流形上的空间密度聚类算法研究     

刘峰  刘希玉  刘弘 《中国海洋大学学报(自然科学版)》2007,37(4):681-684,626

研究流形上的聚类分析，针对基于密度的空间聚类引入了流形概念，提出1种基于流形的密度聚类算法，该方法将流形的概念与聚类相结合，可以适用于样本为复杂分布的聚类。文中通过实例证明此算法的有效性。  相似文献   

Application of HCA and PCA in the discrimination of not polluted tubular wells from tubular wells with incidence of anthropogenic pollution in Western Amazon Region     

《中国地球化学学报》2006,25(B08):165-165

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Tracing leachates at waste sites using geophysical and geochemical modelling     

Bo Olofsson  Hillevie Jernberg  Andreas Rosenqvist 《Environmental Geology》2006,49(5):720-732

Tracing leachates at landfills is usually carried out using either geophysical methods or chemical analyses of groundwater. There are often problems with fingerprinting pollution sources or clarifying the spreading pattern due to a wide variety of possibilities giving similar anomalies. The aims of the project were to evaluate the advantages of combining results from multigeophysical modelling and statistical/chemical modelling in order to identify pollution sources and the spreading pattern and to test a new technique for chemical fingerprinting. The project was carried out at a landfill in central Sweden using geophysical measurements and modelling of CVES, GPR and VLF as well as chemical modelling using M3 (multivariate mixing and mass balance calculations). The results indicate that by combining geophysical modelling and chemical calculations, the possibilities of fingerprinting the origin of pollution as well as delineating the spreading pattern are significantly increased.  相似文献   

利用主成分分析法提取绿洲水体专题信息的研究   总被引：4，自引：2，他引：4  

丁建丽 《云南地理环境研究》2005,17(2):11-14

水资源对于以荒漠为背景的绿洲具有极其重要的作用,及时掌握绿洲水体的动态变化定量信息,对于合理调控绿洲区域生态环境,可持续发展区域经济活动具有重要意义。针对塔里木盆地南部特有的极端干旱地区,选择策勒绿洲为重点研究靶区,采用主成分分析方法,提取1990和1998年两幅卫星图像中水体专题信息。与以往方法相比,该方法不仅可有效避免常规分类法中存在的误差累积,结果出现较多伪变化信息的缺陷;亦可减小辐射差异对光谱比较法的极大限制,从而直接获得水体变化信息,实现过程简单、清楚,可操作性强。  相似文献   

Lake Neor reveals how mountain vegetation responded to 7000 years of hydroclimate variability in northwestern Iran     

Khadijeh Alinezhad  Elias Ramezani  Morteza Djamali  Arash Sharifi  Alireza Naqinezhad  Cyril Aubert  Emmanuel Gandouin  Ali Pourmand 《第四纪科学杂志》2021,36(4):598-610

Palynological and geochemical analyses provide valuable information about modern and past climatic regimes and vegetation. The impact of climate and humans on past vegetation in the semi-arid areas of northwestern Iran has received increased interest in the wake of warming temperatures in the Middle East. Palynological and down-core XRF elemental abundances from a peat core from Lake Neor enabled a reconstruction of vegetational changes of the past 7000 years over the highlands of northwestern Iran. Periods of increased arboreal pollen (AP) types and high (Artemisia + Poaceae)/Chenopodiaceae ratios along with low titanium abundances, high percentages of total organic carbon, more negative δD values, and higher carbon accumulation rates suggest a relatively wet climate. These conditions have persisted during the periods 6700–6200, 5200–4450 and 3200–2200 cal a bp. The overall low AP values, substantial rise of Chenopodiaceae, high Ti abundances and low values of palaeo-redox proxies, are all evidences of a drier climate, as has been reconstructed for the periods 6200–5200 and 4030–3150 cal a bp and the last 2200 years. An important feature of the last centuries is the increase of anthropogenic and pastoral indicator pollen types. Our results may provide basic data to predict future trends in vegetation dynamics under future climate change in western Asia.  相似文献   

Assessing soil salinity using WorldView-2 multispectral images in Timpaki,Crete, Greece   总被引：2，自引：0，他引：2  

D. D. Alexakis  I. N. Daliakopoulos  I. S. Panagea  I. K. Tsanis 《国际地球制图》2018,33(4):321-338

Salinization is one of the major soil degradation threats occurring worldwide. This study evaluates the feasibility of operational surface soil salinity mapping based on state-of-the-art Earth Observation (EO) products captured by sensors on-board WorldView-2 (WV2) and Landsat 8 satellites. The proposed methods are tested in Timpaki, south-central Crete,Greece, where brackish water irrigation puts soil health at risk of soil salinization. In all cases, EO products are calibrated against soil samples collected from bare soil locations. Results indicate a moderate correlation of observed EC_e values with the investigated remote sensing parameters. Regarding sensitivity to saline soil, the yellow band displays higher values. Comparison between methods used in the literature shows that those developed specifically for soil salinity, and especially index S5, perform better. The proposed ‘detection index’ and 3D PCA transformation methodology perform reasonably well in detecting areas with high EC_e values and provide a simple and effective operational alternative for saline topsoil detection and mapping.  相似文献   

REPRESENTATION OF SPECTRA BY CONTINUOUS FUNCTIONS     

BJRN K.ALSBERG 《地理学报(英文版)》1993,(3)

A general framework for manipulating spectra as functions in traditional multivariate methods such asPCA and PLS is described.The functional representation is very convenient for compression,ensuringsmoothness and continuity.There are two fundamentally different types of representations:(a)byfunctions and(b)by function coefficients.The use of coefficients is the most practical way of analysis.  相似文献   

Analyzing multi-year rice-fallow dynamics in Odisha using multi-temporal Landsat-8 OLI and Sentinel-1 Data     

Parvesh Kumar Chandna  Saptarshi Mondal 《地理信息系统科学与遥感》2020,57(4):431-449

ABSTRACT

Sustainable intensification of existing cropland is one of the most viable options for meeting the escalating food demands of the ever-increasing population in the world. Accurate geospatial data about the potential single-crop (rice-fallows) areas is vital for policymakers to target the agro-technologies for enhancing crop productivity and intensification. Therefore, the study aimed to evaluate and understand the dynamics of rice-fallows in the Odisha state of India, using SAR (Sentinel-1) and Optical (Landsat OLI) datasets. This study utilized a decision-tree approach and Principal component analysis (PCA) for the segmentation and separation of different vegetation classes. The estimated overall accuracy of extracted rice-fallow maps was in the range of 84 to 85 percent. The study identified about 2.2, 2.0 and 2.1mha of Rice-Fallows in the years 2015–16, 2016–17, and 2017–18, respectively. The combined analysis (all three years) of rice-fallow maps identified about 1.34mha of permanent rice-fallows, whereas the remaining 0.6–0.8mha area was under the current-fallow category. About 50% of the total permanent rice-fallows were detected in the rainfed areas of Mayurbhanj, Bhadrak, Bolangir, Sundargarh, Keonjhar, Baleswar, Nawarangpur and Bargarh districts. The study also illustrated the time-series profiles of SMAP (soil moisture) datasets for the ten agroclimatic zones of the Odisha, which can be utilized (along with rice-fallow maps) for the selection of crop and cultivars (e.g. short or medium duration pulses or oilseeds) to target the rice fallows. The approach utilized in the current study can be scaled up in similar areas of South and South-east Asia and Africa to identify single-crop areas for targeting improved technologies for enhanced crop productivity and intensification.  相似文献   

中国夏季降水异常分布的非线性特征   总被引：2，自引：2，他引：2  

居丽丽  郭品文  徐同 《气象与减灾研究》2007,30(2):13-17

运用基于前馈型人工神经网络的非线性主成分分析方法(NLPCA),对中国近50 a夏季降水异常分布的非线性特征进行了分析。结果表明,中国夏季降水的异常分布具有一定的非线性特征,当夏季降水距平的一维NLPCA近似在非线性主成分取极端相反位相时,对应的空间分布型表现出明显的不对称性;一维NLPCA对夏季原始降水距平场的近似,比传统一维PCA的近似更为逼真。  相似文献   

基于主成分分析的ENVISAT ASAR数据在福建省漳州市香蕉园地提取中的应用(英文)     

汪小钦  王钦敏  凌飞龙  朱晓铃  江洪 《地球空间信息科学学报》2009,12(2):142-145

Banana is one of the main economic agrotypes in Zhangzhou, Fujian Province. The multi-temporal ENVISAT ASAR data with different polarization are used to classify the banana fields in this paper. Principal component analysis (PCA) was applied for six pairs of ASAR dual-polarization data. For its large leaves, banana has high backscatter. So the value of banana fields is high and shows very bright in the 1st component, which makes it much easier for banana fields extraction. Dual-polarization data provide more information, and the VV and VH backscatter of banana show different characters with other land covers. Based on the analysis of the radar signature of banana fields and other land covers and the 1st component, banana fields are classified using object-oriented classifier. Compared to the field survey data and ASTER data, the accuracy of banana fields in the study area is 83.5%. It shows that the principal component analysis provides the useful information in SAR images analysis and makes the extraction of banana fields easier. Supported by the Program for New Century Excellent Talents in University (NCET-05-0573), Fujian Science and Technology Project (No.2006I0018), the Science Project of the Education Department of Fujian Province(No. 2006F5022).  相似文献