Target-based coherent beam combining of an optical phased array fed by a broadband laser source

The target-based phasing of an optical phased array (OPA) fed by a broadband master oscillator laser source is investigated. The specific scenario examined here considers an OPA phasing through atmospheric turbulence on a rough curved object. An analytical expression for the detected or received intensity is derived. Gleaned from this expression are the conditions under which target-based phasing is possible. A detailed OPA wave optics simulation is performed to validate the theoretical findings. Key aspects of the simulation set-up as well as the results are thoroughly discussed.     

基于数字散斑的大型机翼弹性形变测量技术

飞机机翼在飞行过程中受气动力影响会发生弹性形变,导致机翼外载荷大小与分布变化,危及飞行安全。该文针对民用飞机在飞行过程中机翼弹性形变测量的需求,分析大型飞机的结构负荷,采用多组摄像机组合标定、机载摄像机位姿修正、大倾角散斑图像解算等视觉测量技术,开展多摄像机组合的大翼展数字散斑形变测量方法研究,设计适用于C919飞机飞行试验的机载翼面弹性形变测试系统。通过实验室仿真试验与精度对比分析,形变测量精度能够满足机翼弹性形变测量要求。     

基于快速散斑结构光三维重建的在线测量系统

在流水生产线中实现工件表面三维信息的快速获取及尺寸的快速测量是当前辊压成形等制造业智能化升级过程中的迫切需求。基于散斑投影的三维重建方法仅需利用单幅物体散斑图像即可重建出物体表面的三维数据,在流水线工件快速测量中具有一定优势。本文对散斑三维重建中较为耗时的对应点搜索算法进行了优化,并在此基础上研制出适用于辊压成形制造生产线的工件快速三维测量系统。实验结果显示,该系统具有较快的三维数据重建速度,测量误差在0.035 mm范围内,能够满足辊压成形工件三维结构尺寸的快速在线测量需求。     

On development of portable digital holographic speckle pattern interferometry system for remote‐access monitoring and documentation in art conservation

Artworks are delicate objects representative of the most high values of human kind that require constant control over the situation they are in and effective actions to preserve them and deliver them safely to next generations. As such, the non‐destructive or minimally destructive nature of operator–artwork interactions has been considered as essential in this field. The complete diagnosis of the status of the art object signifying a full knowledge of invisible defects and their morphology allows its timely and correct maintenance and ensures its durability. It is herein presented the basic technical information on the development of a portable system termed Digital Holographic Speckle Pattern Interferometry (DHSPI) for the structural diagnosis of works of art. DHSPI has been tested on a variety of conservation problems over the years. It is a completely portable and fully PC driven automated system for the detection and non‐destructive diagnosis of the structural alterations of an artwork, whether they are defects lying on the subsurface or between the layers below it, the fringe number information allows the depth estimation and the complete documentation. The system exploits the benefits of a highly coherent laser beam as essential presupposition for remote on‐field access—that is the main emphasis given here—to immovable/movable art objects. It takes advantage of a CCD camera as photosensitive medium to record the interference of the retro reflected object laser beam from the object under consideration with a twin reference laser beam. The device allows micro projections of the defects on the surface of the object to be detected with a resolution that corresponds to half the wavelength of the laser beam. Local disparities, in relation to the total response of the object, are directly correlated to the detected microdisplacement of object surface as structural defects. Special tailor‐made software allows full control of the system, processing of the data, and extraction of anomalies. Direct visual qualitative observation of the displacement processes is followed as captured in the monitor. A second custom‐made software—not presented in detail here—enables further processing of the results to improve their imaging, quantification, and dimensioning. The final result is a quantitative map of alterations, the coordinates, and the classification of their risks which can be also extracted if further information is necessary. The qualitative or quantitative documentation map can be used as a guide to the conservator for maintenance and restoration work. Further on, the system also allows observation of the object's response to climate changes in order to predict the formation of alterations or the evolution of existing ones providing the only known direct tool for scheduling preservation strategies.     

保留细节的迭代非局部均值超声波图像去噪

针对超声波医学图像的斑点噪声滤除问题,提出一种保留细节的迭代非局部均值滤波方法。在非局部均值滤波基础上使用迭代操作,重新定义邻域相似块搜索范围的形式,使每个像素点的邻域相似块搜索范围随着迭代过程逐步增大,每一轮迭代的相似块搜索数量保持不变;引入一种边缘检测算子,对每轮迭代滤波前和滤波后的图像进行融合。实验结果表明,所提方法有更好的噪声滤除及细节保留效果,算法计算复杂度更低。     

基于粒子群算法分析随机相位对全息图的质量影响

因为相息图具有很好的衍射效率,所以经常被用 在计算全息中。在计算相息图时,随机相位被加入 到物体对象中从而扩散全息图中的物体光,但随机相位的添加会造成重建图像中产生相当大 的散斑噪声。 为了改善这一问题,本文首先针对随机相位的范围进行分析,研究了初始的随机相位对全息 图成像质量的 影响,再通过粒子群算法寻找最优的随机相位范围。在计算全息图时会存在部分信息的丢失 ,所以对全息 图进行迭代运算能弥补全息图间的差异。故在本文还将结合改进的迭代傅里叶变换算法来有 效的改善重建 图像的质量,即提出了一种基于粒子群算法分析有限随机相位对全息图质量影响的方法。通 过对以上过程 进行数值模拟和光学实验,最后的实验结果表明,通过寻找最优的随机相位范围以及改进的 迭代傅里叶变 换算法能够改善重建图像的散斑噪声得到高质量的重建像。     

基于极坐标和蒙特卡罗估计的超声图像去噪方法

针对超声图像采集特性和斑点噪声分布特点, 提出极坐标系下融合蒙特卡罗估计的斑点噪声抑制方法。首先对极坐标系下含噪图像进行对数变换, 然后再与估计点相关的任意径向方向进行全局域采样, 根据样本点与估计点空间相关性和斑点噪声分布模型构造权重因子, 最后利用蒙特卡罗方法实现斑点噪声似然加权估计。实验结果表明, 该算法在滤除斑点噪声的同时, 更好地保持了图像细节信息。     

SAR图像相干斑特征参数假设检验方法

为了快速评估合成孔径雷达（SAR）图像的相干斑质量,选取等效视数（ENL）作为评估指标,给出了单样本参数检验和双样本参数检验两种方法,并用两组实际图像数据进行了实验．实验结果表明,本文方法可以快速准确地判断SAR图像的相干斑质量．     

数字散斑相关的亚像素搜索方法比较

针对数字散斑相关方法中的二次曲面拟合、高斯曲面拟合、双线性插值、梯度法等常用的亚像素搜索技术进行了研究,建立亚像素搜索实验系统,对上述亚像素搜索技术的精度和效率进行了比较分析.结果表明,在上述几种方法中梯度法的搜索精度最高.     

激光散斑位移测量方法研究

激光散斑测量法是在全息方法基础上发展起来的一种测量方法,这种方法具有很强的实用价值。散斑位移测量不仅可以实现离面微位移的测量,也可以进行面内微位移测量。主要是对面内微位移进行了测量研究,利用设计的测量系统将物体发生位移前后的散斑图由CCD记录下来,分别用数字散斑相关法和散斑照相法对散斑图像进行了分析处理,并得出了相应的结论。最后,对以上两种测量法的特点和测量误差产生的原因都作了简单的分析和比较。