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     

Polarimetric detection of objects buried in snowpack by a syntheticaperture FM-CW radar

Presents experimental results of polarimetric detection of objects buried in a natural snowpack by a synthetic aperture FM-CW radar. First, the principle of polarimetric imaging in the Co- and Cross(X)-pol radar channels is outlined based on the scattering matrix and the characteristic polarization states for a specific target. Then, polarimetric measurements were carried out to detect objects buried in a natural snowpack 230 cm deep. The targets included two orthogonally placed metallic plates, an ice layer within the snowpack, and a human body. It is shown that the polarimetric FM-CW radar clearly enhances target signatures and that it serves to significantly improve detection in snowpack. Several polarimetric detection results are displayed, demonstrating the potential capability of characteristic polarization imaging and the usefulness of FM-CW radar     

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     

Effect of wind on FM-CW radar backscatter from a wet snowcover

The most important factor affecting the microwave properties of a snowcover is the liquid water content (snow wetness). An FM-CW (26.5-40-GHz) radar has been used to investigate the influence of snow wetness on the magnitude of radar backscatter from a snowcover. The radar backscatter measurements from a wet snowcover on a windy day suggest that evaporative cooling due to the wind may reduce the amount of liquid water at the snowcover surface     

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     

A FM-CW radar proximity sensor for use in mechatronic products

The need for a low cost medium range proximity sensor for use in mechatronic products is identified and discussed with particular reference to automotive applications. One candidate solution to this need, a 27 GHz frequency modulated continuous wave radar system, is presented for use as a range finder. The method of releasing the range information from the returned signal is described together with the results from off-line data analysis. A real-time system for implementation in a typical product is outlined.     

Sequential methods in radar detection

Certain sequential tests of statistical hypotheses known as sequential probability ratio tests (SPRT) possess an optimum property that they can accelerate, on the average, the termination of the test or alternately execute the test in the same time with less error, or with the same error but on less distinguishable hypotheses than a fixed sample-size test. These properties are of practical importance when applied to the radar problem, but in the application of sequential methods to radar surveillance some modification of an SPRT is frequently necessary. In particular, design problems relating to phased array radars are considered. This paper reviews the problem of angle search constraints, existence of multiple resolution elements in range and velocity, possibility of a flexible allocation of pulses, and fluctuations of radar cross sections of targets. Representative numerical results are included to indicate what performance can be expected with the use of sequential methods. An attempt is made to present an integrated theoretical and practical picture. Key references are listed.     

Development of an automated windshear detection system usingDoppler weather radar

The US Federal Aviation Administration (FAA) is developing the Terminal Doppler Weather Radar (TDWR) system to determine the location and severity of LAWS (low-altitude windshear) phenomena and other weather hazards (e.g. tornadoes and turbulence) and to provide the pertinent information to real-time air traffic control users. The FAA program for developing and evaluating the TDWR is described, with emphasis on the resolution of key technical issues such as separation of the radar return due to the low-altitude weather phenomena from that caused by various clutter sources and the automatic detection of the phenomena by means of pattern recognition applied to images depicting the weather reflectivity and Doppler shift. These technical issues have been addressed using experimental data obtained using a testbed radar in representative meteorological regimes. The system performance has been assessed using numerous experimental windshear data sets with corresponding `truth' developed by experienced radar meteorologists from a number of organizations. It is shown that the system provides very reliable detection of strong microbursts in a variety of environments with a gust-front detection capability that supports effective planning of airport runway use     

Multiple radar targets detection by exploiting induced amplitude modulation

This work deals with the problem of detecting and estimating multiple radar targets present in the same range-azimuth resolution cell of a surveillance radar system with a mechanically rotating antenna. In the first part of the work, we tackled the problem of estimating target complex amplitudes, Doppler frequencies, and directions of arrival, and a consistent estimator based on the asymptotic maximum likelihood (AML) method was derived. In this second part, we tackle the "detection problem," which consists of determining the number of targets. First, the target parameters are estimated, assuming a maximum number of possible targets. Subsequently, these estimates are used in a successive hypotheses test procedure. The statistic of the test at each step of the procedure is derived by using an asymptotic expression of the generalized likelihood ratio test (GLRT) statistic. Performance of the proposed algorithm is investigated through both asymptotical analysis (as concerning the probability of false alarm) and Monte Carlo simulation.     

Backscattering measurements by an FM radar method

This paper describes a method for measuring the backscattering cross section of an arbitrary target using FM radar techniques. This method has a merit that it does not require a nonreflecting background behind the target, by the use of a high selective amplifier in the FM radar. The principles of this measuring method and the results of the measurements are described.     

A Study of UWB FM-CW Radar for the Detection of Human Beings in Motion Inside a Building

A study of an ultrawideband frequency-modulated continuous-wave radar with an extended frequency sweep from 0.5 to 8 GHz is presented. It has been applied to through-the-wall human detection. This work presents the modeling of wall attenuation followed by real measurements. The radar system is presented, and trials of human being tracking are shown. This radar will enable large stand-off distance capabilities and dasiadasiain-depthpsilapsila building detection.     

空间碎片地基雷达探测综述

微动特征是空间碎片目标特性研究与识别的重要特征量。为提升非相干散射雷达在空间碎片微动特征提取中的应用,设计了一种基于雷达的目标微动特征提取方法,包括距离徙动修正、目标平动速度和加速度余项修正、时频分布计算、逆Radon变换等,并利用曲靖非相干散射雷达实测回波数据进行分析验证。结果表明,利用非相干散射雷达实测回波可有效提取空间碎片自旋或翻滚半径、周期、频率以及姿态角等特征参数,进而初步判断其形状,仿真和实测数据分析结果与预期情况基本相符。本文工作验证了电离层非相干散射雷达用于空间碎片微动特征提取的可行性,为空间碎片监测与目标特性研究识别提供了新技术手段。

     

复杂环境下基于多层激光雷达的障碍检测

为了完成复杂环境中无人自主导航车的障碍检测任务，应用四线激光雷达，提出了一种新的障碍检测算法，该算法利用检测区域的坡度信息进行障碍检测，包括候选障碍点的提取、干扰点的滤除及障碍点的聚类分割三个步骤。为了克服激光雷达检测盲区与抑止测量过程中干扰噪声的影响，运用了卡尔曼滤波算法对目标障碍进行了滤波处理。试验结果表明，障碍检测算法稳定可靠。     

NONPARAMETRIC DETECTION OF RADAR TARGET IN NONHOMOGENEOUS ENVIRONMENTS

This poaper is devoted to the performance evaluation of the Generalized Sigu(GS). Trimmed Generalized Sign(TGS), Modified Savage(MS). Mann-Whitney(MW) and a new proposed detector in multiple target situations. The analysis is carried out for both fluctuating and nonfluctuating received signals. The simulation results show that the new proposed detector has the best detection performance in homogeneous as well as nonhomogeneous background conditions, while TGS procedure is better than the GS detector in distinguishing the primary target from the secondary interfering ones.     

LFMCW雷达高速运动目标检测与估计

针对LFMCW雷达高速运动目标的检测问题,本文提出了一种二次混频与MTD处理相结合的方法。根据上、下调频差拍信号对称特点,采用二次混频处理解决多周期信号中心频率偏移问题,同时实现了距离-多普勒解耦合。MTD处理则等效地实现了多周期信号的积累,并得到目标速度估计。然后根据速度估计值对差拍信号进行运动补偿,获取目标距离信息。性能分析结果表明,与传统MTD方法相比,在输入信噪比一定的情况下,该方法的处理增益不受目标多普勒的影响,因此更适用于高速运动目标的检测。仿真结果验证了该方法的有效性。     

Minimization of end-fire radar echo of a long thin body by impedance loading

A theory on the minimization of the end-fire radar echo of a long, thin body by an impedance loading technique is presented. When a long, thin body is illuminated by a plane wave in the region of longitudinal incidence, a large backscatter is observed. This backscatter is due to the induced traveling wave which is reflected from the rear end of the body. By an appropriate impedance loading, this backscatter can be minimized. In this paper, the induced current on a long, thin and loaded cylinder is studied. The optimum impedance loading which minimizes the end-fire radar echo is explicitly obtained. Theoretical results are compared with the experimental data and an excellent agreement is obtained.     

The detection of chirped radar signals by means of electron spin echoes

The application of the electron spin echo phenomenon to the detection of chirped microwave pulses is considered. The attainable time resolution is determined by the width of the paramagnetic resonance line, and the length of the received waveform is limited by the phase memory time of the spin packets in the active material. Pulse compressions of 1000:1 appear to be feasible. A typical device of this kind would require to be operated at liquid helium temperatures. It could be adapted so that in itself it provided maser amplification of the compressed pulses.     

海面大气环境下雷达作用距离的预报方法

研究了海洋大气环境条件下雷达对已知散射截面积目标作用距离的预报方法。通过气象信息得到大气折射率剖面,利用抛物型方程计算出电磁波传播单程损耗,利用雷达方程得到目标的传播损耗门限,最后得到雷达对目标的最远作用距离。实测结果表明,此方法是可行的。     

脉冲噪声下基于FLO-WHT的雷达回波LMFS检测

线性调频信号(LMFS)是雷达回波信号的一种常见形式,Wigner-Hough变换(WHT)常用于LMFS的检测。复杂环境下雷达回波中的尖峰脉冲噪声服从α稳定分布,在这种噪声环境下WHT性能退化。基于此提出了能工作在稳定分布噪声环境下的分数低阶伪Wigner-Ville时频分布方法(FLO-PWVD),结合已有的Hough变换,提出了分数低阶伪Wigner-Hough变换(FLO-PWHT)新方法。在脉冲噪声环境下,应用FLO-PWHT对多个LMFS信号进行检测,计算机仿真结果表明,提出的FLO-PWHT算法性能明显优于已有的PWHT方法,能较好地在脉冲噪声环境下工作,且具有一定的韧性。