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101.
Qiliang Liu Wenkai Liu Min Deng Yaolin Liu 《International journal of geographical information science》2019,33(9):1718-1738
The discovery of spatial clusters formed by proximal spatial units with similar non-spatial attribute values plays an important role in spatial data analysis. Although several spatial contiguity-constrained clustering methods are currently available, almost all of them discover clusters in a geographical dataset, even though the dataset has no natural clustering structure. Statistically evaluating the significance of the degree of homogeneity within a single spatial cluster is difficult. To overcome this limitation, this study develops a permutation test approach Specifically, the homogeneity of a spatial cluster is measured based on the local variance and cluster member permutation, and two-stage permutation tests are developed to determine the significance of the degree of homogeneity within each spatial cluster. The proposed permutation tests can be integrated into the existing spatial clustering algorithms to detect homogeneous spatial clusters. The proposed tests are compared with four existing tests (i.e., Park’s test, the contiguity-constrained nonparametric analysis of variance (COCOPAN) method, spatial scan statistic, and q-statistic) using two simulated and two meteorological datasets. The comparison shows that the proposed two-stage permutation tests are more effective to identify homogeneous spatial clusters and to determine homogeneous clustering structures in practical applications. 相似文献
102.
Examining the Relationship Between Spatial Configurations of Urban Impervious Surfaces and Land Surface Temperature 总被引:1,自引:0,他引:1
The urban heat island(UHI) effect has significant effects on the quality of life and public health. Numerous studies have addressed the relationship between UHI and the increase in urban impervious surface area(ISA), but few of them have considered the impact of the spatial configuration of ISA on UHI. Land surface temperature(LST) may be affected not only by urban land cover, but also by neighboring land cover. The aim of this research was to investigate the effects of the abundance and spatial association of ISAs on LST. Taking Harbin City, China as an example, the impact of ISA spatial association on LST measurements was examined. The abundance of ISAs and the LST measurements were derived from Landsat Thematic Mapper(TM) imagery of 2000 and 2010, and the spatial association patterns of ISAs were calculated using the local Moran’s I index. The impacts of ISA abundance and spatial association on LST were examined using correlation analysis. The results suggested that LST has significant positive associations with both ISA abundance and the Moran’s I index of ISAs, indicating that both the abundance and spatial clustering of ISAs contribute to elevated values of LST. It was also found that LST is positively associated with clustering of high-ISA-percentage areas(i.e.,>50%) and negatively associated with clustering of low-ISA-percentage areas(i.e.,<25%). The results suggest that, in addition to the abundance of ISAs,their spatial association has a significant effect on UHIs. 相似文献
103.
For spatial analyses, raster land cover/use maps are converted into points, where each point holds attribute of its corresponding land cover/use. However, these are not identical in terms of areas or shapes; thus assigning a point to each isolated shape is not an adequate solution and for that gridding is suggested. Square, hexagon and triangle are among the basic land use gridding systems where each of them has its own advantages in such process. This research aims to compare the systems in providing accurate representations of the original land cover/use maps, assess the data loss while increasing resolution and suggest suitable gridding system. The research finds the errors in area and feature numbers as criteria for selected classes. Modules that find out errors in each scale considering each criterion and class alone are proposed. The modules suggest both the best system for each criterion alone and for combined criteria. 相似文献
104.
对三维潜标拖缆在规则波作用下的动力响应进行了研究,首先基于集中质量法给出了缆绳在规则波作用下的控制方程,然后提出了两种不同类型的自由端边界条件:质点型和艇型自由端边界条件,前者把拖体视为作三个自由度线运动的质点,而后者把拖体视为作六自由度运动的艇体,最后用有限差分法进行了数值研究。数值计算结果表明潜标拖缆在规则波的作用下,不仅作近似的简谐振动,还会在横向、垂向产生一个偏移量,该偏移量的大小随浪向角的变化而变化,另外受遭遇频率的影响,振动的幅值也随浪向角的变化而呈现不同的特征。 相似文献
105.
106.
根据蓄冰中央空调的控制要求设计了一个基于西门子可编程逻辑控制器(PLC)的两级监控系统,现场工作站由PLC与触摸屏组成,作为现场监控及数据采集平台;管理工作站由工控计算机和打印机组成,作为主要的人机界面(HMI),除能打印数据及远程监控现场工作站外,还具有现场工作站的所有功能。实际运行结果表明,设计的监控系统能实时监视和控制蓄冰中央空调状态,有效地提高空调系统的制冷量及制冷效率。 相似文献
107.
H. Htún M.R. Payne G. Beaugrand P.C. Reid A.B. Sand H. Drange B. Hansen J.A. Jacobsen D. Bloch 《Progress in Oceanography》2009,80(3-4):149-162
Pronounced changes in fauna, extending from the English Channel in the south to the Barents Sea in the north-east and off Greenland in the north-west, have occurred in the late 1920s, the late 1960s and again in the late 1990s. We attribute these events to exchanges of subarctic and subtropical water masses in the north-eastern North Atlantic Ocean, associated with changes in the strength and extent of the subpolar gyre. These exchanges lead to variations in the influence exerted by the subarctic or Lusitanian biomes on the intermediate faunistic zone in the north-eastern Atlantic. This strong and persistent bottom-up bio-physical link is demonstrated using a numerical ocean general circulation model and data on four trophically connected levels in the food chain – phytoplankton, zooplankton, blue whiting, and pilot whales. The plankton data give a unique basin-scale depiction of these changes, and a long pilot whale record from the Faroe Islands offers an exceptional temporal perspective over three centuries. Recent advances in simulating the dynamics of the subpolar gyre suggests a potential for predicting the distribution of the main faunistic zones in the north-eastern Atlantic a few years into the future, which might facilitate a more rational management of the commercially important fisheries in this region. 相似文献
108.
109.
This article introduces a software package named GeoSurveillance that combines spatial statistical techniques and GIS routines to perform tests for the detection and monitoring of spatial
clustering. GeoSurveillance provides both retrospective and prospective tests. While retrospective tests are applied to spatial data collected for a
particular point in time, prospective tests attempt to incorporate the dynamic nature of spatial patterns via analyzing time-series
data to detect emergent clusters as quickly as possible. This article will outline the structure of GeoSurveillance as well as describe the statistical cluster detection methods implemented in the software. It concludes with an illustration
of the use of the software to analyze the spatial pattern of low birth weights in Los Angeles County, California.
相似文献
110.