed receiving antennas are investigated by means of computer simulations. The scattered electric field and expected measured voltage are computed, using an EFIE [electric-field integral equation], and the method of moments (MoM). Then, an equivalent-circuit model of the underwater antenna is investigated, with a focus on two dominant antenna parameters: the impedance and the voltage measured between the wire terminals. Calculations and computed results are compared with off-shore measurements     

Underwater image enhancement with image colorfulness measure

Due to the absorption and scattering effects of the water, underwater images tend to suffer from many severe problems, such as low contrast, grayed out colors and blurring content. To improve the visual quality of underwater images, we proposed a novel enhancement model, which is a trainable end-to-end neural model. Two parts constitute the overall model. The first one is a non-parameter layer for the preliminary color correction, then the second part is consisted of parametric layers for a self-adaptive refinement, namely the channel-wise linear shift. For better details, contrast and colorfulness, this enhancement network is jointly optimized by the pixel-level and characteristic-level training criteria. Through extensive experiments on natural underwater scenes, we show that the proposed method can get high quality enhancement results.     

超电大目标与分形海面复合散射研究

舰船与海面构成复合目标,其雷达散射截面(RCS)的研究一直是电磁计算领域中的重点和难点。文中建立了Weierstrass分形海面和目标三角面元的几何模型以及基于物理光学法(PO)和弹跳射线法(SBR)的海面目标的电磁散射模型。采用OpenGL图形编程技术与C++多线程处理技术设计了一款可视化目标电磁散射预估系统(ESEE)V1.0,对比典型目标体RCS 与商业软件FEKO 的计算结果,验证了ESEE的可靠性。通过计算不同海况的海面RCS 及超电大尺寸舰船与海面复合散射RCS,分析了海面散射以及超电大目标与海面复合散射特性。     

Surface electric fields and impedance matrix elements of stratifiedmedia

For the various geometrical configurations of waves in stratified media, we consider the important case when both source and field points are located on the same interface separating two different dielectric media. We denote this configuration as surface electric field case. In this paper, the electric fields are calculated numerically without using potentials. For the surface electric field case the integrand of the electric field grows with k_ρ^3/2 for large κ_ρ making the Sommerfeld integral singular. To calculate the surface electric fields in the spatial domain, we previously applied a technique of higher order asymptotic extraction. In the higher order asymptotic extraction, the higher order asymptotic parts were calculated analytically. The remainder, which has an integrand decays as κ_ρ^-3/2 was calculated numerically along the Sommerfeld contour path of integration. In this paper, we use a different extraction technique, the half-space extraction. After the half-space extraction, the integrand of the Sommerfeld integral of stratified media decays exponentially and the integral is calculated along the Sommerfeld integration path. The half-space extraction part is calculated by numerical integration along the vertical branch cuts. The surface electric fields for stratified media using half-space extraction and higher order asymptotic extraction are in good agreement. To validate the accuracy of the solution, we also compute the impedance matrix elements using surface electric fields, testing, and basis functions all in the spatial domain. The results are then compared with the results of the spectral domain method. The comparisons of the complex impedance matrix elements are tabulated and show that the difference is less than 2%