准外差干涉计量算法分析及应用

采用最小二乘方法，在更一般的意义下推导了准外差干涉计量的相位计算公式，提出了测量误差与采样方式、采样次数、信噪比及相位漂移的关系，提出了相位算法选择的基本依据。建立了准外差全息干涉计量系统，能对条纹图进行全场、高精度、全自动的定量分析；将其应用于实际物体变形的测量之中，给出了实验结果。     

重轨InSAR平地干涉相位特性研究

鉴于平地干涉相位的补偿是重轨合成孔径雷达干涉测量（InSAR）的重要环节以及平地干涉相位特性对于InSAR处理过程中的参数选择和基线重估计的重要意义,本文针对不同参考面对平地干涉相位特性的影响以及如何利用平地干涉相位特性实施干涉基线重估计的问题进行了研究,从理论上推导出了参考面为平面和球面情况下平地干涉相位以及平地干涉相位频率的标量表示方法,对平面、球面和WGS84椭球面三种不同参考面所对应的平地干涉相位特性进行了对比分析,给出了利用平地干涉相位和平地干涉相位频率方法进行干涉基线重估计的算法理论。研究表明,利用平地干涉相位特性可以实施干涉基线重估计,而考虑到参考面选择对平地干涉相位的影响,在进行干涉处理过程中必须选择适当的参考面。     

合成孔径声纳干涉相位图噪声抑制方法分析

讨论了合成孔径声纳的干涉相位图降噪问题。利用加性噪声模型,分析了四种降噪算法:像素平均法、非线性条件邻域均值法、模糊中值法和向量滤波法。通过仿真数据生成的干涉相位图进行降噪分析得到结论:通过像素平均法和条件邻域均值法降噪后不能准确地生成高度图,不推荐在实际中使用。而模糊中值法和向量滤波法通过降噪可以准确地生成高度图。通过相位图残留点数和高度图方差对比发现,向量滤波法性能最优,是一种快速有效的噪声抑制方法。     

基于二进小波的雷达干涉图条纹探测相位解绕

以二进小波和相位解绕理论为基础，利用二进小波变换的快速算法，对雷达干涉条纹图进行多尺度相位突变边缘探测，进而根据信号和噪声的奇异性在二进小波变换下的局部模极大值随尺度变化的不同演化规律，提出了对雷达干涉条纹图的噪声有一定压制的基于二进小波的干涉条纹检测的相位解绕算法，结果表明，在噪声没有严重破坏相位突变边缘的情况下，相位解绕结果是令人满意的。     

干涉SAR相干系数估计的快速算法

在SAR干涉测量中,相干系数是干涉图像对相位稳定性的衡量标准。干涉基线距和地表地形都影响相干系数的计算,在通常的相干系数的计算中,需要补偿由基线和地形引起的干涉相位,造成相干系数计算中计算量的大大增加。本文应用了一种不需要进行相位补偿的相干系数计算方法,并与通常的相干系数的计算方法相比较。实验结果证明,本算法在保证一定的相干系数计算精确性的基础上,大大提高了相干系数的计算效率,可以应用于快速浏览相干图像对,以评价其用于相干测量时的质量好坏。     

干涉合成孔径雷达高程重建中平面波模型分析

详细推导了平面波模型在干涉SAR高程重建中引入的相位误差和高程误差，引入高程波动、相对高程波动和绝对高程波动等特性对平面模型的适用性进行评定。TopSAR和CCRS InSAR系统的仿真结果表明，要实现高精度的高程重建，必须采用电磁波波前的球面模型而放弃平面波模型。     

振荡器相位噪声对双站SAR成像影响分析

研究了振荡器的相位噪声对双站SAR系统成像的影响．根据振荡器的相位噪声的幂律模型,给出了双站SAR回波相位误差模型影响及其与单站模型的差异,基于相位噪声变化快慢对成像影响的差异,将其划分成线性误差、二次相位误差和高频误差三种分量,分别定量分析了它们对双站SAR图像偏移、聚焦及副瓣特性的影响．     

一种正弦相位调制光纤干涉条纹相位稳定方法

为了消除环境因素(尤其是振动和温度波动)在物体表面三维形貌测量中的影响,基于正弦相位调制(SPM)发展了一种光纤干涉条纹相位稳定技术。利用马赫-泽德光纤干涉仪结构和杨氏双孔干涉原理实现高密度的余弦分布干涉条纹投射。利用两光纤干涉臂端面的菲涅尔反射生成迈克尔逊干涉信号,由光电探测器(PD)检测后送入相位控制系统。采用相位生成载波的方法提取干涉信号的相位,并将生成的补偿信号闭环反馈给压电陶瓷驱动器,与正弦相位调制信号相加后共同驱动压电陶瓷,补偿环境因素带来的相位漂移,实现干涉条纹相位的稳定。环境因素对条纹相位的影响低于57 mrad,实验结果验证了该方法可行性。     

希尔伯特变换实时全息干涉条纹相位提取

实时全息干涉法可以观察记录整个测试过程中条纹图的动态变化,传统相位提取算法只适合于静态干涉条纹图相位的提取.根据实时全息干涉条纹和希尔伯特变换的特点,提出了利用希尔伯特变换提取实时全息干涉条纹相位值的方法,采用了高通滤波的方法减少背景光强的影响,对铝片受力变形实验中实时全息干涉条纹的相位变化分布进行了提取.实验表明:希尔伯特变换法适合于动态条纹的相位提取,可以自动提取实时全息干涉测量过程中全场各点在任意两个时刻间的相位变化值,且测量结果与实时全息干涉条纹人工分析结果一致.     

干涉合成孔径雷达复图像配准精度分析和方法

基于干涉合成孔径雷达（Interfermetric Synthetic Aperture Radar-InSAR）的系统模型、干涉相位误差的统计特性，分析InSAR配准精度与干涉相位误差之间的确定关系，讨论复图像配准过程中存在的问题，给出实用的InSAR复图像配准方法。通过对SIR-C/X-SAR意大利Enta火山干涉数据的处理，得到了精确的配准结果。     

Phase unwrapping in three dimensions with application to InSAR time series

The problem of phase unwrapping in two dimensions has been studied extensively in the past two decades, but the three-dimensional (3D) problem has so far received relatively little attention. We develop here a theoretical framework for 3D phase unwrapping and also describe two algorithms for implementation, both of which can be applied to synthetic aperture radar interferometry (InSAR) time series. We test the algorithms on simulated data and find both give more accurate results than a two-dimensional algorithm. When applied to actual InSAR time series, we find good agreement both between the algorithms and with ground truth.     

Phase unwrapping using an extrapolation-projection algorithm

We explore an approach to the unwrapping of two-dimensional phase functions using a robust extrapolation-projection algorithm. Phase unwrapping is essential for imaging systems that construct the image from phase information. Unlike some existing methods where unwrapping is performed locally on a pixel-by-pixel basis, this work approaches the unwrapping problem from a global point of view. The unwrapping is done iteratively by a modification of the Gerchberg-Papoulis extrapolation algorithm, and the solution is refined by projecting onto the available global data at each iteration. Robustness of the algorithm is demonstrated through its performance in a noisy environment, and in comparison with a least-squares algorithm well-known in the literature.     

Phase unwrapping by region growing

The phase unwrapping problem consists in mingling out an integer field whose values make the original wrapped phase field continuous. Even if in principle the problem is very simple--a direct integration of the wrapped phase field suffices--in the presence of noise and/or undersampling, the solution is no longer unique and the direct integration methods usually fail to find an acceptable solution. This work presents what is to my knowledge a new unwrapping algorithm that attempts to find the solution by iteratively merging and shifting the continuous areas until a single region is built or no further moves are possible. Unlike the tile methods, the regions can have arbitrary shape and need not be ingle-connected so that, by removing the predefined size and shape constraint, the algorithm is very robust. The greater freedom of the regions' shape makes their handling more problematic, so that certain implementation aspects, critical to algorithm performance, are presented here. Some unwrapping examples are also presented and memory requirements are discussed.     

Phase reconstruction and unwrapping from holographic interferograms of partially absorbent phase objects

A method for automated phase reconstruction from holographic interferograms of nonideal phase objects based on a two-dimensional Fourier transform is described. In particular, the problem of phase unwrapping is solved because earlier techniques are inappropriate for the phase unwrapping from interferograms of partially absorbent objects. A noise-level-dependent criterion for the binary mask that defines the unwrapping path for the flood algorithm is derived. The method shows high noise immunity, and the result is reliable provided that the true phase is free of discontinuities. The phase distribution in the outmasked regions is estimated by a linear least-squares fit to the surrounding unwrapped pixels.     

Phase unwrapping through demodulation by use of the regularized phase-tracking technique

Most interferogram demodulation techniques give the detected phase wrapped owing to the arctangent function involved in the final step of the demodulation process. To obtain a continuous detected phase, an unwrapping process must be performed. Here we propose a phase-unwrapping technique based on a regularized phase-tracking (RPT) system. Phase unwrapping is achieved in two steps. First, we obtain two phase-shifted fringe patterns from the demodulated wrapped phase (the sine and the cosine), then demodulate them by using the RPT technique. In the RPT technique the unwrapping process is achieved simultaneously with the demodulation process so that the final goal of unwrapping is therefore achieved. The RPT method for unwrapping the phase is compared with the technique of least-squares integration of wrapped phase differences to outline the substantial noise robustness of the RPT technique.     

Phase unwrapping for noisy phase map using localized compensator

Phase unwrapping for a noisy image suffers from many singular points. Singularity-spreading methods are useful for the noisy image to regularize the singularity. However, the methods have a drawback of distorting phase distribution in a regular area that contains no singular points. When the singular points are confined in some local areas, the regular region is not distorted. This paper proposes a new phase unwrapping algorithm that uses a localized compensator obtained by clustering and by solving Poisson's equation for the localized areas. The numerical results demonstrate that the proposed method can improve the accuracy compared with other singularity-spreading methods.     

Phase recovery from a single interferogram with closed fringes by phase unwrapping

We describe a new algorithm for phase determination from a single interferogram with closed fringes based on an unwrapping procedure. Here we use bandpass filtering in the Fourier domain, obtaining two wrapped phases with sign changes corresponding to the orientation of the applied filters. An unwrapping scheme that corrects the sign ambiguities by comparing the local derivatives is then proposed. This can be done, assuming that the phase derivatives do not change abruptly among adjacent areas as occurs with smooth continuous phase maps. The proposed algorithm works fast and is robust against noise, as demonstrated in experimental and simulated data.     

Phase reconstruction from undersampled intensity patterns

We demonstrate the uniqueness and convergence of phase recovery from high-spatial-frequency and undersampled intensity data. Furthermore, this is accomplished without the ambiguities that arise in phase unwrapping and without the need to employ a priori information. The method incorporates the technique of line integration of the phase gradient to find the first approximation to the phase and the algorithm of synthetic interferograms to find the unknown phase with high accuracy. The method may be used with any experimental method that at a certain data processing step obtains generalized sine and cosine intensity functions.     

Adaptive Quality Guided Phase Unwrapping Algorithm for Whole‐Field Digital Photoelastic Parameter Estimation of Complex Models

Abstract: With advancements in digital image processing and data acquisition, a separate branch of photoelasticity namely digital photoelasticity came into existence. Here, intensity information of the acquired image is used for the evaluation of whole‐field photoelastic parameters. Digital photoelasticity provides only wrapped phasemaps of isoclinics and isochromatics and they have to be unwrapped in different ways for getting the continuous‐phase values. In the case of the isochromatic phasemap, ambiguity removal prior to unwrapping is essential. In this paper, a 10‐step phase‐shifting methodology is proposed and a new strategy for obtaining the isochromatic phasemap free of ambiguity is demonstrated. Isoclinic unwrapping is performed by a new adaptive quality guided algorithm. Adaptive in the sense that isoclinic phase unwrapping is done autonomously even in the presence of isotropic points/π jumps occurring in the isoclinic phasemap. The isochromatic phasemap is also unwrapped using the quality guided path follower. The methodology is validated for the problem of a ring under diametral compression and later shown for three other models which have complex stress fields. Wherever possible, the parameters obtained by the new methodology are compared with analytical or numerical methods and the comparison is quite good.