Emissivity Measurements on Metallic Surfaces with Various Degrees of Roughness: A Comparison of Laser Polarimetry and Integrating Sphere Reflectometry

Both integrating sphere reflectometry (ISR) as well as laser polarimetry have their advantages and limitations in their ability to determine the normal spectral emissivity of metallic samples. Laser polarimetry has been used for years to obtain normal spectral emissivity measurements on pulse-heated materials. The method is based on the Fresnel equations, which describe reflection and refraction at an ideally smooth interface between two isotropic media. However, polarimetry is frequently used with surfaces that clearly deviate from this ideal condition. Questions arise with respect to the applicability of the simple Fresnel equations to non-specular surfaces. On the other hand, reflectometry utilizing integrating spheres provides a measurement of the hemispherical spectral reflectance, from which the normal spectral emissivity can be derived. ISR provides data on spectral-normal-hemispherical reflectance and, hence, normal spectral emissivity for a variety of surfaces. However, the resulting errors are minimal when both the sample and the reference have a similar bidirectional reflectance distribution function (BRDF). In an effort to explore the limits of polarimetry in terms of surface roughness, room temperature measurements on the same samples with various degrees of roughness were performed using both ISR and a laser polarimeter. In this paper the two methods are briefly described and the results of the comparison are discussed.     

高精度保偏光纤拍长测试

基于光相干域偏光测试技术,提出了一种高精度的保偏光纤拍长测试方法,实现了不同结构、不同尺寸保偏光纤的拍长测试。阐述了光相干域偏光测试技术原理并推导出测量方程;以迈克尔逊干涉仪为基础建立了测试系统并采用调制解调技术实现了信号的高精度检测。实验结果表明,系统的测量精度为0.01 mm。在此系统上进行了测试精度和重复性研究并对不同结构和尺寸的八种保偏光纤进行了实际测量,拍长测量精度和重复性均优于0.01 mm。     

基于Wishart分布和MRF的多视全极化SAR图像分割

提出一种新的多视全极化SAR图像分割方法.将描述多视协方差矩阵的Wishart分布与马尔可夫随机场模型结合起来,利用迭代条件模型法(ICM)求取最大后验概率准则下的分割结果,其中ICM所需的初始分割图由基于Wishart分布的最大似然法获得.NASA/JPL实验室AIRSAR系统多视全极化数据的实验结果表明,与几种常用方法相比,本文方法分割精度更高,分割结果图中孤立像素少,图像连通性好.     

基于简缩极化数据的三分量分解模型

基于部分极化波的二分理论,提出了一种针对简缩极化数据的三分量分解模型。该模型将简缩极化数据的Jones相干矩阵分解成表面散射、偶次散射和体散射三种散射机制Jones相干矩阵之和,进一步得到这三种散射机制各自的散射功率。选取德国根多夫市普拉特灵(Plattling)地区的TerraSAR-X全极化数据生成简缩极化数据,用提出的三分量分解模型对得到的简缩极化数据进行分解,并将分解结果与全极化数据的Pauli分解结果进行对比。实验结果表明:提出的简缩极化数据三分量分解模型能够很好地描述表面散射和体散射的散射行为。但是,相比全极化数据的分解结果,提出的模型高估了体散射分量,导致偶次散射分量偏小,这个问题需要进一步的研究来解决。     

Polarimetry for four Stockes parameters in space

Continuously growing attention has been paid to potential of polarimetry to provide additional information of remote sounding of the earth and other planets and to detect some special targets. In the present paper the polarimetric technique in space for all the four Stockes parameters is presented.     

Distributed Measurement of Strain using Optical-fibre Backscatter Polarimetry

Abstract: Fully-distributed optical-fibre sensing (FDOFS) systems are developing rapidly and are offering significant advantages for measurement functions in a variety of structural applications, especially in the oil industry, the power supply industry, the aerospace industries and civil engineering construction.
Polarization techniques are well established in FDOFS, and in the analysis of polarization-mode dispersion (PMD) for optical-fibre telecommunications. However, a major problem has been that of determining, from one end of the fibre, the distribution of the full polarization properties of a monomode optical fibre, along its length, with some specific spatial resolution.
This paper will present a new technique for providing this full information, and thus for measuring the distribution of any parameter, external to the fibre, which can modify its polarization behaviour. As a result, for example, it becomes possible to measure simultaneously the distributions of temperature and of a strain field comprising, in the latter case, the longitudinal and the two transverse components of direct strain, plus the transverse shear strain.
The technique comprises an extension of polarization-optical time domain reflectometry (POTDR) [16], and necessitates on-line processing. Details of the physical principles, the algorithms and the polarimetry will be presented, together with results illustrating the measurement accuracies which can be achieved.     

基于极化相似度的全极化SAR自动目标识别算法

提出了一种基于极化相似度的全极化SAR自动目标识别算法,并利用仿真得到的全极化SAR数据进行了识别实验。该方法将极化相似度量引入到局部极大值匹配算法中,有机地结合了散射中心特征点的空间域和极化域的信息。针对目标绕雷达视线的旋转,以及系统极化测量误差引起的极化倾角变化,给出了极化倾角估计和补偿算法,并实验研究了极化倾角对识别结果的影响。仿真识别结果表明,全极化数据的平均识别率明显优于单极化,证明了该算法的有效性。     

Simultaneous false-colour imaging of birefringence, extinction and transmittance at camera speed

A polarized light imaging technique is introduced that simultaneously captures and unfolds transmittance, fast/slow axes directions and birefringence or linear dichroism from single camera exposures. The technique, based on the rotating polarizer method, is capable of sampling an object through polarizers at four different angles in a single image with the use of an image multiplexer. The range of possible applications is demonstrated with examples from the fields of biology, medicine, forensics and material sciences.     

Polarimetric Classification in a Tailings Deposition Area at the Timika Mine Site, Indonesia

Abstract.  Preliminary results indicate that polarimetric synthetic aperture radar (SAR) data can be useful in characterizing remote tailings sites in Indonesia. Recent launches of polarimetric radar satellites offer new opportunities to use such data. Wishart polarimetric radar classification was used to map tailings conditions and vegetative stress. We assessed the accuracy of our analysis and found that almost all scatterers could be discriminated properly, and that the technique was particularly useful in distinguishing saturated versus relatively dry tailings. Since tropical regions are subject to severe atmospheric disturbances, tailings stability is a major issue; there is thus high potential value in using radar remote sensing to aid revegetation and tailings stabilization.     

Wishart分布矩阵行列式值的统计特性及其在参数估计中的应用

 极化协方差矩阵行列式值表征了Pol-SAR图像目标散射极化散布程度,它在参数估计中表现出突出的优势,研究行列式值的物理内涵及其统计特性对揭示行列式值的优势的本质有着重要的理论价值.在此背景下,将表征目标散射极化散布程度的标准行列式值与表征目标散射随机性的极化熵、极化散度进行了比较,给出了它们与平面极化度和方向极化度的数学关系,指出他们在描述目标散射随机特性方面具有部分一致性,存在差异的本质在于三个随机性描述参数对极化方向随机度和平面极化度的加权方法的不同.然后研究了极化协方差矩阵行列式值的统计分布特性,给出了极化协方差矩阵行列式值的概率密度函数,指出在视图数和样本数足够的情况下,其行列式值的测量均值是渐进无偏估计.针对样本数较少时等效视图数参数估计误差较大的问题提出了最大似然修正算法,提高了小样本数目时的等效视图数参数估计精度.最后用仿真数据对理论推导进行了验证,结果表明了理论结果的正确性.极化协方差矩阵行列式值的统计特性和目标散射随机性参数的研究为目标极化散射随机特性、参数估计和目标检测等的研究提供了新思路.