Acoustic detection of invisible damage in aircraft composite panels

The wing and body panels of modern commercial and military aircraft often consist of a three-layer structure in which two thin skins of fibre-reinforced composite or of aluminium are held apart by a much thicker core consisting of a honeycomb structure made from either folded paper-like material impregnated with aramid resin or from thin, folded aluminium sheet. A major maintenance inspection problem arises from the fact that impact by a heavy soft object has the potential to deflect the skin and damage the core, after which the skin can return to its original shape so that the defect is nearly invisible. This paper gives details of an acoustic inspection system that can reveal such damage and provide information on its nature and size using a hand-held “pitch-catch” device that can be scanned over the suspected area to produce a visual display on a computer screen. The whole system operates in the frequency range 10-30 kHz and embedded programs provide optimal examination procedures.     

Superresolved imaging of remote moving targets

We present a superresolving approach that allows one to exceed the diffraction limit and recover highly resolved contours of moving targets from a sequence of low-resolution images. The presented approach is suitable for remote sensing applications. The resolution decoding algorithm that is used to recover the high-resolution features of the target can be run partially via optical means and that way can be used to reduce the required computational complexity.     

Acoustic sounding of wind velocity profiles in a stratified moving atmosphere.

The paper deals with analytical and numerical studies of the effects of atmospheric stratification on acoustic remote sensing of wind velocity profiles by sodars. Both bistatic and monostatic schemes are considered. Formulas for the Doppler shift of an acoustic echo signal scattered by atmospheric turbulence advected with the mean wind in a stratified moving atmosphere are derived. Numerical studies of these formulas show that errors in retrieving wind velocity can be of the order of 1 m/s if atmospheric stratification is ignored. Formulas for the height at which wind velocity is retrieved are also derived. Approaches are proposed which allow one to take into account the effects of atmospheric stratification when restoring the wind velocity profile from measured values of the Doppler shift and the time interval of acoustic impulse propagation from a sodar to the scattering volume and back to the ground.     

多特征级联式检测变轮廓运动目标

总结了变轮廓运动目标的特点,并将其应用到方向盘上操作手数的检测中。提出了先进行方向盘自动定位,再快速检测其上操作手数目的技术路线。预定位中运用Haar特征的AdaBoost分类器进行初检,得到包含目标轮廓的图像。利用HOG特征的Real-AdaBoost分类器进行精确检测,并确定操作手位置点集。对取得的操作手质心点坐标集进行奇异值分解并拟合椭圆,获取图像中方向盘位置,最终实现操作手的快速准确检测。算法在保证了原算法的实时性和准确性外,提高了检测系统应用的灵活性。     

Acoustic images of objects moving under an inhomogeneous layer

The possibilities and limitations of the methods of obtaining acoustic images of objects moving under an inhomogeneous scattering layer are considered. It is shown that the previously proposed algorithms of signal processing that select a random phase modulation from the received field make it possible to reconstruct the images of extended objects observed through an inhomogeneous medium in the presence of strong stationary reflectors. The proposed methods are compared with the Zverev's method of an inverse aperture synthesis in a dark field.     

远距离动目标实时测试系统设计

 设计的动目标实时测试系统,主要用于检查武器系统在“零飞”工作方式下的系统联动精度,测试被测系统的跟踪瞄准误差。在对远距离、动目标的监测中,采用双光路设计,长焦距、短焦双筒结构,电切换方式等实现对远、近目标的实时观测, 双光筒安装在同一机体上,通过偏心镜框、偏心圈等保证两者的同轴度要求,夹具具有俯仰、方位的微调机构,方便在校炮时光轴与炮轴线一致性调节,并可实现数据的高精度、高保真测量。对焦距为50 mm和300 mm的镜筒静态测角精度进行了测试。实测结果表明：系统测角精度分别小于0.4 mrad和0.2 mrad,完全满足指标要求。该测试系统采用模块化设计,满足可靠性与通用性要求,可广泛应用于军事和民用等诸多领域。     

Hybrid multi-resolution detection of moving targets in infrared imagery

A hybrid moving target detection approach in multi-resolution framework for thermal infrared imagery is presented. Background subtraction and optical flow methods are widely used to detect moving targets. However, each method has some pros and cons which limits the performance. Conventional background subtraction is affected by dynamic noise and partial extraction of targets. Fast independent component analysis based background subtraction is efficient for target detection in infrared image sequences; however the noise increases for small targets. Well known motion detection method is optical flow. Still the method produces partial detection for low textured images and also computationally expensive due to gradient calculation for each pixel location. The synergistic approach of conventional background subtraction, fast independent component analysis and optical flow methods at different resolutions provide promising detection of targets with reduced time complexity. The dynamic background noise is compensated by the background update. The methodology is validated with benchmark infrared image datasets as well as experimentally generated infrared image sequences of moving targets in the field under various conditions of varying illumination, ambience temperature and the distance of the target from the sensor location. The significant value of F-measure validates the efficiency of the proposed methodology with high confidence of detection and low false alarms.     

一种水下运动目标被动报警的新算法

根据矢量水听器的测向原理和算法，提出了一种目标方位角的变化实现水下运动目标低频高精度的报警方法。该报警系统以水下设施为平台，对靠近设施的运动目标的方位进行跟踪测量，并在目标距离水下设施最近时给出报警信号，以达到有效地避免事故的目的。与传统的利用声级变化报警或主动回波测距报警方法相比，该方法具有低频、作用距离远和高精度的特点。     

红外序列图像弱小动目标检测的研究

针对云天背景下的红外运动弱小目标,提出了一种融合检测的方法。根据视觉的固视微动特性进行单帧图像的目标增强,利用帧差分方法检测多帧图像的动目标,最后将这两种处理结果进行基于调制的融合,并经过图像分割,从而达到动目标检测的目的。仿真结果表明该检测方法能够有效地实现复杂背景下的弱小动目标检测。     

星空背景下的运动点目标轨迹提取

针对星空图像中运动点目标轨迹难于提取的问题,提出了有限帧最小二乘轨迹关联算法。采用相邻帧差分、自适应阈值分割、连通域处理和质心计算等步骤实现了疑似目标的定位。根据星点目标运动轨迹近似为直线、运动的连续性和相关性等特点,利用有限帧最小二乘线性拟合预测目标位置,以预测位置为中心开搜索窗,关联匹配真实目标,并通过置信度检验确认并提取目标运动轨迹。整套算法简单,易于实现,通过实拍星图实验,验证了该算法效果好,实时性强。     

提高近程运动目标实时测距性能的方法研究

为了提高机场泊位引导系统中激光测距的精度和频率,对测距方法、脉冲展宽的影响、系统接收信噪比、接收带宽、阈值设定方法等几个方面进行了研究。通过改进自触发脉冲飞行时间激光测距法,提高发射信号峰值功率,采用合适滤波器、减小接收系统带宽、设置自适应阈值等手段有效提高了测距系统对近程运动目标的测距性能。采用半实物仿真手段进行动态测距实验,结果表明,测距机的动态测量精度小于2cm,满足泊位系统测距性能的要求。     

基于追踪补偿的运动物体计算关联成像方法

计算关联成像是利用成像物体的反射或透射信号与结构化的参考光进行多次关联成像,具有了灵敏度高、抗干扰能力强等优点。当物体和计算关联成像系统存在相对运动时,在成像过程中物体的反射或透射信号与参考光的光场涨落失去关联性,进而会产生运动模糊。从二阶关联函数的角度推导了运动成像导致模糊的原因以及追踪补偿原理;恢复计算关联成像系统中参考光和桶探测器收集的光强值的关联性,实现了计算关联成像中的追踪补偿策略;计算机仿真解释了计算关联成像光路中对物体平移干扰进行补偿的策略,证实了该追踪补偿方法对运动物体成像的有效性,克服了物体与成像系统之间的相对运动引起的成像质量下降。方法为关联成像对运动物体的识别、跟踪、遥感和实时在线成像提供了技术手段。     

高速运动目标的自适应线谱增强算法研究

本文研究了低信噪比、目标高速运动情况下,多普勒频移较大时针对线谱信号的自适应增强算法。对海试数据的分析表明,常规自适应线谱增强算法对多普勒频移下的线谱增强效果明显,但要求信噪比较高,且实时性较差;基于高阶累积量对角切片的自适应线谱增强算法对非线性高斯色噪声下的线谱增强效果显著,但对低信噪比环境下变化线谱的跟踪性能较差;频域批处理自适应线谱增强算法对低信噪比下的线谱信号具有很好的增强效果,降低了运算量。     

掩埋目标声散射特性及其实验

基于变分原理建立2D-FE弱形式解模型,针对轴对称掩埋目标进行散射远场的快速、高精度数值计算。入射波垂直于对称轴,给出:掩埋深度不变,以1°为间隔,改变掠射角所得到目标散射声压级相对于垂直海底照射获得结果的差值随频率、掠射角变化的表达式;掠射角不变,以0.1m为间隔,改变掩埋深度得到的散射声压级相对于浅掩埋条件下获得结果的差值随频率、深度变化的表达式。实验结果表明:在回波最强的正横方向,掩埋弹性目标表现出的共振散射特性与在自由场空间中具有相似性,表明了掩埋条件下目标内填充的透射和表面环绕波理论的适用性,验证了大掠射角入射得到散射声压级差值的变化规律。研究成果对宽带、高频入射声波探测更深掩埋目标提供思路。     

基于粒子滤波的运动目标光电定位仿真研究

运动目标的光电定位不能像静止目标那样简单做均值滤波,鉴于此,引入粒子滤波算法,它不仅可以应用于线性系统,而且还适用于非线性系统。结合光电定位需求,详细推导了计算公式及初值和参数选取公式,对只含测量噪声以及含有测量和运动噪声等的海面运动目标光电无源定位算法进行了仿真计算,验证了算法的有效性,讨论了噪声强度对滤波效果的影响,滤波参数选择对滤波效果的影响,目标运动方式对滤波跟随性的影响,重采样算法对滤波效果的影响等。所得结论为:粒子滤波可用于运动目标光电定位过程,可有效降低定位误差;粒子滤波算法具有较强鲁棒性,适用于噪声较大、目标运动形态变化大等情况。     

利用声辐射模态重构任意目标的散射声场

水下目标散射声场的重构可以作为水下目标散射特性的研究基础。本文主要利用声辐射模态对水下目标进行散射声场重构研究。首先,在借助声传递矩阵给出的任意结构声辐射模态的流体域求解方法基础上,通过理论证明了目标的散射声压与声辐射模态具有函数关系。其次,借助声场分布模态的概念,同时考虑到声场分布模态病态及声压测量易受噪声污染,提出基于声辐射模态的正则化散射声场重构算法。仿真结果表明,波数越低,重构所需声辐射模态阶数越少,在较高波数时仅需总模态数的大约20%即可对声场进行重构。与基于边界元的声场重构算法相比,计算量减小了至少80%,且克服了赫姆霍兹积分方程最小二乘法仅对球壳结构的重构效果较好而不适用于长条形结构重构的缺陷。     

Acoustic radiation of moving dipoles and axial quadrupoles consisting of discrete antiphased monopoles

An acoustic field generated by a moving dipole that consists of two antiphased monopoles and an axial quadrupole represented as a combination of four discrete monopoles with corresponding phases was analyzed. It was revealed that the angular distribution of the pressure amplitude of the distributed source depends on the additional phase incursion between interfering waves due to the anisotropic character of the medium. The angular characteristics of the pressure amplitude of the distributed dipole and quadrupole, which depend on the orientation and velocity of their motion, were mathematically simulated. The results were compared with the conclusions drawn by other researchers.