大气遥感远紫外光谱仪绝对光谱辐照度响应度定标方法研究

主要针对可应用于空间高层大气遥感的远紫外光谱仪的光谱辐照度响应度定标方法进行研究。针对远紫外波段光谱测试标准装置少,实验系统所需真空度高,实验稳定性难以维持,传统漫反射板和积分球辐亮度定标方法在远紫外波段局限性大、难以利用等特点,研究了适用于远紫外光谱仪器的光谱辐照度绝对辐射定标方法,搭建了相应的真空实验系统,以一台远紫外光谱仪原理样机为对象对研究方法进行了实验验证。实验系统以标准氘灯、真空紫外单色仪和准直系统组成照射系统,将出射准直光辐照度用标准探测器进行标定,三者共同组成了标准光谱辐照度光源;利用该光源照射原理样机并读出相应信号,最终获得光谱辐照度响应度,从而实现了利用标准探测器进行照度传递的远紫外光谱仪器绝对光谱辐射定标,有效的进行了仪器定标。该方法定标不确定度约为7.7%,对远紫外波段空间高层大气遥感光谱仪的地面辐射定标研究具有重要意义。     

超大动态范围日盲紫外辐照度光源

为实现对动态范围达120dB的日盲紫外增强型电荷耦合器件(SBUV-ICCD)的辐照度定标,设计并实现了超大动态范围日盲紫外辐照度光源。首先估算出SBUV-ICCD的辐照度定标所需的动态范围,其次采用氘灯、积分球、高精度光阑及平直光轨等,基于辐照度距离平方反比定律实现了光谱结构不变,而辐照度在极大动态范围内连续变化的光源,并对其进行了动态范围及稳定性测试。结果表明,该光源实际覆盖辐照度0.278～2.8×10-7μW.cm-2,稳定性为0.93%/3h,能够满足SBUV-ICCD定标的需要,且可复用于紫外探测器面均匀性测试、成像系统辐亮度定标等。     

A practical means for calibrating an LED-based photometric stereo system

Conventional Photometric Stereo (PS) techniques are usually based on the assumption that the light sources are assumed sufficiently far from the object that all incoming light can be modeled using parallel rays. Meanwhile, for near-field lighting conditions the light sources are close to the object so the parallel ray model cannot be used. To determine the surface normal for each point on the object more accurately, the incoming light direction should be calculated individually for each point. In this work, based on a simple PS setup consisting of LED lamps and one camera, we present a practical method for calibrating lighting directions. First, an optical model of an LED was introduced in the calibration procedure to represent the surface irradiance and image irradiance more accurately. A reference sphere was used for the calibration so that the LED optical axis could be estimated by extracting the specular points from the reference sphere. By introducing the LED emitting model, distance between the LED and the specular point along the optical axis can be calculated. Thus, the incident lighting directions for various image points can be estimated individually. To improve the estimation robustness, a non-linear fitting approach was also applied. Experiments were conducted using objects and the results are compared with traditional methods to demonstrate its feasibility and improvement.     

Optical refractometry based on Fresnel diffraction from a phase wedge

A method that utilizes the Fresnel diffraction of light from the phase step formed by a transparent wedge is introduced for measuring the refractive indices of transparent solids, liquids, and solutions. It is shown that, as a transparent wedge of small apex angle is illuminated perpendicular to its surface by a monochromatic parallel beam of light, the Fresnel fringes, caused by abrupt change in refractive index at the wedge lateral boundary, are formed on a screen held perpendicular to the beam propagation direction. The visibility of the fringes varies periodically between zero and 1 in the direction normal to the wedge apex. For a known or measured apex angle, the wedge refractive index is obtained by measuring the period length by a CCD. To measure the refractive index of a transparent liquid or solution, the wedge is installed in a transparent rectangle cell containing the sample. Then, the cell is illuminated perpendicularly and the visibility period is measured. By using modest optics, one can measure the refractive index at a relative uncertainty level of 10(-5). There is no limitation on the refractive index range. The method can be applied easily with no mechanical manipulation. The measuring apparatus can be very compact with low mechanical and optical noises.     

基于探测器标准的高精度光谱辐射标准光源

本文在评述低温绝对辐射计和SIRCUS发展的基础上,讨论了基于探测器标准的光谱可调谐自校准标准光源的工作原理、发展与应用前景。在探测器型光谱辐射标准研究方面,工作在液氦温度的低温绝对辐射计不确定度达0.01%。美国国家标准与技术研究院(NIST)建立的均匀光源光谱辐照度和光谱辐亮度响应度定标装置(SIRCUS)采用一系列激光器,由低温绝对辐射计传递的硅陷阱探测器定标,不确定度已达到0.1%,成功应用于空间遥感仪器高精度辐射定标。分析认为,发展中的基于探测器标准的光谱可调谐自校准标准光源,定标精度高,自行校正老化、衰减,保证了定标精度长期稳定。     

新一代高温黑体和同步辐射装置及其在地外太阳光谱辐照度测量中的应用

在地外太阳光谱辐照度测量和大气定量遥感等项研究的推动下,近二、三十年,国际上光谱辐射计量技术发展十分迅速。基于先进的高温技术、优异的高温热解石墨材料和独特的设计,全俄光学物理测量研究所(VNIIOFI)研制出温度高达3 200～3 500 K、具有高均匀性和高稳定性的大面积普朗克高温黑体光源。基于低温绝对辐射计的滤光片辐射计迭代测温技术,使高温黑体温度测量不确定度小于0.5 K。在德国物理技术研究院(PTB),将这种高温黑体直接用于国际空间站地外太阳光谱测试仪器(SOLSPEC)的辐射定标,定标综合不确定度小于0.5%～1%。2008年德国物理技术研究院(PTB)建成名为计量光源(MLS)的新一代专用同步辐射存储环并投入使用。为调节同步辐射的光谱分布,稳态下其能量可设置为105～630 MeV任意值,相应特征波长随之从735 nm改变至3.4 nm。为在不改变光谱分布情况下改变光强,电子束流可调节 11个量级,即从 1个存储电子(相当于1 pA)到200 mA。美国国家标准技术研究院(NIST)在同步辐射紫外辐射装置(SURF Ⅲ)3号光束线上建立了使用同步辐射的光谱辐照度定标装置(FICUS),为紫外传递标准光源定标,光谱范围200～400 nm,相对测量不确定度1.2% (k=2)。新一代同步辐射装置为地外太阳光谱辐照度测量仪器,如SUSIM,SOLSTICE,SBUV,SIM和SOLSPEC等,短波段高精度辐射定标奠定了技术基础。该文描述新型高温黑体和同步辐射装置的建立与发展,光谱辐照度和光谱辐亮度标准的传递及国际比对并评述它们在太阳光谱辐照度测量中的应用。     

Traceability in Fluorometry: Part II. Spectral Fluorescence Standards

The need for the traceable characterization of fluorescence instruments is emphasized from a chemist’s point of view, focusing on spectral fluorescence standards for the determination of the wavelength- and polarization-dependent relative spectral responsivity and relative spectral irradiance of fluorescence measuring systems, respectively. In a first step, major sources of error of fluorescence measurements and instrument calibration are revealed to underline the importance of this issue and to illustrate advantages and disadvantages of physical and chemical transfer standards for generation of spectral correction curves. Secondly, examples for sets of traceable chemical emission and excitation standards are shown that cover a broad spectral region and simple procedures for the determination of corrected emission spectra with acceptable uncertainties are presented. With proper consideration of the respective measurement principle and geometry, these dye-based characterization procedures can be not only applied to spectrofluorometers but also to other types of fluorescence measuring systems and even to Raman spectrometers.     

太阳辐射的在轨监测和定标

采用宽视场设计,逐轨扫描太阳式测量方式的FY-3A太阳辐射监测仪,结合在轨一年半的太阳辐照度观测数据和地面实验与理论分析,研究了影响定标精度的因素,给出了修正方程和曲线,并通过与世界辐射基准(WRR)的地面外场定标实验,得到了FY-3A上的三台绝对辐射计的比例系数R1=1.008 3,R2=1.006 6和R3=1.006 5。日地距离的理论分析和实际太阳辐照度测量曲线均证明:地球近日点太阳辐照度值最大,远日点太阳辐照度值最小,且在±3.34%范围内随日期变化。利用天文公式,结合遥感源包中的准确测量时间,给出了日、地修正系数。另外,分析了冷空间背景辐射对定标精度的影响,给出了冷空间辐射值的计算公式,并结合宽视场设计和扫描式测量的特点,重点分析了采光结束时刻和刚捕获太阳光时刻入射角的差异给辐照度测量带来的影响,通过几何关系给出了入射角修正系数方程及修正曲线。最后,综合各定标修正系数,给出了在轨定标方程和定标曲线,并分析了定标精度。     

静态傅里叶变换光谱仪的微阶梯反射镜设计及制作

静态傅里叶变换光谱仪的反射镜采取微阶梯反射镜，使光谱仪可在无需空间驱动装置的前提下实现空域上各级次的同时采样。通过理论研究和对测试数据的对比分析，确定使用楔形玻璃条制作微阶梯反射镜。此方法采用常规光学零件加工工艺制作1个楔形玻璃块和10个楔形玻璃条，然后按序选取楔形玻璃条，并逐一光胶在楔形玻璃块的斜面上，且相邻楔形玻璃条的接触面用紫外胶固连；水平方向反复推动相邻后一个楔形玻璃条直到检测仪器测量出相邻楔形玻璃条的阶梯厚度差达到要求为止；用紫外灯固化紫外胶；重复以上步骤制作出所需台阶数目的微阶梯反射镜。和别的制作方法相比，此方法安全性和可行性高，而且具有一致性、台阶厚度可控特点，可制作出台阶高度误差为0.124 μm、表面粗糙度为12 nm的微阶梯反射镜，达到系统设计要求。     

高量值红外辐射照度校准技术研究

主要研究了1 000 W/m2以上红外辐照度测量仪的校准问题。针对红外辐照度测试仪实际使用情况，讨论了配备和未配备光学系统的测量仪校准方法，对于每种类型的辐照度测量仪给出了不同校准架构的校准算法。提出了利用高亮度大口径辐射源进行高量值辐照度的校准原理，组建了一套实验室专用的高量值红外辐照度校准装置，利用3 000 ℃腔式黑体和800 ℃大尺寸面源黑体进行了实际校准，给出了校准结果。最后讨论了现有高量值红外辐射照度校准方法的改进方向。     

激光点阵扫描法绝对定标太阳辐射计直射通道研究

利用可调谐激光器作为光源,以溯源于低温绝对辐射计的标准传递探测器作为激光束功率测量探测器,采用激光点阵扫描方法在太阳辐射计有效孔径光阑面形成均匀照度场,精确测量太阳辐射计870 nm无偏直射通道中心波长处绝对辐照度响应度。利用灯-单色仪系统扫描获得该通道相对光谱辐照度响应度,最终在实验室条件下获得该通道绝对光谱辐照度响应度,联合大气层外太阳照度谱数据通道内积分得到该通道大气层外响应常数V₀值,与NASA的GSFC中心的2009年定标结果差异仅为3.75%,定标不确定度达到2.06%,验证了这一新技术的原理可行性。     

圆柱筒式脉冲光源辐射均匀性的模拟

圆柱筒式脉冲均匀光源在各种光学标定中有广泛应用.应用Monte-Carlo方法对光子进行跟踪模拟,通过变权重法和固定权重法两种算法得到出光面接收的相对光照度.当内壁反射类型、光源的位置、圆柱筒的高度与直径比不同时,出光面形成的光照度均匀性不同.通过模拟结果可知,当内壁为漫反射时,圆柱筒长度与直径比越大,出光面的光照度越均匀;但当比值大于3/2时,均匀性已无明显变化.最终得到满足标定实验要求的圆柱筒的最佳结构.     

一种用于UV-A、UV-B波段地基观测的光谱辐射计

研制了一台可以在250 nm~400 nm波段测量绝对光谱辐亮度和绝对光谱辐照度的扫描式光谱辐射计,辐亮度辐照度相对定标准确度2％,可用于UV-A、UV-B紫外波段地基观测.通过在云南丽江地区(26°52＇N,100°13＇E)开展的大气散射光谱辐亮度和地面太阳直射紫外光谱辐照度观测试验,进一步检验了仪器的性能.观测数据与利用MODTRAN模式模拟计算值存在约8％的偏差,分析了产生偏差的相关因素.     

宽波段太阳辐照度仪光谱定标方法研究

宽波段太阳辐照度仪采用fèry棱镜分光,利用线阵CCD反馈控制光谱扫描,波长覆盖范围为400~2 500nm.为实现该仪器的高准确度光谱定标,在实验室内利用单波长激光器和OPO激光器分别作为光源.通过光谱扫描,得出定标波长与CCD像元的对应关系.根据棱镜参量和光路设计参量推导出全波段内光谱定标方程,实现全波段光谱定标.通过与其他特征波长比较,分析得出光谱定标合成不确定度优于0.5nm.用定标好的仪器进行室外测量,将测量结果与大气辐射传输软件modtran4模拟结果相比对,可得实际测量的大气吸收峰与模拟结果一致.将该方法在红外波长区域定标结果与传统的多项式拟合光谱定标方法对比,显示该定标结果优于传统多项式拟合方法.证明该定标方法的正确性和仪器设计的合理性.     

Constructing feature points for calibrating a structured light vision sensor by viewing a plane from unknown orientations

To calibrate a structured light vision sensor, it is necessary to obtain at least four non-collinear feature points that fall on the light stripe plane. We propose a novel method to construct non-collinear feature points used for calibrating a structured light vision sensor with a planar calibration object. After the planar calibration object is moved freely in the range of measuring of the structured light vision sensor at least twice, all the local world coordinates of the feature points falling on the light stripe plane can be readily obtained in site. The global world coordinates of the non-collinear feature points in the local world coordinate frame can be computed through the three-dimensional (3D) camera coordinate frame. A planar calibration object is designed according to the proposed approach to provide accurate feature points. The experiments conducted on a real structured light vision sensor that consists of a camera and a single-light-stripe-plane laser projector reveal that the proposed approach has high accuracy and is practical in the vision inspection applications. The proposed approach greatly reduces the cost of the calibration equipment and simplifies the calibrating procedure. It advances structured light vision inspection one step from laboratory environments to real world use.     

平顶线结构光的中心检测算法及光刀平面标定

针对传统线结构光光刀平面标定方法测量精度不高,应用范围小的问题,提出基于平面标靶的线结构光系统光刀平面标定,对无激光的标靶图片进行迭代摄像机标定,有激光的标靶图片进行光刀平面标定.提出光强符合均匀分布的平顶激光检测中心算法,将平顶激光建模为矩形的台阶函数,估计背景亮度和前景亮度,确定亮条纹宽度,再将窗口内的有效像素参与重心计算,得到光条纹中心.用该算法对不同噪声及不同量块的图片进行处理,结果表明,处理后图像的均方根误差分别在0.149pixel和0.176pixel内,表明该算法抗噪声能力强、精度高.用该算法提取光条中心,计算光条在标靶上的位置,根据至少两个姿态下的光条中心三维点,基于最小二乘法拟合光刀平面.通过迭代摄像机标定和光刀平面标定,利用三角测量法,在立体视觉模型下获取物体的三维点云数据.实验测量两个距离为100.5mm的标准球,相机与标准球距离为500mm,比较两球心距离与标准距离,测得平均误差为0.236mm.表明平顶激光检测中心算法切实可行,光刀平面标定方法基本满足要求.     

A Multi-Spectral Polarimeter for Measurements of Direct Solar and Diffused Sky Radiation: Calibration and Measurements

A multi-spectral polarimeter (FPR1000) is designed to measure the radiance and degree of polarization of the sky radiation as well as the extinction of solar irradiance using the same optical system. This enables us to make consistent measurements of the direct solar and diffused sky radiation. Measurements are made at the same wavelength regions as Polarization and Directionality of the Earth’s Reflectances (POLDER) and Ocean Color and Temperature Scanner (OCTS) onboard Advanced Earth Observing Satellite (ADEOS). Based on measurements for the Langley plot calibration made at Mauna Loa Observatory, the calibration constants are obtained by considering the effect of absorption by water vapor and uniformly mixed gas. Preliminary analyses of the measurements of sky radiation and direct solar irradiance carried out in the western part of the Pacific Ocean are presented. Combined measurements of the extinction of solar irradiance, and the radiance and degree of polarization of sky radiation could be useful in improving retrieval of optical characteristics of aerosol and for atmospheric correction.     

均匀线状激光等离子体X光单色源和软X光胶片响应特性的标定

利用均匀线聚焦激光产生的等离子体和软X针孔透射光栅谱仪获得了均匀的线状软X光单色光源.在这一光源基础上,利用加阶梯膜的新方法首次标定了国产无保护层5F软X光胶片在软X光波段的响应特性.     

高灵敏度瞬态辐射高温计

 新研制了一台瞬态辐射高温计。它在设计上做了以下改进，采用：（1）双向色性分光镜作为分光器件，将各个通道波长的分光率提高到85%以上；（2）低输入阻抗宽频高增益（50 dB）信号放大技术做为高温计的后续电路，大大提高了高温计的探测灵敏度，同时也保证了测量系统的快速响应；（3）光谱辐照度方法做零前标定，使零前标定工作方便和可靠。以氯化钠单晶作为实例，测量了它在36.0~60.0 GPa冲击压力下的热辐射历史，获得了1 500~3 600 K冲击温度范围内的瞬态光谱辐射，高温计的响应时间优于5 ns。     

星载太阳紫外光谱监视器的地面辐射定标

星载太阳紫外光谱监视器是一种小型化、高精度紫外-真空紫外光谱辐射计,它有两种工作模式,即探测太阳紫外光谱辐照度的太阳模式和探测大气的太阳后向散射紫外光谱辐亮度的大气模式。对应这两种工作模式分别建立了紫外-真空紫外光谱辐照度和紫外光谱辐亮度定标装置。光谱辐照度标准灯直接辐照仪器的漫反射板进行仪器的光谱辐照度响应度定标,光谱辐照度标准灯辐照标准漫反射板形成朗伯面光源进行仪器的光谱辐亮度响应度定标。误差分析表明:160~250 nm光谱辐照度绝对定标误差为6.5%,250~400 nm为4.3%;250~400 nm光谱辐亮度绝对定标误差为5.9%。星载太阳紫外光谱监视器获得的地外太阳紫外光谱辐照度与大气的太阳后向散射光谱辐亮度数据,同国际上的观测结果相比一致性达±10%。