Synthetic aperture FM-CW radar applied to the detection of objectsburied in snowpack

Presents the principle of synthetic aperture frequency modulated continuous wave (FM-CW) radar and demonstrates the detection results of several objects buried in natural snowpack using the radar system. First, the synthetic aperture technique is explained with emphasis placed on showing that the Fourier transformed beat signal obtained by the FM-CW radar is equivalent to one kind of Fresnel hologram, which leads the authors to use the SAR technique. Then a radar system operative in the microwave L-band is explored to detect objects buried in natural snowpack. Several detection results are presented demonstrating the potential capability of high resolution imaging in the azimuth direction, comparing with real aperture images     

Detection of objects buried in wet snowpack by an FM-CW radar

A real-aperture FM-CW radar system was developed for the detection of objects buried in heavily wet snowpack. This radar uses the L-band microwave frequency with a maximum output power of 100 mW and utilizes digital signal processing techniques. A laboratory simulation and two field experiments were carried out to detect and map various objects embedded in the snowpack. It was possible to map a metallic pipe 3 cm in diameter at a depth of 70 cm and a 10×60-cm metallic plate at a depth of 90 cm in natural snowpack. Fundamental detection results are presented     

Two-dimensional and full polarimetric imaging by a syntheticaperture FM-CW radar

Applies the principle of radar polarimetry to a synthetic aperture frequency-modulated continuous wave (FM-CW) radar and presents results based on two-dimensional (2D) full polarimetric imaging. It is shown that the polarimetric target reflection coefficients obtained by the synthetic aperture FM-CW radar are elements of a Sinclair scattering matrix, although the coefficients are derived from a wide band signal. Using the scattering matrix optimization procedure, a 2D polarimetric imaging experiment (including Co-Pol maximum, minimum, span, and phase imaging) of an orthogonally placed linear target set was successfully carried out in the laboratory. This result demonstrates the validity of N-band (8.2-9.2 GHz) FM-CW radar polarimetry, and it presents a demonstration of a full polarimetric 2D FM-CW imaging radar system     

Advanced polarimetric subsurface FM-CW radar

The subsurface radar suffers from two typical problems, i.e., strong clutter from surface and severe wave attenuation in the underground. This paper presents a unique countermeasure to these problems using a polarimetric FM-CW radar and an equivalent sensitivity time control (STC) technique. The authors apply the polarimetric filtering principle to suppress surface clutter either in the Co-pol channel or in the X-pol channel of synthetic aperture radar, yielding to polarimetric enhanced target image. This technique works when the surface clutter and target have different polarization properties. Moreover, they use an equivalent STC technique specially suited for FM-CW radar for a deep object sounding to compensate wave attenuation within the ground. These techniques contribute to a significant improvement of the radar performance and the detection image contrast, although the detection of the target is in general a much more complicated topic. The field experiments were carried out to show the usefulness of the method. Some detection results are presented     

Human body detection in wet snowpack by an FM-CW radar

An FM-CW radar system was applied to detect a human body buried in a very wet snowpack. This radar uses the L-band microwave frequency with a maximum output power of 100 mW, and utilizes digital signal processing techniques. Field experiments were carried out to detect and map a human body embedded at a depth of 125 cm in a natural snowpack. The radar is shown to have a potential ability to detect avalanche victims, indicating that it may become a tool for snow rescuer operations     

Polarimetric radar interferometry for improved mine detection andsurface clutter rejection

A recently developed technique, polarimetric radar interferometry, is applied to tackle the problem of the detection of buried objects embedded in surface clutter. An experiment with a fully polarimetric radar in an anechoic chamber has been carried out using different frequency bands and baselines. The processed results show the ability of this technique to detect buried plastic mines and to measure their depth. This technique enables the detection of plastic mines even if their backscatter response is much lower than that of the surface clutter     

Wide-band polarimetry and complex radar cross section signatures

Information about radar targets has to go beyond the scalar radar cross section (RCS) for target classification purposes. The necessary target information is constrained in the complex RCS matrix. The authors show the theoretical derivation of this matrix and of the related scattering matrix. Both matrices contain the target's complex RCS for arbitrary polarization. The mathematical procedures for basis transformation that is, the evaluation of influences of polarization, are given. Equipment for wide-band, coherent RCS measurements with calibration targets and a 20-term error correction algorithm is presented. Using the complex RCS matrix, polarimetric target signatures are derived and plotted for simple objects. The target classification is finally based on the polarimetric signatures and the characteristic parameters derived from them. The basis of these are measurements of relevant samples and target RCS modeling     

飞机目标全极化双基地散射特性研究

采用成熟的商用电磁计算软件中的快速多层多极子方法计算了全尺寸飞机目标的全空域全极化双基地散射特性数据,统计了全极化双基地RCS起伏特性,指出4种极化双基地RCS的统计特性类似,而单基地共极化和交叉极化RCS存在较大差异;统计了单/双基地极化比的分布特性,发现单/双基地交叉极化与共极化比情况差异较大,而共极化比类似,所得结论为全极化双基地雷达飞机目标探测试验研究提供参考。      

干扰条件下极化雷达目标检测性能分析

推导了受干扰目标的极化协方差矩阵及其统计特性,建立了干扰条件下最优极化检测器的数学模型,在此基础上以水面舰船和装甲车辆为例分析了不同干扰功率与干扰机极化配置方式对极化雷达目标检测性能力的影响,揭示了利用压制性干扰降低极化雷达目标检测性能的最佳干扰功率需求。     

基于极化联合特征值的雷达弱小目标检测方法

针对海杂波背景下雷达弱小目标检测问题,提出了一种基于极化联合特征值的雷达弱小目标检测方法。该方法利用多极化通道回波数据计算极化相干矩阵的最大特征值,然后将待检测单元的最大特征值与参考单元最大特征值、最小特征值、算数平均值和几何平均值的算数平均之比分别作为检验统计量实现检验判决。仿真和实测数据处理结果表明：基于极化联合特征值的雷达弱小目标检测方法较基于特征值的检测方法性能提高2 dB,较极化检测最优滤波器性能提高1.5 dB,较功率最大综合检测方法、SPAN检测方法性能提高5 dB,极化联合最大特征值-几何平均方法综合检测效果最好。     

极化雷达测量体制研究进展

文中从极化雷达发展趋势的角度,对极化测量关键技术进行了梳理,明确了极化测量雷达体制的概念和内涵,并通过暗室测量实验和仿真实验比较了各测量体制间的差异和优缺点,证明了在目标极化特性快起伏情况下,分时极化测量不能完整准确地反映目标极化特性,此时瞬时极化测量的性能明显优于分时极化测量,并指出了紧凑极化体制的特点及应用。     

基于联合稀疏性的高分辨全极化雷达成像研究

针对频率步进体制高分辨全极化雷达,本文研究了基于稀疏信号表示的高分辨全极化雷达成像,并提出了一种基于极化平滑l₀范数算法的成像方法.算法中的联合稀疏性度量综合利用了目标在全极化下的散射特性,因而成像结果兼具全极化处理和稀疏优化算法的优点,不仅能以较少的观测回波获得高分辨距离像,还能全面准确反映目标全极化散射特性,有利于目标识别等进一步应用.仿真和暗室实测数据实验结果验证了本文方法的有效性.     

高分辨雷达目标极化检测仿真实验与结果分析

在宽带高分辨雷达目标极化检测的理论与模型基础上,利用某隐身飞机与某战斗机实测宽带全极化散射数据以及杂波模型,进行了两种典型情况下的高分辨极化检测仿真实验,验出了实验结果,分析验证了文献[1]中的结论.     

干扰背景下瞬时极化测量雷达的目标识别预处理技术

该文以瞬时极化测量雷达的攻防对抗为背景,分析了单极化有源干扰机形成的假目标的极化散射特性。分析结果表明,在同样的干扰样式下,干扰机在分时极化测量雷达和瞬时极化测量雷达下生成的假目标具有不同的散射特性。在单极化有源假目标极化散射特性分析基础上,针对对抗条件下极化雷达无法准确测量目标散射矩阵的情况,提出了一种基于不完整极化测量的目标识别预处理方法。该方法能够有效获取目标三个极化散射矩阵序列,它们可以用作目标识别的稳健特征量。     

全偏振态同时探测实时彩色偏振成像技术

偏振光学成像技术作为一种新型的光学成像技术,通过对光波偏振特性的探测,增加了信息的探测维度,有利于全面、准确地获取目标的信息.文中阐述了偏振成像的探测方法,典型偏振成像系统的分类;详细介绍了一种基于Stokes矢量方法的分孔径全偏振态同时探测的实时彩色偏振成像相机;利用该相机进行了全偏振度成像实验和偏振去雾成像实验.实验表明全偏振态同时探测偏振成像技术在提高成像探测距离、目标细节获取及恢复等方面具有一定优势,能够为现代光学成像探测系统提供重要的技术补充.     

基于和差波束极化特性的目标极化散射矩阵测量方法研究

该文建立了一种基于常规单脉冲体制的目标全极化散射矩阵测量算法。首先证明了该型雷达天线具有复杂的极化结构,并且对回波信号的极化特性有一定的敏感性。利用单脉冲雷达和差通道的极化特性在获取目标角度信息的同时利用一个脉冲重复周期即可完成目标极化散射矩阵的测量,降低了全极化单脉冲雷达研发的系统复杂度和设计成本,通过电磁计算和仿真分析验证了上述研究的正确性。这对于开发现有雷达装备的极化测量处理能力、提升其抗干扰和目标识别能力具有一定的启发和指导意义。     

Analysis of target response of FM-CW radar

Detection and location of different targets buried in ground or constructional walls depends to a great extent on the knowledge of expected target return response. The analysis of the target-radar response for FM-CW ground probing radar is performed with the aid of a signal flow diagram relating the target response and the radar performance. A plane wave model for the radar radiated electromagnetic waves is adopted and the analysis is carried out for two typical targets; a finite thickness slab and a sphere. Computed returns based on this analysis are compared with those obtained experimentally from a 1-2 GHz FM-CW radar scheme and a very close agreement is found. A computational study is conducted on the response of planar target model, and important conclusions are reached upon relevant to ground probing problem.     

PolSAR成像的固定极化干扰机有源诱饵目标鉴别及抑制

针对合成孔径雷达(Synthetic Aperture Radar,SAR)成像中真假目标难以区分的问题，提出了一种极化合成孔径雷达(Polarmetric SAR,PolSAR)成像固定极化转发式干扰诱饵目标鉴别方法。该方法首先通过极化熵对目标进行分类，提取低极化熵的目标并对目标进行Wigner-Ville分布(Wigner-Ville Distribution,WVD)变换，再利用Hough变换计算WVD图像中的曲线斜率，将计算出的多普勒调频率与理论调频率进行对比，进而完成真实目标与假目标的鉴别，最终通过极化对消对鉴别出的目标进行抑制。实验结果验证了该方法的有效性。     

米波频段飞机目标全极化散射仿真与特性分析

该文基于全极化雷达对空探测和目标识别的应用需求,研究了飞机目标全极化散射特性,特别是交叉极化散射的产生原理和可利用性。在米波频段对隐身和非隐身飞机目标开展了数值建模和仿真计算;分析对比了不同飞机目标的极化散射空域分布特性,分析了不同的外形结构产生强交叉极化的条件。结果表明:非隐身飞机具有较丰富的极化散射特性,有利于雷达目标的极化识别。      

Development of a ground-based radar for scattering measurements

A ground-based C-band scatterometer system has been constructed at the Multimedia University, Malaysia. This is an inexpensive FM-CW radar that was efficiently constructed from a combination of commercially available components and in-house fabricated circuitry. The system has full polarimetric capability for determining the complete backscattering matrix of a natural target. It will be used to conduct in-situ backscatter measurements on Earth terrain, such as vegetation fields, forests, and soil surfaces. This paper presents the system design and the evaluation results of the scatterometer system. The system was tested at a football field. A metal sphere was used as the calibration target. The backscattering matrices of an 8" trihedral corner reflector and of a 4" /spl times/ 8" dihedral corner reflector were measured. The dihedral was rotated at different angles to provide different sets of polarimetric data. The results were compared with the theoretical values to verify the effectiveness of the calibration technique. The external calibration and internal calibration procedures, as well as the approach used in measuring the relative phase response, are discussed.