CCD的输出响应与相机MTF测试

以往在测试CCD相机的调制传递函数 (MTF)时 ,通常未考虑CCD像元的输出响应对测试的影响 ,因而导致了相机的MTF测试数据与理论计算值存在着一定的偏差。在采用高对比度靶标对线阵CCD相机MTF进行测试时 ,根据对测试数据的分析 ,发现在CCD像元的响应中包含着一种不同于像元暗电流的基底响应。通过考察CCD在不同照度下的输出响应 ,将以往的CCD绝对定标公式进行扩展 ,可以得出CCD像元的基底响应与暗电流对计算相机MTF的影响关系。据此 ,可以在CCD相机系统测试过程中得到相机的真实MTF数据 ,并且为CCD相机的图像后期处理提供了一种方法     

TG-2/MAI CCD像元响应特性不一致性的在轨分析及校正（英文）

CCD像元响应特性的差异是制约MAI成像质量及其数据定量化应用的主要因素之一。为了提高MAI数据质量,本文基于全量程多段分析与校正法,利用2016年9月至2018年3月期间共104403帧观测数据,分别对MAI偏振通道和非偏振通道的像元响应特性的不一致性开展了在轨分析与校正,并利用GOME-2和MODIS数据产品对校正结果进行了验证。首先,假定观测样本足够多,即每个CCD像元观测的样本具有相同的遍历性,则各CCD像元对应的所有样本的平均DN值可以代表CCD各像元的响应特性;其次,利用104 403帧观测数据构建各个通道的参考图像,并利用MAI中心5×5像元给出各参考图像对应的标准DN值;在此基础上分别对MAI偏振通道和非偏振通道开展了像元响应特性的分析,结果表明, MAI各通道均存在CCD像元响应特性不一致的问题,各通道的不一致性大约在4%～10%之间,对偏振通道而言,同一偏振波段的三个偏振通道之间像元响应特性的不一致性有一定的相似性,像元响应特性不一致性的差异基本在1%以内。然后,将MAI近两年的观测数据分为前后两个时间段进行对比分析。结果表明:前后两个时间段偏振通道和非偏振通道的图像均具有很好的一致性,即CCD像元响应特性未随时间发生显著变化,这也进一步验证了前面MAI数据量充足的假定。因此,可以利用全量程多段校正法逐通道逐像元开展CCD像元响应特性不一致性的校正。基于该方法校正后, MAI图像质量得到显著改善,图像四周响应偏低的区域明显改善,基本和周围像元的响应达到了同一水平;图像更加平滑,颗粒感基本消除;部分区域的场景发生了变化,特别是碎云等反射率介于中低反射率之间的目标。基于GOME-2的交叉对比结果表明,MAI 565, 670和763 nm波段反射率与GOME-2的参考反射率之间的平均绝对偏差分别由校正前的1.6%, 4.2%和2.2%减小至校正后的0.5%, 2.6%和0.4%;此外,基于多通道云识别方法开展的云检测表明,校正后的MAI云检测结果与MODIS云检测产品一致性更好。因此,全量程多段校正方法可以有效解决MAI CCD像元响应特性的不一致性,显著提高MAI在轨观测的质量,且该方法也可以应用于其他CCD仪器的在轨校正。     

TG-2/MAI CCD像元响应特性不一致性的在轨分析及校正

CCD像元响应特性的差异是制约MAI成像质量及其数据定量化应用的主要因素之一。为了提高MAI数据质量，本文基于全量程多段分析与校正法，利用2016年9月至2018年3月期间共104403帧观测数据，分别对MAI偏振通道和非偏振通道的像元响应特性的不一致性开展了在轨分析与校正，并利用GOME-2和MODIS数据产品对校正结果进行了验证。首先，假定观测样本足够多，即每个CCD像元观测的样本具有相同的遍历性，则各CCD像元对应的所有样本的平均DN值可以代表CCD各像元的响应特性；其次，利用104 403帧观测数据构建各个通道的参考图像，并利用MAI中心5×5像元给出各参考图像对应的标准DN值；在此基础上分别对MAI偏振通道和非偏振通道开展了像元响应特性的分析，结果表明，MAI各通道均存在CCD像元响应特性不一致的问题，各通道的不一致性大约在4%～10%之间，对偏振通道而言，同一偏振波段的三个偏振通道之间像元响应特性的不一致性有一定的相似性，像元响应特性不一致性的差异基本在1%以内。然后，将MAI近两年的观测数据分为前后两个时间段进行对比分析。结果表明：前后两个时间段偏振通道和非偏振通道的图像均具有很好的一致性，即CCD像元响应特性未随时间发生显著变化，这也进一步验证了前面MAI数据量充足的假定。因此，可以利用全量程多段校正法逐通道逐像元开展CCD像元响应特性不一致性的校正。基于该方法校正后，MAI图像质量得到显著改善，图像四周响应偏低的区域明显改善，基本和周围像元的响应达到了同一水平；图像更加平滑，颗粒感基本消除；部分区域的场景发生了变化，特别是碎云等反射率介于中低反射率之间的目标。基于GOME-2的交叉对比结果表明，MAI 565，670和763 nm波段反射率与GOME-2的参考反射率之间的平均绝对偏差分别由校正前的1.6%，4.2%和2.2%减小至校正后的0.5%，2.6%和0.4%；此外，基于多通道云识别方法开展的云检测表明，校正后的MAI云检测结果与MODIS云检测产品一致性更好。因此，全量程多段校正方法可以有效解决MAI CCD像元响应特性的不一致性，显著提高MAI在轨观测的质量，且该方法也可以应用于其他CCD仪器的在轨校正。     

基于B样条插值算法的亚像元技术的研究

亚像元动态成像技术是目前实现卫星相机小型化及提高相机空间分辨率的一种有效方法。在不改变TDICCD相机的焦距、成像距离,以及TDI CCD器件的像元尺寸的前提下,亚像元动态成像技术可以提高相机的空间分辨率。利用B样条插值算法,研究了TDI CCD相机的图像的亚像元动态插值问题,由两幅相机输出的原始图像经过算法得到比原图像分辨率高的图像,并对比了该算法与其它几种算法的效果,分析结果表明,该算法较其它算法得到的高分辨率图像的效果更佳。     

航天TDI CCD相机成像拼接快速配准算法设计与分析

为解决卫星灵活机动多模式成像中多片TDI CCD拼接像元失配的问题,提出了一种实现TDI CCD相机成像搭接与错位像元快速拼接配准的匹配算法。通过分析卫星侧摆成像过程焦平面上像移速度矢量变化导致的多片TDI CCD拼接成像像元失配现象,设计了成像速度矢量光线追迹与齐次坐标变换方法,计算了侧摆成像过程中影响图像失配的偏流角、像移速度矢量和两片TDI CCD拼接纵向错位方向和横向搭接方向的像元数目。利用小卫星姿态控制系统半物理仿真平台和TDI CCD原理样机系统对两片TDI CCD拼接像元匹配算法进行实验验证。结果表明:视场角为10°的TDI CCD相机在卫星侧摆30°成像时,经过1个拼接周期后,两片TDI CCD拼接纵向错位和横向搭接像元数目由初始的148.5和50变为137和49,其中横向搭接像元数目与理论计算结果仅有0.1pixel的偏差,纵向错位像元数目与理论计算结果基本一致。经实验和理论对比分析,所设计的纵向错位与横向搭接像元快速拼接配准算法能够解决TDI CCD图像拼接的准确性,确保图像像元匹配进而获得高质量的图片。     

矩形靶标测试CCD相机调制传递函数的研究

利用矩形靶标测量CCD相机的整机调制传递函数时,由于靶标与CCD像元之间存在初始角度误差与初始位置误差,实验测得的调制传递函数小于CCD相机实际调制传递函数。根据调制传递函数的定义,模拟CCD对具有初始角度误差与初始位置误差的矩形靶标成像,推导出了CCD像元的亮度分布公式,从而给出了调制度与初始角度误差和初始位置误差的关系,并分别对具有初始角度差、初始位置差的情况进行分析。最后利用像元间的亮度差推导出计算初始角度误差的理论公式并进行了仿真验证。     

光学相关法测量空间相机像移的性能研究

为了测量由卫星姿态不稳定或振动等原因引起的空间相机的亚像元像移,使用了光学联合变换相关器(JTC)对安装在相机焦面上的辅助面阵CCD采集到的相邻两帧图像进行相关运算.给出了使用该方法测量像移的原理,搭建了实现JTC的光学实验平台,对JTC测量相机像移的性能进行了实验研究.结果表明,使用JTC完全可以测量空间相机的亚像元...     

多光谱CCD相机配准的图像校正

通过分析线阵CCD的成像过程,对多光谱CCD相机成像的彩色图像合成方式进行了研究,提出了一种处理方法。通过将各谱段CCD的每个像元信号分别扩展成一个二维像素数组后再进行彩色合成,尝试了利用后期处理的方式校正多光谱相机的配准偏差,改善了相机彩色合成图像的质量。结果表明,这种对CCD信号进行处理的合成方式为空间遥感相机的研制提供了一种技术手段,既能减小配准偏差的影响,同时又能够在不改变相机性能的情况下改善相机输出彩色图像的质量。     

基于微光像增强器的偏振成像系统设计与实验

为验证用微光像增强器实现偏振成像的可行性,根据偏振成像原理,设计了基于分时型偏振成像技术的微光偏振检偏器。选用三代像增强器和高动态范围数字CCD,设计了相应大口径成像物镜和中继光学耦合透镜,获得了高透过率、高调制函数(MTF)的图像耦合性能。采用数字CCD、数字图像采集卡,编写了相应图像处理软件,实现了实验室和野外微光条件下的人造目标和自然景物的偏振探测成像。结果表明,原始图像中目标与背景对比度之比为1.35,基于微光像增强器的偏振成像系统的目标与背景对比度之比为2.35,微光偏振成像能够提高夜间环境下人造目标和自然背景的对比度。     

TDICCD亚像元技术应用于小相对孔径光学系统

TDI CCD器件和亚像元成像技术都是实现相机小型化的有效途经,TDI CCD器件和亚像元成像技术结合应用于小相对孔径光学系统具有重要的应用价值.就成像系统需要满足Nyquist频率处静态传函≥0.2条件对系统进行了分析、讨论,并就设计中引入信噪比指标提出了一点建议.     

Polarization detection with polarization interference imaging spectrometer

A new method of measuring the intensity and state of polarization of optical radiation by means of the high resolution polarization interference imaging spectrometer (PIIS) is introduced and theoretically investigated in this paper. The error accuracy analysis is proposed, and it is proved that the system is very stable and precise in theory. In this new way, the polarized characteristics of light could be taken good use to analyze and distinguish objects in passive remote sensing with the PIIS, which means that the polarization interference imaging spectrometer now can be used not only as cameras and interferometers but also as polaristrobometers.     

利用偏振干涉成像光谱仪进行偏振探测的新方法

以往对干涉成像光谱仪的研究通常仅限于对光的干涉特性的利用，即由目标干涉图得到其光谱图，而忽略了其丰富的偏振信息.为了在利用光的干涉特性的同时还充分利用光的偏振特性，在原有偏振干涉成像光谱仪的基础上，结合现有的干涉成像光谱技术与偏振探测原理，提出了一种利用现有偏振干涉成像光谱仪获取探测目标的偏振参数(偏振度、偏振方位角等)的新方法，并对其精度误差进行了理论分析，证明了其不但具有较高的稳定性而且具有极高的测量精度.因此，若把以往的偏振干涉成像光谱仪看作是照相机与光谱仪功能的结合，则现在可以将之理解为成像仪、光 关键词： 偏振探测 偏振干涉成像光谱仪 Stokes参量 Savart偏光镜     

Holographic recording and retrieval of polarized light by use of polyester containing cyanoazobenzene units in the side chain

We examined the holographic recording properties of polyester containing cyanoazobenzene units in the side chain. It was revealed that, when a linearly polarized object beam with an arbitrary polarization direction was recorded, the retrieved beam had the same polarization state as that of the object beam, with a constant diffraction efficiency of 0.1. Moreover, two object beams with mutually orthogonal linear polarization could be recorded and retrieved separately from the same area. This is, to our knowledge, the first example of holographic polarization multiplexing. The retrieved images were found to resolve details of ~40line pairs/mm and a 40-mum -pitched checkerboard pattern. The resolution of the system is limited by the CCD cameras that are used. Polarization encoding to increase the storage capacity and (or) the signal-to-noise ratio of holographic data recording is also discussed.     

偏振显示及椭圆偏振光测量实验

以单束正交线偏振光为光源,利用角向偏振显示器,采用CCD摄像机进行图像采集,利用Matlab软件进行图像处理,设计了一种由He-Ne激光器、角向偏振显示器组成的偏振光偏振方向显示系统,并研究了其角度特性.实验结果表明:系统在起偏器的起偏角分别为0°、90°、180°、270°、360°时,角向偏振显示器偏振显示角度的测量准确度分别为0.480°、0.168°、0.528°、0.421°、0.340°,测量精确度分别为0.208°、0.576°、0.660°、0.603°、0.466°,测量数据拟合曲线的线性相关系数为0.999.结合1/4波片,检偏器和分光比为50:50的分束器,构建了椭圆偏振光测量系统,完成了椭圆偏振光测量实验,椭圆率为0.198.     

基于偏振菲涅尔反射比分布的主动偏振成像目标辨别方法

由于偏振特性是材料自身所决定的物理特性,其偏振图像含有丰富的目标信息,利用偏振信息对目标进行识别一直是国内外目标探测领域的研究热点,而主动偏振成像较之被动偏振成像更具有信噪比高以及可控性好等优势。在详细分析了偏振菲涅尔反射比分布的理论基础上,提出了一种利用探测物体表面的偏振菲涅尔反射比的主动偏振成像方法。该方法在发射端将偏振方向正交的两种偏振态的光源交替照射到目标场景中,在探测端用分别装有两个偏振方向垂直的偏振片的CCD采集偏振图像。同时,将探测端架构在不同的探测方向采集目标经主动光源照射后的偏振数据,最后将这些数据传输到计算中心,通过最优化拟合技术反演出不同目标的光学常数,由于不同目标的表面材质不同,其反映出的光学常数就不同,从而达到辨识不同材质目标的目的。实验分别采用了仿真数据和实测数据来验证该方法的有效性。仿真实验显示,所提出的方法利用材料的光学常数对不同材料进行区分不仅是科学的而且更方便有效。实测数据进一步验证了该方法能够较好的恢复出目标的相关光学常数,尤其在区分金属和非金属材料方面表现突出,并且探测方法结构简单实用,在目标探测、伪装识别等领域中有较大应用前景。     

New studies on scattering properties of different kinds of soot and carbon-black

New polarization and brightness curves as a function of scattering angle are studied at λ=632.8 and 543.5 nm using PROGRA2 instruments (Propriétés Optiques des Grains Astronomiques et Atmosphériques) for four different kinds of soot and for two samples of carbon-black levitating in the cloud. The soot samples are also studied on the deposited surface. Two of the soot samples are issued from incomplete combustion of Toluene liquid solvent under two different combustion conditions. Two others are issued from a solid polymer. Polymethyl Methacrylate or PMMA under two different combustion conditions. These new studies are done using new more sensitive cameras than previous ones, allowing darker agglomerates to be detected.     

Temporal filtering with fast ICCD cameras in Raman studies

A common problem when applying Raman scattering in applied research is spectral interference from laser‐induced fluorescence. Extensive work has been invested in developing spectral and polarization filters as well as modulation schemes to refine spontaneous Raman signals. This current work, however, focuses on utilizing the temporal domain using a picosecond laser system and ICCD cameras with relatively short decay of the camera gate to prevent the fluorescence tail from being captured in Raman experiments. Further, the approach of using an ICCD camera to perform temporal filtering is compared to earlier proposed detection schemes using streak cameras or Kerr gates. The temporal‐filtering scheme is evaluated in a spectroscopic investigation where a background subtraction algorithm is presented. The temporal‐filtering scheme was also evaluated for Raman imaging of a levitated water droplet surrounded by fluorescing toluene vapor. Furthermore, the temporal‐filter detection scheme was simulated in order to provide straight forward evaluation tools to estimate the potential of performing temporal filtering with a laser/camera system considering: laser‐pulse duration, time jitter, camera‐gate characteristics, gate delay times, fluorescence lifetimes, and relative signal strength between the Raman and fluorescence signal. The fluorescence signal was modeled with a closed two‐level system, and the simulated results were compared to results from an investigation of the rising slope of toluene fluorescence. These evaluation tools and experimental investigations may serve as guidelines for planning and performing Raman measurements in situations where traditional filter‐rejection schemes are insufficient. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental Study on the Spatial Performance of Photorefractive X-ray Semiconductor Ultrafast Response ChipEI北大核心CSCD

The traditional ultrafast electric vacuum devices are usually based on the mechanism of photoelectric conversion, and their performance is restricted by factors such as material response and space-charge effect. It is difficult for the devices like microchannel plate framing cameras, Dilation X-ray Imager (DIXI) , streak cameras to achieve high temporal resolution (100 fs similar to 1 ps) and spatial resolution (similar to mu m) two-dimensional imaging. Ultrafast imaging technology based on photorefractive effect is a new ultrafast diagnostic technology, which has the advantages of high spatiotemporal resolution, all-optical, all and anti radiation. The nonequilibrium carrier lifetime of low temperature grown AlGaAs (LT-AlGaAs) can reach ps-level. The Ultrafast Response Chip (URC) made of LT-AlGaAs has the characteristics of high temporal resolution, meanwhile, good spatial performance is the other key factor for its application. In this paper, the spatial performance of LT-AlGaAs URC is experimentally studied using X-ray, generated by high-energy nanosecond pulsed laser-produced plasma, as the signal. The results show that the URC has the ability of high spatial resolution and large-scale imaging in the X-ray energy dynamic range of 120: 1. The optimal spatial resolution is >= 35 1p/mm (R) MTF = 0.1, and the imaging frame can reach 6.7 mm x 6.7 mm. The results further verify the feasibility of ultrafast diagnostic technology based on photorefractive materials. In the future, LT-AIGaAs URC will be combined with ultrafast framing technologies such as dispersion framing and polarization chirp framing to realize multi-frames and high spatiotemporal resolution two-dimensional imaging.     

A. 高速摄影机和判读设备

本文介绍了间歇式、棱镜补偿式、转镜高速摄影机和判读仪的新进展,也涉及到十八届国际高速摄影与光子学会议展览会的部分内容。     

Evaluating NIR-Red and NIR-Red edge external filters with digital cameras for assessing vegetation indices under different illumination

Consumer-grade digital cameras with or without external filters are recognized as a cost-effective method of vegetation monitoring. These cameras could produce time series information related to biophysical properties of vegetation. This paper evaluates the use of low-cost external filters with digital cameras for assessing vegetation indices (VIs). The system was implemented for ground-based (handheld) remote sensing in assessing biophysical properties of vegetation like plant phenology and Chlorophyll content. It also has high potential for above-canopy measurement using low-altitude remote sensing (LARS). In this study the modified cameras were used to capture near-infrared (NIR), red-edge (RE), and red (R) bands using proposed external filters. We use the low-cost NIR-R and NIR-RE external filters with modified cameras and tested the cameras performance using custom chamber under different illumination. Based on our findings, a method was proposed for enhancing the value of VI, which comprised the extracted DN of two broadbands like NIR and R. New ranges of broadband in red edge area (RE_high and RE_low) are proposed as alternative bands in estimating Chlorophyll content. In addition, evaluation and implementation for assessing VIs are detailed in this study.