Assessing tundra-taiga boundary with multi-sensor satellite data

Monitoring the dynamics of the circumpolar boreal forest (taiga) and Arctic tundra boundary is important for understanding the causes and consequences of changes observed in these areas. This ecotone, the world's largest, stretches for over 13,400 km and marks the transition between the northern limits of forests and the southern margin of the tundra. Because of the inaccessibility and large extent of this zone, remote sensing data can play an important role for mapping the characteristics and monitoring the dynamics. Basic understanding of the capabilities of existing space borne instruments for these purposes is required. In this study we examined the use of several remote sensing techniques for characterizing the existing tundra-taiga ecotone. These include Landsat-7, MISR, MODIS and RADARSAT data. Historical cover maps, recent forest stand measurements and high-resolution IKONOS images were used for local ground truth.It was found that a tundra-taiga transitional area can be characterized using multi-spectral Landsat ETM+ summer images, multi-angle MISR red band reflectance images, RADARSAT images with larger incidence angle, or multi-temporal and multi-spectral MODIS data. Because of different resolutions and spectral regions covered, the transition zone maps derived from different data types were not identical, but the general patterns were consistent.     

MODIS图象的云检测及分析

云一直是遥感图象处理、图象分析的一大障碍.为了解决这一问题,试图探讨利用中分辨率成像光谱仪MODIS检测云的方法,该方法充分考虑到MODIS数据具有36个光谱通道,特别是红外波段细分的特点,先是基于云的波谱特性采用多光谱综合法、红外差值法及指数法来对MODIS图象上的云点进行检测,鉴于这些方法有一定的局限性,因而还运用了一种基于空间结构分析和神经网络的云自动检测算法;最后将各种方法的云检测结果进行相互映证和对照分析,结果表明,这些方法检测到的云互相吻合,说明利用MODIS图象可成功地检测云点像元.这不仅为云的去除奠定了良好基础,而且也可以提高图象识别、图象分类及图象反演的精度.     

A risk analysis of abstraction-related subsidence based on roughness analysis

The intense abstraction from more than 50 wells located in Irapuato City, Mexico, is inducing soil fracturing. The subsidence process is generating faults and fractures that affect the urban infrastructure. Up to 18 fault systems have been detected with accumulated vertical displacements from 10 mm to 2.1 m. A risk assessment was carried out based on roughness analyses from a multispectral image with a pixel size of 15 × 15 m and fault mapping. The paper demonstrates how a roughness image, supported by false colour imagery, can provide a quick analysis of the actual and potential damage to houses and infrastructure.      

红外成像制导技术发展现状与展望

随着信号处理、半导体技术的飞速发展,近几年红外成像制导技术取得了长足的进展.为了对该领域相关技术进行总结,为未来的研究工作提供参考,首先介绍了红外成像制导技术的概念,分析了红外光学系统、红外焦平面探测器以及图像处理等红外成像制导中的关键技术的发展现状.参考国内外红外成像制导领域的发展趋势,结合作者多年从事可见光、红外成像制导技术研究积累的经验以及对该领域关键技术的理解,预测了未来红外成像制导技术的发展方向.     

A modified statistical approach for image fusion using wavelet transform

The fusion of images is an important technique within many disparate fields such as remote sensing, robotics and medical applications. For image fusion, selecting the required region from input images is a vital task. Recently, wavelet-based fusion techniques have been effectively used to integrate the perceptually important information generated by different imaging systems about the same scene. In this paper, a modified wavelet-based region level fusion algorithm for multi-spectral and multi-focus images is discussed. Here, the low frequency sub-bands are combined, not averaged, based on the edge information present in the high frequency sub-bands, so that the blur in fused image can be eliminated. The absolute mean and standard deviation of each image patch over 3 × 3 window in the high-frequency sub-bands are computed as activity measurement and are used to integrate the approximation band. The performance of the proposed algorithm is evaluated using the entropy, fusion symmetry and peak signal-to-noise ratio and is compared with recently published results. The experimental result proves that the proposed algorithm performs better in many applications.     

一种多光谱图像和全色图像融合算法

文章提出了一种新的基于独立成分分析的多光谱图像和全色图像的融合算法:对于两幅图像的重叠区域,使用独立成分分析去除遥感图像中高阶数据冗余问题,通过独立成分分析使得所分离的各个分量进行叠加从而得到最终的融合结果,从而提高了融合后图像的信息量和信噪比,同时使融合图像兼具全色图像的高分辨率和多光谱图像中特有的对目标某些独特特征的精细描述,使融合图像包含更丰富更有效的信息.     

多光谱图象的真实感融合

多光谱信息融合是指将从多光谱探测器获得的同一场景的多光谱信息特征组合到一起，并利用它们在时空上的相关性及信息上的互补性，以利到对景物更全面，清晰的描述，其真实感成像是指融合后的图像能保留原多光谱图像目标在特定条件下的光谱特征，针对用同一种方法来融合不同场景图象存在的问题，通过分析现有融合方法的优缺点和它们适用的场合，提出了一种综合的图象融合方法，该方法对相关性较弱，且互补性明显的图象对，采用一种新的基于人类视觉系统HVS的自适应加权平衡的融合方法来进行融合，这样能突出目标的光谱特性，而对于相关性较强的图象对，则根据场景目标距离的远近，分别采用小波变换和主成份分析来进行融合，实验表明，该方面能适合于不同类型的场景，其得到的融合结果优于用单种方法进行融合的结果，也有利于对目标的探测和识别。     

水稻叶面积指数的多光谱遥感估算模型研究

LAI是生态系统研究中最重要的结构参数之一,它是估计多种植冠功能过程的重要参数。通过两年的水稻田间试验,使用美国ASD背挂式野外光谱辐射仪(ASDFieldSpec),获取1999～2000年两年晚稻整个生育期的光谱数据,采用计算机测算图斑面积法测定LAI;根据已有的卫星传感器通道波段(MSS、RBV、SPOT、TM、CH)和它们的组合(比值植被指数、归一化差植被指数),以及具有物理意义的光谱区域(蓝区、绿区、黄边、红光吸收谷、红边、紫区、可见光区、近红外区、全部波段)等共有27个变量构建多光谱变量组,采用5个单变量线性与非线性拟合模型,用1999年试验数据为训练样本,建立水稻LAI的多光谱遥感估算模型。结果表明:适用于水稻LAI估算的多光谱变量是植被指数变量好于波段变量;RVI与NDVI比较,RVI好于NDVI。用2000年试验数据作为测试样本数据,对其精度进行评价和验证,非线性模型的精度高于线性模型的精度,其中以SPOT3/SPOT2为变量的对数模型,拟合R2与预测R2达到了最大,其RMSE和相对误差(%)为最低,因此,认为它是估算LAI的最佳模型。
     

利用边缘检测对高分辨率影像中建筑物的提取研究 

遥感作为一种探测技术,越来越广泛地运用到城市建设等应用研究领域中。近年来,高分辨率遥感影像的应用推动了城市遥感进一步向定量化方向发展,同时,也大大增加了数据处理的工作量。如何从海量的遥感数据中筛选出有价值的信息一直是遥感影像处理工作最需要解决的难题。将尝试使用Sobel算子与数学形态学相结合的方法,利用2001年阜新市区的QuickBrid多光谱影像,探索一种高分辨率多光谱影像建筑物的提取方法。
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Covariance intersection based image fusion technique with application to pansharpening in remote sensing

Image fusion of multi-spectral images and panchromatic images has been widely applied to imaging sensors. Multi-spectral images are rich in spectral information whereas panchromatic images have relatively higher spatial resolution. In this paper, we consider the image fusion as an estimation problem, that is to estimate the ideal scene of multi-spectral images at the resolution of panchromatic images. We propose a method of combining the covariance intersection (CI) principle with the expectation maximization (EM) algorithm to develop a novel image fusion approach. In contrast to other fusion methods, the proposed scheme takes cross-correlation among data sources into account, and thus provides consistent and accurate estimates through convex combinations. Since the covariance information is usually unknown in practice, the EM method is employed to provide a maximum likelihood estimate (MLE) of the covariance matrix. Real multi-spectral and panchromatic images are used to evaluate the effectiveness of the proposed EM-CI method. The proposed algorithm is found to preserve both the spectral information of the multi-spectral image and the high spatial resolution information of the panchromatic image more effectively than the conventional image fusion techniques.