共查询到20条相似文献，搜索用时 15 毫秒
1.
《Geofísica Internacional》2014,53(2):117-133
A morphologic analysis of forest cover in a time span of twelve years is presented in this work. Two multispectral LANDSAT TM-4 images of the years 1989 and 2001 were used. These images cover a forest area where significant changes have occurred in such years. These images were expanded in terms of canonical-expansion variables that describe the spatial-spectral response of the forest masses. The images were modeled as a vector field of as many dimensions as the number of bands employed in the analysis. A vector field was constructed using canonical-variable bands. The set of canonical variables for each year was used to quantify a vector change of the forest masses. This vector change quantifies the degree of alteration of the forest masses. A region-growth algorithm was used to segment the areas occupied by the forest. This algorithm uses as input the canonical variables. The result of such segmentation is a binary image named the bitmap. From this bitmap, a morphologic analysis of the area occupied by the forest was undertaken. A DEM generated from a radar interferometric pair of the RADARSAT 1 satellite, was used to perform a cross-reference with the bitmaps. This cross-reference leads to the derivation of the elevation of occurrence of changes in the forest masses. 相似文献
2.
A unique multispectral imager and an associated multispectral analysis framework are described which together constitute a new diagnostic tool for auroral research. By acquiring spatial and spectral data simultaneously, multispectral imaging allows one to exploit physical connections between auroral morphology and the auroral optical spectrum in a way that sequential spectral imaging cannot. The initial research focus is on imaging the transition in the incident energy spectrum during the formation of discrete arcs—that is, when the precipitating population is characterized by <1 keV electrons. A technique is presented which uses two spectral bands (centered at 4278 and 7325 Å) to extend the effective dynamic range of passive imaging to much lower energies. 相似文献
3.
目的:对X射线影像进行图像增强。方法:应用多种互补的图像增强方法,首先采用拉普拉斯法来突出图像中的细节,使用梯度法突出边缘,然后用平滑后的梯度图像掩蔽拉普拉斯图像,通过高提升滤波得到锐化图像,再使用灰度变换增大锐化图像的灰度动态范围。将本文算法的结果与传统图像增强算法的结果进行比较,该算法对X射线影像增强效果显著,相比传统算法有很大的优势。增强后的图像细节更加清晰,优于传统算法的实现效果。结论:本文算法对医学X射线影像具有一定的理论和实际应用价值。 相似文献
4.
以 2 0 0 1年 11月 14日昆仑山 8 1级地震为例 ,运用月均亮温点对点差值分析法和断裂带内外亮温差值分析法 ,研究了活动断裂与震前红外异常的空间关系及发震断裂上震前卫星红外异常的时间演化过程。研究发现 :震前月平均亮温相对于 2 0 0 0年同期平均亮温的增温区沿发震断裂呈条带状分布 ;从震前 1个半月的 2 0 0 1年 10月开始 ,断裂带内外的相对温差发生明显变化 ,断裂带内的平均亮温与其外围的平均亮温差从 - 2℃增加到 1℃ ,相对增温幅度达 2～ 3℃左右 ,地震之后相对温差又回到正常状态。由此可见 ,震前卫星红外增温与东昆仑断裂带存在着明显的对应关系 ;地震前沿断裂带的红外增温大于其它地区。断裂带内外亮温差值分析法是定量研究红外增温与活动断裂的时空关系、挖掘震前增温异常的有效方法 相似文献
5.
A method to map riparian exotic vegetation (Salix spp.) area to inform water resource management 
下载免费PDF全文
下载免费PDF全文 Hydrological processes within riparian environments worldwide are impacted when introduced species invade. Monitoring and management at substantial expense, are subsequently required to combat deleterious effects on the environment and stream hydrology. Willow species (Salicaceae: Salix spp.) introduced into Australia have spread throughout many riparian systems causing adverse environmental impacts, with high rates of water extraction when located within stream beds (in‐stream willows) thus altering hydrology. Strategies exist to manage willows; however, simpler, more cost‐effective methods are required to map and monitor spatial and temporal distributions. A method is presented to discriminate willow stands from surrounding native riparian vegetation using a single, very high 2 m resolution multispectral WorldView‐2 satellite image. A combination of spectral bands ‘coastal blue’ (400–450 nm), ‘red’ (630–690 nm), ‘red edge’ (705–745 nm) and ‘near infrared2’ (860–1040 nm), minimum noise fraction transformation, median filtering and maximum likelihood supervised classification provided the highest discriminatory power within a 25 km2 study area. Of the spectral bands, coastal blue, red edge and near infrared2 are new bands that are not available in other multispectral sensors. These bands proved critical to the success of discriminating willows from other land cover categories (overall accuracy of 97%). Stream channels were defined by incorporating a LiDAR‐derived digital elevation model to discriminate between willows on stream banks and within stream beds. Canopy area estimates of in‐stream willows, coupled with water savings estimates from willow removal, suggest removal of 10.4 ha of Salix fragilis canopy from within river channels in the study area will potentially return 41 ML year?1 to the environment. The method presented improves our understanding of willow impacts on hydrology and aids decisions regarding willow removal for water resource management. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
地球物理勘探中,地震剖面中的同相轴对地质分层、断层解释、有无形成空洞以及其它异常体的检测中作用重要.根据地震剖面上同相轴具有的性质,采用图像边缘检测方法提取同相轴简单且有效.由于边缘检测中常用的Sobel算子和Canny算子检测同相轴时对噪声免疫差,常因噪声因素引起边缘信息缺失导致同相轴提取不连续,本文采用中值滤波并对Sobel算子进行改进,对地震剖面图进行预处理,结合均方差自动确定阈值并进行异常检测,提取完整同相轴.实验结果表明应用该方法可以提取连续、准确的同相轴. 相似文献
7.
采用X射线计算机断层扫描(X-CT)技术观测多孔介质中天然气水合物的生成和分解过程,具有实时、直观和无损等优点。由于颗粒物边缘图像容积效应和X-CT分辨率的限制,多孔介质体系中不同物质的边界域难以确定,从而影响对多孔介质中水合物赋存状态的准确判断。利用Matlab平台图像处理软件中的开闭运算、多值化、梯度图像提取和边缘检测等方法,对实验获得的多孔介质中甲烷水合物的CT图像进行优化处理,获得了更清晰的图像,可有效地提高多孔介质中不同物质边界域的识别效果,有利于准确判断甲烷水合物在多孔介质中的赋存状态。 相似文献
8.
Atmospheric correction of remote sensing imagery based on the surface spectrum’s vector space 总被引：1，自引：0，他引：1
Due to the atmosphere effect,the qualities of images decrease conspicuously,practically in the visible bands,in the processing of earth observation by the satellite-borne sensors.Thus,removing the atmosphere effects has become a key step to improve the qualities of images and to retrieve the actual reflectivity of surface features.An atmospheric correction approach,called ACVSS(Atmospheric Correction based Vector Space of Spectrum),is proposed here based on the vector space of the features’ spectrum.The reflectance image of each band is retrieved first according to the radiative transfer equation,then the spectrum’s vector space is constructed using the infrared bands,and finally the residual errors of the reflectance images in the visible bands are corrected based on the pixel position in the spectrum’s vector space.The proposed methodology is verified through atmospheric correction on Landsat-7 ETM+ imagery.The experimental results show that our method is more accurate and the corrected image is more distinct,compared with those offered by current popular atmospheric correction software. 相似文献
9.
Optimizing statistical classification accuracy of satellite remotely sensed imagery for supporting fast flood hydrological analysis 总被引：1，自引：0，他引：1
Dimitrios D. Alexakis Athos Agapiou Diofantos G. Hadjimitsis Adrianos Retalis 《Acta Geophysica》2012,60(3):959-984
The aim of this study is to improve classification results of multispectral satellite imagery for supporting flood risk assessment
analysis in a catchment area in Cyprus. For this purpose, precipitation and ground spectroradiometric data have been collected
and analyzed with innovative statistical analysis methods. Samples of regolith and construction material were in situ collected and examined in the spectroscopy laboratory for their spectral response under consecutive different conditions
of humidity. Moreover, reflectance values were extracted from the same targets using Landsat TM/ETM+ images, for drought and
humid time periods, using archived meteorological data. The comparison of the results showed that spectral responses for all
the specimens were less correlated in cases of substantial humidity, both in laboratory and satellite images. These results
were validated with the application of different classification algorithms (ISODATA, maximum likelihood, object based, maximum
entropy) to satellite images acquired during time period when precipitation phenomena had been recorded. 相似文献
10.
稀疏角采样与减小X射线源电流可有效降低多能谱CT低辐射剂量,然而会导致投影数据不足且包含较大噪声,重建图像会严重降质。针对这一问题,本文对传统全核变分（TNV）正则化方法进行推广,利用非局部梯度向量构成的雅克比矩阵的低秩特性,提出非局部全核变分（NLTNV）正则化方法。该方法用单个正则项同时建模能谱CT图像的结构相似性、梯度域稀疏性与非局部自相似性3种先验信息,能恢复稀疏角度投影含较大噪声（剂量较低）时图像的结构特征,并且有效缓解了用多正则项建模多能谱CT图像不同先验信息所导致的正则化参数过多问题。此外,基于NLTNV的重建模型为凸优化模型,保证了算法的稳定性与收敛性。实验结果表明,与TNV正则化方法相比,本方法显著提升重建图像的整体质量。 相似文献
11.
鉴于地震数据不连续性检测的重要性,本文提出了一种保持和检测地震图像不连续性(如:岩层,断层,河道等)的方法.通常在图象不连续的地方,象素值会有较大的差异,文中用4×4的方向模板计算目标点周围六个方向上的差值,当最大差值超过某个门限值时,则可认为该点为不连续点,由此来检测地震图像的不连续性.由于包含重要信息的区域受噪声的影响通常比其他地方严重,而且基于差值的不连续性检测算法对噪声较为敏感,所以在不连续性检测之前降低地震图像的噪声是很重要的.普通的平滑去噪方法会造成边缘模糊,不利于不连续性检测.本文采用旋转模板的非线性平滑方法,用四个六边形和一个八边形模板在目标像素周围旋转,用与目标像素标准差最小(最同类)的模板内那些点的均值代替目标像素的值,从而实现对地震图象的保边缘平滑去噪处理.理论模型和实际数据处理结果表明:与Y、Luo等人提出的保边缘平滑方法相比,本文的保边缘平滑处理方法提高了计算效率和峰值信噪比;将文中提出的保边缘平滑方法和基于方向模板的不连续性检测方法结合使用,得到的不连续性检测结果比直接检测更清晰.地震数据解释人员可根据检测到的不连续性来识别断层、岩层、河道等. 相似文献
12.
Derivation of vegetative variables from a landsat tm image for modelling soil erosion 总被引：1，自引：0，他引：1
Steven M. De Jong 《地球表面变化过程与地形》1994,19(2):165-178
A study was carried out to assess the potential use of satellite thematic mapper (TM) images to produce maps of vegetation-related variables for erosion modelling. In a Mediterranean study area in southern France the (semi-)natural vegetation was described at 33 field plots using four quantitative methods: the Fosberg structural classification system, the cover and management factor of the Universal Soil Loss Equation, the leaf area index and the total percentage cover. After radiometric correction of the image, the spectral TM bands were processed following three different methods. Each method aimed at combining the data of the six spectral TM bands into a single band in such a way that the resulting image displayed optimal information on green vegetation cover. The algorithms used comprise the normalized difference vegetation index, the conventional ‘tasselled cap’ transformation and a locally tuned tasselled cap transformation. Only slight differences were found between the different methods to calculate spectral vegetation indices for this particular case. Furthermore, the correlations between the field variables and image-derived spectral indices are generally small. The largest correlations were found for the normalized vegetation index and the leaf area index (r + 0·71) and for the normalized vegetation index and Fosberg's structural vegetation classes (r + 0·76). However, Fosberg's method results in very general classes, which are of little use for soil erosion models. Furthermore, the spectral indices appeared to be sensitive for the vitality of the vegetation. Consequently, an area covered by a sensed, senescent vegetation will not yield a large value for the spectral index, but its soil is protected against splash erosion. This might lead to a misinterpretation of the soil protective cover when satellite images are used. A final conclusion is that a balance has to be found between the more accurate, but time-consuming field surveys to gather information on erosion-controlling factors and a certain loss of accuracy associated with the use of quick and easy remote sensing methods. 相似文献
13.
M. C. W. Baker 《Surveys in Geophysics》1982,5(3):281-293
The principal uses of Landsat imagery in volcanological studies are for regional reconnaisance, for the interpretation of large volcanic structures and to facilitate the comparison of structures in different parts of the world. Standard black and white single band prints and standard false colour composites are the cheapest and most readily available forms of Landsat imagery. However, standard Landsat images have a poorer resolution and lower information content than enhanced images. The most generally useful enhancement techniques for volcanic studies have proved to be destriping. contrast stretching and edge enhancement. Enhancement techniques are illustrated with examples of young volcanic structures from the Central Andes. The next few years should see significant advances in satellite remote sensing technology with higher resolution imagery (down to 10–30m) and imagery in a wider range of spectral bands becoming available.Paper presented at the Symposium Volcanoes of the Earth and Planets, held at the University of Lancaster, March 17, 1981. 相似文献
14.
Volcanic ash cloud detection has been a difficult problem in moderate-resolution imaging spectroradiometer (MODIS) multispectral remote sensing application. Principal component analysis (PCA) and independent component analysis (ICA) are effective feature extraction methods based on second-order and higher order statistical analysis, and the support vector machine (SVM) can realize the nonlinear classification in low-dimensional space. Based on the characteristics of MODIS multispectral remote sensing image, via presenting a new volcanic ash cloud detection method, named combined PCA-ICA-weighted and SVM (CPIWS), the current study tested the real volcanic ash cloud detection cases, i.e., Sangeang Api volcanic ash cloud of 30 May 2014. Our experiments suggest that the overall accuracy and Kappa coefficient of the proposed CPIWS method reach 87.20 and 0.7958%, respectively, under certain conditions with the suitable weighted values; this has certain feasibility and practical significance. 相似文献
15.
重大地震灾害发生以后, 快速准确地提取灾区的道路震害信息对于应急救援工作具有重要意义。 由于地震造成的破坏非常复杂, 没有固定的光谱特征变化模式, 而且影像中存在大量同物异谱和同谱异物现象。 因此, 传统基于光谱特征的遥感影像道路震害提取方法, 不仅提取精度较低, 而且通用性不强, 需要根据不同影像调整参数。 道路边线是一种稳定的道路几何特征, 其特征变化能够准确地表现道路的状态变化。 基于此, 本文研究了一种基于道路边线的震害信息快速提取方法。 该方法利用震后遥感影像提取完好道路边线, 与震前道路线分布数据进行变化检测, 从而实现震害路段的提取。 最后, 利用汶川震区的遥感影像进行实例验证, 与人工解译的结果进行比较。 结果表明, 该方法能够快速准确地提取道路震害信息。 相似文献
16.
N. Tholey 《Surveys in Geophysics》2000,21(2-3):209-222
Earth observation techniques provide digital images of the Earth's surface. In the field of environmental applications, image processing techniques can be used to manipulate the data, in particular to display satellite images in gray level or in a color composition, to radiometrically and geometrically preprocess the data, and to extract thematic information, by visual interpretation or by semi-automatic techniques.This paper presents some basic concepts in digital image processing and givesa general overview of the main processing methods that can be applied to derivegeographical information from Earth observation images. 相似文献
17.
图像增强技术在重磁图像中的应用 总被引：2，自引：0，他引：2
本文综述了图像增强技术在位场数据中的应用现状，并介绍了两种改进的图像增强技术，用于增强重磁图像特征。一种方法借鉴了直方图平滑化的思想，应用于位场彩色影像的色谱的自动确定。该方法的应用能够使色彩合理地配置，从而保证了图像的视觉效果和分辨率。另一种方法基于改进的Radon变化和梯度计算，用于重磁图像中线性特征的检测和增强。该方法能在变化域中突出显示线性特征，从而有利于线性特征的检测和增强。通过对简单图像和实际资料的应用，表明了两种方法在增强特征中的有效性。 相似文献
18.
近年来,单谱与多谱磁共振图像的分割方法研究已经取得了很大进展,并应用于正常年龄的脑发育和脑疾病的诊断研究,例如老年痴呆综合征、脑损伤、脑肿瘤等的临床研究等。据此可以通过多谱MR图像获得多种对比度信息,更加准确表达人体组织及其病理情况。现已提出的大多数方法,把组织分割问题考虑成统计决策、模式识别和聚类、图像处理和分析等问题。在这些方法中用于组织分割的特征主要是单谱/多谱图像的灰度值/矢量,它们不能直接反映组织的物理特征。而且,这些方法将组织分割问题表述成组织磁共振图像中像素不同成分的有限集合。所以,这些组织分割的方法所取得的结果在某种意义上是不够合理的。这篇论文提出了一种基于磁共振图像谱分解的新的组织分割方法,该方法将组织分割问题考虑成组织的磁共振物理参数的估计问题。这个方法不仅用于磁共振成像中脂肪信号的抑止,也用于核磁共振谱中的水信号抑止。因此,这个方法可以称为空间和谱MR成像。 相似文献
19.
基于水体透明度反演的太湖水生植被遥感信息提取 总被引：3，自引：1，他引：2
在使用多光谱遥感图像提取太湖水生植被分布时,由于水体中悬浮物和藻类等物质的影响,容易产生"异物同谱"现象,大面积水体被误分为沉水植被.本文首先通过TM图像反演太湖水体的透明度,基于RVI和NDVI植被指数,分别建立两类决策树,即透明度辅助的分类决策树和无透明度参与的分类决策树,将太湖分为水体、以浮叶植被为主导的水生植被和以沉水植被为主导的水生植被等三种类型.透明度辅助下的 NDVl 分类决策树方法,较好地消除分类过程中的"异物同谱"现象,是进行太湖水生植被分类的一种最好方法选择,把这种方法应用于2002年7月15日的Landsat ETM卫星遥感影像,结果表明太湖中以沉水植被为主导的水生植被约407.6km2,以浮叶植被为主导的水生植被约82.2km2. 相似文献
20.
《水文科学杂志》2013,58(4)
Abstract Monitoring the change of snow-covered area (SCA) in a basin is vitally important for optimum operation of water resources, where the main contribution comes from snowmelt. A methodology for obtaining the depletion pattern of SCA, which is based on satellite image observations where mean daily air temperature is used, is applied for the 1997 water year and tested for the 1998 water year. The study is performed at the Upper Euphrates River basin in Turkey (10 216 km2). The major melting period in this basin starts in early April. The cumulated mean daily air temperature (CMAT) is correlated to the depletion of snow-covered area with the start of melting. The analysis revealed that SCA values obtained from NOAA-AVHRR satellite images are exponentially correlated to CMAT for the whole basin in a lumped manner, where R 2 values of 0.98 and 0.99 were obtained for the water years 1997 and 1998, respectively. The applied methodology enables the interpolation between the SCA observations and extrapolation. Such a procedure reduces the number of satellite images required for analysis and provides solution for the cloud-obscured images. Based on the image availability, the effect of the number of images on the quality of snowmelt runoff simulations is also discussed. In deriving the depletion curve for SCA, if the number of images is reduced, the timing of image analysis within the snowmelt period is found very important. Analysis of the timing of satellite images indicated that images from the early and middle parts of the melt period are more important. 相似文献