海杂波的分段分数布朗运动模型

主要研究了分段分数布朗运动(PFBM)模型在雷达海杂波分形建模中的应用.由于自然界和人造系统中研究对象不具有数学上完美的分形特性, 从而研究对象的分形特性无法在整个尺度区间上成立, 传统上, 海杂波的单一分形模型仅利用无标度区间内海杂波的自相似信息进行参数估计, 并没有考虑海杂波在无标度区间以外的尺度下所包含的信息.分段分数布朗运动从频域角度对海杂波频谱进行分段描述, 对应到时域即从粗略尺度和精细尺度两方面描述海杂波时间序列.结合海杂波产生的物理背景, 该模型可以为海杂波时间序列在粗略尺度和精细尺度下表现出的不同粗糙度提供机理性解释.在此基础上, 还研究了具有不同多普勒频率的运动目标对海杂波的影响, 结果表明运动目标对粗略尺度和精细尺度下海杂波的影响程度是不同的.     

Amélioration de la sensibilité de détection dans un sous-sol

Ground penetrating radar is a technique wich offers a way of viewing shallow soil. The areas of application for geophysical radar are divers and the associated electromagnetic phenomenology has been investigated for detecting targets buried within a realistic model ground environment. The continuous backscatter of field from soil gives rise to clutter, which limits the contrast of near-surface underground target reflections and, therefore, decreases the detection sensitivity of the radar. In this paper, a novel detection scheme is introduced in order to improve the detection sensitivity. This new approach is based on a frequency modulation by a micro-wave signal.     

Optimizing chaos-based signals for complex radar targets

There has been interest in the use of chaotic signals for radar, but most researchers consider only a few chaotic systems and how these signals perform for the detection of point targets. The range of possible chaotic signals is far greater than what most of these researchers consider, so to demonstrate this, I use a chaotic map whose parameters may be adjusted by a numerical optimization routine, producing different chaotic signals that are modulated onto a carrier and optimized for different situations. It is also suggested that any advantage for these chaos-based signals may come in the detection of complex targets, not point targets, and I compare the performance of chaos-based signals to a standard radar signal, the linear frequency modulated chirp. I find that I can optimize a chaos-based signal to increase the cross-correlation with the reflection from one complex target compared to the cross-correlation with the reflection from a different target, thus allowing the identification of a complex target. I am also able to increase the cross-correlation of the reflection from a complex target compared with the cross-correlation with the reflection from spatially extended clutter. I show that a larger output signal-to-noise ratio is possible if I cross-correlate with a reference signal that is different from the transmitted signal, and I justify my results by showing how the ambiguity diagram for a chaos-based signal can be different than the ambiguity diagram for a noise signal.     

利用正弦调频信号的宽带速度敏感特性抑制混响

有源声呐探测水中低速目标时,混响与目标回波的频率接近,目标回波与混响分离困难.根据运动目标与产生混响的散射体在速度域的差异,利用正弦调频信号(SFM)的速度敏感特性实现目标回波与混响的有效分离.推导了 SFM信号宽带混响抑制能力与速度分辨模糊之间的约束关系,建立了波形优化设计的搜索模型.通过多普勒滤波处理将数据从频率域...     

Polarimetric laser radar target classification

Imaging laser radar (ladar) systems have been developed for automatic target identification in surveillance systems. Ladar uses the range value at the target pixels to estimate the target's 3-D shape and identify the target. For targets in clutter and partially hidden targets, there are ambiguities in determining which pixels are on target that lead to uncertainties in determining the target's 3-D shape. An improvement is to use the polarization components of the reflected light. We describe the operation and preliminary evaluation of a polarization diverse imaging ladar system. Using a combination of intensity, range, and degree of polarization, we are better able to identify and distinguish the target from other objects of the same class.     

Detection and tracking of targets in infrared images using Bayesian techniques

Simple yet robust techniques for detecting targets in infrared (IR) images are an important component of automatic target recognition (ATR) systems. In our previous works, we have developed IR target detection and tracking algorithms based on image correlation and intensity. In this paper, we discuss these algorithms, their performances and problems associated with them and then propose novel algorithms to alleviate these problems. Our proposed target detection and tracking algorithms are based on frequency domain correlation and Bayesian probabilistic techniques, respectively. The proposed algorithms are found to be suitable for real-time detection and tracking of static or moving targets, while accommodating for detrimental affects posed by the clutter and background noise. Finally, limitations of all these algorithms are discussed.     

Infrared small moving target detection using sparse representation-based image decomposition

Infrared small moving target detection is one of the crucial techniques in infrared search and tracking systems. This paper presents a novel small moving target detection method for infrared image sequence with complicated background. The key points are given as follows: (1) since target detection mainly depends on the incoherence between target and background, the proposed method separate the target from the background according to the morphological feature diversity between target and background; (2) considering the continuity of target motion in time domain, the target trajectory is extracted by the RX filter in random projection. The experiments on various clutter background sequences have validated the detection capability of the proposed method. The experimental results show that the proposed method can robustly provide a higher detection probability and a lower false alarm rate than baseline methods.     

A novel clutter rejection scheme in color flow imaging

In ultrasound color flow imaging systems, it is important to suppress the clutter signals originated from stationary and slowly moving tissue sufficiently. Without sufficient clutter rejection, the estimation of the blood flow velocity will be inaccurate, and the imaging quality will be poor. In this paper we present a new clutter rejection scheme involving first down-mixing the clutter signals to zero frequency and then cancelling the stationary echo by subtracting the signals from two consecutive pulses. This stationary echo cancelling scheme is easy to be realized with small computational power, and is adaptive to the clutter signals. Theoretical analysis and simulation using RF data prove that it's an efficient and practical clutter rejection scheme for color flow imaging.     

空时多普勒频移域运动小目标的抗干扰探测方法

有源声呐使用多普勒敏感信号可在多普勒频移域分离杂波、混响等干扰和运动目标,但低信干比时强干扰的时间旁瓣泄露和多普勒旁瓣泄露会淹没弱目标.针对该问题,提出了一种基于自适应最小均方(LMS)算法和宽带模糊函数(WAF)的运动小目标抗干扰探测方法.首先在空间多普勒频移域上利用基于LMS的自适应陷波器抑制干扰,然后在快时间多普...     

Indoor human detection based on micro-Doppler features in the presence of interference from moving clutter sources

In this paper, to address the problem of detecting the presence of human in indoor environments in the presence of moving clutter sources, an indoor human detection method that utilizes random forest to process micro-Doppler signatures and a single pair of TX/RX unit is proposed. In contrast to most of the existing methods that use both distance information and micro-Doppler information assuming no interference from moving clutter sources (window curtains, blinds, table fans, etc.), our proposed method relies only on micro-Doppler information for human detection in indoor environments with curtain and fan interferences. Based on our time–frequency analyses on the measured radar data, seven features, i.e., the mean and standard deviation of the doppler centroid, the mean and standard deviation of the span of envelopes, the silhouette size, the positive peak values, and the peak spread, are extracted from spectrograms. These features are fed into a random forest classifier for categorizing the state of a room into one of the five scenarios considered in this work, namely (1) a person entering the room, (2) a person leaving the room, (3) interference from curtain/blind, (4) interference from fan, and (5) an empty room. The proposed system has been validated using real-world experiments and be able to deliver an accuracy of 97.5% in classifying the scenarios.     

Closed-form CRLB and LPI power allocation strategies for MIMO radars with unneglectable clutter

This paper studies clutter’s effect on MIMO radar performance through obtaining closed-form Cramer Rao lower bounds (CRLBs) for the range and velocity parameters versus the powers assigned to the transmit antennas which resulted in more calculation’ complexity. To verify extracted CRLBs, the maximum likelihood estimation’s error variance (MLEEV) of range and velocity were derived in attendance of clutter. Based on obtained closed-form CRLBs, four optimized power allocation (PA) strategies are proposed which consider measurement error statistics as the objective function or constraints to improve radar performance. So, the calculated closed-form CRLBs are simplified to the closed-forms versus assigned powers to the transmitters. Simulation results verify the proposed CRLBs’ accuracy, and improvements have been made by proposed power allocations.     

Target detection beneath foliage using polarimetric synthetic aperture radar interferometry

In this paper, we demonstrate how the new technology of polarimetric synthetic aperture radar (SAR) interferometry can be used to enhance the detection of targets hidden beneath foliage. The key idea is to note that for random volume scattering, the interferometric coherence is invariant to changes in wave polarization. On the other hand, in the presence of a target the coherence changes with polarization. We show that under general symmetry constraints this change is linear in the complex coherence plane. These observations can be used to devise a filter to suppress the returns from foliage clutter while maintaining the signal from hidden targets. We illustrate the algorithm by applying it to coherent L-band SAR simulations of corner reflectors hidden in a forest. The simulations are performed using a voxel-based vector wave propagation and scattering code coupled to detailed structural models of tree architecture. In this way, the spatial statistics and radar signal fluctuations closely match those observed for natural terrain. We demonstrate significant improvements in the detection of hidden targets, which suggests that this technology has great potential for future foliage penetration (FOPEN) applications.     

Target detection beneath foliage using polarimetric synthetic aperture radar interferometry

Abstract

In this paper, we demonstrate how the new technology of polarimetric synthetic aperture radar (SAR) interferometry can be used to enhance the detection of targets hidden beneath foliage. The key idea is to note that for random volume scattering, the interferometric coherence is invariant to changes in wave polarization. On the other hand, in the presence of a target the coherence changes with polarization. We show that under general symmetry constraints this change is linear in the complex coherence plane. These observations can be used to devise a filter to suppress the returns from foliage clutter while maintaining the signal from hidden targets. We illustrate the algorithm by applying it to coherent L-band SAR simulations of corner reflectors hidden in a forest. The simulations are performed using a voxel-based vector wave propagation and scattering code coupled to detailed structural models of tree architecture. In this way, the spatial statistics and radar signal fluctuations closely match those observed for natural terrain. We demonstrate significant improvements in the detection of hidden targets, which suggests that this technology has great potential for future foliage penetration (FOPEN) applications.     

半正弦波相关型三维激光雷达

提出了基于半正弦波-方波相关法的凝视成像三维激光雷达.用傅里叶级数展开对新方法进行了分析.理论分析表明,半正弦-方波相关可以在抑制高频噪音的同时加大调制的交流分量.基于新相关方法的探测系统可以在不损失测距准确度的条件下可以获得更大的输出光功率从而获得更大的探测距离.采用基于新方法的探测装置对~70 m外约100 m2的目标进行了探测实验.实验结果表明,基于新方法的激光雷达在60 m处的分辨率约为0.3 m,从而验证了理论分析的结论.     

Estimation of sea clutter inherent Doppler spectrum from shipborne S-band radar sea echo

Measurement of shipborne radar sea echo is instrumental in collecting the sea clutter data in open sea areas. However,the ship movement would introduce an extra Doppler component into the spectrum of the sea clutter, so the sea clutter inherent spectrum must be estimated prior to investigating the sea clutter Doppler characteristics from the shipborne radar sea echo. In this paper we show some results about a shipborne sea clutter measurement experiment that was conducted in the South China Sea in a period between 2017 and 2018; abundant clutter data have been collected by using a shipborne S-band clutter measurement radar. To obtain the sea clutter inherent Doppler spectrum from these data, an estimation method, based on the mapping relationship between the shipborne clutter spectrum and the inherent clutter spectrum, is proposed. This method is validated by shipborne clutter data sets under the same measuring conditions except for the ship speed. Using this method, the characteristics of the Doppler spectrum lineshapes in the South China Sea are calculated and analyzed according to different sea states, wave directions, and radar resolutions, which can be instrumental in designing the radar target detection algorithms.     

Detection of air target based on multi-fractal analysis in a laser radar

A novel approach for detecting laser radar target based on multi-fraction dimension (MFD) of laser clutters has been proposed. The fractal dimension (FD) of laser clutter and the echoes from the plan are estimated using box-counting dimension algorithm. The intrinsic difference in the spectrum of FD Dq between them is extracted and used to detect targets. Experimental results show that the method based on MFD is more reliable than that on FD and can improve the accuracy of detection.     

Millimeter wave backscatter measurements in support of collision avoidance applications

Millimeter-wave short range radar systems have unique advantages in surface navigation applications, such as military vehicle mobility, aircraft landing assistance, and automotive collision avoidance. In collision avoidance applications, characterization of clutter due to terrain and roadside objects is necessary in order to maximize the signal-to-clutter ratio (SCR) and to minimize false alarms. The results of two types of radar cross section (RCS) measurements at 95 GHz are reported in this paper. The first set of measurements presents data on the normalized RCS (NRCS) as well as clutter distributions of various terrain types at low grazing angles of 5° and 7.5°. The second set of measurements presents RCS data and statistics on various types of roadside objects, such as metallic and wooden sign posts. These results are expected to be useful for designers of short-range millimeter-wave collision avoidance radar systems. Brett Snuttjer is presently an Air Force Lieutenant at Rome Laboratory, Rome, NY 13441     

Costas编码跳频信号多普勒容限及其在多声源宽带正交检测中的应用

针对Costas信号的传统宽带匹配滤波因拷贝信号生成过程复杂而带来的计算复杂度高的问题,给出了一种通过计算宽带回波与窄带近似回波的互相关度进而得到Costas信号多普勒容限的数值计算方法,并提出利用容限值对预测目标多普勒范围进行分段窄带近似处理,从而避免了大量的时域伸缩变换,简化了拷贝信号的生成复杂度,提高了宽带匹配滤波的处理效率。随后,将这种方法扩展应用到多声源多目标的回波检测中,利用Costas信号的正交性及多普勒容限值,设计了一种宽带正交匹配检测器,大大提高了多目标声探测的效率。实验仿真和分析证明了多普勒容限求取方法的正确性及其应用于宽带正交匹配检测的有效性。      

红外小目标图像的背景杂波量化方法

分析了背景杂波对红外小目标检测的影响,研究了一种针对红外小目标图像的背景杂波定量描述方法.提出了背景杂波定量描述方法需要满足的三个条件:与主观判断的结果一致、对于不同的红外图像具有适应性和能够辅助改进目标检测算法.综合考虑了目标与背景的特征,融合了4种特征,提出了一种新的红外背景杂波量化方法.首先采用支持向量机对背景杂...     

On locating low altitude moving targets using a planar acoustic sensor array

It is of engineering importance to locate low altitude moving targets with acoustic methods due to the blindness of the traditional radar detecting. In this paper, an algorithm for locating low altitude moving targets is put forward based on a five-element planar acoustic sensor array. The method is realized through estimations of the sensor-to-sensor time delays of the source signal generated by the low altitude moving target. The angle and range estimation performance of the proposed method are analyzed, respectively, both in theoretical and numerical sense.