空间目标可见光散射特性建模方法研究

针对空间目标的可见光散射特性提出一种建模方法.在分析空间目标所处的背景辐射环境基础上建立了空间目标背景辐射物理模型.对目标表面进行面元划分后,基于辐射理论引入双向反射分布函数模型来描述目标表面面元的光散射特性,将目标各个表面所有面元散射分量叠加建立了目标可见光散射特性的数学模型.建立目标本体坐标系,通过坐标变换确定目标、背景辐射源与探测器的相对位置关系,利用矢量坐标法确定目标对观测系统的“可视表面”.根据给定的目标几何结构尺寸和物性参量仿真获得了目标在轨光学特性.计算结果验证了建模的有效性.     

基于双向反射分布函数的空间卫星紫外动态特性研究

根据目标所处的背景辐射环境,对空间卫星的紫外散射特性进行建模方法研究。依据目标表面材料属性与表面状况对目标表面进行区域分解与网格划分。基于辐射理论引入双向反射分布函数模型来描述目标表面网格单元的光散射特性,将目标各个表面所有网格单元散射分量叠加建立了目标紫外散射特性的数学模型。利用给定的目标几何结构尺寸和物性参数仿真获得了目标在轨动态光学特性。在某一观测角度下太阳帆板在探测光学系统入瞳产生的辐照度值与卫星本体接近,最大量级为10-11W/m2。仿真结果表明太阳帆板在目标特性分析时不可忽略。     

基于双向反射分布函数实验测量的目标散射特性的分析

介绍了一种用双向反射分布函数(BRDF)测定仪进行目标双向反射分布函数测量的方法。以聚四氟乙烯(F4)粉压制板作为反射标准板,给出了F4标准板及所测样品在双向反射分布函数测定仪上的测量数据。被测样片的反射光强度经标定过的漫反射标准板传递,最终在较高分辨率的半球空间内分析计算出了样品在红外(1.06μm和0.86μm)波段的双向反射分布函数。实验结果表明,该方法是一种分析目标散射特性的可行性方法。     

深空背景下空间目标紫外特性建模方法研究

紫外探测具有灵敏度高、虚警率低等特点,空间目标紫外特性分析对空间目标探测具有重要意义.针对空间目标紫外特性提出了一种精确建模方法.根据空间目标的背景辐射环境及表面材料属性,引入区域分解与网格划分的思想,利用双向反射分布函数建立了空间目标紫外特性的数学模型.通过矢量坐标变换,确定了背景辐射源、探测器与目标的相对位置关系.以资源一号卫星和风云三号卫星为例,进行了目标紫外特性的仿真分析,计算获得了目标在探测器入瞳处的紫外辐照度随时间的变化关系.仿真结果验证了建模方法的正确性. 关键词： 空间目标 紫外特性 双向反射分布函数 建模与仿真     

空间目标表面材料光谱双向反射分布函数测量与建模

介绍了双向反射分布函数（BRDF）的绝对测量原理和方法,选用光谱分辨率为3 nm的光谱辐射度计及精度为001°的三维转角系统,搭建了BRDF自动测量平台,对空间目标表面包覆材料在400—2500 nm的光谱BRDF进行了测量.结果表明,BRDF曲线极大值所对应的散射角度一般在镜反射方向左右,其余BRDF值随散射角变化很平缓,从中间向两边逐渐变小,近似成余弦分布.测量误差为495%.应用模拟退火算法,结合BRDF五参量统计模型,获得了测量光谱范围内各波长对应的共2101组五参量值,通过对比参量计算结果和 关键词： 双向反射分布函数 绝对测量 误差分析 参量模型     

基于神经网络的粗糙表面双向反射分布函数建模

分析粗糙表面双向反射分布函数的测量方法,提出一种使用人工神经网络技术建立目标表面材料双向反射分布函数模型的方法。给出测量样品多个入射角度下的BRDF随散射角变化的曲线,从中选取部分曲线输入到神经网络,使用贝叶斯正则化方法训练网络,最终获取双向反射分布函数和入射角、散射角的映射关系模型。使用网络模型计算参与训练和未参与训练的输入角度的散射分布曲线,与实验测量曲线进行比较,结果表明：建立的模型正确,具有应用价值。     

非分辨空间目标光谱双向反射分布函数的实验室平行测量

为了克服非分辨空间目标识别研究中外场观测和计算机仿真手段的局限性,采用实验方法模拟了天基光照场景,用仪器和技术平行类比望远镜观测时光源-目标-探测器方位,并测量了某高保真卫星模型的光谱双向反射分布函数.分析了空间目标光谱散射模型、实验场旋转轴系和环境模拟设备布局.根据在轨卫星的轨道和姿态建立了外场观测几何到室内5轴旋转系统的角度映射关系.利用该关系控制旋转系统实现了对某卫星过境观测的平行模拟,并对目标混合光谱进行了测量和定标.实验结果发表明:目标光谱数据中存在"闪光"和峰值波长迁移现象;旋转系统各轴定位精度为0.5°,光谱数据相对测量误差为0.018%.该方法能实现空间目标观测的全角度平行模拟,测量结果为非分辨目标外形、材料、旋转等特性的识别提供参考.     

基于双向反射分布函数的目标激光测距方程

导航系统中广泛采用激光测距确定星地间距离,双向反射分布函数可精确描述实际物体反射光的情况,是研究激光测距方程的有效手段。结合目标反射几何模型,计算得到透镜各点接收目标反射光强的表达式。对目标光斑和接收透镜进行网格划分,仿真得到透镜面元接收目标反射的光强分布和透镜接收的瞬时光强,并讨论了平面目标的网格步长选取和计算次数。当光束从不同空间位置入射至平面目标表面时,根据探测器-反射棱镜之间距离与接收光强的对应关系得到激光测距方程的待定参数。实测数据验证了理论计算的正确性。     

双向反射分布函数的绝对测量方法

在光谱光度计的校准中，需要在特定的入射和接收的几何条件下进行。在一些情况，校准的几何条件和光谱区受到了限制，因此有必要建立一种可适用于任意几何条件下和更宽光谱区的校准方法。本文介绍了一种校准光谱双向反射的方法，可适用于各种入射和接收的几何条件。从４００～２５００ｎｍ的光谱范围内，确定烧结的聚四氟乙烯标准样品的绝对双向反射系数，参考标准是通过国家计量院传递的方向—半球反射系数。测量用的双向反射分布函数（ＢＲＤＦ）测定仪可以全自动地测量几乎所有可能的几何条件下的绝对双向反射系数     

目标表面可见光谱BRDF的实验测量及优化建模

介绍了一种用双向反射分布函数测定仪进行目标双向反射分布函数测量的方法。运用该测量系统在可见光谱区域对样片进行了实验测量,然后对BRDF实验数据进行谱积分预处理,结合BRDF五参数半经验统计模型,利用遗传模拟退火算法,获取样片的BRDF模型参数,并获得了三维空间的BRDF分布。结果表明,获得的可见光谱BRDF模型能准确反映材料的光散射特性,符合工程要求。     

Infrared imaging characteristics of space-based targets based on bidirectional reflection distribution function

A modeling method of infrared imaging characteristics of a space-based target was presented. Background radiation environment of a space-based target was analyzed and the background radiation mainly consists of direct radiation of the sun, thermal radiation and reflected radiation of the earth. The target surface was divided into regions based on geometrical shape and surface material characteristics and a surface equation of each region was built based on its body coordinate system. Each region was divided into meshes supposing that each mesh is a micro-plane. A bidirectional reflection distribution function (BRDF) model considering the characteristics of surface Gauss statistics and self-shadow was introduced to describe reflected infrared of each mesh of the target surface. The emitted infrared radiation of each mesh of the target surface was described according to its thermal equilibrium temperature. Then a mathematical model on infrared radiation imaging characteristics of the space-based target was built in terms of the given infrared detector. The relative positions of the space-based target, the background radiation sources and the detector are determined by orbital parameters based on coordinate conversion. Visual surfaces of the target to observation system were determined by vector coordinate method. Simulation of optical imaging characteristics of the target in orbit was achieved according to its given geometrical dimensions and physical parameters. The results show the method is feasible and robust for infrared characteristics of the space-based target when single reflection is considered and its surface is regular and can be described in a surface equation. It can provide a facility to real-time analysis of infrared imaging characteristics of the space-based targets.     

植物BRDF研究及应用进展

植物叶片是植物光合作用的重要器官,直接体现了植物生长及营养状况。植物叶片反射、透射的内部理化信息模型间接反映了植物生长过程中物质、能量交换信息,是植物生长过程精细化管理的前提和基础。植物叶片空间光学特性对基于遥感的作物营养状况诊断、虚拟植物光线传输模拟、计算机图形学场景渲染等领域具有重大意义。双向反射分布函数(BRDF)主要研究物体表面反射光的空间分布特性和光谱特性,通过对作物叶片光学特性的获取和测定,准确、高效地表征作物生长参数,并进行定量分析,在植被遥感、农业等领域的研究与应用中有着极大的优势。为了更好地把BRDF技术应用于农业遥感、数字农业等领域中,将针对BRDF测量装置、模型发展和分类及其在植物遥感检测中的应用等环节展开叙述。最后结合综述内容,分析了BRDF技术在农业遥感领域的局限,并对其应用前景进行了展望。     

Numerical modeling of the reflection coefficients for the plane sound wave reflection from a layered elastic bottom

The matrix method and its numerical realization are considered in calculating the complex reflection coefficients and refraction indices of plane sound waves for geoacoustic models of the ocean bottom in the form of homogeneous elastic (liquid) absorbing layers overlying an elastic halfspace. In calculating the reflection coefficients at high frequencies or in the presence of a large numbers of sedimentary layers, a passage from the Thomson-Haskell matrix approach to the Dunkin-Thrower computational scheme is performed. The results of test calculations are presented. With the aim of developing resonance methods for the reconstruction of the parameters of layered elastic media, the behavior of the frequency-angular dependences of the reflection coefficient are studied for various geoacoustic bottom models. The structure of the angular and frequency resonances of the reflection coefficients is revealed. The dependence of the structure (the position, width, and amplitude) of two types of resonances on the parameters of the layered bottom is considered.     

BRDF reference standards for the infrared

A comparison between various recommended reference standards of diffuse reflectance in the IR is presented. It is shown that at a wavelength of 10.6 μm sulfur is the most Lambertian of the tested samples, although its powdery consistence makes it less suitable for use as a standard. Flame sprayed aluminum, with or without gold coating, also approaches a Lambertian surface and is suitable for use as a standard for BRDF measurements at 10.6 μm. Results for the BRDF of sulfur, gold-coated sandpaper, a commercial diffuse gold surface (by Labsphere) and flame sprayed aluminum are presented.     

偶极横波远探测典型地质体解释模型研究及应用

偶极横波远探测技术是近年来发展起来的一门重要的地球物理测井技术,它把常规测井技术的测量范围从井周1 m左右提高到几十米,在井旁裂缝和孔洞等地质体的探测中取得了较好的应用效果。本文根据偶极横波辐射声场和接收声场的互易性,提出了一种快速计算井旁地质体反射声场的解析方法——远场渐近解,实现井旁孔洞、裂缝等典型地质体反射声场的快速计算,分析了不同地质体的远探测成像特征,在此基础之上,与已有实际井资料结合建立了偶极横波远探测的解释模型,并将其应用于海上实际井旁地质体评价。应用结果表明,偶极横波远探测解释模型可用于海上缝洞型地层识别、井旁断层或断裂带判断等,效果明显。     

A method for measuring the phase of the reflection coefficient in the visible range of the spectrum

A method for measuring the phase of the reflection coefficient in the optical wavelength range is proposed. The method is simple in experimental implementation and is based on measuring the energyreflection coefficients of a sample in two media with different refractive indices. Analytical and numerical estimates show that the measurement accuracy of the phase is on the order of 1°. The possibilities of using the results of the phase measurement in practice for a more complete characterization of materials and structures under investigation are considered.     

Vapour and plasma ignition thresholds for visible pulsed-laser ablation of metallic targets

The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result.     

Filtering characteristics of spatial filter for spatial filtering velocimeter

In order to select a suitable spatial filter for the spatial filtering velocimeter, the filtering characteristics of the spatial filters with a rectangular window and rectangular transmittance are investigated by the power spectrum of transmittance function method. The filtering characteristics of differential filters are investigated and compared with that of common ones. The influences of the number of spatial periods on the spectral bandwidth,deviation to central frequency, and peak transmittance are deeply analyzed. The results show that the influence is due to the form of superposition of the signal components and other components, the pedestal and higher-order components, and the superposition results from the finite size of the spatial filter. According to the results, a method is proposed to compensate for the deviation to central frequency.