The measurement of depth motion by speckle photography

We propose three methods for measuring the depth motion (i.e., motion in line-of-sight, not lateral) of bodies with a rough surface by multi-exposure speckle photography. The speckle photographs are processed optically (autocorrelation). The output is a depth-versus-time graph. Two of the three proposed methods have been verified experimentally. The accuracy of the methods can be choosen to be about one wavelength or up to several millimeters.     

Velocity contours by speckle photography

We describe a method of generating velocity contours of an object using speckle photography. The object is illuminated by a series of laser pulses following each other at equal intervals. A speckle record of the object is observed in a spatial filtering setup with a small aperture in the frequency plane. A fringe pattern representing a map of velocity contours is obtained in the output plane.     

Two-dimensional vibrations analysed by speckle photography

Speckle photographs of a laser-illuminated surface vibrating in its own plane give characteristic diffraction spectra. These have been investigated for a surface vibrating sinusoidally along two mutually orthogonal directions with equal amplitudes but differing frequencies. The diffraction patterns obtained are interpreted in terms of the Lissajous figures traced out by each speckle, taking into account the time-of-dwell of a speckle at any point on its trajectory. Results are given for frequency ratios of the two vibrations of 1:1, 2:1, 3:1. 4:1, and for non-integrally related frequencies.     

基于数字散斑照相术测量刚体面内位移

数字散斑照相术通常测量刚体的面内位移。从基本原理着手,研究了基于散斑照相术的两种常用方法,即数字图像相关法和傅里叶变换法。论述了数字图像相关法中的亚像素梯度算法,讨论了如何选择子区的大小,优化测量结果;傅里叶变换法通过对散斑图进行傅里叶变换和数学形态学等一系列操作,获得精确的条纹间距,从而更好地计算面内位移。实验结果表明,傅里叶变换法的测量精度要高于数字图像相关法。     

Holographic interferometry and speckle photography for strain measurement: A comparison

Holographic interferometry and speckle photography are essentially described by the same equations. The sensitivity and the range of displacements at which the methods are applicable are different however. The accuracy of strain measurement, using high resolution opto-electronic evaluation in both cases, is estimated and compared.     

Flow visualization by means of single-exposure speckle photography

A photograph of a flow field is taken under laser illumination. If the exposure is short enough, the velocity distribution in the field will be mapped on the photograph as variations in speckle contrast. These contrast variations can be converted to intensity variations by means of a simple spatial filtering technique, to give a direct picture of the velocity distribution in the flow field. A potential application of this technique to the mapping of retinal blood flow is described.     

Comparative accuracy of holographic interferometry and speckle photography for out-of-plane deformation measurement

Out-of-plane deformation of a surface can be measured either by recording a double exposure hologram, or by taking a double exposure speckle photograph with the camera deliberately de-focused. In the latter case the local surface tilt is measured, and the profile change subsequently obtained by integration. It is shown that errors can arise in speckle photography due to focusing the camera incorrectly, whereas the holographic method is not affected instrumentally. The sensitivity of the speckle method can approach that of holographic interferometry, but without requiring the same interferometric stability of recording apparatus.     

激光散斑摄影术实验

将激光散斑摄影术设计成一个近代物理实验,用于测试位相物体的厚度。这一方法概念新颖、光路设计简便易行,且具有实用价值。在改造和创新近代物理实验方面,这是可取的,本文介绍相关的实验原理、光路设计及其实验内容。     

立体摄影术与数字散斑相关方法相结合用于研究三维变形场

采用立体摄影术与数字图像相关技术相结合的方法测量了三维位移场。首先利用两个CCD摄像机在空间两个不同位置拍摄物体表面在变形前后同一个区域之间的散斑图像;然后利用数字散斑相关技术求解这四幅散斑图像之间的相对位移;最后利用立体摄影的几何转换公式来确定物体表面的三维变形场。给出了该立体摄影测试系统的标定结果以及编织复合材料试件的三维变形测量结果。     

白光数字散斑照像术

本文提出一种新的数字散斑计量术——白光数字散斑照像术.它以两维数字偏心滤波技术实现全场信息的表征,而以数字相关技术实现点信息的表征.文中给出了计量方法、理论分析及实验结果.     

利用散斑照相检测微小位移的实时方法

以CCD作为散斑和杨氏条纹记录设备,以与分屏器相连的电寻址空间光调制器作为滤波器,以计算机作为图像合成、条纹分辨及数据运算处理中心,并同时控制和协调CCD及空间光调制器等设备,实现了利用散斑照相实时、自动测定微小位移的过程.实验结果表明,此种方法获得的测量结果误差较小,具有一定的使用价值.     

Thermoplastic photographic material for vibration measurements by speckle photography

In order to measure vibration amplitudes by speckle photography in quasi real-time, the feasibility of using thermoplastic photographic material for recording a speckle pattern image is studied experimentally to be proved true. An optimum recording condition of the material is also obtained.     

Phase-shifting whole-field speckle photography technique for the measurement of in-plane deformations in real time

A new real-time phase-shifting readout system is developed for quantitative evaluation of full-field correlation fringes obtained by means of Fourier filtering in speckle photography. The proposed method, which uses photorefractive crystals as the recording medium, is capable of mapping the whole-field displacement data from the recorded phase-shifted fringe patterns. Experimental results are presented on a diffuse surface subjected to rotation in its own plane.     

Speckle photography combined with speckle interferometry

By combining speckle interferometry (SI) measurements with speckle photography, the fringe visibility can be kept high despite the presence of a large bulk or rotating motion of the object. This combined technique improves the usability and measuring range of both pulsed and phase-stepped SI-methods. This paper reviews the theory of fringe formation in SI and shows some recent applications of this combined technique.     

Digital speckle photography and speckle tomography in heat transfer studies

The line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Both electronic and photographic methods are employed for specklegram recording. The subsequent specklegram treatment uses the Young's fringes method as well as cross-correlation analysis of small interrogation areas of the recordings. Experimental data for three different heat transfer configurations are obtained and discussed. The first one is natural convection over extended vertical heated plates with forward facing steps, the second is unsteady 3D convective flow around a suddenly heated vertical thin wire, and the third one is a convective plume above a multi-jet flame. Both local and global Nusselt numbers are determined via measuring local surface temperature gradients for these convective flows. The results are compared with Ostrach's theory for a single vertical plate and with the data obtained by Mach–Zehnder interferometry. The 3D temperature fields are reconstructed for axisymmetric convective flows around a suddenly heated vertical wire using quasi-double projection measurement and the Radon inversion. 3D temperature distributions above the combustion zone are reconstructed using multi-projection speckle photography measurements and computerised tomography.     

偏振孔径散斑照相法

本文讨论了偏振片在散斑照相多孔法中的作用,提出了一种新的散斑照相孔径——偏振四孔。     

Some recent advances in electronic speckle photography

Major advances in electronic speckle photography are reviewed. Topics include the correlation properties of laser speckles, the principles and expected accuracy of electronic speckle photography, the effect of the digital recording and evaluation, and some recent applications. These applications involve two techniques for the measurement of 3D deformation fields, measurement of the in-plane strain field components using defocused laser speckle, and measurement of object shape.     

旋转孔径锥镜剪切散斑照相法

本文提出利用旋转孔径和锥镜进行剪切散斑照相,研测动态问题.该法能在一张散斑图上记录下物体动态变形的全过程,在全场滤波时可得到任意时刻的瞬态位移偏导数场.     

Fast transforms for speckle photography fringe analysis

Two image processing techniques for automatic analysis of the Young's fringes diffraction patterns from a double-exposure speckle photograph are described. The techniques involve two-dimensional spectral analysis of the image using the Fast Fourier Transform (FFT) or the Fast Walsh Transform (FWT). The accuracy and reliability of the two techniques are compared as a function of the fringe visibility, and the number of pixels used to represent the image. Walsh analysis is found to offer the same accuracy as Fourier analysis, but in about one third the computation time. The Fourier method is more reliable with fringes of the lowest visibility, however. The ideas presented have relevance to the general problem of detecting and accurately determining the frequency components of a sinusoid in the presence of noise.