高分辨率合成孔径雷达图像的Gamma分布下最大后验概率降斑算法

针对传统的Gamma分布下最大后验概率降斑算法不能有效保留均匀区域的点目标, 不能有效保留弱边缘以及不能有效滤除强边缘区域的斑点等问题, 提出了基于第二类统计量的先验参数估计的高分辨率合成孔径雷达图像Gamma 分布下最大后验概率降斑算法. 使用Mellin卷积和斑点的乘性模型, Gamma先验分布的参数可由观察图像的前两阶对数累积量精确估计.所提算法具有解析的滤波输出, 便于实现.农田和城区的高分辨率合成孔径雷达图像的降斑实验表明, 与传统的Gamma分布下最大后验概率降斑算法相比, 所提算法既能有效保留均匀区域的点目标, 又能有效保留弱边缘, 还能有效滤除强边缘区域的斑点. 关键词： 高分辨率合成孔径雷达图像 Gamma分布下最大后验概率降斑算法 第二类统计量 对数累积量     

Improvement of ultrasound speckle image velocimetry using image enhancement techniques

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.     

Application of improved Speckle contouring technique to surface roughness measurements

One of the well known drawbacks in Electronic Speckle Pattern Interferometry (ESPI) is the poor fringe density due to electronic and speckle noise and decreasing fringe visibility with increasing speckle decorrelation. As recently reported we suggested improving the fringe density and enlarging the measurement range by the incremental addition of phase images. The technique has already been successfully applied to in-plane and out-of-plane displacement field measurements of carbon-fibre reinforced composites. This paper demonstrates how the technique can be used to improve the sensitivity and to extend the measurement range for speckle contouring applications. The angular correlation of the speckle phase images is used to get the desired 3D information of the investigated object surface. It is demonstrated how the angular speckle contouring techinque can easily be automated with respect, for example, to possible industrial applications. Roughness measurements are carried out on milled Rugo test surfaces. All measurements are performed without the usual vibration isolation, and of course, without the treatment of the surface with fine, white powder for contrast enhancement, which would falsify the results.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Optical method for determining the hardness of metals and alloys

We present an optical method for determining the hardness of metals, based on the correlation between the thermal diffusion coefficient and the hardness of the material. Spatial and temporal modulation localized in the nonstationary thermal wave profiles is transferred to the surface of the metal, where the time evolution of the speckle images produced by a probing laser beam is recorded by a CCD camera. A special algorithm for processing the speckle images allows us to determine the thermal diffusion coefficient. Experimental studies on steel samples confirmed the workability of the proposed method. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 460–465, May–June, 2009.     

Reconstruction of 3D ultrasound images based on Cyclic Regularized Savitzky-Golay filters

This paper presents a new three-dimensional (3D) ultrasound reconstruction algorithm for generation of 3D images from a series of two-dimensional (2D) B-scans acquired in the mechanical linear scanning framework. Unlike most existing 3D ultrasound reconstruction algorithms, which have been developed and evaluated in the freehand scanning framework, the new algorithm has been designed to capitalize the regularity pattern of the mechanical linear scanning, where all the B-scan slices are precisely parallel and evenly spaced. The new reconstruction algorithm, referred to as the Cyclic Regularized Savitzky-Golay (CRSG) filter, is a new variant of the Savitzky-Golay (SG) smoothing filter. The CRSG filter has been improved upon the original SG filter in two respects: First, the cyclic indicator function has been incorporated into the least square cost function to enable the CRSG filter to approximate nonuniformly spaced data of the unobserved image intensities contained in unfilled voxels and reduce speckle noise of the observed image intensities contained in filled voxels. Second, the regularization function has been augmented to the least squares cost function as a mechanism to balance between the degree of speckle reduction and the degree of detail preservation. The CRSG filter has been evaluated and compared with the Voxel Nearest-Neighbor (VNN) interpolation post-processed by the Adaptive Speckle Reduction (ASR) filter, the VNN interpolation post-processed by the Adaptive Weighted Median (AWM) filter, the Distance-Weighted (DW) interpolation, and the Adaptive Distance-Weighted (ADW) interpolation, on reconstructing a synthetic 3D spherical image and a clinical 3D carotid artery bifurcation in the mechanical linear scanning framework. This preliminary evaluation indicates that the CRSG filter is more effective in both speckle reduction and geometric reconstruction of 3D ultrasound images than the other methods.     

Comparative analysis of the resolving power of optoelectronic imaging systems upon incoherent and coherent illumination of objects

Results of calculations of the resolving power (according to Foucault) of optoelectronic imaging systems with incoherent and coherent illumination under the conditions of atmospheric phase distortions are presented. It is suggested that incoherent optical images are formed in the case of incoherent illumination and speckle images are formed in the case of coherent illumination. The shape of objects observed is estimated from these images. The resolving powers are shown to be practically the same in the formation of incoherent optical images and speckle images in the case of strong phase distortions and smoothing of images by a matrix photodetector. At the same time, the limiting resolving power in the formation of incoherent optical images is twice as large as in the formation of speckle images.     

Speckle reduction by selective spatial-domain mask in digital holography

An improved method of using a selective spatial-domain mask to reduce speckle noise in digital holography is proposed.The sub-holograms are obtained from the original hologram filtered by the binary masks including a shifting aperture for being reconstructed. Normally, the speckle patterns of these sub-reconstructed images are different. The speckle intensity of the final reconstructed image is suppressed by averaging the favorable sub-reconstructed images which are selected based on the most optimal pixel intensity sub-range in the sub-holograms. Compared with the conventional spatial-domain mask method, the proposed method not only reduces the speckle noise more effectively with fewer sub-reconstructed images,but also reduces the redundant information used in the reconstruction process.     

水下高斯界面背向散射超声散斑场的相位奇异

为了精确描述超声散斑场的特性,提出了采用计算机模拟产生超声散斑场的方法.利用模拟产生的高斯相关随机表面,获得了这类表面远场超声散斑场,同时得到了声强分布和相位分布.与实验产生的散斑场进行对比,建立了超声散斑场接收的实验系统,取与计算模拟相同的参数,获得了实验散斑场.通过对比发现:计算机模拟产生的超声散斑场相位存在奇异点,奇异点周围相位分布类似漩涡,计算机模拟产生的散斑场与实验得到的散斑场强度分布相似,强度值比实验产生的散斑场强度大,携带有用信息的高亮散斑较多,暗点较少,更利于研究和分析.     

Application of laser speckle analysis for the assessment of cementitious surfaces subjected to laser cleaning

This paper focuses on the application of laser speckle technique for the assessment of the effectiveness of laser cleaning of cementitious surfaces. Laser speckle-based methods are non-contact, highly resolving techniques for the measurement of displacement, rotation, and strain of an illuminated area on a rough surface. Since the intensity of reflected light depends on the geometrical microstructure and colour of the samples, any alterations of the surface result in different speckle images. Analysis of speckle images presented here is based on the analysis of the distribution of intensity of reflected light obtained in a selected plane, and analysis of statistical parameters describing such distribution (skewness and kurtosis). A wide range of laser-cleaned mortar samples with different geometrical microstructure and moisture content has been subjected to the assessment by He-Ne laser. Laser speckle method has been successfully used to identify the effectiveness of the laser cleaning process with respect to different surface conditions. It appears that the changes in kurtosis and skewness should be mainly associated with the alterations of geometrical microstructure. Whereas, mean light intensity seemed to depend predominantly on the mortar's absorption characteristics (colour).     

Use of a joint transform correlator architecture for study of speckle displacements

The optical speckle–displacement correlation technique (OSDCT) is proposed for study of in-plane speckle displacements. The joint transform correlator architecture is used to evaluate the displacements of speckle subimages of strained surfaces. The procedure of the correlation response producing as a result of cross-correlation of strainless and strained surfaces in a conventional joint transform correlator (JTC) is considered. The convenient techniques for a joint power spectrum transformation are selected. The systematic and random errors of a mean speckle pattern displacement of a rigid body motion calculated by using the OSDCT and the digital speckle–displacement measurement technique are compared. The robustness of some JTC versions (a conventional JTC, a JTC with median thresholding, a JTC with subset median thresholding, and a fringe adjusted filter JTC) to input noise of speckle patterns and output noise of a correlation response is studied.     

利用散斑图像测量表面粗糙度的计算机模拟及实验

从菲涅耳-基尔霍夫衍射公式出发推导出了粗糙面近场衍射方程。通过对观察面散斑光强统计特性的分析,提出了采用镜射光强分量法测量表面粗糙度的思想。为验证该方法的有效性,首先用计算机模拟产生具有不同统计特性的随机表面,然后对由随机表面产生的散斑场及其光强分布进行计算。计算结果表明,与传统的散斑对比度法相比,散斑镜射光强分量法测量弱粗糙表面粗糙度具有更大的适用范围和更高的测量精度,克服了散斑对比度法易受表面横向相关长度影响的缺点。通过实验对计算机模拟结果进行了验证。     

基于灰度共生矩阵的表面粗糙度研究

介绍了激光散斑的形成及其统计性质,拍摄大量不同加工工艺、不同表面粗糙度标准样块的散斑图像,基于激光散斑图像的灰度共生矩阵及惯性矩、角二阶矩、熵、相关性4个参量,对图像进行了纹理分析.分别绘制了不同加工工艺、不同表面粗糙度标准样块的4个参量与表面粗糙度关系的特性曲线.最后将实验结果和未知表面粗糙度工件的实验数据进行比对,准确估算出了工件的表面粗糙度.     

时间分幅型二维光子计数斑点像探测系统

在简要叙述了云南天文台斑点相机研制的改进的概况之后, 介绍了对新型斑点相机YOSC-4 时间分幅型二维光子计数斑点像探测系统的研制情况及该系统的性能。试验和分析表明: 当进行天文斑点成像观测时, 该系统极限星等达到12m ; 随后给出了一些实际的斑点图观测资料和像复原结果     

基于激光散斑成像的零件表面粗糙度建模

表面粗糙度是衡量机械表面加工水平的重要参数. 通过构建一套激光散斑成像采集系统, 获取了不同表面加工类型和不同粗糙度值的零件表面激光散斑图像. 应用Tamura纹理特征理论提取图像的纹理粗糙度、对比度、方向度特征, 并分析了这三个特征与表面粗糙度的关系. 发现了纹理粗糙度特征与表面粗糙度的单调关系, 推导出平磨、外磨、研磨三种表面加工工艺的粗糙度值与图像纹理粗糙度特征的数学函数关系, 实现了表面粗糙度的测量. 同时, 利用Tamura纹理特征与加工工艺的依赖关系, 建立了基于贝叶斯网络的工艺识别推理模型, 推理出了零件表面加工工艺. 通过为多种加工类型表面建立粗糙度测量模型, 为粗糙度测量提供了新思路. 实验证明所提的粗糙度测量模型能以较高的准确率识别出零件表面加工类型并测量出其表面粗糙度值.     

Temporal difference method for processing dynamic speckle patterns

A temporal difference method for processing dynamic speckle images is proposed. In the method two speckle images of an object, separated by a time interval, are subtracted one from the other to detect whether the speckle structure has changed or not. The rationale of the method is discussed. A variant of the method that allows measuring the area of an activity zone surrounded by a static region is tested in digital simulations. As a demonstrative experiment, that variant is employed to characterize the drying of a damp patch in filter paper.     

高斯相关随机表面及其光散射散斑场的模拟产生和光强概率分析

提出了模拟产生高斯相关随机表面的方法,并模拟产生了这类表面在夫琅禾费面上产生的散斑场.以模拟产生的10000个随机表面作为表面样本系综,对具有不同粗糙度和横向相关长度的表面系综在夫琅禾费面上各点产生的散斑光强系综的概率密度分布进行了分析.发现：(1)散斑场的高斯和非高斯特性在空间上按一定的区域分布,并非整幅散斑图皆为高斯或非高斯散斑;(2)散射表面只包含少数散射颗粒时也可以形成高斯散斑. 关键词：     

Using Speckle Interferometry for Controlling the Units of Multi‐Mirror

Applications of speckle interferometry for measuring displacements of mirrors of multi‐mirror centimeter radiotelescopes are considered and analyzed in modeling experiments. The general principles of speckle photography, speckle interferometry, and the use of two-exposure speckle patterns for the analysis of displacements of rough surfaces (units of the radiotelescope mirrors) are worked out. Experiments are carried out for three possible displacements of the object surface: parallel shifts along the surface itself, rotations, and shifts in the perpendicular direction. The shape and structure of the displaced units do not change. The experiments prove that speckle interferometry is a rather effective and practical tool for measuring shifts and rotations of composite radiotelescope mirrors.     

环形压气机叶栅内部分离流结构分析 第一部分:近壁区分离流

1前言随着对叶轮机械研究的深入,叶轮机械内部的真实复杂流动已成为重要的研究课题。认识扩压叶栅内的流动分离和旋涡的发生、发展及相互作用,对于揭示压气机内部流动机制,改善流动结构,提高其喘振裕度,以及发展喘振控制技术都具有重要意义山。尽管人们已进行了许多研究,但尚未完整充分地认识这一复杂现象的物理现象和物理模型。对处在严重流动分离状态下的环形叶栅内部流动的研究就更为少见。本文应用油膜法显示了从约零度到二十几度多个来流攻角下,一大展弦比叶片低稠度环形压气机叶棚的表面流场。进口气流马赫数约为0．1。叶片进…     

Noncircularity of light field scattered by non-Gaussian reliefs

Dependences of the degree of circularity of a scattered electromagnetic field on the type and the structure of a relief are considered. It is shown that, for strongly rough non-Gaussian surfaces, the degree of circularity of the field is smaller than that for the normal surface, and that the speckle contrast for bimodal surfaces can achieve values greater than unity. Errors that arise upon calculating the contrast and shape of the speckle intensity distribution density are analyzed without taking into account the noncircularity of the scattered field.