非合作无源探测中的假设检验弱目标检测方法

在非合作无源探测系统中,弱目标回波不仅会受到强直达波、强多径的干扰,还会受到强目标的掩盖干扰,因此很难对其进行有效检测。为了解决这一问题,提出了一种基于多择复合假设检验的弱目标检测方法。首先将接收信号投影到多径干扰的正交补子空间内,以消除强直达波和强多径干扰,然后将目标检测看作一个多择复合假设检验问题,建立了与之相应的基本框架模型,利用最大后验估计方法对目标时延、多普勒频移及信号幅度等参数进行估计,构造检验统计量,设置相应的门限,根据假设检验结果,逐个消除强目标干扰从而达到检测弱目标的目的。仿真结果表明,本方法可以有效抑制强直达波、强多径及强目标干扰,有效检测出弱目标,且虚警率低。     

非合作无源探测中的参考信号提纯新方法

非合作无源探测系统通过直达波提纯来获取参考信号,参考信号的纯净程度对系统探测性能具有重要影响.针对非合作无源探测中的参考信号提纯问题,提出了一种基于稀疏特性的参考信号提纯新方法.首先将参考通道接收的混合信号变换到对时延敏感的分数阶傅里叶变换域上,并对直达波信号和多径干扰信号在分数阶傅里叶变换域上的稀疏特性进行了分析;然...     

一种基于多基线载波相位差测量的欺骗干扰检测方法

由于卫星导航信号到达地面的信号功率较低,且民用部分信息公开,极易受到欺骗干扰信号的影响,从而导致接收机解算出错误的位置、速度或时间.针对传统的欺骗干扰检测与抑制方法不能对欺骗干扰进行测向的问题,提出了一种基于阵列多天线接收信号的载波相位差进行欺骗信号检测与抑制的方法.该方法能够在缺少先验知识的条件下,借鉴相关干涉仪测向原理,利用不同阵元接收的同一信号的载波相位差构建观测量,实现接收机捕获信号的波达方向估计,通过与星历解算的卫星方向进行对比可实现欺骗干扰的检测与识别.仿真结果表明,该方法能够实现针对不同卫星的多个欺骗信号的波达方向识别,识别精度较高,具有较好的欺骗干扰检测效果,并且该方法对各种导航系统均适用.     

基于拖曳式干扰机的ISAR微动散射波干扰方法

通过对微多普勒效应的研究,提出了一种新的逆合成孔径雷达（ISAR）散射波干扰方法。将拖曳式干扰机和ISAR接收机分别等效为双基ISAR的发射站和接收站,干扰机对截获的ISAR信号进行微动信息调制并转发至目标,由其散射至ISAR接收机产生散射波干扰效果。干扰信号经ISAR接收机处理后可在真实目标回波成像结果附近产生假目标,且在方位向形成干扰条带。实验结果表明：通过控制干扰机转发参数及微动调制参数可分别实现不同的压制干扰效果。由于拖曳式干扰机与目标距离较近,干扰信号可获得较大功率,且与真实目标回波相参,可获得ISAR二维脉冲压缩处理增益,与传统射频噪声压制干扰方法相比成本较小。     

两种自适应方向图峰值副瓣控制方法比较

自适应阵列（或称自适应波束形成）目前已广泛应用到雷达、声纳和通信领域中用来抑制各种干扰（有意的干扰，杂波干扰和多用户干扰等）。在雷达应用中，为了减轻脉冲欺骗式干扰或旁瓣目标并利用单脉冲雷达来准确测量目标波达方向．要求自适应方向图具有低副瓣和稳定的主瓣形状。在实际应用中，各种失配误差将降低自适应阵列的性能．这些误差包括由于目标的波达方向不精确引起的信号指向误差，由通道失配和位置扰动引起的阵列校准误差和由小样本教引起的协方差矩阵估计误差。在此情况下，自适应波束形成的性能大大下降（干扰抑制性能变差。主瓣失真和高的副瓣）。已提出了一种基于二次约束的集成峰值副瓣控制（integrated peak sidelobe control，简称IPSC）方法。该方法可以精确地控制峰值副瓣电平并产生具有稳定的主瓣形状的自适应方向图。研究IPSC中目标信号的影响和信号消除方案以进一步提高IPSC的性能。并将IPSC方法和最新提出的基于二阶锥规划（second-order cone programming，简称SOCP）的分布式峰值副瓣控制（distfibuted peak sidelobe control，简称为DPSC）新方法在性能上进行了比较。仿真结果表明。在干扰抑制性能和方向图控制质量方面IPSC比DPSC性能优越。此外IPSC比DPSC计算高效。     

基于预估-反馈联合处理的射频噪声干扰抑制算法

针对强射频（RF）噪声干扰下脉压雷达目标检测概率较低的问题,提出了一种基于预估-反馈联合处理的射频噪声干扰抑制算法。首先,对回波信号进行盲源分离预处理,并利用分数阶傅里叶变换（FRFT）的特性对目标回波信号进行参数估计以及窄带滤波处理,滤除大部分干扰和噪声的能量;然后,在数据层运用M/N逻辑法进行点迹处理,并结合径向速度方向判决,实现对目标航迹的预估检测;最后,利用数据层对航迹状态的反馈实时修正滤波器参数,从而在信号层更好地滤除干扰能量,并对中断航迹进行剔除,完成射频噪声干扰的抑制。仿真结果表明：与现有射频噪声干扰抑制技术相比,所提算法具有更优的干扰抑制效果。     

C/GFRP层板冲击损伤红外脉冲雷达热波成像检测技术研究

本文采用落锤式冲击试验机对碳纤维/玻璃纤维混杂增强复合材料（C/GFRP）样块开展不同冲击能量下的撞击试验，进而制备了含有模拟低速冲击损伤检测试件，研制了红外脉冲雷达热波成像检测系统，并利用该系统对不同冲击能量损伤试件开展检测试验研究。采用多种特征提取算法（双路正交解调算法、互相关匹配滤波算法及主成分分析算法）对热辐射响应信号（热波信号）进行数据分析与特征提取，实现了C/GFRP试件冲击损伤脱粘区域的有效识别，得到了不同冲击能量与脉冲雷达热波特征的映射关系。针对C/GFRP平顶孔模拟脱黏缺陷开展红外脉冲雷达热波成像检测试验研究，验证了红外脉冲雷达热波成像检测技术的探测能力。试验结果表明，红外脉冲雷达热波成像检测技术可以实现对C/GFRP低速冲击损伤的有效检测。     

复合材料胶接损伤的指数监测方法

为了监测复合材料胶接损伤,基于主动Lamb波和时频分析,提出了一种复合材料损伤监测的指数法。通过对Lamb波信号进行时频分析,提取波形包络。通过计算得到损伤散射信号,选取对损伤敏感的直达波波包,将此波包在结构出现损伤后的能量变化值与损伤前的能量之比作为损伤指示。该方法不用选择特定的Lamb波模式,解决了Lamb波在复合材料结构中存在的频散、多模式及模式转换给信号分析带来的困难。同时在复合材料胶接的损伤演化试验中,对该方法进行了应用验证研究。结果表明:该方法可以用于复合材料胶接损伤的定性和定量分析。     

航拍高光谱图像中基于投影的自动目标检测算法

针对未知环境条件下的高光谱图像目标检测问题进行了研究，提出了一种基于投影的自动目标检测算法。该算法通过构造正交投影算子预先对部分干扰物信息进行削弱，再以无监督的自动目标搜寻方法找到场景中可能的目标物，将图像数据向可能目标物所张成的子空间投影以增强目标物的信息，然后用匹配的方法完成检测。有效减弱了干扰物对目标检测的影响，缩小了目标搜索的范围。应用此算法对实验采集数据进行处理，取得了较好的结果。     

频率直方图法在复合材料检测中的应用

飞行器中复合材料结构的无损检测大多采用超声波检测方法。在实际检测过程中，类似碳纤维复合材料这样的特殊材料组织的结构比较复杂，所得到的超声波回波信号经常受到较强的结构噪声的干扰，信噪比较低，影响缺陷信号的识别。利用分离谱技术中最小值法，考虑结构噪声幅度对频率变化的敏感性，应用频率统计直方图法，对窄带信号的采样点进行统计、比较，选择绝对值最小的采样点信号作为输出信号，得到最佳频率检测带，对这些频带采用带通滤波器进行滤波，从而较好地将目标回波和结构噪声区分开，更准确地对复合材料构件讲行无损检测。     

Review of shock wave detection method in CFD post-processing

In the present computational fluid dynamics (CFD) community, post-processing is regarded as a procedure to view parameter distribution, detect characteristic structure and reveal physical mechanism of fluid flow based on computational or experimental results. Field plots by contours, iso-surfaces, streamlines, vectors and others are traditional post-processing techniques. While the shock wave, as one important and critical flow structure in many aerodynamic problems, can hardly be detected or distinguished in a direct way using these traditional methods, due to possible confusions with other similar discontinuous flow structures like slip line, contact discontinuity, etc. Therefore, method for automatic detection of shock wave in post-processing is of great importance for both academic research and engineering applications. In this paper, the current status of methodologies developed for shock wave detection and implementations in post-processing platform are reviewed, as well as discussions on advantages and limitations of the existing methods and proposals for further studies of shock wave detection method. We also develop an advanced post-processing software, with improved shock detection.     

Spatial adaptive subspace detection in OTH radar

The work presented here addresses the problem of target detection against spatially structured interference composed of jamming plus noise, where for practical reasons, the received target wavefront may also deviate from the traditional plane wave model. This detection problem arises in over-the-horizon (OTH) radar systems where spatially distributed targets often compete for detection against directional interference that is spread over the entire range-Doppler search space. Conventional detection processing schemes are compared with a recently proposed adaptive subspace detector (ASD) that takes both the spatial structure of the interference and the possibility of target wavefront distortions into account. Experimental array data recorded by the Jindalee sky-wave and Iluka surface-wave OTH radar systems, located in central and northern Australia respectively, is used to evaluate detection performance.     

基于周期Wigner-Hough变换多相编码连续波雷达信号检测算法

为提高雷达侦察截获接收机对多相编码连续波弱信号截获能力,提出了一种基于周期Wigner-Hough变换（Periodic Wigner-Hough Transform,PWHT）的多相编码连续波信号检测算法。研究了线性调频连续波信号的PWHT及性质;分析了多相编码连续波信号时频主脊线的类似线性调频连续波特征;推导了高斯白噪声在PWHT域的统计分布特征,根据多相编码连续波信号与线性调频连续波的相似性,提出了基于PWHT的多相编码连续波信号检测算法,给出了实现流程,并计算出其检测性能和参数估计性能仿真的仿真结果。仿真结果表明：该算法较已有的其他多相编码信号检测算法有更好的弱信号检测能力,最小可检测信噪比至少可以降低3dB,并随着观测时间延长而进一步降低;其参数估计精度具有渐进最优的性质。     

HF OTHR target detection and estimation subsystem

This paper describes the principle of the target detection and estimation with a high frequency ground wave over-the-horizon radar, introduces the structure and the implementation of the detection and estimation subsystem that can process signals in parallel. The accomplished experimental results demonstrate that this system can successfully detect and estimate the over-the-horizon ship and aircraft     

空间目标的空基红外测量技术

地基红外测量系统由于受大气衰减和天空背景的影响,对空间目标的探测能力有限。针对此问题,提出了采用空基红外测量系统实现空间目标红外特性测量的设想,通过从决定红外测量系统探测能力的信噪比和调制对比度2个方面出发,推导出了红外测量系统作用距离公式。并利用大气传输软件计算了长波红外在不同高度下的大气透过率、天空背景,理论分析给出了不同高度的空基红外测量系统对不同辐射面积空间目标的探测距离。仿真结果表明,当空基平台高度大于10km时,长波红外不仅可以观测到光照区内的低轨空间目标,而且还可以观测到阴影区内辐射面积不小于40m~2的低轨空间目标。     

Rotating machinery fault detection and diagnosis based on deep domain adaptation: A survey

In practical mechanical fault detection and diagnosis, it is difficult and expensive to collect enough large-scale supervised data to train deep networks. Transfer learning can reuse the knowledge obtained from the source task to improve the performance of the target task, which performs well on small data and reduces the demand for high computation power. However, the detection performance is significantly reduced by the direct transfer due to the domain difference. Domain adaptation (DA) can transfer the distribution information from the source domain to the target domain and solve a series of problems caused by the distribution difference of data. In this survey, we review various current DA strategies combined with deep learning (DL) and analyze the principles, advantages, and disadvantages of each method. We also summarize the application of DA combined with DL in the field of fault diagnosis. This paper provides a summary of the research results and proposes future work based on analysis of the key technologies.     

基于改进YOLOv4的航空发动机小目标损伤检测研究

智能化的航空发动机损伤检测是飞机故障诊断重要的研究方向,针对现有目标检测模型对航空发动机的小目标损伤检测效果差的问题,提出了一种改进的基于You Only Look Once version 4(YOLOv4)的多尺度目标检测方法。在路径聚合网络（PANet）中构建低层次的特征融合层,将更浅层的特征与深层特征融合,提高网络对小目标损伤的检测性能。为减少网络中的冗余参数,在颈部结构中引入了深度可分离卷积,将标准卷积重构为深度可分离卷积的形式。实验表明：改进后的YOLOv4对小目标损伤的检测精度提升了3.43%,模型大小降低了54.06 MB,同时检测速度提高了31.03%。研究结果表明改进的YOLOv4模型对小目标损伤具有更好的检测性能。     

Spectral-spatial target detection based on data field modeling for hyperspectral data

Target detection is always an important application in hyperspectral image processing field. In this paper, a spectral-spatial target detection algorithm for hyperspectral data is proposed. The spatial feature and spectral feature were unified based on the data filed theory and extracted by weighted manifold embedding. The novelties of the proposed method lie in two aspects. One is the way in which the spatial features and spectral features were fused as a new feature based on the data field theory, and the other is that local information was introduced to describe the decision boundary and explore the discriminative features for target detection. The extracted features based on data field modeling and manifold embedding techniques were considered for a target detection task. Three standard hyperspectral datasets were considered in the analysis. The effectiveness of the proposed target detection algorithm based on data field theory was proved by the higher detection rates with lower False Alarm Rates (FARs) with respect to those achieved by conventional hyperspectral target detectors.     

Probability of Detecting a Swerling I Targetet on Two Correlated Observations

Modern radars characterized by electronically steered beams, frequency agility, and range-ambiguous waveforms can use a processing technique whereby each new detection is followed by a second dwell to verify the initial detection. The second dwell is used to minimize false alarms and to resolve range and/or Doppler ambiguities. Under the assumption of a Swerling I target model, the target cross section remains constant when both dwells occur on the same scan and the same transmission frequency is used. Analytic expressions have been developed for the probability of detecting a Swerling I target on both of the correlated dwells (same target cross section). These expressions are used to calculate the probability of a second dwell detection given a first dwell detection and the probability of at least one detection on two dwells. These probabilities are compared with those of independent dwells (independent target cross sections) which result when two transmission frequencies of sufficient separation are utilized.