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青海湖地区生态环境动态变化遥感监测 总被引:9,自引:0,他引:9
由于青海湖地区的生态环境较为脆弱,且人类活动进一步加剧,人口、资源与环境的矛盾日渐突出,因此,近年来.青海湖及其周边地区的生态环境出现了明显变化,主要表现在水位下降及水域面积减小、草原退化、沙质荒漠化土地面积扩大等。文章采用1975年MSS卫星图像及1987、2000年TM卫星图像作为遥感信息源,并结合地理信息系统方法,旨在查明青海满地区耕地、沙质荒漠化土地和水域等生态环境要素的时空演化规律,为青海湖地区实现资源开发与环境协调发展提供科学依据。监测结果表明,25a来,青海湖地区的耕地及沙质荒漠化土地面积出现明显的扩大,而水域面积出现明显缩小,同时由于湖周各河流土壤侵蚀的加剧,在部分河流入湖处泥沙淤积较为严重,生态环境出现明显恶化。 相似文献
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基于工作流技术的动态GIS服务链研究 总被引:12,自引:0,他引:12
提出了一种基于工作流技术的动态GIS服务链的实现方法,该方法使用抽象GIS服务组合服务链,由GIS服务动态选择机制将抽象服务映射到具体服务,并结合工作流技术,将工作流描述语言描述的GIS服务链流程送入工作流引擎,由工作流引擎管理和监控服务链的运行。 相似文献
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介绍了一个建筑物阴影检测的模型。首先利用摄影测量学原理来计算阴影坐标。即用数字表面模型(digitalsurfacemodel,缩写为DSM)和太阳高度和方位来计算建筑物阴影的空间坐标,并由相机模型计算出每个阴影单元对应的扫描行和相机空间坐标。由高度场光线跟踪判断阴影的可见性,对可见阴影计算出它在投影图像上的坐标。然后在这个结果的基础上再对图像进行阴影的细分割。 相似文献
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M. Kern T. Preimesberger M. Allesch R. Pail J. Bouman R. Koop 《Journal of Geodesy》2005,78(9):509-519
The satellite missions CHAMP, GRACE, and GOCE mark the beginning of a new era in gravity field determination and modeling. They provide unique models of the global stationary gravity field and its variation in time. Due to inevitable measurement errors, sophisticated pre-processing steps have to be applied before further use of the satellite measurements. In the framework of the GOCE mission, this includes outlier detection, absolute calibration and validation of the SGG (satellite gravity gradiometry) measurements, and removal of temporal effects. In general, outliers are defined as observations that appear to be inconsistent with the remainder of the data set. One goal is to evaluate the effect of additive, innovative and bulk outliers on the estimates of the spherical harmonic coefficients. It can be shown that even a small number of undetected outliers (<0.2 of all data points) can have an adverse effect on the coefficient estimates. Consequently, concepts for the identification and removal of outliers have to be developed. Novel outlier detection algorithms are derived and statistical methods are presented that may be used for this purpose. The methods aim at high outlier identification rates as well as small failure rates. A combined algorithm, based on wavelets and a statistical method, shows best performance with an identification rate of about 99%. To further reduce the influence of undetected outliers, an outlier detection algorithm is implemented inside the gravity field solver (the Quick-Look Gravity Field Analysis tool was used). This results in spherical harmonic coefficient estimates that are of similar quality to those obtained without outliers in the input data. 相似文献
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The purpose of this article is to describe the development of a remotely sensed, historical land-cover change database for the northwestern quarter of Chihuahua, Mexico, The database consists of multi-temporal land-cover classifications and change detection images. The database is developed to facilitate future investigations that examine urban–rural linkages as possible drivers of rural land-use and land-cover changes. To develop the needed land-cover change database, this study uses the North American Landsat Characterization (NALC) MSS triplicates because of their temporal depth and spatial breadth. Challenges exist, however, to effective classification and change detection using the NALC triplicates, including illumination differences across multiple scenes and periods caused by topographic and solar variations and the lack of ground reference data for historic periods. Therefore, creation of the database is a four step process. First, extensive pre-processing is performed to enhance comparability of multi-date images. Pre-processing includes topographic correction, mosaic creation and multi-date radiance normalization. Second, ancillary sources of land-cover data are combined with visual interpretations of enhanced images to define reference pixels used to classify the images using the maximum likelihood algorithm. Third, classification accuracy is assessed. Fourth, post-classification change detection is performed. Results indicate significant image improvements after pre-processing that permit very good overall classification (86.26% classified correctly) and change detection. To conclude, findings are presented that indicate significant changes to arid grasslands/shrublands and forest resources in mountainous regions. 相似文献
100.
A. Ankilov A. Baklanov M. Colhoun K. -H. Enderle J. Gras Yu. Julanov D. Kaller A. Lindner A. A. Lushnikov R. Mavliev F. McGovern T. C. O'Connor J. Podzimek O. Preining G. P. Reischl R. Rudolf G. J. Sem W. W. Szymanski A. E. Vrtala P. E. Wagner W. Winklmayr V. Zagaynov 《Atmospheric Research》2002,62(3-4)
During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles. 相似文献