摆扫式面阵CCD航空相机的像旋转分析

航空相机在进行拍照时,通常采用45°扫描反射镜绕光轴摆扫或步进,进行多行迹摆扫式拍照,以增大对地面景物的观测范围,但当扫描镜绕光轴旋转对物体进行观测时,物体反射像也将绕轴进行旋转,目标相对探测器(CCD)产生了像旋转。通过运用光线矢量与光轴旋转变换的方法,建立了相机的数学模型。根据该模型,针对扫描反射镜旋转所产生的像旋转,利用光学矩阵建立了扫描镜转角与像旋转角之间的关系,对比各种消除像旋方法的优缺点,提出了采用扫描镜与像面旋转机构同步旋转结合的方法实现消除像旋,为工程设计提供了必要参考。     

扫描反射镜光学机械消像旋转方法

1引言 在航天遥感中,为了扩大观测范围,通常采用反射镜扫描方案.扫描装置是多光谱扫描仪的重要组成部分,其性能的优劣关系到能否可靠地为系统提供准确的信息,对遥感仪器整体性能的优劣起着关键作用.随着遥感数据应用的不断深入,对遥感器的探测灵敏度要求也越来越高.采用多元探测器并行扫描或串行扫描(实现时间延迟积分技术)是提高扫描仪性能的重要手段.但采用多元探测器的仪器在扫描观测角变化时,焦平面上的像不允许发生旋转,否则会使各像元对应的视场无法配准,导致图像畸变.     

45°指向镜成像畸变特性分析和校正

为扩大观测范围,航天遥感仪器通常采用45°指向镜扫描.在采用多元探测器的遥感仪器中,焦平面上所成的像不允许产生像旋,否则会使各个像元所对应的视场无法配准.因此,研究相应的像消旋方法,消除45°指向镜成像系统带来的像旋转,使其能够更好地应用于生产实践,是一个十分迫切的问题.对45°指向镜生成的图像的畸变特性进行了分析,同时根据每个像元坐标与地面坐标的对应关系,给出了校正图像畸变的方法.合成图像和真实图像的模拟实验结果表明:提出的畸变校正方法能够很好地校正45°指向镜的成像图像,在工程应用中具有重要的实用意义.     

航空相机的像旋转特性分析及其补偿方法

航空相机在多航迹成像方式中,随着45°反射镜绕光轴旋转对物进行扫描,物体反射像也将绕光轴进行旋转,为此必须采取消除像旋转的措施来保证成像质量.为阐述产生像旋转的原因,分析了扫描反射镜的像旋转特性;并在探讨消除像旋技术理论的基础上,提出了一种反射镜与探测器同步转动消除像旋转的方法.在多航迹工作方式中,此方法为相机扫描机构连续扫描成像提供了必要条件.利用此方法还改进了以往步进式扫描机构的惯量大、扫描效率低的问题,并在实际工程中得以应用和证明.试验结果表明,该方法的同步旋转误差小于1/3像元,能够获得良好的图像效果.     

天文望远镜无偏消旋镜装调方案设计及验证

地平式天文望远镜在跟踪观测过程中,因方位轴与地球自转轴不重合及库徳光路中的折轴反射镜在望远镜跟踪过程中相对转动,会引入物方及像方视场旋转。传统的消旋K镜可以消除视场旋转,但会带来较大的仪器偏振,不利于望远镜实现高精度偏振测量。无偏消旋镜由5块反射镜组成,通过优化设计可以保证在消除像旋的同时减小仪器偏振,但其不规则的结构设计使装调过程面临新的挑战。针对无偏消旋镜提出双光路自准直装调方案,基于MATLAB仿真分析了镜面误差及光轴偏差对装调结果的影响,并对无偏消旋镜进行实验室装调及偏振检测。结果表明:无偏消旋镜经装调后倾斜误差可控制在15 arcsec以内,其仪器偏振明显低于传统K镜。     

45°镜系统扫描轨迹分析及其对像旋校正的影响

分析了 45°镜系统的扫描规律及其对像旋校正的影响.给出了像旋图像的地面软件校正结果.结果表明在充分考虑了地球曲率、探测器的离轴及探测器安装角度影响的情况下, 45°镜系统对地面无漏扫,适当增加扫描角度,扫描系统获取的总视场内的地面信息无丢失,像旋对系统空间分辨率及图像的配准无影响,像旋图像可以通过软件方法进行校正.     

摆扫式航空遥感器像旋补偿方法

针对航空遥感器前端扫描反射镜旋转带来的像旋,提出了一种焦平面与扫描反射镜同步旋转的消旋方法。利用矢量法对像旋的方向进行了详细计算,得出消旋方向与扫描反射镜旋转方向相反的关系,提出了一种双轴系齿轮联动、双电机伺服控制的消旋方法,该方法精度高、像旋残留少,并对轴系的回转精度、齿轮的传动精度、双电机的伺服控制精度进行了检测。检测结果表明:轴系的回转精度为0.8″,齿轮的传动精度达到34″,双电机伺服控制精度优于1′。试验结果表明,用此种方法进行消旋,像旋的残留仅为0.03 mm,经过某项目成像验证,得到的图片便于拼接应用。     

45°旋转反射镜扫描性质的讨论

讨论45°旋转反射镜的扫描性质,对该扫描模式进行评价,给出它在遥感中的适用性。     

航空相机的像面旋转特性分析

航空相机利用45°反射镜绕光轴旋转对地物的扫描进行多航迹成像,45°反射镜绕光轴旋转时,物体反射像也将绕光轴进行旋转,造成像面信息无法配准,为此必须采取适当的措施来消除像旋转,保证相机成像质量。从产生像方旋转的原因出发,基于光学反射成像理论,通过实例分析,归纳总结出扫描反射镜、光学成像物镜、折返镜对航空相机像面旋转特性的作用和影响,给出判断像旋转方向的一般方法,并以此为补偿像方旋转的理论依据,提出了一种新型的补偿方法。通过地面试验,获得了完全消除像旋转的图像信息,结果表明：该方法的同步旋转误差造成的最大像移量小于1／3像元,能够获得良好的图像效果而没有模糊,验证了像方旋转理论的正确性,及其补偿方法的可行性和实用性。     

基于FPGA/DSP的数字视频消像旋系统设计

为消除因探测器姿态变化造成的图像旋转,保持观测图像的稳定状态,采用可编程逻辑门阵列(FPGA)和数字信号处理器(DSP)构建数字硬件平台。给出了实时消像旋的完整硬件结构与相应算法。设计采用ITU-656标准数字视频格式,用VHDL硬件描述语言实现整个消像旋算法的FPGA设计。实验结果表明,旋转角度在0°￣360°之间,能实时消除探测器转动引起的图像旋转,旋转后图像清晰稳定。因而基于FPGA和DSP实现实时图像消旋(旋转)的方法具有很大的实际应用价值。     

CT fan beam reconstruction with a nonstationary axis of rotation

To reconstruct an image using computed tomography (CT), the axis of rotation must pivot at the same point on the reconstruction plane that the X-ray source and the CT detector assembly rotate about around the imaged object. This pivot point is used as a reference point for backprojecting pixel values to their proper coordinates. Reconstructing an image with a nonstationary axis of rotation would backproject pixel values to incorrect coordinate points. A convolution filtered backprojection algorithm has been derived for correcting images that were acquired with a nonstationary axis of rotation using the fan beam geometry with a collinear (flat) detector. The correction method accounts for the vertical displacements of the axis of rotation as the CT scanner rotates around the imaged object, as may be the case when sagging occurs. Software simulations are performed to show how the algorithm corrects for the shift in the axis of rotation     

Direct comparison of a xenon and a solid-state CT detector system: measurements under working conditions

Measurements of various image quality parameters were carried out with two different detector systems in an otherwise unchanged medical computed tomography (CT) scanner. As all other components of the scanner and the image reconstruction system remained identical, we were able to quantify the difference in performance between a Xenon gas ionization detector and a new solid-state scintillation detector in an isolated fashion. We determined noise, spatial resolution, and artifact behavior and assessed the potential for dose reduction. No significant impact of the detector change on absolute CT values of a calibration phantom was observed. Spatial resolution was improved by more than 10% for the solid-state system. As the system's modulation transfer functions were measured with a wire phantom and otherwise unchanged scanner geometry and image reconstruction algorithm, the increase of resolution is explained by the improved temporal response of the solid-state detector. At the same time, noise was reduced by 12% for a 20-cm diameter water phantom. The noise reduction corresponds to a possible reduction of patient dose by 23% for constant image quality, which is in good agreement with our prediction by estimations of both systems total detective quantum efficiency. Also, a significant improvement of scatter rejection was found for the solid-state system.     

使用Monte Carlo方法对光子-物质的相互作用进行模拟

在医学影像获得方法中，核医学与传统的放射线探测，扫描仪探测，核磁共振相比，是唯一能获得器官功能性信息的方法，但它获得的图像质量不如其他方法。开发了一种图像探测仪并使用Monte Carlo方法对其各组成部分进行模拟从而可以通过调整参数来获得高分辨的图像。     

Polarimetry of illumination for 193 nm immersion lithography

We have constructed a theory of polarimetry of illumination used in 193 nm lithography equipments, fabricated a polarimeter mask, and demonstrated it for a hyper-NA (numerical aperture) immersion lithography scanner. The polarimeter mask comprises newly developed thin polarizers and wide-view-angle quarter-wave (λ/4) plates. Although a light traveling through these polarization devices on the polarimeter mask reaches an image detector at the wafer level through a projection optics, Stokes parameters of the illumination light can be measured with no influence from polarization characteristics of the projection optics between the mask and the image detector.     

W-band Imaging Detector with Incoherent Illumination

A single-pixel imaging detector operating in W-band is described. It is based on a wideband receiving module using direct detecting circuitry and a transmitting unit with a pulse-modulated wideband noise source. The detector consists of a single transmit / receive channel mounted on a programmable scanner in an X-Y plane configuration. A LabView interface integrated with MatLab is employed allowing image continues reconstruction line-by-line. The application of incoherent illumination generated by a frequency-limited noise source improves image quality compared with conventional coherent sources used in active imagers. An image processing algorithm using a binary threshold level is considered with some examples of image reconstruction employing the detector.     

Image restoration in computed tomography: estimation of the spatially variant point spread function

An indirect method for determining the point-spread-function (PSF) in computed tomography (CT) is described. Unlike experimental techniques in which a resolution phantom is scanned to obtain the system PSF, the approach estimates the parameters of a model which describes the two-dimensional X-ray beam profile at each point as a convolution of the appropriately scaled focal spot intensity and detector sensitivity distributions. The model was validated by experimental measurement of the focal spot intensity distribution. Using known X-ray beam profiles, the PSF of a CT scanner can be derived by simulating the data collection process and applying conventional image reconstruction techniques. Visual comparison of directly measured and computed PSFs reveals an asymmetry resulting from misregistration of the phantom wires and the image grid.     

填充因子对微扫描系统成像质量影响分析

填充因子是探测器阵列设计的一个重要参数,因此有必要研究填充因子对微扫描系统成像质量的影响。以22微扫描方式为例,在详细分析微扫描技术能够减少由探测器欠采样造成的混淆效应的基础上,仿真了不同填充因子下的输出图像,引进结构相似度(SSIM)的评价指标,从图像质量评价的角度对仿真图像进行定量分析。仿真结果表明填充因子的增大能够减少混淆效应,提高成像质量。指出探测器填充因子的增大虽然能提高成像质量,但是对成像质量的影响是有限的,对图像的改善程度不大,并不是影响像质的主要因素,这对微扫描成像系统的设计提供了理论和应用参考。     

The design of an animal PET: flexible geometry for achievingoptimal spatial resolution or high sensitivity

Presents the design of a positron emission tomograph (PET) with flexible geometry dedicated to in vivo studies of small animals (TierPET). The scanner uses two pairs of detectors. Each detector consists of 400 small individual yttrium aluminum perovskite (YAP) scintillator crystals of dimensions 2×2×15 mm³, optically isolated and glued together, which are coupled to position-sensitive photomultiplier tubes (PSPMTs). The detector modules can be moved in a radial direction so that the detector-to-detector spacing can be varied. Special hardware has been built for coincidence detection, position detection, and real-time data acquisition, which is performed by a PC. The single-event data are transferred to workstations where the radioactivity distribution is reconstructed. The dimensions of the crystals and the detector layout are the result of extensive simulations which are described in this report, taking into account sensitivity, spatial resolution and additional parameters like parallax error or scatter effects. For the three-dimensional (3-D) reconstruction a genuine 3-D expectation-maximization (EM)-algorithm which can include the characteristics of the detector system has been implemented. The reconstruction software is flexible and matches the different detector configurations. The main advantage of the proposed animal PET scanner is its high flexibility, allowing the realization of various detector-system configurations. By changing the detector-to-detector spacing, the system is capable of either providing good spatial resolution or high sensitivity for dynamic studies of pharmacokinetics     

基于长波576×6扫描型热像仪的改进设计

通过对长波576×6扫描型热像仪的扫描器组件摆扫频率、探测器配置、AD采样速率、信号处理速度以及图像数据的隔行和插值处理等的改进,提高热像仪的帧频至25 Hz,使之转为标准热像仪,以满足一般红外跟踪观察系统的要求。     

红外探测器内部颗粒物对图像的影响

在高灵敏度的红外光学系统中,来自系统内部的热辐射是影响系统探测性能的重要因素之一。污染颗粒物通常是杂散辐射的主要来源,除了光学元件的表面污染,探测器内部也会存在污染颗粒物。文中主要研究探测器内部颗粒物对焦平面光场分布产生的影响。根据红外辐射及散射原理建立了相应的理论模型,对探测器内部不同温度、不同位置的颗粒物在焦平面上形成的光场分布进行了仿真计算和对比分析,并进行了实验验证。结果表明,探测器内部如有颗粒杂质,在一定的使用环境下,可在探测器焦面上产生黑斑、白斑、黑点白斑等异常现象,而这些异常光场分布会对场景中的红外目标物产生干扰,造成误判,从而影响对目标的准确识别。因此应采用措施以保证探测器内部的洁净度,防止颗粒物的产生。