近海激光通信分集技术对大气湍流扰动抑制的实验

为评估分集收发技术在近海面激光通信系统应用中对大气湍流扰动的抑制作用,设计了基于对多路1 550 nm激光光斑同步采集的验证实验方案。采用由时统终端触发的FPGA+多核DSP架构的实时图像处理系统实现目标中心位置的提取与目标灰度和的统计,进而得到激光从发射端至接收端的到达角起伏方差和闪烁指数。分别比较了等功率条件下单路发射和双路发射间、双孔径接收与等效单孔径接收间的到达角起伏方差和闪烁指数,同时比较了不同跨距下双孔径接收的效果。实验表明,在发射功率相同的情况下,与单路发射相比,双路发射能够有效地抑制因大气湍流扰动产生的到达角起伏和光强闪烁;在接收面积相同情况下,双孔径接收较单孔径接收所产生的到达角起伏与光强闪烁更弱,且在一定范围内,双孔径间的跨距存在最优值。     

利用传统全息片实现合成孔径数字全息的研究

分析了传统全息片的微观结构,介绍了细光束成像和合成孔径数字全息记录、再现的基本原理,研究了利用传统方法拍摄的散射物体透射式、振幅型全息片实现合成孔径数字全息的方法,给出了实验结果。理论分析和实验结果表明,利用传统透射式、振幅型全息片,通过光学显微镜放大制作子数字全息图和合成孔径数字全息图,经计算机处理是可以得到完整再现像的,其性质与细激光束照射成像一致。用子全息图再现像的复振幅叠加方法和采用子全息图再现像的强度叠加方法均可实现合成孔径数字全息图的再现,且强度叠加方法的视觉效果要好些,但它们对缩小再现像中散斑的尺寸没有帮助。用子全息图拼接成的合成孔径全息图得到的再现像效果最好,可以缩小再现像中散斑的尺寸,信噪比、分辨率均有提高。要得到更好的再现像,需要用更多的子数字全息图拼接成尺寸更大的合成孔径数字全息图。     

基于强度调制的编码孔径光谱偏振测量方法

为实现在单次成像条件下获取图像的光谱偏振信息,提出了一种基于强度调制的编码孔径测量方法。该方法采用消色差1/4波片、多级相位延迟器和检偏器组成的光谱偏振强度调制模块,将入射光的Stokes参量各元素谱调制到不同的频率上,利用编码孔径和色散棱镜组成的光谱成像系统对该调制光谱进行压缩编码,并通过CCD进行探测。利用TwIST算法重构出经调制的光谱信息,对各个频谱通道进行分离重构出Stokes元素谱。以单一像素点为例,对入射光强度调制、光谱重构及Stokes参量的解调进行了数值模拟。结果表明:该方法可实现对稀疏图像的光谱偏振信息的获取,该过程仅需对图像进行一次测量,因此具备高速获取能力。     

基于高速A/D转换器的视频数据采集系统

针对视频采集系统需要对摄像头输出的复合视频信号进行快速转化、采样、存储的要求,设计基于高速A/D转换器TLC5510的视频采集系统。模拟视频信号通过A/D转换器转化为8位灰度值,16位微处理器MC9S12DG128B通过普通IO口,控制FIFO存储器uPD42280写入和读取A/D转换结果,实现视频图像数据的高精度采集。分析了主要芯片的工作原理及时序,描述了软件控制图像数据采集流程。并将采得数据经过处理,与实际图像对比。实验结果表明,该系统在单行扫描时间50μs内能采集160个以上的有效像素点,成像质量高,能满足简单图像处理算法对数据的要求。     

Specification of the observation model for regularized image up-sampling.

Regularization is one of the most promising methods for image up-sampling, which is an ill-posed inverse problem. A key element of such a regularization approach is the observation model relating the observed lower resolution (LR) image to the desired higher resolution (HR) up-sampled image, used in the data-fidelity term of the regularization cost function. This paper presents an algorithm to determine this observation model based on a model of the physical acquisition process for the LR image, and the ideal acquisition process for the desired HR image, both from the same underlying continuous image. The method is illustrated with typical scenarios corresponding to LR and HR cameras modeled by either Gaussian or rectangular apertures. Experiments with some regularized image up-samplers demonstrate the importance of using the correct, adapted observation model as determined by our algorithm. Index Terms-Camera aperture, data fidelity, image up-sampling, interpolation, multidimensional signal processing, observation model, power spectral density (PSD), super-resolution.     

双孔径红外变焦光学系统设计

为了解决红外变焦系统短焦部分冷反射严重的问题,提出了一种双孔径设计方法,设计了一种双孔径红外变焦光学系统。系统工作波段为中波3.7 ～4.8 m,焦距为30/150/300 mm,10变倍比,具有100%冷光阑效率。对双孔径系统的短焦部分和单孔径系统短焦部分的冷反射强度进行了对比分析,双孔径系统的冷反射得到有效控制。双孔径红外变焦光学系统具有像质好、变倍比大、短焦冷反射小、结构紧凑的特点,可使大变倍比的红外变焦光学系统在红外成像系统中得到广泛应用。     

SAR图像质量外场试验与评估技术

SAR图像质量评估是评判SAR系统性能的关键指标,常用SAR图像质量评估参数包括目标分辨率、峰值旁瓣比和积分旁瓣比等。首先介绍了SAR图像质量评估参数的定义;其次分析了SAR图像质量评估参数测试误差,给出了单个角反射体时积分区间对积分旁瓣比的影响,以及多个角反射体时图像质量评估参数测试误差,并进一步给出了定标场地设计要求;最后介绍了SAR图像质量评估软件系统。SAR图像质量评估技术研究已在SAR系统试验中得到应用,开发的评估软件系统在sAR图像质量评估中具有一定的推广价值。     

基于统计理论的SAR图像斑点噪声滤波算法分析

合成孔径雷达图像固有的斑点噪声严重降低了图像的可解译程度,影响了后续目标检测、分类和识别等应用。文中通过对基于统计理论的SAR图像斑点噪声滤波方法进行比较分析,得出单个滤波器难以从去噪和边缘保持方面均达到最佳效果的结论。     

单发多收模式下无源雷达成像研究

首先分析了无源雷达成像系统的目标回波形式,得到了目标散射分布函数和雷达接收信号之间的傅里叶变换对关系;对单个外辐射源的情况,提出了利用部署多个接收站等效合成大的孔径对目标进行成像的方法.由于采集的数据非均匀分布且数据量很少,本文采用极坐标格式对数据进行处理,充分利用了原始精确数据,有效提高了成像质量.理论推导和计算机仿真结果说明该方法是可行的.     

多波段红外目标跟踪与辐射特性测量系统

介绍了一种对动态目标进行红外成像跟踪与辐射特性测量的系统。该系统采用大口径红外成像镜头,图像信号经放大、A／D转换和图像非均匀性校正,输出与目标辐射量成正比关系的数字图像信号。红外成像跟踪采用FPGA结合软件处理方法实现对目标的实时自动识别,进行形心、边缘与相关跟踪的计算。红外辐射特性测量采用基于PCI总线的高速图像采集板进行实时图像采集与显示。红外定标建立输出信号和标准黑体绝对辐射量的关系曲线,将原始的图像灰度数据换算为辐射通量密度。经外场试验证明该系统稳定可靠。     

基于GPS多普勒频移的SAR运动补偿研究

受平台载荷限制,无人机载SAR无法装载大型高精度定位设备,从而导致运动补偿精度较低,成像质量较差.结合SAR单帧图像积累时间较短的特点,基于GPS多普勒频移实现了高精度相对定位和运动补偿,获取了无人机载SAR高分辨图像.对基于GPS多普勒频移相对定位算法进行了推导,对算法性能进行试验验证与分析.试验结果表明,在较短持续时间内,算法的定位精度优于传统的基于伪距解算的定位算法.在此基础上,把算法应用于SAR运动补偿,获得了高分辨SAR图像,取得了较好的补偿效果.     

Assessment of Atmospheric Propagation Effects in SAR Images

TerraSAR-X, the first civil German synthetic aperture radar (SAR) satellite, was successfully launched on June 15, 2007. After 4.5 days, the first processed image was obtained. The overall quality of the image was outstanding; however, suspicious features could be identified which showed precipitation-related signatures. These rain-cell signatures are thoroughly investigated, and the physical background of the related propagation effects is provided. In addition, rain-cell signatures from former missions like SIR-C/X and the Shuttle Radar Topography Mission are provided for comparison. During the commissioning phase of TerraSAR-X, a total of 12 000 scenes were investigated for potential propagation effects, and about 100 scenes revealed atmospheric effects to a visible extent. Some of the particularly interesting events were selected and are discussed in greater detail. An interesting case of data acquisition over New York will be presented, which shows typical rain-cell signatures, and the SAR image will be compared with weather-radar data acquired nearly simultaneously (within the same minute). By comparing the images, it can be clearly seen that reflectivities in the weather-radar image of 50 dBZ may cause visible artifacts in SAR images. Furthermore, in this paper, we discuss the influence of the atmosphere (troposphere) on the external calibration of TerraSAR-X. By acquiring simultaneous weather-radar data over the test site and the SAR acquisition, it was possible to flag affected SAR images and to exclude them from the procedure to derive the absolute calibration constant. Thus, it was possible to decrease the 1 sigma uncertainty of the absolute calibration factor by 0.15 dB.     

Analytical modelling and software implementation of synthetic aperture radars

Synthetic aperture radar (SAR) imaging systems are a complement to passive remote sensing. However, the process of image formation is so complex that the final image in the system is formed only after three basic steps: raw data acquisition, forming the signal and the image space. In addition, there are various factors that are involved in the information recorded by SAR within the system and outside the system, such as radar, platform, processing algorithm, imaging region and channel. Each of these factors has been formed by many parameters and this issue adds to the complexity of the behaviour of SAR. Therefore, due to the complexity, providing a model that describes how the SAR imaging system works is highly important. In this paper, the performance of SAR in the image formation section is analytically modelled at first, and then implemented as software. Raw data acquisition is performed in CST software and the signal and image formation are performed in MATLAB software. This implementation provides many abilities, such as better interpretation of SAR images, simulating the effect of the important parameters in SAR images, etc.     

Depth-focused interior echo imaging

This paper is concerned with an echo imaging system which utilizes focused beams of an aperture along a specific contour, for example, a line or a circular arc, in both the transmit and receive modes for data collection. Such data collection strategies are useful for imaging internal structures of a target which are located at a certain depth relative to the aperture; unfocused echo signature of an interior structure possesses a low signal-to-clutter/noise power ratio, and is not desirable. The conventional methods for depth-focused echo imaging use transmit/receive focusing on a set of prescribed points in the spatial domain (that is, a two-dimensional grid); this is exceedingly time-consuming though it does not require any postprocessing of the measured data. The proposed scheme of depth-focusing along a contour requires a significantly smaller time period for data acquisition, and relies on a relatively fast Fourier-based method for image formation. This Fourier-based method is shown to be applicable in near-field as well as far-field imaging scenarios, and does not put any restrictions on the size of the aperture, the size of the target area, and the frequency of radiation. The approach is applicable in depth-focused imaging with a mechanically rotating focused aperture, or a phased array. Results are provided.     

Nonactive antenna compensation for fixed-array microwave imaging.II. Imaging results

Model-based imaging techniques utilizing microwave signal illumination rely heavily on the ability to accurately represent the wave propagation with a suitable numerical model. To date, the highest quality images from our prototype system have been achieved utilizing a single transmitter/single receiver measurement system where both antennas are manually repositioned to facilitate multiple illuminations of the imaging region, thus requiring long data acquisition times. In an effort to develop a system that can acquire data in a real time manner, a 32-channel network has been fabricated with all ports capable of being electronically selected for either transmit or receive mode. The presence of a complete array of antenna elements at data collection time perturbs the field distributions being measured, which can subsequently degrade the image reconstruction due to increased data-model mismatch. Incorporating the nonactive antenna-compensation model from Part I of this paper into our hybrid element near field image reconstruction algorithm is shown to restore image quality when fixed antenna-array data acquisition is used. Improvements are most dramatic for inclusions located in near proximity to the antenna array itself, although cases of improvement in the recovery of centered heterogeneities are also illustrated. Increases in the frequency of illumination are found to warrant an increased need for nonactive antenna compensation. Quantitative measures of recovered inclusion shape and position reveal a systematic improvement in image reconstruction quality when the nonactive antenna-compensation model is employed. Improvements in electrical property value recovery of localized heterogeneities are also observed. Image reconstructions in freshly excised breast tissue illustrate the applicability of the approach when used with our two-dimensional microwave imaging system.     

基于基模高斯光束的单光子捕获概率研究

建立了一种自由空间量子密钥分配的单光子捕获概率理论模型。基于基模高斯光束,推导了单光子捕获概率的表达式。得到影响单光子捕获概率的主要参量是发射机的跟瞄误差、光束远场发散角、发射机和接收机的链路距离和接收机天线孔径。针对低轨卫星-地面站间链路进行了数值仿真分析,得到单光子捕获概率一般在10-3~10-5量级。     

虹膜识别平台搭建和数据库建设

介绍了一个高性价比的虹膜识别系统解决方案,其中包括一套自动化虹膜采集仪以及上位机识别软件.同时基于该平台,通过对序列图像进行质量评价,构建了一个中等规模的高质量虹膜数据库,并给出了数据库的几个关键参数,为虹膜识别算法的研究提供了很好的支持.     

前视多通道合成孔径雷达解模糊成像方法

传统合成孔径雷达方位向分辨率仅由合成孔径提供,但在正前视区域多普勒分集有限,成像性能迅速下降且前视成像也存在固有的左右多普勒模糊问题。针对上述问题该文讨论前视多通道合成孔径雷达系统模型,提出一种理想直线航迹下空域零点约束自适应波束形成的成像方法,有效综合阵列实孔径和合成孔径提高正前视区域的成像质量,利用有限阵列空域自由度实现左右多普勒解模糊。首先对回波数据大前斜成像处理,得到左右模糊的图像,然后进行波束形成,将各通道图像加权并且相干累加,实现左右多普勒解模糊以及方位分辨率增强。仿真实验表明空域零点约束自适应波束形成的成像方法可对前视场景进行高分辨成像。     

主动红外探测式视觉生命探测系统

针对地震后救援现场光照度低、温度变化复杂等特点,设计一款视觉生命探测系统,该系统主要由图像采集、图像传输、图像处理及显示、系统控制四模块构成。当救援现场光照度≥1.0 lx时,系统对救援现场进行可见光图像采集;当救援现场光照度<1.0 lx时,采用红外主动探测方式,即系统近红外光源打开,CCD接收救援现场反射的近红外光并将其转化为图像信号。同时,为提高救援现场环境成像的信噪比,系统中图像处理模块对采集的图像进行相应处理。该系统可实现低照度下震后救援现场的高清晰成像要求,为救援人员制定高效可行的救援方案提供决策依据。     

三维快速因式分解后向投影算法

后向投影算法具有精确成像、易于补偿、适于多种阵列构型及信号形式等优点,广泛应用于雷达成像领域。针对三维成像中,巨大计算量带来的低运算效率问题,文中利用孔径分块的方式将二维快速因式分解后向投影（FFBP）扩展至三维成像应用,建立了适于三维FFBP成像的三维极坐标系,对三维FFBP中孔径划分问题、算法实现问题以及计算效率问题进行了分析。仿真结果验证了该算法,其成像效率可提高13.8倍。