二维虚光栅移相莫尔条纹相位提取算法

目前二维干涉图所采用的相位提取算法大多以傅里叶变换法为主,而傅里叶变换法对噪声比较敏感。虚光栅移相莫尔条纹法具有较高的提取精度,而且抗噪性较好。在一维干涉图的基础上,提出了一种适用于二维干涉图相位提取的二维虚光栅移相莫尔条纹法,该方法通过构造一定相移量的二维虚光栅实现相位提取。与傅里叶变换法对比研究的仿真结果表明:对于同一幅二维干涉图,在干涉图不含噪声的情况下,傅里叶变换法与该方法的相对重构误差分别是5.52%和3.46%;在干涉图含噪声的情况下,随着噪声的增加,该方法在抗噪性方面的优势越来越明显。对二维横向剪切干涉仪零位校准装置所采集到的二维干涉图进行处理,实验结果表明,傅里叶变换法和该方法所得到的测量结果均方根值分别为0.0053λ和0.0037λ(λ=632.8 nm)。     

单幅干涉条纹图的高精度波面重建技术

结合莫尔条纹、傅里叶变换和数字相移技术实现了对单幅干涉条纹图的高精度相位计算和波面重建.首先,用计算机生成与被处理干涉条纹频率相近的数字相移条纹图,与实际干涉条纹图叠加得到相移莫尔条纹图;然后,利用傅里叶变换、双频滤波、傅里叶反变换和相移技术得到干涉条纹图的相位数据;最后利用波面拟合技术重构原干涉条纹图对应的波面形状.研究结果表明,该技术不仅消除了干涉仪硬件相移产生的非线性误差和滤波时的频谱移中误差,高精度获得了单幅干涉条纹图对应的波前,而且简化了系统的机械结构.同时,对环境的要求明显降低,特别适用于生产现场的检测.     

干涉光谱重建中的相位误差检测方法对比研究

干涉条纹相位误差检测与校正是傅里叶变换光谱重建中的关键技术之一。本文对同步 法、傅里叶变换法和局部傅里叶变换法三种典型干涉条纹相位误差检测方法的效果进行了对 比研究。仿真及实际数据实验发现上述方法在处理缓变与快变的干涉条纹相位误差及干涉条 纹有噪声时存在很大差异:同步法适宜于处理相位误差缓变的干涉条纹,而傅里叶变换法和 加窗傅里叶变换法适用于处理相位误差快变的情况;傅里叶变换法在高信噪比情况下具有较 好的性能,加窗傅里叶变换法在低信噪比下具有较强的鲁棒性。     

条纹投影动态3维测量中相位高精度估计

为了提高条纹投影动态3-D形貌测量精度, 采用加窗傅里叶分析辅助相移的方法来减小运动导致的相移误差。首先采用加窗傅里叶分析法估计变形条纹间的实际相移量, 然后采用最小二乘法估计出变形条纹的高精度相位分布, 最后由估计的相位计算得到场景3维形貌。理论分析了物体运动对相移量的影响, 通过仿真研究了所提方法的相移量估计精度, 并搭建了实验系统进行验证。结果表明, 实验中采用所提方法的相位恢复精度达到0.1673rad, 比现有方法有明显提高。该方法用来提高条纹投影动态3-D形貌测量中相位精度是有效的。     

一种校正全息干涉计量中非线性相移的新方法

相移技术对实现全息干涉计量中条纹的自动分析有非常重要的作用.在理论分析的基础上,提出用非线性方差法替代傅里叶峰值探测法,即用最小方差替代寻找最小值匹配函数的方法来校正全息干涉计量中PZT装置的非线性相移.实验研究结果表明,采用上述非线性方法校正相移比线性方法校正相移的误差大大降低.     

电子散斑干涉载频调制形貌测量技术

提出了电子散斑干涉(ESPI)载频调制测量物体形貌的方法.在ESPI中,物体表面的微小偏转可引入包含物体高度信息的载波干涉条纹,具有灵敏度高的优点.用摄像机采集该载波条纹图,利用傅里叶变换法可解调出物体高度的位相信息,从而实现物体的形貌测量.     

激光剪切干涉三维形貌测量

针对物体表面的三维形貌测量问题,提出了一种基于激光剪切干涉条纹的三维形貌测量方法。该方法利用激光剪切干涉原理产生密集的干涉条纹,将干涉条纹阵列照射到待测表面。利用四步相移法和解包裹算法求解被测物体表面的连续相位,进而获取曲面表面高度信息,最后建立被测物体三维形貌。本文对楔形薄片和木块进行了测试,初步实验结果证明了该方法原理的可行性。该方法可以与显微镜相配合,进一步发展可用来测量微结构3D形貌,在微测量领域具有很大的应用前景。     

双波长同步干涉检测中基于莫尔条纹加乘变换的合成波长载频交叠干涉术

双波长同步干涉测量(ＳＤＷＩ)能够以更高的效率扩展传统单波长干涉测量的测量范围, 但是难以直接从双波长同步干涉测量中生成的加性莫尔条纹包络线中解耦提取所需波长较长的拍频合成波长(λｓ )信息? 本文提出了一种从加性莫尔条纹图中提取相位分布信息的合成波长载频交叠干涉术。通过莫尔条纹加乘转换,在得到乘性莫尔条纹图中,合成波长的干涉信息以叠加形式独立于其他波长的干涉信息。随后,从 ４ 帧乘性莫尔条纹图的频谱滤波提取出相移为 π/ ２ 的合成波长移相干涉图。最 后,对提取的 ４ 帧合成波长移相干涉图进行重新排列合成单一时空条纹图(ＳＴＦ)。 通过将时域相移转换为空域载频,利用频谱 滤波和傅里叶逆变换提取出合成波长的测试相位。与传统的双波长空域傅里叶变换解调理论相比,本论文方法在不消除背景分 量的情况下,所需空域线性载频仅为前者的 ０.１２７ 倍左右。 仿真和实验结果验证了本文方法的可行性和适用性。     

基于双频横向剪切干涉系统的三维形貌测量

近年来,结构光投影三维成像技术被广泛地应用至各个领域。该技术通常采用投影仪投影条纹,导致投影条纹的空间周期和精度有限,且在测量微小视场时会存在条纹强度不均匀、条纹焦面景深不够等问题。为解决该类问题,基于剪切干涉条纹的高空间分辨率优势,提出了一种利用横向剪切干涉条纹测量物体三维形貌的系统和方法。该系统利用激光波前以不同角度入射平行平板会产生不同频率干涉条纹这一性质,旋转平行平板改变剪切干涉条纹频率,利用低频条纹指导展开高频条纹相位。同时利用干涉条纹的入射角度与形变量内在联系,通过几何关系获得相位与高度的映射关系,以达到重建物体三维形貌信息的目的。实验验证了该系统及方法的可行性,证明了其对测量微小物体或视场有着明显的应用价值。     

条纹图像相位提取方法研究

条纹图像的相位提取在现代干涉测量中起着十分重要的作用。从算法原理、研究现状和适用范围等几个方面对比分析了现有的几种条纹图像的相位提取方法,包括相移法、载波法和基于经典算法的相位提取方法。经分析发现,相移法理论上具有较高的解调相位精度,但需获得多幅不同相位的条纹图和保持机械稳定性,这使得其只适用于静态或准静态干涉测量;而在瞬态或动态干涉测量中,载波法能从单幅图像中获得相位,自动化程度高,且对外界环境要求低,适用于开放条纹;基于经典算法的相位提取方法通过评价函数的设计及参数优化来获得相位,但处理时间相对过长,适用于封闭条纹。综合分析,载波法具有更广泛的应用前景。     

2—D Fourier Transform Method for Optical Measurement of 3—D Surface

A emthod of 2-D Fourier transform used in 3-D surface profilometry is proposed,analyzed and compared with 1-D Fourier transform method in theory and practical measuring result.It was proved that the 2-D Fourier transform method has more advantages over 1-D Fourier transform methodd in biggest crook-rate limits,accuracy and sensitivity of measuring.Styudy on measuring object surface details with large crook-rate changing accurately used new higher-power index low-pass filter of spatial frequency domain.A new method of automatic produced reference grating image and error-correcting is proposed.One undeform row of deform grating image is used to extend a complete reference grating image,and some error-correcting method is used to process the result to get accurate surface shape and the deflection of reference surface normal line deviated from the axle of camera.By this new method,one deform rectangle grating image is only used to get the 3-D shape accurately.     

Retrieval of aerosol optical properties from multi-angle satelliteimagery

The authors have been investigating a novel method for retrieving atmospheric aerosol optical properties over land. The described method makes use of the presence of spatial contrasts, within the imagery, and compares the spatial Fourier transforms of the multiangle images at zero and nonzero spatial frequencies. An initial guess for the aerosol properties is made and the Fourier components of the surface reflectance distribution are retrieved at zero and nonzero frequencies. A comparison of the angular shape of the retrieved functions is then used to establish whether the initial guess for the aerosol parameters was correct. Other than the need to define a relationship between the angular variation of the Fourier transform of the intrinsic surface angular reflectance at the zero and nonzero frequencies, the method assumes no prior knowledge about the aerosols or surface characteristics. The authors discuss sensitivities to various aerosol properties     

CT filtration aliasing artifacts

Two methods for filtering computerized tomography (CT) projections for the filtered backprojection reconstruction algorithm are evaluated. The methods are based on derivations made in the spatial and Fourier domains. The Fourier method of filtration produces images with DC shifts and low-frequency shading. The spatial method does not generate similar artifacts. It is shown that the artifacts result because of aliasing artifacts that arise when a spatial waveform with infinite extent is sampled in the Fourier domain. It is also shown that it is possible to connect the artifacts generated with the Fourier method by replacing the DC and the first two frequency components with the corresponding terms from the discrete Fourier transforms of the filter used in the spatial method.     

Quantitative characterization of electron micrograph image usingfractal feature

In this investigation, texture analysis was carried out on electron micrograph images. Fractal dimensions and spatial grey level co-occurrence matrices statistics were estimated on each homogeneous region of interest, The fractal model has the advantages that the fractal dimension correlates to the roughness of the surface and is stable over transformations of scale and linear transforms of intensity. It can be calculated using three different methods. The first method estimates fractal dimension based on the average intensity difference of pixel pairs. In the second method, fractal dimension is determined from the Fourier transformed domain. Finally, fractal dimension can be estimated using reticular cell counting approach. Moreover, automatic image segmentation was performed using fractal dimensions, spatial grey level co-occurrence matrices statistics, and grey level thresholding. Each image was segmented into a number of regions corresponding to distinctly different morphologies: heterochromatin, euchromatin, and background. Fractal dimensions and spatial grey level co-occurrence matrices statistics were found to be able to characterize and segment electron micrograph images     

三界面激光谐振反射器特性研究

本文应用薄膜光学的特征矩阵法计算三界面谐振反射器的特性,给出了用于全息红宝石双脉冲激光器的镀膜三界面谐振反射特性和温度调谐特性曲线,并对其作出了深入的研究.     

A new method of modeling three-dimensional MIC/MMIC circuits: thespace-spectral domain approach

A new space-spectral domain analysis is developed to characterize arbitrarily shaped, spatial three-dimensional (3-D) discontinuities in microwave integrated circuits (MICs) and monolithic microwave integrated circuits (MMICs). The method is very general and combines the advantages of the spectral-domain analysis (SDA) with that of the one-dimensional method of lines (MOL). The unique combination of the one-dimensional SDA, using a continuous Fourier transformation, with the one-dimensional MOL, using a discrete Fourier transformation, makes it possible to analyze circuit configurations which were difficult or impossible to analyze before. A comparison of data obtained from the space-spectral domain approach (SSDA) and the SDA and measurements for a rectangular patch resonator shows excellent agreement. The new approach is numerically very efficient and can be applied to planar transmission lines on insulating as well as semiconducting substrates with and without open boundaries. Several resonator structures are analyzed to demonstrate the usefulness of this new method     

A system model and inversion for synthetic aperture radar imaging

A system model and its corresponding inversion for synthetic aperture radar (SAR) imaging are presented. The system model incorporates the spherical nature of a radar's radiation pattern at far field. The inverse method based on this model performs a spatial Fourier transform (Doppler processing) on the recorded signals with respect to the available coordinates of a translational radar (SAR) or target (inverse SAR). It is shown that the transformed data provide samples of the spatial Fourier transform of the target's reflectivity function. The inverse method can be modified to incorporate deviations of the radar's motion from its prescribed straight line path. The effects of finite aperture on resolution, reconstruction, and sampling constraints for the imaging problem are discussed.     

基于两次傅里叶变换的时域MUSIC波达方向估计

针对基于频域多重信号分类（MUSIC）的波达方向（DOA）估计方法在有效快拍数较少情况下的不稳定问题,提出了一种基于两次傅里叶变换的时域MUSIC波达方向估计方法。首先,通过傅里叶变换将各阵元接收数据转换为频域数据,并按扫描角度对各阵元数据进行相位补偿;然后,再通过傅里叶变换将补偿后的频域共轭数据转换为时域复解析数据,在时域构建相移后的协方差矩阵;最后利用特征分解求取具有正交特性的噪声子空间,获得扫描方位空间谱,实现对波达方向估计。数值仿真及实测数据处理结果均表明,相比频域MUSIC方法,在一次有效快拍条件下,所提方法可稳定获得具有正交特性的噪声子空间,实现对波达方向估计;稳定性得到了5 dB的改善,背景噪声级和旁瓣级得到了3 dB以上的改善,因此该方法可明显提高目标检测和方位估计性能。     

十字形频率选择表面单元的传输系数分析

传输系数是频率选择表面的一项重要技术指标。简要介绍了利用谱域Galerkin法计算平面频率选择表面传输系数的方法。该方法以平面波谱展开和傅里叶变换为基础,通过矩量法求解频率选择表面电流,进而求得传输系数。对一个十字形频率选择表面的传输系数进行了测量和计算,并将测量结果和计算结果进行了比较,两者吻合得较好,验证了本方法的正确性。