植被双向反射模型研究综述

探讨了双向反射系数分布函数的基本概念及物理含义,并按模型处理方法,把迄今所建的各种植被双向反射模型分为:辐射传输模型,几何光学模型和随机过程模型三大类。并比较分析了三类模型的基本特点。     

卫星表面光学反射特性建模与仿真研究

在研究空间相机成像效果探测问题时,针对提高探测相机成像真实效果的需要,研究了卫星表面光学反射特性的建模与仿真方法.利用双向反射分布函数(BRDF)仿真卫星表面的光学反射特性,将卫星表面物理特性与其光学反射特性有机地结合起来.在VC.Net环境下开发卫星表面光学反射特性仿真软件,并将软件集成到空间探测相机成像效果仿真平台上.利用平台进行成像仿真实验,生成真实感仿真图片.仿真结果表明,BRDF能够精确仿真卫星表面的光学反射特性,使成像效果仿真更加准确和逼真.     

基于BRDF模型的玉米叶片散射特性分析

本文完成了对红光和近红外光源下的玉米不同叶位的散射光分布的测量.通过对测量结果进行计算分析得到了样本的BRDF值.并建立了相应的Cook-Torrance模型,定量计算分析了不同叶位样本在不同入射光下的散射特性.结果表明,用这种方法分析叶片的散射特性是可行和有效的.     

一种真实物体表面反射属性采集与建模方法

为了快速获取物体表面反射属性数据和三维几何数据,研制了一套包括相机、光源、三维扫描仪、控制系统等的物体表面反射属性数据采集系统,在此基础上,提出一种单材质物体表面反射属性建模方法.该方法根据物体反射特性对漫反射与镜面反射分别建模,能够逼真地构造出物体表面反射属性模型,并且保证了参数求解的稳定性.最后设计并实现了反射属性模型编辑工具.实验结果表明,利用该编辑工具可以实时、可视地调整模型参数,从而满足用户对反射属性模型编辑的需求.     

不透明材质反射属性采集及建模技术综述

在计算机图形学和计算机视觉领域,材质反射属性模型能够展现真实世界中材质复杂、丰富的光学现象,但反射属性数据具有高维度且材质反射现象复杂多变的特性,因此其采集和建模技术一直是研究的热点及难点.文中介绍了近年来国内外对不透明材质反射现象的采集及建模技术方向取得的最新研究进展,并给出了分析和总结.最后对该领域研究存在的挑战和未来发展趋势提出了一些看法.     

一种实时红外场景仿真方法

文章实现了一种实时红外场景仿真技术。首先,完成了红外场景仿真系统的设计与现实工作;其次,生成目标区域的红外仿真图像,仿真过程中使用了VEGA标准材质库,考虑了大气效应对红外辐射的衰减作用;最后,利用三维建模技术,建立相应的三维红外场景,并提供实时漫游功能。实验结果表明,该方法生成的红外仿真图像与实拍图像的变化规律基本一致,为生成目标区域的红外图像数据库创造了条件。     

一种新型城市双向反射模型及其对比研究

城市地区由于地表结构复杂,地表类型多样,使得利用遥感技术计算该类型区域的地表反射率及提取地表参数时面临较大困难.本文针对以上问题,基于几何光学模型的思想建立了一种新型的城市地区双向反射模型.该模型通过对可视光照建筑面、可视阴影建筑面、可视地表光照面、可视阴影地表4种几何分量的计算来确定城市地区的双向反射率,并且与现有的“街区”模型进行了对比.结果表明,本文提出的城市地区双向反射率模型具有较高的精度和较快的速度.     

基于表观BRDF的泡沫金属辐射特性反演测量方法

泡沫金属是通过在金属基体上形成大量孔隙结构而得到的一类新型多功能材料,在太阳能利用、强化换热等领域有重要应用价值,其辐射特性参数是分析其内部辐射传递的必要物性数据。提出一种基于表观双向反射分布函数（ BRDF）测量数据反演泡沫金属热辐射物性的方法,利用测量的多角度入射的表观BRDF数据结合辐射传递方程求解来反演泡沫金属的等效辐射特性。对泡沫铁镍（50 ppi ）、泡沫铜（90 ppi）及泡沫镍（30 ppi）三种泡沫金属样品在波长660 nm激光照射下1/2半球空间的表观BRDF分布进行了实验测量,并对其辐射特性进行了反演,首次获得了这三种材料的辐射特性参数,其辐射物性表现出明显的半透明性质,散射反照率随着孔隙数密度的增加而增加,散射相函数呈后向散射占优。     

一种有效计算大气红外辐射传输效应的方法

红外辐射在大气中的传输特性对红外成像仿真研究具有重要意义.本文以红外辐射的传输理论为基础,综合考虑大气分子的吸收、散射,气象条件以及海拔高度等因素,提出了一种以大气条件为基本参数,计算红外成像仿真中大气光谱透过率的方法,并对算法进行了仿真实现;通过对不同条件下计算结果的分析,表明用该算法得出的结论与实际红外成像的规律基本相符,且可以满足实时性和准确性的要求,能够增强红外成像仿真的可信度,具有很好的应用价值.     

基于GPU的虚拟战场红外仿真技术研究

实时红外视景仿真已成为红外成像武器系统设计与评估的重要方法,在军事和国民经济中有着广泛的应用前景。红外仿真的关键环节在于红外视景图像的生成,提出了一种基于GPU实现红外辐射计算模型的方法,将辐射传输模型中温度、辐射特性等数据的计算移植到GPU中,充分利用了GPU的可编程特性以及强大的并行运算能力,高效生成了精度较高的红外场景图像。     

A Copula‐Based BRDF Model

In this paper, we introduce a novel approach for modeling surface reflection. We focus on using a family of probability distributions called Archimedean copulas as BRDF models. The Archimedean representation has an attractive property in that the multivariate distributions are characterized by their marginal distributions through a single univariate function only. It is shown that the proposed model meets the reciprocity property of reflection. Based on measured BRDF data, we demonstrate that the proposed approach provides a good approximation to BRDF. Empirical comparisons are made with some classically used BRDF models.     

Regularized kernel-based BRDF model inversion method for ill-posed land surface parameter retrieval

In this paper, we consider the direct solution of the kernel-based bidirectional reflectance distribution function (BRDF) models for the retrieval of land surface albedos. This is an ill-posed problem due to nonuniqueness of the solution and the instability induced by error/noise and small singular values of the linearized system or the linear BRDF model. A robust inversion algorithm is critical for the BRDF/albedo retrieval from the limited number of satellite observations. We propose a promising algorithm for resolving this kind of ill-posed problem encountered in BRDF model inversion using remote sensing data.New techniques for robust estimation of BRDF model parameters are needed to cope with the scarcity of the number of observations. We are reminded by Cornelius Lanczos' dictum: “Lack of information cannot be remedied by mathematical trickery.” Thus identifying a priori information or appropriate constraints, and the embedding of the information or constraints into the regularization algorithm, are pivotal elements of a retrieval algorithm. We develop a regularization method, which is called the numerically truncated singular value decomposition (NTSVD). The method is based on the spectrum of the linear driven kernel, and the a priori information/constraint is based on the minimization of the l₂ norm of the parameters vector. The regularization algorithm is tested using field data as well as satellite data. Numerical experiments with a subset of measurements for each site demonstrate the robustness of the algorithm.     

Robust estimation of BRDF model parameters

The effect of the Bidirectional Reflectance Distribution Function (BRDF) is one of the most important factors in correcting the reflectance obtained from remotely sensed data. Estimation of BRDF model parameters can be deteriorated by various factors; contamination of the observations by undetected subresolution clouds or snow patches, inconsistent atmospheric correction in multiangular time series due to uncertainties in the atmospheric parameters, slight variations of the surface condition during a period of observation, for example due to soil moisture changes, diurnal effects on vegetation structure, and geolocation errors [Lucht and Roujean, 2000]. In the present paper, parameter estimation robustness is examined using Bidirectional Reflectance Factor (BRF) data measured for paddy fields in Japan. We compare both the M-estimator and the least median of squares (LMedS) methods for robust parameter estimation to the ordinary least squares method (LSM). In experiments, simulated data that were produced by adding noises to the data measured on the ground surface were used. Experimental results demonstrate that if a robust estimation is sought, the LMedS method can be adopted for the robust estimation of a BRDF model parameter.     

基于形变模型的红外人脸鲁棒识别*

针对人脸识别中的光照、表情和遮挡变化三大难题,引进热红外人脸克服光照变化,并且采用融合局部形变模型的人脸分类方法克服表情和遮挡变化。该方法将热红外测试人脸看成人脸库的线性组合,并用形变模型表示,通过 最小优化求解组合系数,根据系数的稀疏性进行人脸识别。为了进一步提高算法的鲁棒性,采用人脸分片加权的策略。在Equinox人脸库上通过大量实验表明：基于红外光的人脸识别性能明显高于可见光对光照变化的影响;融合局部形变模型的人脸识别方法可以有效地提高识别率且克服红外人脸识别中的眼镜干扰与表情变化问题。     

BRDF模型及其反演研究的现状及展望

介绍了二向性反射的物理模型及半经验模型在理论研究中的新进展,并分析了各个模型的优缺点,为模型选择提供了依据;同时对模型反演的策略和方法及最新研究进展进行了概述。在此基础上,对实验研究、理论研究以及应用研究中存在的主要问题及目前的一些解决方案进行了分析,并讨论了遥感反演研究的未来发展方向。     

CMOS红外传感器的模型研究

对基于标准CMOS工艺的二极管型红外传感器进行物理建模和理论推导,并对所建模型进行了仿真。该红外传感器利用二极管两端的电压随温度变化特性来感测红外线。从电流与温度变化的关系着手,推导出电压与温度变化关系,对红外传感器的一些重要参量进行了讨论。仿真结果表明:所建模型基本与实验结果相符。     

Integration and Case Analysis of BRDF Model based on Linear Kernel\|driven Model#br#

Anisotropic reflectance is the intrinsic characteristic of an object surface.over the past few decades,various BRDF models have been developed for investigating the relationship between the vegetation canopy and reflectance anisotropy.This helps to retrieve biophysical parameters from the anisotropic reflectance patterns of vegetation canopy.In this study,for the purpose of assisting potential users to use these models,and to improve the understanding of the BRDF modeling,several BRDF models that are widely used in the remote sensing community have been integrated with the current version of the MaKeMAT (Multi\|angular Kernel\|driven Model Analysis Tool),based on the Interactive Data Language (IDL).This work retains all functions of the current version of the MaKeMAT model,meanwhile,adds some new functions by integrating these physical BRDF models.Undoubtedly,this work facilitates the potential users to process BRDF data and make further analysis in their work by operating a simpler visual interface.This helps to build a rapid communication between the kernel\|driven BRDF models and the physical BRDF models.Our initial results show that this model\|integration practice is a valuable reference for potential users to devise a similar technique.Our case study in coupling these physical BRDF models with the kernel\|driven models present a high correlation between them,with the determination of coefficients (R²) reaching 0.899~0.989 in the red and NIR bands.     

Use of a Kalman filter for the retrieval of surface BRDF coefficients with a time-evolving model based on the ECOCLIMAP land cover classification

The goal of this study is to demonstrate the asset in using a Kalman filter to improve the spatial coherence and time consistency of surface Bidirectional Reflectance Distribution Function (BRDF) and albedo retrievals from moderate resolution sensor data sets. For this purpose, we use a simple surface model describing BRDF seasonal evolution for the land cover classes of the ECOCLIMAP database. The application of temporal composition windows used so far for BRDF retrieval is limited in regions characterized by a high frequency of cloud coverage, which induces a lot of gaps in the temporal series. Instead, the present method ensures a continuous production of surface BRDF parameters thanks to the Kalman filter recursive data processing. An application of the method is performed with SPOT/VEGETATION data over the western Africa equatorial region for the year 2003. Compared to presently available products from VEGETATION and MODIS instruments, this new approach allows to fill the gaps and improves the retrieved parameters time consistency. Another interesting possibility of the Kalman filter is the production of surface biophysical variables in quasi-real-time for applications that require a frequent update of the surface parameters.     

红外数字TDI成像非均匀性校正

目的 红外数字TDI（time delay integration）先经过信号的模拟数字转换,再进行时间延迟累加,曝光方式比较灵活,能够提高探测系统灵敏度以及探测目标信噪比,在航空航天遥感应用领域具有广泛的应用,红外数字TDI通常采用扫描方式成像,既具有扫描成像的特点,其本身又是一个小面阵,在信息获取上具有扫描和凝视双重特性,在信息处理端,成像非均匀性是限制其成像质量的关键因素,降低输出图像的非均匀性,对开展目标探测、识别等研究和应用具有重要意义。方法 通过分析成像系统的每个部分,建立成像输入输出模型,并讨论模型中各个参数对成像非均匀性的影响,指出优化系统非均匀性的途径;对图像非均匀性校正分为盲元补偿和有效像元的非均匀性校正,对盲元进行邻域像素替代和邻域像素平均的交替迭代补偿提高了盲元的补偿率,对有效像元分析了所有像元的响应特性,选择了曲线拟合的目标校正曲线对系统灰度输出与输入能量之间的非线性进行校正,并引入校正因子对非扫描方向上的非均匀性进一步校正。结果 使用上海技术物理研究所研制的640×8中波红外数字TDI探测器进行了黑体定标验证,结果表明,在特定温度下的黑体成像经过校正后的非均匀性由19.44%下降到4.01%,外场实验获得的红外TDI图像上的横条纹明显减少和弱化。结论 通过分析对目标场景成像从光信号到电信号的整个链路,得到影响成像非均匀性的具体参数,对红外数字TDI成像系统设计具有一定参考意义;使用本文方法对红外数字TDI成像进行了盲元补偿和非均匀性校正,成像非均匀性显著下降,验证了该方法的有效性。