Atmospheric noise on the bispectrum in optical speckle interferometry     

S. N. Karbelkar  Rajaram Nityananda 《Journal of Astrophysics and Astronomy》1987,8(3):271-274

Based on a simple picture of speckle phenomena in optical interferometry it is shown that the recent signal-to-noise ratio estimate for the so called bispectrum, due to Wirnitzer (1985), does not possess the right limit when photon statistics is unimportant. In this wave-limit, which is true for bright sources, his calculations over-estimate the signal-to-noise ratio for the bispectrum by a factor of the order of the square root of the number of speckles.  相似文献   

ASAR斑点噪声模型验证及噪声滤除效果评价   总被引：3，自引：0，他引：3  

王军战  张友静  鲍艳松 《地球信息科学学报》2008,10(2):183-189

ASAR合成孔径雷达数据因影像中相干斑点噪声的存在,影响了地物信息定量的提取与应用效果。本文结合雷达信号传输理论,推导出适于ASAR多视图像的功率概率分布。并从理论推导和试验两方面证实了ASAR影像符合乘性噪声模型。利用乘性噪声模型的滤波算法,采用不同滤波器和不同大小窗口对ASAR影像的斑点噪声进行了滤除,并用平滑指数、边缘保持指数等因子对滤除结果进行评价,通过对比发现:7×7窗口的Enhanced Lee滤波的效果最好。  相似文献   

A physical and numerical investigation of the failure mechanism of weak rocks surrounding tunnels     

《Computers and Geotechnics》2014

The large-scale construction of railway tunnels in China is hindered by several challenges, including large depths, large tunnel cross-sections, and fragile geological conditions. In this paper, we explored a new physical and numerical simulation method that improves upon the currently used methods to investigate the deformation and failure modes of weak rocks surrounding a tunnel. We also compared the results from physical tests and numerical simulations with the field measurements to demonstrate the effectiveness of the proposed numerical simulation method. In the physical model test, an artificial speckle field was developed by staining quartz sand particles and mixing the particles with barite powder and petroleum jelly in preset proportions. The artificial speckle field was employed in the digital speckle correlation method (DSCM) to monitor the evolution of the strain field on the surface of the plain strain model for tunneling during loading. A secondary strain-softening constitutive model using the numerical modeling code FLAC^3D was developed (degradation constitutive model) by considering the deformation modulus degradation in the numerical simulation. The failure mode of weak rocks surrounding a tunnel in the physical model test was examined using the developed degradation constitutive model. Both the physical and numerical results revealed that the least stable area was the shear wedge along the minimum principal stress, which was confirmed in the damage zone of the surrounding rocks. The results were consistent with previous research findings. The results of the DSCM in the physical model test indicated that the shear wedge in the middle part of the tunnel and the cracks around the arch of the tunnel were induced by shear strain, whereas the collapse of the arch was attributed to a combination of tensile strain and shear strain. A comparison of the physical and numerical simulation results demonstrated that the degradation constitutive model can be used to describe the extent and depth of the excavation damage zone of tunneling. A comparison of the displacements from the numerical simulation and field measurements indicated that the degradation model can be used to capture the displacement of weak rocks surrounding tunnels.  相似文献   

基于特征保持的线性多通道最优求和SAR图像滤波算法     

杨沈斌  李秉柏  申双和  张萍萍 《测绘学报》2006,35(4):364-370

在线性多通道最优求和滤波算法的基础上,提出一种基于特征保持的线性多通道最优求和滤波算法。该方法结合图像局域方差系数和具有恒虚警概率的比值结构检测,对滤波窗口内图像的纹理结构进行检测和判断,有区别地进行滤波去噪。该算法在去除斑点噪声的同时,可减少边缘、线及点目标等纹理信息的损失。  相似文献   

基于序列非线性滤波SAR影像水体自动提取     

窦建方  陈鹰  翁玉坤 《海洋测绘》2008,28(4):69-72

由于合成孔径雷达（SAR）图像中固有斑点噪声的强烈影响，某些对于光学图像有很好效果的目标提取区域分割方法，但是对于SAR图像来说，效果不很好，针对水体目标的亮度及形状分布特征，不作阈值分割处理，而采用序列非线性滤波处理方法，可以快速有效地实现SAR影像水体目标的自动提取识别。  相似文献   

Infrared speckle interferometry of eleven binaries using a bispectral analysis     

I. I. Balega  Yu. Yu. Balega  K.- H. Hofmann  G. Weigelt 《Astronomy Letters》2001,27(2):95-98

Infrared speckle-masking observations of eleven binary systems with the 6-m Special Astrophysical Observatory telescope are presented. A resolution of 43 mas in J (1.25 µm) and 76 mas in K (2.2 µm) has been achieved in reconstructed images. Accurate magnitude differences, separations, and position angles have been determined for all the resolved binaries. The pair HR 1071 with an abnormally low lithium abundance is considered in more detail.  相似文献   

基于乘积模型的极化SAR滤波   总被引：1，自引：0，他引：1  

邓少平  李平湘  张继贤  黄国满 《武汉大学学报(信息科学版)》2011,36(10):1168-1171

提出了一种基于乘积模型的极化SAR滤波方法。首先基于乘积模型分离纹理信息和极化信息,然后分别独立地进行滤波,最后再合成协方差矩阵。实验表明,本方法有效可行,有较好的极化保持性能。  相似文献   

改进的多视PolSAR非局部均值滤波算法     

陈建宏  赵拥军  黄洁  刘伟  赖涛 《测绘科学技术学报》2014,(5)

像素点间相似性度量是非局部均值滤波算法的关键所在。从信息论角度出发,提出了一种改进的多视Pol SAR非局部均值滤波方法。该算法在综合分析各类矩阵测度基础上,选定Kullback-Leibler距离作为最优相似度量,结合多视极化相干矩阵服从复Wishart分布,给出了极化相干矩阵的KL距离,并在预处理中应用了极化旋转。实验结果表明,改进方法能够在保持边缘细节的同时有效抑制相干斑。  相似文献   

冲击载荷作用下岩石动态断裂试验研究   总被引：2，自引：0，他引：2  

宋义敏  何爱军  王泽军  陈浩哲 《岩土力学》2015,36(4):965-970

以自行研制的可调速落锤冲击试验机进行加载,通过高速相机搭建数据采集系统,采用数字散斑相关方法作为试验的观测方法,开展5组不同预制裂纹长度的花岗岩试件在冲击载荷作用下的动态断裂试验。并对岩石I型裂纹在冲击载荷作用下的位移场演化、裂纹动态断裂的裂尖张开位移、裂纹尖端的扩展历史、动态断裂的应力强度因子进行了定量研究。试验结果表明：对于单一试件而言,在落锤开始与岩石试件的边界接触到试件的预制裂纹开始扩展整个过程中,裂纹尖端的应力强度因子KI呈递增趋势,KII与KI相比,相差1～2个数量级。对于不同预制裂纹试件,在落锤冲击加载作用下,总体表现为一定的预制裂纹长度范围内,随着预制裂纹的长度增加,裂纹尖端应力强度因子呈增加的趋势。  相似文献   

Deformation Field around the Stress Induced Crack Area in Sandstone by the Digital Speckle Correlation Method   总被引：1，自引：0，他引：1  

ZHAO Yonghong  MA Shaopeng 《《地质学报》英文版》2009,83(3):661-672

Abstract: The deformation field around sub-cracks was calculated using the digital speckle correlation method. First, the uni-axial compression tests on sandstone samples containing a pre-fabricated fracture were made. Photomicrographs showing the characteristics of the sub-crack development were taken using a scanning electron microscope (SEM). From these photomicrographs, the real-time images showing the initiation, growth and coalescence of sub-cracks and micro-cracks in the sandstone specimens were obtained and the effects of loading level as well as grain boundaries on the development of cracks were analyzed. Second, the intensity images of the sandstone specimen surface were captured from the observations of the SEM corresponding to different loading levels. Then correlation computation was carried out for the sequential pairs of intensity images to evaluate the displacement components, as well as the strain field. The results show that the deformation varies in different areas separated by sub-cracks during rock damage processes.  相似文献