共查询到19条相似文献,搜索用时 140 毫秒
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为能有效地对地下空穴进行探测和识别,提出了一种基于基本振子线电流辐射模型的改进后向投影算法。分析了地下介质的物理模型,构建了地下腔体的成像模型及基于 FDTD 的全波电磁仿真模型,推导了半空间电磁波传播时延补偿的计算公式,验证了改进成像算法对地下腔体成像的有效性;分析了目标照射面结构对成像的影响,分别对照射面为凸面、平面、凹面三类目标进行了成像分析,得到能对凸面、平面照射面进行有效成像但不能对凹面照射面进行有效成像的结论,在岩、土体中孔穴的成像中得到了验证,并给出了多个孔穴存在时的三维像。 相似文献
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由于地下介质和空气的电磁特性不一致,探地雷达的发射信号在不同介质中传播时,传播速度和传播路径会发生改变,传播速度不再保持恒定,而且传播路径也不再是沿直线传播.当地下介质由单一均匀介质组成时,理论计算传播路径需要求解一个四次方程,计算量大,特别是地下介质由多个单一均匀介质组成时,无法得到解析的理论计算结果.根据电磁波的传播特性,给出了电磁波在地下单层介质传播时的简易计算方法.并以此为基础,首次给出了地下多层介质时的简易计算方法和解析结果.实际计算结果表明:简易计算结果与理论结果保持一致,比工程化计算方法的精度更高,计算量基本不变. 相似文献
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合成孔径雷达(SAR)与传统光学传感器不同,其利用主动发射电磁波和接收电磁波技术来获取目标区域的二维图像。在实际场景(特别是城区场景)成像中,存在大量直线型延展目标,如建筑物的边缘、桥梁等,且SAR的回波信号中不仅含有电磁波经过目标返回的直接回波,还包括电磁波经过目标与环境背景(地面、水面等)多次反射的干扰回波(即“多径效应”),造成SAR成像中存在多径“鬼影”。现阶段多径抑制方法大多基于点目标模型,难以解决实际场景中由直线型延展目标与环境背景产生的多径鬼影问题。因此,本文提出了基于SAR参数化稀疏成像模型的延展目标多径抑制方法,在稀疏目标与环境背景产生多径效应的情况下,能够实现对直线型延展目标的高质量成像。首先,基于不同回波路径下目标的散射模型,建立了延展目标多径观测模型,有效描述了不同回波路径下点目标与线目标散射特性;然后,采用交替方向乘子法(ADMM)对上述延展目标多径观测模型中不同回波路径下目标的散射系数向量进行了精确估计;最后,基于上述估计结果,提出不同回波路径下的图像重构方法,将各条回波路径的能量都集中到真实目标区域,实现了直线型延展目标的高质量成像。高精度电磁计算数据验证... 相似文献
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由于冲激脉冲探地雷达平均功率低,限制了其作用距离和探测深度,多用于近地表和浅低层探测。为了提高系统的作用距离和探测深度,常采用频率步进探地雷达。利用频率步进信号的大带宽和高平均功率的特点,不但可以提高作用距离和探测深度,而且成像分辨率可以大为改善。由于介质与空气的介电特性不一致,电磁波的传播路径和传播速度会发生相应的改变,常用的回波模型和合成孔径成像方法不再使用。本文推导出了频率步进探地雷达的回波信号模型,并结合SAR成像理论,针对地下目标探测的特点,提出了分层聚焦的SAR成像处理方法,取得了良好的效果。 相似文献
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利用谐振特性实现目标辨识是雷达探测领域研究的热点问题之一,地下目标在电磁波照射下也会产生外部谐振现象,该谐振信号与媒质特性、目标固有特性有关。该文通过FDTD方法计算了地下目标的瞬态谐振特性以及损耗媒质参数对目标谐振信号的影响,利用极点展开方法(SEM)对计算结果进行了分析,在计算分析的基础上研究了利用谐振特性识别地下目标的可行性。结果表明:在一定条件下,利用目标的外部谐振特性可以识别地下目标。 相似文献
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空间监视雷达系统中,目标的检测与参数估计是首先需要解决的问题。以电子篱笆型空间监视雷达为例,研究了分数阶傅里叶变换(FRFT)在其信号处理中的应用。在对空间目标穿越雷达视场时的速度及其变化率进行分析的基础上,建立了空间目标回波信号模型。然后推导出FFT方法的最大信号积累时长的解析表达式,对比分析了基于FFT和FRFT的目标检测性能。最后,对FRFT的参数估计精度进行了推导。研究表明,利用FRFT可以有效地积累目标回波信号的能量,提升加速运动目标的检测性能,对信号参数估计的精度接近于其CRLB。 相似文献
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A time-harmonic electromagnetic plane wave obliquely incident on a half-space or a slab consisting of a so-called Ω medium is considered. The up- and down-going eigenmodes in the Ω medium are derived and used to calculate the reflection and transmission coefficients for TE and TM modes. The Brewster angles for an Ω half-space are computed. Numerical results for the co- and cross-polarized reflection and transmission coefficients for an Ω slab are presented. 相似文献
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For pt.I see ibid., vol.36, no.3, p.221 (1994). The electromagnetic field inside a lossy half-space for the case of a transient electromagnetic plane wave impinging on the half-space from free space is derived. The losses in the half-space are modeled by assuming either a static (J=σE) or a dynamic (τ∂J/∂t+J=σ0E) conducting medium. Solutions are derived directly from the first order system of partial differential equations, i.e. the Maxwell equations. Plots for the total fields at the half-space boundary are given and expressions for the fields anywhere inside the half-space based on these boundary fields are given. Asymptotic formulae for late and early times are derived for the case of a step function as well as a square pulse plane wave 相似文献
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Transmission of electromagnetic waves into time-varying media 总被引:3,自引:0,他引:3
Expressions are obtained for the electromagnetic fields transmitted into the time-varying medium when a plane wave is incident upon either a dielectric or dispersive half-space. Solutions are obtained for the case when the medium is changed in a stepwise fashion, and also for the case when the medium varies slowly and continuously. 相似文献
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Electromagnetic Modeling for Microwave Imaging of Cylindrical Buried Inhomogeneities 总被引:1,自引:0,他引:1
《Microwave Theory and Techniques》1986,34(10):1064-1076
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. 相似文献
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A Model for Currents and Voltages Induced Within Long Transmission Cables by an Electromagnetic Wave
A model is presented for determining the transient currents and voltages induced within a long coaxial cable by a uniform plane traveling wave whose variation with time may be specified. The cable may be located above or within a half-space lossy dielectric with the wave incident from the half-space lossless dielectric. This results in a model for either aerial or buried cables with the source of the wave located in the atmosphere. A method is also presented for generalizing the approach to more complex cables encountered in communication systems. A demonstration of the applicability of this model is presented by analyzing the response of a 0.375-in coaxial cable for both aerial and buried situations. An incident electromagnetic wave with a rectangular time domain waveform is used to demonstrate the transient response. This waveshape is adequate to clearly indicate the transient phenomena. It is found that voltage enhancement results in both aerial and buried cables when the incident wave approaches grazing incidence. This voltage enhancement can be significant especially for aerial cables. Cable shield current enhancement also results for an aerial but not for a buried cable. 相似文献
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