Multiple spectral similarity metrics for surface materials identification using hyperspectral data

Modern hyperspectral imaging and non-imaging spectroradiometer has the capability to acquire high-resolution spectral reflectance data required for surface materials identification and mapping. Spectral similarity metrics, due to their mathematical simplicity and insensitiveness to the number of reference labelled spectra, have been increasingly used for material mapping by labelling reflectance spectra in hyperspectral data labelling. For a particular hyperspectral data set, the accuracy of spectral labelling depends considerably upon the degree of unambiguous spectral matching achieved by the spectral similarity metric used. In this work, we propose a new methodology for quantifying spectral similarity for hyperspectral data labelling for surface materials identification. Developed adopting the multiple classifier system architecture, the proposed methodology unifies into a single framework the differential performances of eight different spectral similarity metrics for the quantification of spectral matching for surface materials. The proposed methodology has been implemented on two types of hyperspectral data viz. image (airborne hyperspectral images) and non-image (library spectra) for numerous surface materials identification. Further, the performance of the proposed methodology has been compared with the support vector machines (SVM) approach, and with all the base spectral similarity metrics. The results indicate that, for the hyperspectral images, the performance of the proposed methodology is comparable with that of the SVM. For the library spectra, the proposed methodology shows a consistently higher (increase of about 30% when compared to SVM) classification accuracy. The proposed methodology has the potential to serve as a general library search method for materials identification using hyperspectral data.     

若干高光谱成像新技术及其应用研究

高光谱成像数据已广泛应用于地质、海洋、农林、水文、城市、环境和军事等领域,对经济的可持续发展发挥了促进作用。随着研究的深入和应用的拓展,对高光谱成像系统的技术要求呈现多样化趋势。本文简要回顾了国内外高光谱成像技术的主要发展历程,依次阐述了运动补偿高光谱成像、紧凑型热红外高光谱低温光学、宽谱段一体化机载高光谱集成、基于AOTF分光的凝视型高光谱成像以及阶跃集成滤光片等具有代表性的高光谱成像关键技术,并简要介绍了这些新技术在天宫一号、嫦娥三号等国家重大任务中的应用情况。     

地面成像光谱数据的田间杂草识别

地面成像光谱数据兼具高光谱分辨率与高空间分辨率,在田间杂草识别中具有很好的应用前景。目前基于机器视觉的杂草识别方法以形状特征为主,当作物杂草形态相似时识别的困难和利用高光谱特征以像元为单元识别时效率较低,不利于实时自动化除草,因此,本文提出一种综合面向对象与高光谱特征匹配的杂草识别方法,在对作物杂草对象样本的形状特征和光谱曲线提取分析的基础上,建立基于形状特征规则与光谱角匹配的植物对象识别决策树,用于识别实验田中的作物杂草对象。实验结果表明,当场景中某些不同种类植物对象的形态相似时,基于形状特征规则与光谱角匹配的杂草识别方法可借助高光谱特征精细区分植物对象的种类,且在形状特征规则约束下使用高光谱特征匹配法识别植物对象,可克服"同物异谱"和"同谱异物"现象带来的不确定性,该方法识别精度可优于仅使用光谱角匹配法的情况,并优于使用颜色和形状分析技术的情况。     

The long-wave infrared (8-12 μm) spectral features of selected rare earth element—Bearing carbonate,phosphate and silicate minerals

Rare earth elements (REEs) are a group of metals essential to high technology industries. This high demand, combined with a high supply risk, has led to an understanding that REEs are critical to society. Despite the potential that hyperspectral imaging (HSI) data offers for a fast and non-invasive characterization of the REEs, it is still poorly understood whether REEs have some information in the long-wave infrared (LWIR; 8–12 μm) wavelength range that can be used for their identification. To partially fill this gap, we have investigated the spectroscopy of twelve REE-bearing mineral samples using relatively high spatial and spectral resolution LWIR hyperspectral imaging data. These samples were formerly characterized using electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and hyperspectral imaging data acquired in the 0.4–2.5 μm wavelength range. Results from these analyses were compared to and used to guide the analysis of the HSI data recorded in the LWIR range. This information was further compared to a reference spectral library of rare earth oxides. Our findings suggest that the spectral features of the samples can generally be traced to the asymmetric degenerate stretching and bending modes of the X-O (X = C, Si, P) groups. Moreover and contrary to what has been observed in the shorter wavelengths, there are no definitive spectral features in the LWIR wavelength region that could be assigned to any specific REE.     

Lithological mapping from hyperspectral data by improved use of spectral angle mapper

The spectral angle mapper (SAM), as a spectral matching method, has been widely used in lithological type identification and mapping using hyperspectral data. The SAM quantifies the spectral similarity between an image pixel spectrum and a reference spectrum with known components. In most existing studies a mean reflectance spectrum has been used as the reference spectrum for a specific lithological class. However, this conventional use of SAM does not take into account the spectral variability, which is an inherent property of many rocks and is further magnified in remote sensing data acquisition process. In this study, two methods of determining reference spectra used in SAM are proposed for the improved lithological mapping. In first method the mean of spectral derivatives was combined with the mean of original spectra, i.e., the mean spectrum and the mean spectral derivative were jointly used in SAM classification, to improve the class separability. The second method is the use of multiple reference spectra in SAM to accommodate the spectral variability. The proposed methods were evaluated in lithological mapping using EO-1 Hyperion hyperspectral data of two arid areas. The spectral variability and separability of the rock types under investigation were also examined and compared using spectral data alone and using both spectral data and first derivatives. The experimental results indicated that spectral variability significantly affected the identification of lithological classes with the conventional SAM method using a mean reference spectrum. The proposed methods achieved significant improvement in the accuracy of lithological mapping, outperforming the conventional use of SAM with a mean spectrum as the reference spectrum, and the matching filtering, a widely used spectral mapping method.     

光谱角—欧氏距离的高光谱图像辐射归一化

辐射归一化旨在减小不同时相遥感影像间因获取条件不一致而导致的非地表辐射变化的差异,是土地覆盖变化监测的重要前提条件。本文根据高光谱图像上同类地物的谱形及数值的相似性,利用光谱角距离(SAD)和欧氏距离(ED)双重判定选取不变特征点,提出了一种基于光谱角—欧氏距离的辐射归一化方法。在评价指标中除了常用的均方根误差和相对偏差,更增加了高光谱特色的衡量光谱保真性指标:皮尔森系数、光谱扭曲程度。利用高光谱遥感CHRIS图像对本文提出方法进行验证,并与基于多元变化检测(MAD)的辐射归一化方法比较。结果表明,本文方法不仅在辐射特性上优于基于多元变化检测(MAD)的方法,而且具有保持光谱特性的优势,具有较好的应用前景。     

高光谱遥感影像混合像元分解研究进展

受高光谱成像仪低空间分辨率及复杂地物的影响,高光谱遥感图像存在大量混合像元。为提高地表分类精度以及满足亚像元级目标探测的需求,混合像元分解技术一直是高光谱遥感研究热点之一。本文主要对高光谱混合像元分解技术中的核心问题:端元数目估计、端元提取算法、丰度估计算法进行综述,系统地分析了各种典型算法的原理及优缺点,进一步阐述研究过程中建立高精度遥感混合反演模型与遥感产品业务化中的混合像元分解技术难题,同时针对今后混合像元分解技术发展方向,指出在继续引入新型算法理论方法基础上,结合用户应用需求,推进高光谱混合像元分解算法业务化应用,为高光谱遥感工程化应用提供支持。     

对地观测高光谱激光雷达发展及展望

对目标空间三维—光谱信息的高分辨一体化获取与应用,是对地观测技术发展的前沿科学问题.结合高光谱成像与激光雷达测距的技术优势,对地观测多光谱/高光谱激光雷达遥感技术手段应运而生,并成为遥感技术未来发展的重要方向.本文分3个阶段详细回顾了对地观测高光谱激光雷达系统的发展历程,并针对其独有数据类型阐述了数据处理研究方面的探索...     

Pan Sharpening for Hyper Spectral Imagery Using Spectral Mixing-Based Color Preservation Model

With nanometric spectral resolution and number of bands as high as 220, Hyper spectral sensors like Hyperion and AVIRIS are gaining wide appreciation. Narrow, continuous wavelength of bands upon a vast spectrum of electromagnetic wavelength enables better precision in identification of materials by distinguishing between their unique spectral signatures. However, their poor spatial resolution is a major impediment in realising the full potential of hyperspectral imaging. Efforts are being made worldwide to improve the spatial resolution of hyperspectral imagery by fusing them with registered panchromatic imagery of higher resolution. However, most of the conventional methods fail to preserve the spectral fidelity of the fused images due to severe color distortion. Here, we propose an efficient paradigm to sharpen hyperspectral imagery with high spatial information content and minimal color distortion using color normalization by Lαβ and intensity image generation using Spectral Mixture Analysis. Quantitative assessment indices have been calculated to prove that our method is superior in terms of minimization of color distortion and maximization of spatial details as compared to other methods.     

Understanding the Unique Spectral Signature of Winter Rape

Driven by significant technological developments in the hyperspectral imaging, material mapping using reference spectra has received renewed interest of the remote sensing community. The applicability of reference spectral signatures in image classification depends mainly on the material type and its spectral signature behaviour. Identification and spectral characterization of materials which exhibit unique spectral behaviour is the first step in this approach. Consequently there have been active researches for the identification of surface materials which exhibit unique spectral signatures. The uniqueness of reflectance signature of winter rape relative to its co-occurring crop species was reported in this study. Reflectance spectral libraries constructed from field spectral reflectance measurements collected over five agricultural crops (alfalfa, winter barley, winter rape, winter rye, and winter wheat) during four subsequent growing seasons were classified by the linear discriminant analysis (LDA). Further, the reference field spectral database was used for the spectral feature fitting and classification of a historical HyMAP airborne hyperspectral imagery acquired at a separate site, by spectral library search. Results indicate the existence of a meaningful spectral matching between image and field spectra for winter rape and demonstrate the potential for transferring spectral library for hyperspectral image classification. The observed consistency in the discrimination of winter rape demonstrates experimentally the fundamental principle of remote sensing which suggests the theoretical existence of unique spectral signatures for materials which can be incorporated as reference spectral signatures for hyperspectral image classification.     

高光谱图像子空间的波段选择

为降低高光谱遥感数据光谱空间的冗余度,提出一种快速的波段选择方法。该方法在波段子空间下进行,依次选择各子空间中方差最大的波段作为初始波段,设定目标函数,然后逐子空间替换波段使得目标性能更加优化,直至没有替换可以使得目标更优为止。在两个公开高光谱影像数据集上对比3种常用波段选择方法(ABC、AP、ABS)来验证提出方法的有效性,实验结果表明:(1)在印第安纳数据上,本文方法与ABC、AP、ABS所选波段子集相比平均相关性分别降低22.04%、52.61%、55.71%,最佳指数分别提高0.58%、51.73%、0.95%,总体分类精度分别提高0.16%、1.39%、23.07%,在搜索效率上与同类型的ABC方法相比提高6.61%—69.02%;(2)在帕维亚大学数据上,本文方法与ABC、AP、ABS所选波段子集相比平均相关性分别降低2.38%、0.51%、32.83%,最佳指数分别提高1.34%、17.97%、12.92%,总体分类精度分别提高0.31%、0.69%、8.53%,在搜索效率上与同类型的ABC方法相比提高19.13%—86.34%。本文提出的波段选择方法能够选择合适的波段子集满足不同的应用需要,是一种有效的波段选择方法。     

A Multiple SVM System for Classification of Hyperspectral Remote Sensing Data

With recent technological advances in remote sensing sensors and systems, very high-dimensional hyperspectral data are available for a better discrimination among different complex land-cover classes. However, the large number of spectral bands, but limited availability of training samples creates the problem of Hughes phenomenon or ‘curse of dimensionality’ in hyperspectral data sets. Moreover, these high numbers of bands are usually highly correlated. Because of these complexities of hyperspectral data, traditional classification strategies have often limited performance in classification of hyperspectral imagery. Referring to the limitation of single classifier in these situations, Multiple Classifier Systems (MCS) may have better performance than single classifier. This paper presents a new method for classification of hyperspectral data based on a band clustering strategy through a multiple Support Vector Machine system. The proposed method uses the band grouping process based on a modified mutual information strategy to split data into few band groups. After the band grouping step, the proposed algorithm aims at benefiting from the capabilities of SVM as classification method. So, the proposed approach applies SVM on each band group that is produced in a previous step. Finally, Naive Bayes (NB) as a classifier fusion method combines decisions of SVM classifiers. Experimental results on two common hyperspectral data sets show that the proposed method improves the classification accuracy in comparison with the standard SVM on entire bands of data and feature selection methods.     

显著性权重RX高光谱异常点检测

高光谱图像异常点检测中,传统RX异常点检测算法忽略了空间相关性,背景估计不准确。本文提出了一种基于图像局部邻域光谱显著性分析的加权RX算法。该算法通过引入图像显著性分析,对基于概率密度为权重的图像背景建模进行改进,建立光谱显著性权重图,重新定义RX算法中的均值向量和协方差矩阵,并给不同的目标赋予不同的权值,达到优化背景估计的目的。利用合成高光谱数据和真实高光谱数据进行异常点检测实验,结果表明,对于同一组数据,本文算法检测到的异常点数比传统算法多,虚警率较低,有效地提高了检测率。     

线性混合光谱模型高光谱压缩感知

高光谱压缩感知(HCS)对于解决机载或星载高光谱数据的存储与实时传输具有重要意义。目前,线性混合模型(LMM)已被成功应用于HCS;然而,由于光照条件、地形变化以及大气作用等的影响,所获取的地物光谱会发生扰动,从而限制了HCS重建质量的提高。在LMM基础上,通过引入光谱修正项来修正光谱扰动,提出了光谱扰动修正的LMM (SPC_LMM);在此基础上,进一步提出了基于SPC_LMM的HCS (HCS_SPC_LMM)方法。该方法在采样端仅对原始高光谱图像进行光谱维压缩采样,基于压缩采样数据,将SPC_LMM应用HCS的重建,利用交替方向乘子法(ADMM)分别估计SPC_LMM中各分量的最优值,以获得最优的高光谱图像重建质量。实验结果表明,HCS_SPC_LMM能够获得优于其他典型HCS方法的重建质量。     

基于无人机高光谱影像波段选择的薇甘菊分类

薇甘菊是危害最严重的外来入侵物种之一,其生长与传播极其迅速,对我国森林生态系统造成了严重破坏,相关管理部门需要一个有效的薇甘菊监测手段。传统人工调查方式需要投入大量的人力物力,成本高昂、效率低下;近年来快速发展的高光谱遥感技术为薇甘菊的监测提供了新思路。本文以无人机搭载的Nano-Hyperspec高光谱仪获取的广东省增城林场遥感影像数据为基础,对高光谱数据进行几何校正、影像降噪处理、辐射定标及坏带波段剔除等影像预处理;运用最佳指数因子法（OIF）、自适应波段法（ABS）、自动子空间划分（ASP）与自适应波段相结合的波段选择法（ASP+ABS）3种方法进行波段选择,获取信息量较大且波段间相关性较低的特征波段组成薇甘菊分类最佳波段组合,生成3幅遥感影像;最后采用支持向量机方法（SVM）对生成的3幅不同遥感影像进行分类,以分类结果的精度评价3种波段组合对薇甘菊高光谱特征的响应程度,选出更能反映薇甘菊的光谱特征的波段组合。试验结果表明,针对Nano-Hyperspec遥感影像数据,使用OIF波段选择法,研究区内薇甘菊的制图精度和用户精度分别为74.62%、66.52%;使用ABS波段选择法,研究区内薇甘菊的制图精度和用户精度分别为74.37%、67.43%;使用ASP+ABS波段选择法,研究区内薇甘菊的制图精度和用户精度分别达到95.98%、92.98%,分类精度最佳,相较OIF法中薇甘菊的制图精度和用户精度分别提高了21.35%、26.46%,相较ABS法中薇甘菊的制图精度和用户精度分别提高了17.15%、19.3%。可见,本文使用的子空间划分与自适应波段相结合的波段选择方法相较其他两种波段选择方法能更好地反映薇甘菊的光谱特征,可为薇甘菊监测提供有效的技术手段。     

可编程红外焦平面光谱成像技术研究

短波红外焦平面光谱成像技术已广泛应用于各个领域,在应用中发现背景辐射对系统成像质量及信噪比有明显的影响.本文针对影响系统信噪比的因素进行研究,基于可编程的短波红外焦平面探测器技术,提出设置背景参考行和差异化增益的方法,对背景辐射实时监测,并提高弱信号波段的信噪比.经过实验验证,相比于其他系统,采用此方法的短波红外焦平面超光谱成像系统在成像质量和信噪比方面明显提高.研究还表明,利用可编程的特性,选择任务需要的特征光谱波段,还可以进一步提高工作帧频,以满足更高分辨率的航天光谱成像.     

Dimensionality reduction of hyperspectral data using spectral fractal feature

A new approach for dimensionality reduction of hyperspectral data has been proposed in this article. The method is based on extraction of fractal-based features from the hyperspectral data. The features have been generated using spectral fractal dimension of the spectral response curves (SRCs) after smoothing, interpolating and segmenting the curves. The new features so generated have then been used to classify hyperspectral data. Comparing the post classification accuracies with some other conventional dimensionality reduction methods, it has been found that the proposed method, with less computational complexity than the conventional methods, is able to provide classification accuracy statistically equivalent to those from conventional methods.     

高光谱热红外遥感：现状与展望

高光谱热红外数据中蕴含着丰富的长波光谱信息,可以更精细的揭示地气耦合过程导致的辐射变化,反映热红外谱段特有的地物诊断特征,同时高光谱特性也可以为热红外关键特征参数的病态反演问题提供更合理的假设和约束条件,具有重要的研究价值和应用前景。高光谱热红外遥感技术自诞生起,在吸纳多光谱热红外遥感技术的基础上迅速发展,成为热红外遥感领域的重要研究方向和突破点。然而,当前高光谱热红外遥感存在着可用数据不足,处理方法传统,反演精度有限,应用难以有效实施等问题。为进一步明晰高光谱热红外遥感的研究进展和现存挑战,本文在高光谱热红外相关文献深入分析的基础上,梳理了高光谱热红外研究的发展脉络和热点,介绍了现有国内外主要的高光谱热红外传感器,分析了高光谱大气效应校正、地表温度和发射率分离以及地气关键特征参数一体化反演的现状和问题,总结了相关典型行业应用,展望了高光谱热红外的发展方向,以期为未来高光谱热红外研究工作的开展提供借鉴和帮助。     

高光谱数据截断加权核范数稀疏解混

受仪器和观测条件限制,高光谱数据易受噪声污染,给数据解译带来挑战。针对传统稀疏解混模型抗噪性能差的问题,本文提出一种截断加权核范数稀疏解混方法,利用高光谱图像像元之间的相关性减轻噪声对丰度估计的干扰。该方法借助低秩表示在挖掘数据内在低维结构方面的优势,在稀疏解混中加入基于截断加权核范数的低秩约束,并结合加权稀疏技术,在稀疏正则项中引入空间邻域权重。截断加权核范数对丰度矩阵的奇异值向量分段处理,可以更好地实现丰度矩阵的低秩逼近,使丰度图像保持空间一致性并保留更多细节信息,空间加权策略则增强了丰度图像的空间连续性。模拟高光谱数据、Cuprite矿区真实数据和红树林高光谱数据实验表明,与其他先进的稀疏解混方法相比,所提方法具有更好的抗噪性,能够提高解混精度。