Effect of Surface Waves from a Moving Object on Its Image During Reconstruction using Aperture Synthesis

The reconstruction of an image of the cross section of a thin wire obtained by an ultrasonic detector in an aqueous medium at a frequency of 1.3 MHz with a monochromatic probing signal is considered. The image was reconstructed using a synthesized aperture by correlation processing of a trajectory Doppler signal with calculated reference trajectory signals from point objects. The disturbing effect of the ultrasonic wave reflected from the surface wave generated by the moving wire on the image reconstruction is taken into account. The results of reconstruction of the image of the wire cross-section from model and experimental trajectory signals in the presence of a surface wave are given.     

Effect of the radiation pattern on the quality of object image reconstruction in circular aperture synthesis

This paper addresses the problem of the acoustic wave reception sector of a tomograph detector in an aqueous medium, whose solution anticipates the development of a tomograph with circular aperture synthesis in monochromatic probing. In the theoretical consideration of the problem of object image reconstruction, the transducer radiation pattern was assumed to be isotropic in the plane, i. e. disk-shaped, with an unlimited circular reception sector, which allows investigation of the internal structure of the object in the plane of the radiation pattern disk. The effect of the deviation from isotropy due to the limitation of the acoustic wave reception sector on the results of image reconstruction of a point object is determined by modeling the reconstruction of a point object image from trajectory Doppler signals received by the detector moving on a circular path around the point object.     

一种合成孔径声呐图像目标分割方法

合成孔径声呐图像的信噪比低于普通光学图像,使图像分割成为合成孔径声呐图像处理中的重要环节。本文研究了表示合成孔径声呐图像数据分布的瑞利混合模型,结合马尔科夫随机场模型,将其应用于声呐图像水下目标(亮区)分割;通过最大期望算法分别估计目标和背景的瑞利混合模型参数,并利用该参数使用Graph cut方法进行马尔科夫随机场图像分割,通过重复迭代,最后形成稳定的目标分割结果;对实际的声呐图像进行了数据分析及目标分割,结果表明瑞利混合模型在描述合成孔径声呐声图上有良好的性能,可以改善目标分割的效果。     

捆绑式望远镜图像信噪比测量及分析

空间暗弱目标的探测需要大口径、短焦距的望远镜系统。本文提出将多镜筒捆绑在一起对同一空域进行观测,通过软件的方式对采集的图像进行叠加来抑制背景随机噪声、提高图像的信噪比和整体系统的探测能力。为了对上述设想进行验证,搭建了捆绑式望远镜系统实验平台,通过实际观测及事后处理验证了该设想并给出分析结果。实验结果表明：图像信噪比平均提高1.58倍,探测能力近似提高0.5个星等。证实该技术可以系统的探测能力,并保持了其对应焦距并不缩小。     

Efficiency of software and algorithms of aperture synthesis in passive sonar devices on test and real signals

A SynApp program is developed for studying the algorithms of processing data obtained by arrays with a synthesized aperture in passive sonar devices. Various synthesis algorithms are compared, and the best algorithm is chosen on the basis of particular criteria. Inspection of program operation with signals obtained by a real array demonstrates the efficiency of synthesis with the use of the ETAM algorithm. Application of synthesis in passive sonar devices is proved to reduce the array aperture without deterioration of the bearing quality. The effect of the changes in the array subaperture used for synthesis and the size of the synthesized aperture (number of synthesis steps) on the bearing quality is studied.     

点扫描激光共焦显微镜物镜参数的确定

在设计点扫描激光共焦显微镜测量系统时 ,物镜参数的选择是至关重要的 ,因为它的数值孔径大小直接影响着系统的测量精度。本文对系统测量精度达到 1μm时物镜参数的选择进行了详细的阐述。     

基于锁相放大器的全光纤式激光多普勒测速系统

为了提高激光多普勒测速系统的测量精度及其实用性,基于锁相放大器和光纤设计搭建了一套激光多普勒测速系统。该系统的优点在于,锁相放大器的引入能够放大信号并可避免杂散光影响,从而大大提高系统的信噪比;此外,利用光纤取代传统的传输与接收光路,有效避免振动、灰尘、杂散光等环境因素影响,使实验条件大大简化。利用该系统测量移动平面镜和漫射面镜的结果表明,该系统能够准确测量移动物体的速率,误差在1%以内。该系统将来可应用于在线监测活体组织的血液流速测量中。     

Calculation of the object edge position after its projection in a spatially noninvariant coherent optical system

Specific features of half-plane image formation in a spatially noninvariant (aberration-free) coherent optical system of the 2F–2F telecentric type with a limited aperture of the projection objective (in the absence of the spatial frequency filter) are studied. The dependence of the light intensity behavior at a point corresponding to the half-plane edge in the image on the object position is found in an analytical form on the basis of approximating the Fresnel functions by analytical functions. As the half-plane approaches the boundary of the field of vision of the system determined by the objective aperture diameter, the light intensity is demonstrated to deviate significantly from that in the case of the axial position of the half-plane, which may lead to noticeable measurement errors in inspecting the geometric parameters of objects by the projection method in transmitted light.     

Mask-assisted deterministic phase-amplitude retrieval from a single far-field intensity diffraction pattern: two experimental proofs of principle using visible light

We recently developed a simple closed-form algorithm, which allows one to reconstruct the complex scalar wavefield at the exit surface of a sample, from the intensity of its far-field coherent diffraction pattern which is obtained in the presence of a suitable object-plane mask. In the first variant of this algorithm, the sample is contained within a uniformly illuminated sharp rectangular aperture in which at least one transverse dimension is at least twice that of the object. In the second variant, the sample is uniformly illuminated and is transversely displaced from an opaque rectangular mask in the object plane. For both variants, the far-field diffraction pattern is first Fourier transformed and then differentiated with respect to both transverse coordinates, in order to deterministically yield a series of independent reconstructions of the sample. Here we give an experimental demonstration of each of these two variants of our technique, using visible light.     

复合式多点测量速度干涉仪光学系统设计

为满足爆炸冲击作用下物质界面的速度测量需求,设计了一种复合式多点测量的速度干涉仪。采用物方和像方双远心光路,将光纤阵列出射的照明激光定点投射到待测物面上,实现了针状滴注式照明,充分利用了照明激光能量,且保证了待测物面在运动过程中具有恒定的照度。成像系统像面采用末端为大芯径的锥形光纤接收信号光,既保证了物面运动过程中信号光与光纤的有效耦合,又保证了信号的单模输出,以便进入单模光纤马赫-曾德干涉仪进行差频干涉。采用具有微小楔角、沿直径方向镀矩形带状45°反射膜的反射镜,将照明光路与成像光路同轴,并校正了成像系统的大量像散。该干涉测量系统在物面运动10mm的行程中,物面滴注式照明照度保持恒定,像面光斑大小没有超出大芯径的光纤芯径。此光学系统能够满足爆炸冲击界面的大行程速度测量需求。     

环形稀疏孔径结构的研究

介绍环形稀疏孔径的结构,分析环形光瞳的填充因子,并推导出环形稀疏孔径调制传递函数(MTF)的解析式。用MATLAB软件对其进行模拟,并利用Zemax光学设计软件设计环形稀疏孔径光学系统,得到调制传递函数图像,与理论推导的结果相吻合。采用标准分辨率板,在不同填充因子的环形稀疏孔径光学系统下进行模拟成像;利用分数阶微分算子对模拟所得的图像进行图像加强,改善环形稀疏孔径光学系统成像质量。     

Measurement of the width of thin,cylindrical, transparent objects by phase contrast light microscopy6

Measurement of the width of a thin, cylindrical, transparent object by phase contrast light microscopy has been frustrated by the absence of an established relationship between the true width of the object and its apparent width in the phase contrast image. We have solved this problem by devising a simple method by which individual glass fibres may be measured using both phase contrast light microscopy and electron microscopy. Using this method we have constructed calibration curves relating the diameter measured by phase contrast microscopy to the real diameter of the fibres. These curves are linear in the range 0.10-2.5 μm real diameter, with slopes close to unity and intercepts of about 0.2 μm. Thus widths of such objects are overestimated. The precise value of the intercept is related to the overall numerical aperture of the optical system. Each calibration curve permits the true width of a cylindrical object to be estimated by phase contrast microscopy with an accuracy of better than ±0.05 μm. We have found that greater precision is obtained by taking measurements of light micrographs subjectively using a microcomparator rather than objectively using a microdensitometer.     

Phase Retrieval with a Diffractive Micro Lens Array

Multi-plane phase retrieval is a well established technique for reconstructing both, amplitude and phase of an object wave. This standard technique works best, if the intensity of the object wave changes rapidly along the optical axis. For slowly varying intensities, the iterative procedure may not converge at all. To overcome this limitation we combined the standard technique with a periodic phase element. We demonstrate that a binary diffractive micro lens array with overlapping aperture significantly improves the convergence of phase retrieval and thus the quality of reconstruction. Thus multi-plane phase retrieval can be applied for both rough and smooth phase distributions.     

Ultrabroad-band tomography of remote objects

A method for restoring the images of remote objects with the system??s instrument function in ultrabroad-band (UBB) pulse sounding is considered. The system is a synthetic-aperture radar combined with a parabolic reflector. The aperture was synthesized via UBB scanning with a transceiver over the near-focus plane of a parabolic rereflector. Such a scheme allows the boundary of the maximum offset of a sounded object to be displaced at a distance equal to 2?C3 diameters of the parabolic reflector. An additional advantage of the system that contains a parabolic reflector (rereflector) consists in the possibility of focusing radiation to a specified remote spatial region. In support of the validity of this method, we represent the results of numerical and physical modeling.     

Heuristic optimization in penumbral image for high resolution reconstructed image

Penumbral imaging is a technique which uses the fact that spatial information can be recovered from the shadow or penumbra that an unknown source casts through a simple large circular aperture. The size of the penumbral image on the detector can be mathematically determined as its aperture size, object size, and magnification. Conventional reconstruction methods are very sensitive to noise. On the other hand, the heuristic reconstruction method is very tolerant of noise. However, the aperture size influences the accuracy and resolution of the reconstructed image. In this article, we propose the optimization of the aperture size for the neutron penumbral imaging.     

Inverse model of fiber probe aperture size using a non‐destructive method

This study establishes a set of theoretical line segment fabrication models of near‐field photolithography using radiation field theory—Dill's exposure model and Mack's development model. By combining the theoretical line segment fabrication model and experiments, this work constructs a novel theory of inverse calculation of fiber probe aperture size using the non‐destructive method. The experimental and simulation results obtained using the theoretical line segment fabrication model are compared; the error between these results is utilized as an objective function. The Levenberg–Marquardt method is used to search and rationalize the convergence criterion. Fiber probe aperture size that fits the experimental and theoretical model is inverse calculated. According to the results, the probe aperture obtained by this inverse model is d=250.6 nm, while the average size certified by SEM is d_avg=253.4 nm, the close match indicated that the probe aperture calculated with the inverse model is reasonable and can be accepted. The lithographic fabrication profile can be predicted with the inverse model to get the probe aperture and, then, cooperated with the theoretical simulated values and experimental parameter control. Such a fabrication has an application value for industry. This non‐destructive fiber probe aperture measured model can overcome the bottleneck at present to get this value by destructive measurement, thus, it has surmounted contribution in fiber probe aperture measuring techniques. SCANNING 31: 211–220, 2009. © 2010 Wiley Periodicals, Inc.     

基于狭缝光阑的剪切散斑干涉动态测量

为了精确、实时地测量物体表面的动态形变,提出了基于狭缝光阑的空间载波剪切散斑干涉系统。该系统通过倾斜迈克尔逊干涉仪的一个平面镜来产生剪切量和载波频率,实现空间频谱的移动;采用一个可调节的狭缝光阑控制散斑大小和空间频谱宽度。基于傅里叶变换与反变换在空间频率域上提取所需的频谱并计算相位图,最后通过一幅干涉条纹图得到相位分布信息。采用该系统对一个中心加载、四周固支的薄铝板进行了动态测量,分析了光学系统参数对测量结果的影响。结果表明,采用像素尺寸为4.65μm×4.65μm的高分辨率相机,焦距为8mm的成像镜头,设置剪切量为25mm,狭缝光阑X方向的尺寸为1mm时,可得到高质量的剪切散斑相位图。该方法可以在25frame/s的采集速度下,以43.6°的视场角实现动态形变的测量,可测形变峰值为0.5~30μm。     

基于彩色CCD的高温场辐射测温方法

针对基于彩色CCD的高温场辐射测温问题,提出利用红、绿基色值进行比色测温来获取单一光圈快门组合内的最大测温范围,并进一步利用变换光圈快门组合来使得测温范围能够覆盖高温生产的常用温度范围;通过标定减少CCD光谱响应带宽和被测对象光谱发射率对测温精度的影响,提高测温精度.在此基础上,开发了CCD高温场测量仪.计量校准结果表明,测温仪具有较高的测温精度和实用性,能够满足常见高温生产过程对于温度测量的应用要求.     

The influence of the aperture of illumination on the accuracy of microscope-photometric measurements of internal transmittance

The conical shape of the bundle of illuminating rays in the microscope causes a systematic error of transmittance measured with a microscope photometer in comparison with the (true) transmittance measured with a macrophotometer in which the ray bundle is cylindrical. The error is evaluated by the ratio of transmittance measured with the microscope photometer to the true transmittance. It is calculated for the following model objects: parallel-sided plates, wedges, spheres and circular cylinders. The results of calculations show that the error increases with decreasing transmittance, increasing angle of the cone of rays (evaluated by the effective numerical aperture of illumination), and increasing relative size of photometric field. On the whole, the error can be neglected if the true internal transmittance is greater than 0.1 (10%), the numerical aperture is less than 0.45 and the radius of the photometric field (in the object plane) is less than one-fifth of the thickness of the object.