Fluctuating Target Detection in Clutter Using Sidelobe Blanking Logic

In an earlier paper, Maisel [6] considered two-channel detection systems using a sidelobe blanking logic when a nonfluctuating target was present. This paper is an extension of the earlier work to include fluctuating targets. The Swerling I, II, III, and IV models are considered when single-pulse detection is of interest. An adaptive threshold procedure is also briefly discussed whereby the probability of false alarm at any given resolution cell is maintained constant, even though the input clutter level may vary from cell to cell or from beam position to beam position. Useful data are presented for detection probabilities in the range 0.5 to 0.9, for false alarm probabilities in the range 104 to 10-8, and for a false detection probability of 0.1 for a sidelobe target yielding an apparent signal to total noise power density ratio of 13.0 dB in the main beam receiver.     

A Practical PRSD System for Multiple Target Detection

A block diagram of a practical system using the sequential detection technique for radar detection of multiple targets is given. The system is designed to obtain better detection probability with a lower value of signal-to-noise ratio for a given false-alarm probability and average transmitted power. The total pulse duration is divided into a number of range elements which are tested for the presence or absence of a target before switching the antenna beam to the next position.     

Optimal Digital Beam Splitting for Radar Beacon Systems

Beam splitting for a radar beacon system that scans in azimuth is investigated from a theoretical viewpoint. The video output is quantized into two levels corresponding to a detection and no detection. Further, the antenna sensitivity profile is described by sin ?/?. For this system, a digital method of beam splitting that minimizes angular error is developed. Prior information about the probable location of targets can be included. Both Bayesian and minimax approaches are developed. The minimax estimate of the target azimuth is the average of the angles at which beacon signals are detected. The antenna beam can be interpolated by a factor of 10 when the signal power is 3 dB above the noise and without prior azimuth information The interaction of beam splitting and detection is discussed.     

A Precise Optical Instrumentation Radar

An instrumentation tracker is described which provides real-time positional data on high-speed cooperative targets with precisions of ±1 m at ranges between 300 m and 10 km. Unambiguous range is determined by a precise digital FM-CW ranging technique at a rate of 15 per second. A target-mounted beacon and a narrow laser ranging beam permit measurement of target position to values much less than target dimension. Azimuth and elevation angles are read out by precision shaft angle encoders and recorded in binary form, along with range and time, on magnetic tape or directly into a real-time computer.     

Beam overlap impact on phased-array target detection

The impact of beam overlap on the probability of detection during a single scan of a phased-array volumetric scan radar is examined. Rectangular and triangular beam packing arrangements are considered. Beam positions near the beam most centered on the target are allowed to contribute to the detection process. The treatment of the impact of beam overlap on target detection for a phased array is consistent with the results that would be achieved by proper use of the search radar range equation     

Difference beam aided target detection in monopulse radar

The classical detection step in a monopulse radar system is based on the sum beam only,the performance of which is not optimal when target is not at the beam center. Target detection aided by the difference beam can improve the performance at this case. However, the existing difference beam aided target detectors have the problem of performance deterioration at the beam center, which has limited their application in real systems. To solve this problem, two detectors are proposed in this paper. Assuming the monopulse ratio is known, a generalized likelihood ratio test(GLRT) detector is derived, which can be used when targeting information on target direction is available. A practical dual-stage detector is proposed for the case that the monopulse ratio is unknown. Simulation results show that performances of the proposed detectors are superior to that of the classical detector.     

Target State Estimation in a Multitarget Environment Using Multiple Sensors

An approach for target detection/state estimation that views theproblem as one of a finite state search over the target parameterspace is presented. This approach allows for a natural way toassociate different types of measurements, such as frequency andcoherence from multiple sensors, and also for dealing with multipletargets, dropouts, and clutter. We describe our model and present acomputationally efficient search algorithm for target detection andtarget state estimation in a multitarget environment based on thismodel. The results of a two-sensor, multitarget computer simulationare discussed.     

Adaptive Radar Beacon Forming

Propagation errors along paths between an array radar and a distribution of targets cause degradations in angle measurements and detection range. The overall objective of the research described in this paper was to analyze and demonstrate the use of conjugate reflections for compensating adverse effects of path errors. The effect of reflecting the conjugate of an incident wave is described mathematically and is demonstrated by computer simulation. Repeated conjugate reflections are shown to result in the formation of a single beam usually focussed on a target highlight. Echoes from this spatial reference, or "beacon" are shown to provide the means by which aperture phase errors may be effectively compensated. Results of radar simulations include two-way patterns computed for an example involving a distribution of three-point targets and half-wave-length Gaussian aperture errors. Without compensation a gain loss of 12 dB is computed; with error correction, based on echoes from an adaptively focussed beam, the two-way pattern is within a small fraction of a dB of the ideal pattern. The effect of noise on adaptive beacon forming was considered for a case involving one target. Repeated conjugate reflections improve signal-to-noise ratio as long as the effect of noise is less than the effect of aperture dephasing on the power reflected back to the target. An example is presented in which signal-to-noise ratio at the output of the receiver combining network is increased from 4 to 11.8 dB.     

Maximum-Likelihood Detection of Unresolved Radar Targets and Multipath

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiplebeam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.     

惯性信息辅助的大视角目标快速精确定位

目标定位技术广泛应用于航空领域的侦察机、无人机等各类侦察打击任务中,目标定位精度的高低及效率对作战效果具有重要影响。针对仿射尺度不变的特征变换(ASIFT)算法对远距离大视角目标定位精度较低、速度较慢的问题,提出了一种基于惯性信息辅助的大视角目标快速精确定位方法。该方法首先对目标实测序列图像构造尺度空间,结合FAST特征检测与FREAK特征描述的方式进行匹配,实现对待定位目标的快速提取;然后利用机载惯性信息求解目标实测图与参考图之间的透视变换矩阵,利用该矩阵对实测图进行变换以减小图像间视角差异,克服了ASIFT算法盲目匹配计算的弊端,并通过FAST特征检测与FREAK特征描述相结合的方式提升了大视角图像的匹配速度;最后通过单应性矩阵映射关系实现对目标的精确定位。实验结果表明,大视角目标快速精确定位方法匹配耗时比ASIFT算法的减小了1个数量级,定位精度比目标平均值定位算法精度提高了1个数量级,有效提高了图像匹配定位在航空领域的应用效率。     

Binary Signal Detection with Decision and Information Feedbacks

This paper analyzes a sequential feedback detection scheme derived by Kramer's nonsequential intermittent one; in addition to the noiseless information feedback channel, it makes use of a noiseless decision feedback channel. Expressions for the normalized average evergy per symbol, average decision time, probability of error, and average power are derived. The comparison with the nonsequential intermittent scheme shows that the proposed one allows an appreciable gain in transmission rate and requires a smaller peak-to-average power ratio.     

Passive ranging of a low observable ballistic missile in agravitational field

In this paper we present an estimation algorithm for tracking the motion of a low-observable target in a gravitational field, for example, an incoming ballistic missile (BM), using angle-only measurements. The measurements, which are obtained from a single stationary sensor, are available only for a short time. Also, the low target detection probability and high false alarm density present a difficult low-observable environment. The algorithm uses the probabilistic data association (PDA) algorithm in conjunction with maximum likelihood (ML) estimation to handle the false alarms and the less-than-unity target detection probability. The Cramer-Rao lower bound (CRLB) in clutter, which quantifies the best achievable estimator accuracy for this problem in the presence of false alarms and nonunity detection probability, is also presented. The proposed estimator is shown to be efficient, that is, it meets the CRLB, even for low-observable fluctuating targets with 6 dB average signal-to-noise ratio (SNR). For a BM in free flight with 0.6 single-scan detection probability, one can achieve a track detection probability of 0.99 with a negligible probability of false track acceptance     

Detection of moving targets in wideband SAR

A likelihood ratio is proposed for moving target detection in a wideband (WB) synthetic aperture radar (SAR) system. WB is defined here as any systems having a large fractional bandwidth, i.e., an ultra wide frequency band combined with a wide antenna beam. The developed method combines time-domain fast backprojection SAR processing methods with moving target detection using space-time processing. The proposed method reduces computational load when sets of relative speeds can be tested using the same clutter-suppressed subaperture beams. The proposed method is tested on narrowband radar data.     

基于红外视觉/激光雷达融合的目标识别与定位方法

近年来,基于可见光图像的目标识别在无人车感知领域得到了广泛应用.然而,可见光图像目标识别无法应用于弱光和黑暗环境.针对于此,提出了一种基于红外视觉/激光雷达融合的目标识别与定位算法.首先,通过基于颜色迁移的数据增强训练方法,提高了红外目标识别算法的泛化性能.继而,提出了一种基于激光雷达修正的单目深度估计方法,通过视觉图...     

大展弦比复合材料机翼的非线性颤振分析

大展弦比机翼在气动力作用下产生较大变形,颤振速度和颤振频率随之发生明显变化,线性理论难以获得比较合理的解答。综合考虑了结构几何非线性、气动非线性和材料各向异性对机翼运动状态的影响,将复合材料机翼建模为非线性薄壁单闭室截面梁,建立机翼的运动方程,并使用小扰动分析的方法得到机翼在平衡位置附近的振动方程。采用Theodorsen非定常气动理论构建气动模型,获得机翼在平衡位置附近的非线性颤振方程,并利用v-g法判定机翼颤振稳定性。通过算例演示了一些非线性颤振的特点,讨论了铺层角、展弦比、机翼线密度等参数对颤振速度的影响,并与线性理论得到的结果进行对比。     

双基地及其联网系统的定位方法及精度分析

讨论的双基地系统中,发射站只起照射目标的作用,而接收站测量距离和、方位角及俯仰角。分析了双基地系统的目标定位方法和定位误差。通过分析定位精度在受控区域内的分布,提示了双基地系统的定位性能。文中对组网双基地系统的定位处理方法进行了讨论,其中采用WLS(Weighted Least Square)算法进行数据融合处理,仿真结果表明,联网双基地系统的定位精度大有提高。     

Optimum Steady State Position, Velocity, and Acceleration Estimation Using Noisy Sampled Position Data

A one-dimensional tracking filter based on the Kalman filtering techniques for tracking of a dynamic target such as an aircraft is discussed. The target is assumed to be moving with constant acceleration and is acted upon by a plant noise which perturbs its constant acceleration motion. The plant noise accounts for maneuvers and/or other random factors. Analytical results for estimating optimum steady state position, velocity, and acceleration of the target are obtained.     

基于改进SSD的舰船目标精细化检测方法

以SSD为代表的主流深度学习方法在目标检测领域取得了显著的成绩，但由于该类方法只能以矩形框给出目标的概略位置，检测结果具有很大的背景冗余区域，特别是港口密集停泊的舰船在图像中会出现区域重叠，导致误检和漏检。针对以上问题，提出了一种具有旋转不变性的舰船目标精细化检测方法，该方法综合利用可变形卷积、可变形池化、旋转的边框回归和旋转的非极大值抑制等模块的优点，借鉴MobileNet架构对网络加速，通过学习密集区域目标的几何形变，有效预测目标的旋转角度，最终以旋转的矩形框给出目标的位置。实验结果表明，该算法可实现多类舰船目标类型区分和目标朝向判定的功能，有效地解决了实际应用中的目标精确定位定向难题，提高了自动目标识别的精确性，并满足工程应用的实时性要求。     

Nonparametric Radar Extraction Using a Generalized Sign Test

A nonparametric procedure used in a constant false alarm rate (CFAR) radar extractor for detecting targets in a background of noise with unknown statistical properties is described. The detector is based on a generalization of the well-known two-sample sign test and thus requires a set of reference noise observations in addition to the set of observations being tested for signal presence. The detection performance against Gaussian noise is determined for a finite number of observations and asymptotically, for both nonfluctuating and pulse-to-pulse Rayleigh fluctuating target statistics. It is noted that the performance loss, as compared to the optimum parametric detector, depends critically on the number of reference noise observations available when the number of hits per target is not large. In the same case a much larger loss is also found for a pulse-to-pulse fluctuating target even though the asymptotic loss is the same as for a nonfluctuating target. A comparison is finally made with a detector based on the Mann-Whitney test, which usually is considered to be one of the better nonparametric procedures for the two-sample case.