GPSAR浅地表目标电磁特性分析

利用机载或车载地表穿透合成孔径雷达可以实现远距离大区域地表目标快速探测.为了降低虚警,需要根据目标的电磁特征设计检测器来区分目标和杂波.提出运用时域有限差分方法结合傅里叶变换进行地表穿透合成孔径雷达浅地表目标电磁特征计算的方法.首先根据复杂背景媒质的散射特性获取目标的激励场,然后分析复杂背景下目标的电磁特性.利用该方法模拟了平坦地面下的金属地雷的散射特性,并与矩量法的计算结果进行了比较,结果基本一致.我们模拟了高斯起伏地面下的M6A1金属地雷,理论数值计算结果与实测数据结果基本吻合.模拟结果显示浅地表金属地雷图像具有双峰特征,它将有效地提高地雷检测性能.     

车载前视GPSAR浅地表杂波特性分析

车载前视地表穿透合成孔径雷达(GPSAR)能够穿透地表获得浅埋目标图像,可用于较大面积区域的快速探测.目前制约GPSAR浅埋目标检测实用化的主要障碍是探测环境复杂而带来的虚警过高.而对GPSAR浅地表杂波特性分析是指导检测器设计进而提高检测性能的前提.文中针对车载前视GPSAR图像杂波局部与整体统计特性不一致的情况,给出一种基于多维概率密度函数的GPSAR图像浅地表杂波特性分析方法.该方法揭示了局部图像与整体图像的浅地表杂波特性的区别与联系.可从理论上解释车载前视GPSAR图像浅地表杂波的实际统计结果,为指导检测器设计和提高浅埋目标检测性能奠定了基础.     

轨道UWB地表穿透SAR探雷验证系统

轨道地表穿透合成孔径雷达（GPSAR）是为了评估UWBSAR在地雷目标探测中的可行性和效能，而用高于地面数米支架作为轨道构建的一个地雷目标探测系统。文中首先介绍了轨道GPSAR的系统框架，接着介绍了该系统在射频／耦合抑制、近场SAR成像，以及埋设地雷目标检测方面所作的工作，最后，用一系列实测试验数据及其处理结果验证了轨道GPSAR检测地雷目标的性能。     

车载前视地表穿透SAR多视处理中的关键技术研究

地表穿透合成孔径雷达(GPSAR)工作在低频区,具有地表穿透获得浅埋目标二维高分辨图像的能力。利用车载前视GPSAR可以在前进过程中对前方地雷和雷场进行远距离快速探测,是探雷的发展趋势。由于相干斑噪声会影响目标检测,该文研究了适合车载前视GPSAR的多视处理,提出了地距平面聚焦BP算法和地距平面图像折射和色散影响校正方法。提出的方法能解决多视处理中图像配准和浅埋目标二层介质成像问题。通用Rail-GPSAR实测数据对车载系统实际工作情况的模拟,验证了该文提出的方法能有效提高图像的等效视数和辐射分辨率。     

一种复杂背景下浅地表金属地雷识别方法

提出运用时域有限差分(FDTD)方法结合遗传算法进行机载或车载地表穿透合成孔径雷达(CPSAR)浅地表金属地雷识别的方法.该方法利用地雷的一维散射中心个数及其相对位置的匹配函数获取地雷结构信息,从而将真实目标分辨出来.利用FDTD法建立了浅地表地雷的散射模型,为了验证该模型,模拟了高斯起伏地面下M6A1金属地雷的散射特性,仿真数据和测试数据基本吻合.对高斯起伏地面下两类金属地雷目标的分类识别,表明该方法具有良好的目标识别能力.     

埋地金属地雷电磁散射计算

目前超宽带SAR探雷实用化的主要问题是虚警率过高,为了降低地雷检测的虚警,需要根据地雷的电磁散射特性设计检测器.本文把金属地雷等效为双圆柱结构,利用旋转体的结构特征用矩量法计算了半空间地雷的电磁散射,并与轨道地表穿透SAR实测数据进行了比较,两者结果基本吻合,验证了计算方法的有效性.     

装有金属引信的埋地介质地雷电磁散射计算

本文由等效原理推导了埋在有耗、色散土壤中的装有引信的介质地雷的电磁场积分方程,根据地雷的旋转对称特性,利用矩量法计算了半空间地雷的电磁散射,并与车载地表穿透SAR的实测数据进行了对比,两者比较一致,验证了计算方法的有效性.     

超宽带SAR浅地表地雷聚焦与定位技术

机载或车载超宽带合成孔径雷达可以大区域快速探测单个地雷和雷场,是探雷的发展趋势。由于传统成像算法基于均匀媒质的假设,在浅地表目标成像中不再适应。该文首先建立了浅地表目标回波模型,定量分析了折射和色散对成像的影响。基于回波模型,提出了分别在回波域和图像域补偿折射和色散影响的浅地表后向投影(Subsurface Back-Projection, SBP)成像算法。但是对未知区域进行地雷探测时,无法获得目标埋设深度和入射角先验信息。针对这个问题,提出了基于图像域SBP成像算法的粗、精补偿分级处理流程,实现了大区域多目标精确聚焦定位。最后利用Rail-GPSAR探雷试验系统实测数据验证了该文方法的有效性。     

探地雷达地杂波抑制方法研究进展

下视探地雷达是检测地雷的一种有效手段.强烈的地表反射回波即地杂波会淹没浅层埋藏的非金属地雷的微弱回波,从而导致很高的检测虚警概率.如何尽可能完全抑制地杂波而又不损失回波中的目标信息成为探地雷达地雷检测的关键技术问题.本文以地雷检测为应用背景,对目前已有的主要的地杂波抑制方法进行了综述.     

探地雷达地杂波抑制方法研究进展

下视探地雷达是检测地雷的一种有效手段.强烈的地表反射回波即地杂波会淹没浅层埋藏的非金属地雷的微弱回波,从而导致很高的检测虚警概率.如何尽可能完全抑制地杂波而又不损失回波中的目标信息成为探地雷达地雷检测的关键技术问题.本文以地雷检测为应用背景,对目前已有的主要的地杂波抑制方法进行了综述.     

A novel SVM for Ground Penetrating Synthetic Aperture Radar landmine detection

The use of vehicle-or air-borne Ground Penetrating Synthetic Aperture Radar （GPSAR） to quickly detect landmines over large areas is becoming a trend. However, producing too many false alarms in GPSAR landmine detection is a major challenge in practical applications of GPSAR. Support Vector Machine （SVM）, employing structural risk minimization theory, does not need large amounts of training data, which makes it suitable for solving the landmine detection problem. In this paper, a novel SVM with a hypersphere instead of a hyperplane classification boundary is proposed for landmine detection in GPSAR. The HyperSphere-SVM （HS-SVM） can be trained with both landmine and clutter data, or with landmine data only, which are called the two-class HS-SVM and the one-class HS-SVM, respectively. The HS-SVM has better generalization capability than the traditional HyperPlane-SVM （HP-SVM） with respect to varying operating conditions. Quantitative comparisons have been made using real data collected with the rail-GPSAR landmine detection system, which show that both the two-class and the one-class HS-SVMs have better detection performance than the HP-SVM.     

Foreword to the Special Issue on Subsurface Sensing Using Ground-Penetrating Radar (GPR)

The 17 papers in this special issue focus on subsurface sensing using ground-penetrating radar (GPR). These papers describe new approaches to subsurface sensing, including developments in electromagnetic wave propagation imaging/inversion of GPR data and antenna/radar technologies. Associated applications range from glaciology to pavement evaluation to landmine detection.     

超宽带合成孔径雷达金属地雷双峰特征增强算法

机载超宽带合成孔径雷达(UWB SAR)探雷实用化的最大问题是虚警太多,而增强金属地雷双峰特征有助于有效剔除虚警。该文基于双峰显著度最大准则,提出了基于图像域后滤波器的双峰特征增强算法及后滤波器参数优化方法。实测数据处理结果表明,该算法能够有效提高怀疑目标中金属地雷的双峰显著度,从而提高最终金属地雷检测性能。     

A statistical approach to landmine detection using broadbandelectromagnetic induction data

The response of time-domain electromagnetic induction (EMI) sensors, which have been used almost exclusively for landmine detection, is related to the amount of metal present in the object and its distance from the sensor. Unluckily, there is often a significant amount of metallic clutter in the environment that also induces an EMI response. Consequently, EMI sensors employing detection, algorithms based solely on metal content suffer from large false alarm rates. To mitigate this false alarm problem for mines with substantial metal content, statistical algorithms have been developed that exploit models of the underlying physics. In such models it is commonly assumed that the soil has a negligible effect on the sensor response, thus the object is modeled in "free space." We report on studies that were performed to test, the hypotheses that for broadband EMI sensors: 1) soil cannot be modeled as free space when the buried object has low metal content and 2) advanced signal processing algorithms can be applied to reduce the false alarm rates. Our results show that soil cannot be modeled as free space and that when modeling soil correctly our advanced algorithms reduced the false alarm probability by up to a factor of 10 in blind tests     

Ultra-wide-band synthetic-aperture radar for mine-field detection

A full-wave model is developed for electromagnetic scattering from buried and surface land mines (both conducting and plastic), taking rigorous account of the lossy, dispersive, and potentially layered properties of soil. The (polarimetric) theoretical results are confirmed via synthetic-aperture radar (SAR) measurements, performed using the US Army Research Laboratory's BoomSAR, with which fully polarimetric ultra-wide-band (50-1200 MHz) SAR imagery is produced. The SAR system is used to acquire a large database of imagery, including a significant distribution of naturally occurring clutter. Several techniques are used for mine detection with such data, including several detectors that are based on target features gleaned from the modeling, as well as a matched-filter-like detector that directly incorporates the target signatures themselves. In addition, the theoretical model is used to predict wave phenomenology in various environments (beyond the limited range of parameters that can be examined experimentally). Since the efficacy of radar-based subsurface sensing depends strongly on the soil properties, we perform a parametric study of the dependence of such on the target RCS, and on possible landmine resonances     

基于压缩感知的地雷散射结构提取

利用目标信号的先验稀疏性,通过压缩感知(Compressive Sensing, CS)算法可以实现对目标的稀疏成像,获取其空间散射结构。该文将CS理论应用于车载前视步进频率超宽带探地雷达(Vehicle-mounted Stepped-frequency Forward-looking Ground Penetrating Virtual Aperture Radar, SFGPVAR)系统,通过建立电磁散射模型,指出金属地雷目标可近似为旋转不变的对称圆柱体,在对电磁仿真和实测数据分析的基础上,得到超宽带SFGPVAR系统中金属地雷具有孤立的双散射点结构,双点间距与雷达入射角等因素无关,且只与地雷的物理尺寸相关,使得在成像空间满足稀疏分布条件,因此利用CS算法可以实现地雷空间散射结构的提取。该文最后通过对SFGPVAR系统实测数据处理验证了CS算法提取地雷散射结构的可行性以及地雷双散射点结构特征的稳健性,该方法不仅拓展了地雷目标特征提取的新思路,也为具有简单离散散射结构目标的检测鉴别探索出一条新路。      

Effects of soil electromagnetic properties on metal detectors

This paper presents an analysis, based on existing work in geophysics and nondestructive testing, of the effects of soil electromagnetic properties on the functioning of metal detectors widely used to detect buried landmines. The host soil is modeled as a half-space having real and frequency-independent electrical conductivity but frequency-dependent complex magnetic susceptibility. The analysis technique has been applied to three examples of soil of practical importance, namely, nonconducting soil with frequency-independent susceptibility, nonconducting soil with frequency-dependent susceptibility, and nonmagnetic soil with constant conductivity. Simplifications are made to clearly explain a number of previous field and experimental observations, for example, the greater influence of magnetic properties than of electrical conductivity on the performance of metal detectors. Results also show that soil magnetic properties affect continuous wave and pulsed-induction detectors differently. The effect that electrical conductivity and magnetic susceptibility of the host soil have on the signal produced by a target is investigated by computing the response of a buried small metallic sphere. Computations show that in some cases, which could represent practical landmine detection scenarios, the signal from the soil can dominate that due to the target, making it hard to detect the target. Further, it is shown that magnetic soil can alter a target's spectral response, which implies that, contrary to present practice, object identification techniques should take into account the electromagnetic parameters of the host medium.     

一种超宽带SAR地雷散射方位不变特征提取新方法

利用机载或车载超宽带合成孔径雷达(UWB SAR)可以实现大区域地雷和雷场远距离快速探测,是探雷的发展趋势.为了降低地雷检测中的虚警,需要提取有效的地雷特征区分地雷和杂波.本文提出了一种基于高维时频分布(HDTFD)的地雷散射方位不变特征提取方法,具体实现可采用高维Wigner-Ville分布(HDWVD)和高维Choi-Williams分布(HDCWD)等.基于HDTFD特征提取方法能够在保持高空间分辨的同时,有效提取散射函数中关于频率和方位角信息.利用Rail-GPSAR系统实测数据比较了基于HDWVD和基于HDCWD特征提取方法在分辨率、交叉项抑制和方位不变特征提取等方面的性能.实测数据处理结果说明基于HDCWD特征提取方法更适合实际数据处理.