Feature tracking for projection registration in laboratory-scale reflective tomography laser radar imaging

In range-resolved reflective tomography laser radar imaging system, for accurate image reconstruction, all projections must be aligned to the center of target rotation. Due to the unknown location of the axis of rotation and random target translation, the center of target rotation in each projection cannot be measured accurately and images reconstructed based on range-resolved projections without registration would be dislocated. Here, we apply a feature tracking method to align projections data for tomographic reconstruction in laboratory-scale laser radar imaging. The target was placed on a spin table with an unknown and fixed axis, and the oscillatory motion of the target translation was simulated by a second order inertia filter to accord with the real satellites vibrations. The experimental simulation results demonstrate the effectiveness of this method to improve images reconstruction equality. The application of this method to actual radar imaging in remote distance was discussed and the differences were compared with the lab setups.     

Comparison of results of interferometric phase extraction algorithms for three-dimensional flow-field tomography

A comparison of the results of interferometric phase information retrieval and subsequent tomographic reconstruction from deformed wavefront projections by phase unwrapping is presented. In interferogram processing, conventional fringe tracking and Fourier transform methods have been utilized for comparison. With these methods by injecting carrier fringes, the projection data of any axial cross section can be extracted in all projection directions to implement three-dimensional tomographic reconstruction. The results of experiments of a simulated temperature field prove that the phase extraction based on the Fourier transform method produces tomographic reconstruction much superior to the conventional fringe tracking technique.     

Equations of motion from chaotic data: A driven optical fiber ring resonator

We apply a recently proposed method for the reconstruction of equations of motion from a time series to experimental chaotic optical data and find the theoretically expected Ikeda model. In contrast to phase space reconstruction methods, it is based on nonlinear regression and maximal correlation, and the resulting model can be investigated further. We demonstrate the retrieval of physical parameters by calculating the experimentally not accessible phase evolution of a non-stationary data set.     

位相恢复法与X射线激光等离子体密度诊断

 详细介绍了XUV波段Gabor全息及位相恢复法去除Gabor全息孪生像的全部过程,分析了X射线激光Gabor全息术对等离子体和实验条件的要求,编程对全息图的制作、反演以及位相恢复法的全过程进行了模拟,并对三个模型进行了计算比较。     

激光投影成像式运动目标位姿测量与误差分析

为了实现室内运动目标位姿的高精度测量,建立了一套激光投影成像式位姿测量系统.该系统利用两两共线且交叉排列在同一平面上的点激光投射器作为合作目标捷联在运动目标上,通过与光斑接收幕墙的配合共同组成运动目标位姿测量基线放大系统,利用高速摄像机实时记录幕墙上投影光斑的位置,利用摄像机标定结果求解投影光斑的世界坐标,利用投影光斑之间构成的单位向量建立运动目标位姿解算模型.最后,根据测量原理推导了图像坐标提取、摄像机外部参数标定、光束直线度与目标位姿解算结果之间的误差传递函数.实验结果表明,当摄像机的视场范围为14 000mm×7 000mm时,测量系统的姿态角测量精度为1′(1δ),位置测量精度为5mm,且误差大小与目标位姿测量误差传递函数理论计算值一致,验证了本文提出的目标位姿测量方法与测量误差传递模型的准确性,能够满足目标位姿测量高精度的要求.     

X-ray in-line phase tomography of multimaterial objects

We present a method for phase retrieval from x-ray Fresnel diffraction patterns for multimaterial objects. Previously, homogeneous object assumptions have been used and have been introduced in the Radon domain. Here, we apply prior knowledge in the object domain, which permits the introduction of multiple materials. This is achieved first by a tomographic reconstruction of an attenuation scan and then introduction of the prior followed by a forward projection step to yield the a priori phase maps. The method is applied to the reconstruction of an object of known composition consisting of both soft and hard materials and is shown to perform better than previously proposed algorithms.     

Measurement of the laser beam intensity distribution using optical tomography

Optical tomography is proposed as a method for studying the intensity distribution in the laser beam cross section. The tomographic projection of the beam cross section is obtained with the help of an optical fiber possessing a high radiation resistance, which makes it possible to employ this technique for studying high-power laser radiation. The results of tomographic reconstruction of the bean cross section from experimental projections are compared with the results of reconstruction from model projections.     

对一种线性相位反演波前测量方法的数值仿真

 利用数值仿真方法对一种基于线性相位反演波前测量方法的性能进行了详细分析。讨论了这种线性相位反演波前测量方法的定标过程,描述了基于线性相位反演算法的波前传感器的基本组成结构。利用数值仿真计算,分析了系统自身像差和模式标定系数对这种波前传感器性能的影响,通过复原矩阵条件数,分析了靶面像素和这种波前测量方法的空间分辨力的关系。仿真结果验证了该种新型线性相位反演波前测量方法的可行性。     

基于相位展开的三维流场干涉层析术

提出用傅里叶变换进行干涉图相位展开（ＰｈａｓｅＵｎｗｒａｐｐｉｎｇ）的办法直接恢复变形波面，从而可以提取轴向任意截在上的投影数据，实现真正意义上的三维层析，模拟温度场实验证明基于相位展开的投影数据提取方法能够更好的完成层析计算。     

Application of single-beam homodyne SPIDER for the control of complex spectral phase profiles

We investigate the range of application of single-beam homodyne spectral phase interferometry for direct electric field reconstruction (SPIDER) for multiphoton microscopy. Simulations and experimental studies performed on model spectral phase profiles show that the phase reconstruction technique used in this method makes the phase retrieval quality highly sensitive to the complexity of the profile. In addition, we show that the use of iterative processes is likely to deteriorate the phase retrieval quality, especially for strongly varying phase profiles. These effects are illustrated and quantified for sinusoidal and quadratic spectral phase profiles.     

High resolution inverse synthetic aperture radar imaging of three-axis-stabilized space target by exploiting orbital and sparse priors

The development of inverse synthetic aperture radar(ISAR) imaging techniques is of notable significance for monitoring, tracking and identifying space targets in orbit. Usually, a well-focused ISAR image of a space target can be obtained in a deliberately selected imaging segment in which the target moves with only uniform planar rotation. However, in some imaging segments, the nonlinear range migration through resolution cells(MTRCs) and time-varying Doppler caused by the three-dimensional rotation of the target would degrade the ISAR imaging performance, and it is troublesome to realize accurate motion compensation with conventional methods. Especially in the case of low signal-to-noise ratio(SNR),the estimation of motion parameters is more difficult. In this paper, a novel algorithm for high-resolution ISAR imaging of a space target by using its precise ephemeris and orbital motion model is proposed. The innovative contributions are as follows. 1) The change of a scatterer projection position is described with the spatial-variant angles of imaging plane calculated based on the orbital motion model of the three-axis-stabilized space target. 2) A correction method of MTRC in slant-and cross-range dimensions for arbitrarily imaging segment is proposed. 3) Coarse compensation for translational motion using the precise ephemeris and the fine compensation for residual phase errors by using sparsity-driven autofocus method are introduced to achieve a high-resolution ISAR image. Simulation results confirm the effectiveness of the proposed method.     

H2O温度二维分布的滤波反投影重建

利用可调谐半导体吸收光谱技术实现燃烧场温度二维分布重建。设计H2O模型温度分布范围为300~1300 K,高斯型分布,利用Radon变换模拟实验测量结果。采用滤波反投影算法重建了两条吸收谱线强度场,进而得到气体温度二维分布,重建结果与模型符合较好。研究了不同投影数目和随机噪声对重建结果的影响,结果表明:随着投影数目的减少和噪声幅值的增加,重建温度分布均方误差增大,图像重建效果变差。当投影数目减小到4个,重建温度场已不能完全反映原始温度场信息。     

空间非合作目标自旋速率测量方法与实验

为了实现对失稳、快旋空间非合作目标运动状态的测量,提出一种基于单目相机序列图像的测量方法。根据目标与探测器的投影几何关系,推导和证明了测量方法的可行性。根据空间光照环境的特点,给出一种基于MSER特征的图像处理方法,用于稳定提取目标在图像中的投影角。根据获得的多帧序列投影角值,通过设定合理的多项式拟合模型,计算非合作目标的自旋速率。最后通过在轨图像数据,进一步验证了方法的有效性和测量精度。实验结果表明:对于某60°/s的快旋非合作目标,用1 Hz帧频的单目相机观测150 s,该方法对目标的测量均值为60.07°,测量标准偏差为0.05°/s,实现了稳定可靠、高精度的空间非合作目标运动状态测量。     

适用于非匀速直线航迹的FFBP算法在SAS中的应用

时域的快速因式分解后向投影(FFBP)算法便于进行运动补偿,能够更好地适应方位向速度的不均匀和非直线航迹。本文探讨了在合成孔径声呐(SAS)系统中采用FFBP算法针对有一定起伏的非匀速直线航迹成像时的解决方法,参考方位向的速度信息进行非均匀的孔径合并策略,同时在利用相位中心重叠法(DPC)估计出声呐基阵对所规划航迹的左右侧移量后,用最小二乘准则拟合出一条理想的直线航迹并将FFBP算法处理中的初级子图像的原点补偿至此直线。实际海试数据处理结果证明了所提出的方法能够以较好的性能进行成像。     

光学投影式三维轮廓测量技术综述

主要用于散射物体的宏观轮廓测量的光学投影式轮廓测量技术可以分为两大类：直接三角法和相位测量法。直接三角法包括激光逐点扫描法、光切法和新近出现的二元编码图样投影法。相位测量法以测量投影到物体上的变形栅像的相位为基础，包括莫尔法、移相法、傅氏变换法等等。本文以基于相位测量和光栅投影法为重点综述了光学投影式轮廓测量技术的几种典型方法，讨论了它们的优缺点，并分析了研究热点和发展方向。     

A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging

Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique.By using two-dimensional(2D) gratings,the observable contrast is extended to two refraction directions.Recently,we have developed a novel reverse-projection(RP) method,which is capable of retrieving the object information efficiently with one-dimensional(1D) grating-based phase contrast imaging.In this contribution,we present its extension to the 2D grating-based X-ray phase contrast imaging,named the two-dimensional reverseprojection(2D-RP) method,for information retrieval.The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption,the horizontal and the vertical refraction images.The obtained information can be used for the reconstruction of the three-dimensional phase gradient field,and for an improved phase map retrieval and reconstruction.Numerical experiments are carried out,and the results confirm the validity of the 2D-RP method.     

Analysis of algebraic reconstruction technique for accurate imaging of gas temperature and concentration based on tunable diode laser absorption spectroscopy

An improved algebraic reconstruction technique(ART) combined with tunable diode laser absorption spectroscopy(TDLAS) is presented in this paper for determining two-dimensional(2D) distribution of H_2O concentration and temperature in a simulated combustion flame.This work aims to simulate the reconstruction of spectroscopic measurements by a multi-view parallel-beam scanning geometry and analyze the effects of projection rays on reconstruction accuracy.It finally proves that reconstruction quality dramatically increases with the number of projection rays increasing until more than 180 for 20 × 20 grid,and after that point,the number of projection rays has little influence on reconstruction accuracy.It is clear that the temperature reconstruction results are more accurate than the water vapor concentration obtained by the traditional concentration calculation method.In the present study an innovative way to reduce the error of concentration reconstruction and improve the reconstruction quality greatly is also proposed,and the capability of this new method is evaluated by using appropriate assessment parameters.By using this new approach,not only the concentration reconstruction accuracy is greatly improved,but also a suitable parallel-beam arrangement is put forward for high reconstruction accuracy and simplicity of experimental validation.Finally,a bimodal structure of the combustion region is assumed to demonstrate the robustness and universality of the proposed method.Numerical investigation indicates that the proposed TDLAS tomographic algorithm is capable of detecting accurate temperature and concentration profiles.This feasible formula for reconstruction research is expected to resolve several key issues in practical combustion devices.     

IGES文件B样条曲线的激光扫描投影方法研究

激光扫描投影系统可以通过在目标面上投影出待投影零部件轮廓线框的方式来辅助工人装配,使用该系统进行辅助装配可以有效解决由传统装配方式所引起的效率慢、精度低等问题.为了解决自研激光扫描投影系统不能直接读取零部件外形数模,影响激光扫描投影系统的实际应用价值,拖慢工作效率等问题.提出了IGES文件B样条曲线的激光扫描投影方法研...     

Fast optical computerized topography

The topography of samples is recovered from the phase reconstruction by solving the Transport Intensity Equation (TIE). The TIE is solved by expanding the equation into a series of Zernike polynomials, leading to a set of appropriate algebraic equations. In the experiments laser light was used and the illuminated region defined the boundary conditions on the target. The phase was uniquely reconstructed and the geometry of the target was calculated. The novel technique has been successfully tested on a transparent phase plate as well as on a gold coated one. Using this technique with illumination of a short laser pulse makes it well suited for reconstructing surfaces of moving objects.     

基于代数迭代算法的燃烧火焰温度场和气体浓度场重建研究

基于TDLAS(tunable diode laser absorption spectroscopy)技术,以水汽作为目标气体,采用直接吸收的测量方式,探测了甲烷空气预混平焰炉燃烧区域水汽的吸收光谱信号,通过ART(algebraic reconstruction technique)代数迭代算法对燃烧场温度和水汽浓度分布进行了模拟重建和实验研究,模拟重建采取5×5共25个网格的正方形重建区域,假定25个网格的一个温度浓度二维分布,模拟28条激光束从不同的角度方位穿越重建区域,得到模拟射线下的投影值,经ART算法重建,结果显示温度场和水汽浓度场的重建偏差均在1%以内。实验采用分布反馈式激光器作为光源,选取H₂O的7 153.722,7 153.748和7 154.354 cm-1三条吸收线作为测温谱线,其中前两条线不区分作为一条吸收线来处理。使用平移台多方位平行扫描,共获取30路光谱吸收信号,经数据处理、算法重建和双线比值法测温原理得到了圆形平焰炉16个不同区域的温度浓度值,且炉面偏向中心区域温度浓度值较高,边缘较小,结果表明代数迭代算法能够很好地实现燃烧区域温度场和水汽浓度场的反演。