旋转粗糙目标动态散斑统计特性研究

针对旋转目标视线角和角速度的特征识别问题,基于激光散射理论,分析了可见光波段激光中旋转对称目标动态特性,设计了多姿态旋转运动目标的时序散斑测量光路.研究结果表明:采用多幅图相关函数计算方法对时序图进行处理,得到了不同视线角和角速度的动态散斑归一化时间相关函数曲线.给出了目标范围为0.5r/min~6r/min角速度,范围为20°~90°视线角与时间统计特性的关系.     

Statistical property of dynamic speckles produced by a rotating cylinder object

高斯光束照射以固定角速度旋转的粗糙圆柱体表面,反射空间形成随着被测表面运动变化的动态散斑.研究了照射面积大于圆柱曲面条件下在远场衍射区形成的动态散斑统计特性,得到了不同入射条件及不同圆柱时动态散斑强度起伏空间-时间归一化相关函数.结果表明:随着圆柱半径、旋转速度以及照射光斑有效面积的增大,动态散斑强度起伏相关性快速减小;当圆柱旋转速度恒定,动态散斑光强起伏相关函数的峰值随着探测点之间距离的增大而减小,但峰值的位置随之而增大;在近似点照射情况下随着圆柱半径的增大空间相关长度基本不变,而相关时间性明显增大.     

旋转圆柱目标的动态散斑统计特性(英)

高斯光束照射以固定角速度旋转的粗糙圆柱体表面,反射空间形成随着被测表面运动变化的动态散斑。研究了照射面积大于圆柱曲面条件下在远场衍射区形成的动态散斑统计特性,得到了不同入射条件及不同圆柱时动态散斑强度起伏空间-时间归一化相关函数。结果表明:随着圆柱半径、旋转速度以及照射光斑有效面积的增大,动态散斑强度起伏相关性快速减小;当圆柱旋转速度恒定,动态散斑光强起伏相关函数的峰值随着探测点之间距离的增大而减小,但峰值的位置随之而增大;在近似点照射情况下随着圆柱半径的增大空间相关长度基本不变,而相关时间性明显增大。     

经成像系统二次调制的动态散斑的空时相关性质

高斯光束经位于成像系统共轭面的两个散射体(其中一个是恒速运动)后,在距像面为菲涅尔区的观测面上形成了串级动态散斑场.理论分析和实验测量结果均表明,这种动态散斑的空-时相关函数与一次散射形成的动态散斑相比,对散射体的运动十分敏感,但其时间相关长度与速度的倒数仍然保持线性关系.     

菲涅耳衍射区和夫琅和费衍射区的动态部分相干光散斑场特性

研究了菲涅耳衍射区和夫琅和费衍射区动态部分相干光散斑的特性.利用部分相干光互强度传播的理论，得出了在部分相干光照明时，由运动散射体产生的动态散斑光强时空交叉的自相关函数的一般形式，并由此得出了散斑沸腾和平移的一般规律.通过适当选择光源和调整光路参数，在实验上得到了菲涅耳和夫琅和费衍射区的部分相干光散斑，对夫琅和费面上的动态部分相干光散斑的平移和沸腾现象进行了定性研究；采用光子计数及数据自动采集的方法，对部分相干光散斑随时间的演化及动态部分相干光散斑的沸腾进行了定量测量.这些实验结果与理论结果相符合. 关键词： 部分相干光动态散斑 时空交叉相关函数 沸腾     

运动界面上反射超声散斑空间运动的研究

在Kirchhoff 衍射理论的基础上，应用随机信号相关原理，推导了作刚体运动的界面上反射超声散斑在空间运动时，保持其复振幅相关的必要条件.由此得到超声散斑的空间运动公式.界面、超声散斑和超声接收探头之间的相对运动，导致界面孔径的改变.分析表明，在保持界面孔径相关的条件下，界面所允许的最大平移量和转角值，与声源位置、接收用聚焦探头的数值孔径、超声入射角以及观察角有关.应用数字相关技术和三维扫描信号采集系统，根据散斑场子集相关系数的单峰性质，对超声散斑空间运动公式进行了实验验证.实验结果表明，理论分析所得的 关键词： 超声散斑 相关原理 空间运动     

基于动态散斑时频特性的合作目标微动参数反演

基于激光动态散斑的时频信号,建立了一套适用于角反射器阵列的微动参数反演算法。首先利用物理光学方法推导了角反射器及角反射器阵列激光散斑的实时强度公式,然后基于短时傅里叶变换研究了散斑功率谱形成机制及其数字特征,最后提出了频谱相关法及时频-相幅变换算法,并采用该方法提取了动态散斑时频谱线周期及振幅分布,反演了三种典型运动状态下目标的自旋周期及旋转轴指向。结果表明:基于几个周期的散斑强度序列,所提反演算法可以得到高精度的旋转周期及视线角,但对旋转轴方位角的反演精度相对较差,需要更多的观测数据才能得到满意的结果。     

测量平板玻璃折射率实验中激光散斑削减方法的探究

本文描述了以激光为光源测量平板玻璃折射率实验中成像场产生散斑的现象,并获得了一种简单有效的散斑削减方法.理论上激光经过漫散体后产生微光束干涉场,利用统计学的规律,总结出了散斑元之间对比度的影响因素.实验中,选取动-静毛玻璃对作为削减器件,利用静止漫散体增加入射光的粗糙程度,通过缓慢旋转的运动漫散体,可将散斑对比度降为4%左右,使干涉条纹清晰可见.     

双散射光合成场动态散斑的统计性质

本文研究了在两束高斯光束照明条件下,由旋转散射体产生的双散射光合成的远场动态散斑的统计性质.这种动态散斑的统计性质由它的强度涨落的空-时相关函数描述.文中推导了这个函数的解析表达式,并采用了光子计算及光子相关技术,从实验上证实了这个表达式的正确性.     

纵向运动双散射散斑场的动态特性研究

研究了慢纵向运动双散射散斑场的统计性质,得出纵向运动双散射散斑振幅自相关函数、强度涨落自相关函数,并由此得出,夫朗和费衍射区内的接收平在上任意点上的自相关函数是时间的非平稳随机过程,而在光轴附近小区域内,强度涨落自相关函数是时间的平稳随机过程,相关时间与散射体纵向运动速度或反比,理论和实验结果相一致。     

Experimental study of the angular correlation function in the double passage of waves through a one-dimensional random phase screen

Abstract

Experimental results are presented for the angular correlation function of far-field speckle patterns scattered in the double passage of waves through a one-dimensional random phase screen. The experiment for the correlation measurement was set up to use a CCD camera to obtain the image of the speckle patterns in the scattering directions for each given angle of incidence; the cross-correlation function is then calculated from the digitized images. The theoretical analysis of the motion of the speckle as the source is moved, as given by Escamilla, is verified experimentally. It is found that in contrast with the memory effect line of speckle motion, the speckle pattern produced in the region of observation tracks the backscattering direction.     

Angular correlation function of wave scattering by a random rough surface and discrete scatterers and its application in the detection of a buried object

Abstract

The scattering of waves by a buried object is often obscured by the clutter around it. Such clutter can be attributed to the scattering by random rough surfaces and random discrete scatterers. Recent studies show that, because of the memory effect, the angular correlation function can suppress the effects of clutter and make the scattering by the buried object more conspicuous. In this paper, we study the angular correlation function of wave scattering by a buried object underneath a layer of random discrete scatterers and a non-Gaussian random rough surface. Such problems are common when the target is buried below a rough surface that is underneath a layer of vegetation. Numerical results are illustrated for various parameters of rough surfaces and discrete scatterers. The angular correlation function is calculated by frequency and angular averaging. It is shown that the use of the angular correlation function can enhance target detection in the presence of clutter.     

Detection of a small defect on a rough surface

We report experimental results that show that the far-field correlation function is sensitive to a small local change in rough-surface geometry, where the speckle spatial correlation rather than the sample ensemble average is adopted. The angular cross-correlation function of the far-field speckles scattered by one-dimensional random rough surfaces is measured when a polarized beam of light is incident upon the rough surface from vacuum, where one part of the surface used is a thin dielectric film deposited upon a glass substrate and the other part is identical to the first except for a localized defect. We envisage application of this sensitivity property to inspection of a sample with a defect by means of speckle mapping.     

利用散斑空一时相关性测散射体的慢运动

本文研究了利用远场动态散斑的空-时相关性测量散射体运动速度矢量的理论和实验技术.作者在推导出远场动态散斑空-时相关函数的基础上,提出并建立了一种新的微机辅助检测系统.利用它从实验上证明了在单高斯光照明、散射体平动情况下运场动态散斑的空-时相关性,以及空-时相关的差分与运动速度之间的线性关系.通过测量动态散斑的空-时相关性获取散射体的运动速度矢量.实验结果与理论分析吻合.     

透过散射介质对直线运动目标的全光成像及追踪技术

光散射是限制光传输以及降低和破坏光学成像性能的主要因素,透过复杂散射介质对运动目标的全光成像是光学领域极具挑战性的技术之一.本文提出一种利用散斑差值自相关透过散射介质对运动目标进行实时追踪的方法.采用赝热光照明,基于光学记忆效应理论,通过对运动目标采集的两帧散斑做差值,然后做自相关运算,计算目标移动的距离,实现对目标的实时追踪,并且利用相位恢复算法进行简单处理就可以重建隐藏目标.对该方法进行了实验验证,成功地对隐藏的运动目标实现了成像与追踪.这种透过散射介质对运动目标的全光成像及实时追踪技术,在生物医学等领域具有重要应用潜力.     

The autocorrelation of speckles in deep Fresnel diffraction region and characterizations of random self-affine fractal surfaces

This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e. the roughness w, the lateral correlation length ξ and the roughness exponent α, from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with α= 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.     

Speckle interferometry and Doppler diagnostics of microflows of scattering liquids

A relation for the correlation function of intensity fluctuations of the speckle field formed upon scattering of focused light radiation in blood flows in microvessels is obtained. The width of the intensity-fluctuation spectrum is shown to depend not only on the velocity of the flow, but also on its scattering characteristics. Simulation of the processes of scattering of light beams in random flows is performed by the Monte Carlo method. The expression for the first spectral moment of the Doppler signal is derived both on the basis of the theory of radiative-energy transfer and within the framework of the speckle-interference approach; comparison of the obtained results is carried out.