共查询到20条相似文献，搜索用时 15 毫秒
1.
Christophe Vigny 《Journal of Geodesy》1996,70(5):300-306
In june 1990, NASA's Crustal Dynamics Project (CDP) has established a geodetic footprint for the Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) systems located near Fort Davis, Texas using GPS measurements. The purpose of such a footprint is to assess both the tectonic and physical stability of the main observing monuments. Included in the survey were four new monuments forming a 20 to 30 km quadrilateral, as well as four existing monuments near the McDonald Laser Ranging System (MLRS), the Harvard Radio Astronomy (HRA) 85' antenna, and the new 85' antenna of the Very Long Baseline Array (VLBA).This network was partly reoccupied by the University of Texas Austin in may 1992. Three additional sites not observed in 1990 were occupied, two of them being old monuments in the observatory area (Harvard-RM4 and VLBA-SLR), and a new monument 80 km away across the closest active fault near Valentine, Texas.Thanks to existing ties between nearby monuments in the observatory area, the comparison between the two epochs was made possible. Significant motion of more than 1 cm of any of the implied sites over a two year period can be ruled out. Despite this quite reassuring results, smaller displacements cannot be detected mainly because of the poor quality of the 1990 data. Therefore it is strongly advised that a third occupation of the footprint sites takes place in the close future. Such a survey, occuring five years after the first one and three years after the second one, should definitely answer the questions on the Fort Davis area stability at the millimeter per year level. 相似文献
2.
Patrick J. Fell 《Journal of Geodesy》1986,60(3):181-192
The Fourth International Geodetic Symposium on Satellite Positioning was held in Austin, Texas from 28 April to 2 May 1986.
The symposium was organized as a forum for the discussion of recent geodetic activities related to precise positioning using
observations from the Navy Navigation Satellite System (Transit) and the NAVSTAR Golbal Positioning System (GPS). In addition,
the sympsium promoted an exchange of ideas on the future direction of GPS geodetic activities and provided a summary of the
status, policy, and plans for both the GPS and Transit systems. This report summarizes the proceedings of the meeting. 相似文献
3.
Studies the spatial patterns of location error and of classification error in spatio-temporal datasets, assess the role of environmental factors in determining error rate and pattern, and test for possible correlation within and between these error types in space and time. A multiple regression was used to determine the effects of local environmental factors (topography, vegetation cover) on each error type. Topographic structure and vegetation cover had significant effects on location error, where larger error was associated with north-facing aspects, steeper slopes and woody vegetation cover. Classification error was also affected by topography, and vegetation cover. Slope was the major factor that affected classification quality. Strong correlation was found between error in different time steps, for both error types. Correlation between these two error types in the same time step was much smaller and in most cases insignificant. 相似文献
4.
A spatial panel ordered-response model with application to the analysis of urban land-use development intensity patterns 总被引：1，自引：0，他引：1
This paper proposes and estimates a spatial panel ordered-response probit model with temporal autoregressive error terms to analyze changes in urban land development intensity levels over time. Such a model structure maintains a close linkage between the land owner’s decision (unobserved to the analyst) and the land development intensity level (observed by the analyst) and accommodates spatial interactions between land owners that lead to spatial spillover effects. In addition, the model structure incorporates spatial heterogeneity as well as spatial heteroscedasticity. The resulting model is estimated using a composite marginal likelihood (CML) approach that does not require any simulation machinery and that can be applied to data sets of any size. A simulation exercise indicates that the CML approach recovers the model parameters very well, even in the presence of high spatial and temporal dependence. In addition, the simulation results demonstrate that ignoring spatial dependency and spatial heterogeneity when both are actually present will lead to bias in parameter estimation. A demonstration exercise applies the proposed model to examine urban land development intensity levels using parcel-level data from Austin, Texas. 相似文献
5.
Ye. P. Sorokina 《地理信息系统科学与遥感》2013,50(2):165-176
Industry concentrated in cities is a major source of geochemical pollution. It is suggested that this technogenic impact on the environment can be measured by techniques developed in geochemistry. The specific nature of the pollutants can be identified and their levels of concentration (mostly in the soil) can be measured against normal background values. This allows areas of pollution to be classified and mapped in terms of the composition and concentration of pollutants from industrial emissions. Translated from: Voprosy geografii, Vol. 120, 1983, pp. 55-67, by Robert K. Holz and Warren Hamill, University of Texas, Austin. 相似文献
6.
发现犯罪时空分布规律并预测犯罪发生,是提高警务策略有效预防、控制犯罪的重要方法。在分析财产犯罪时空规律的基础上,利用BP神经网络模型自动学习训练各因子与财产犯罪的非线性关系,建立了财产犯罪预测模型。针对BP神经网络模型易陷入局部最优和模型不稳定的缺陷,提出了利用遗传算法（GA）选择各因子最优的初始化权重和参数,并以此作为BP神经网络模型的初始化权重矩阵,通过对历史数据的学习及训练建立了改进后的GA-BP神经网络模型。利用某市2007~2012年财产犯罪、人口、GDP、土地利用等35个综合影响因子数据,对改进前后的模型进行了预测对比试验。结果表明,改进后的GA-BP神经网络模型成功克服了BP模型的缺陷,收敛迭代最小次数从117次改进到8次;10次计算收敛迭代次数最大误差从370次提高到5次;模型预测精度（RMES）从0.043 0提高到0.019 95。 相似文献
7.
从质量管理系统三大要素的角度,具体阐述了3D产品基础质量检查的全过程,阐明了人-机-环境因素,特别是环境因素中的人文环境因素对质量检查效能的重要影响.对提高工作效率,保障产品检查工作正常、有序的运行,保证产品质量具有指导意义. 相似文献
8.
《制图学和地理信息科学》2013,40(2):127-140
This study presents a method to model population densities by using image texture statistics of semi-variance. In a case study of the City of Austin, Texas, we first selected sample census blocks of the same land use to build population models by land use. Regression analyses were conducted to infer the relationship between block population densities and image texture statistics of the semi-variance. We then applied the population models to an area of 251 blocks to estimate populations for within-blocks land-use areas while maintaining census block populations. To assess the proposed method, the same analysis was performed while census block-group populations were maintained, and the aggregated block populations were compared with original census block populations. We also tested a conventional land-use-based dasymetric mapping method with pre-calculated population densities for land uses. The results show that our approach, which is based on initial land-use stratification and further image-texture statistical modeling of population, has higher accuracy statistics than the conventional land-use-based dasymetric mapping method. 相似文献
9.
干旱区生态系统极易受到气候及土地利用变化的影响,其生物多样性格局及其形成机制是重要的生态学问题。基于新疆地区鸟类及哺乳动物物种多样性数据,结合气候、地形和长时间序列的植被遥感参数产品FAPAR数据等,主要在不同的土地利用类型及海拔带上采用单因子相关分析方法探讨了物种丰富度格局的形成机制。总体来说,不同生境类型中,植被遥感参数因子(DHI、NDVI等)与两种类群物种丰富度分布的相关性强于与气候因子(温度、降水)的相关性。具体而言,植被遥感参数因子中,基于FAPAR的生境指数因子与丰富度的相关性大于基于植被指数的因子(DHI_cumNDVI_cumEVI_cum);气候因子中,在草地生境或者较低的海拔上,年均降水因子对于丰富度分布的解释力强于年均温度因子。这表明在新疆地区,影响鸟类与哺乳类动物物种丰富度分布的主导理论是生境异质性假说与环境稳定性假说,其解释力在多种生境内均强于生产力与环境热量。 相似文献
10.
Aspects of urban transportation have significant implications for resource consumption and environmental quality. The level of travel activity, the viability of various modes of transportation and hence the level of transportation-related emissions are influenced by the structure of cities, i.e., their urban forms. While it is widely recognized that satellite remote sensing can provide spatial information on urban land cover and land use, its effective use for understanding impacts of urban form on issues such as transportation requires that this information be integrated with relevant demographic information. A comprehensive bi-national urban database, the Great Lakes Urban Survey (GLUS), comprising all cities with populations in excess of 200,000 has been created from Landsat imagery and national census and transportation survey information from Canada and the United States. A suite of analysis tools are proposed to utilize information sets such as GLUS to investigate the link between urban form and work-related travel. A new indicator, the Employment Deficit Measure (EDM), is proposed to quantify the balance between employment and worker availability at different transit horizons and hence to assess the viability of alternate modes of transportation. It is argued that the high degree of residential and commercial/industrial land uses greatly impact travel to work mode options as well as commute distance. A spatial interaction model is developed and found to accurately predict travel distance aggregated at the census tract level. We argue that this model could also be used to explore the relative levels of travel activity associated with different urban forms. 相似文献
11.
Yikang Wang Yuhao Kang Haokun Liu Ce Hou Bing Zhou Shan Ye Yuyan Liu Jinmeng Rao Zhenghao Pei Xiang Ye Song Gao 《Transactions in GIS》2023,27(2):450-475
With the increasing demands for geospatial analytics in industry and academia, the need for Geographic Information Systems/Science (GIS) education is on the rise. A growing number of departments in geography have launched or expanded their GIS graduate programs. However, the factors influencing students choosing GIS programs have not been examined yet. In this study, we looked at Chinese students applying for overseas GIS programs and examined factors influencing their decision-making. We distributed the survey in GISphere, one of the largest GIS international student communities, and 84 valid questionnaires were returned. We analyzed the spatial and demographic patterns of Chinese students applying for overseas GIS programs. We identify five main factors that affect their choices of GIS programs: (1) education quality and awareness, (2) physical, social, and political environments, (3) improved employment prospects, (4) personal recommendations, and (5) the application process. Our study offers implications for the development of GIS graduate programs. We anticipate that the conclusions drawn from this research will benefit and advance geography and GIS education globally. 相似文献
12.
F. Benjamin Zhan 《国际地球制图》2013,28(3):77-81
Abstract Results of a survey to find out whether the GIS program in the Department of Geography at Southwest Texas Stare University (SWT) has served its graduates well are presented. In recent years, a considerable amount of effort has been given to the development of strategies for expanding the existing horizon of GIS education, integrating existing programs, and improving the ways in which GIS education is delivered. This study takes a different approach and seeks to get input from geography graduates who have secured a job in the real world for improving a university GIS program. Based on 26 responses to the survey, employment categories of SWT geography graduates are examined first. Then, geography courses that are considered most helpful in career development by the survey participants are identified. Third, useful GIS courses and essential skills required by the marketplace in the real world as suggested by the survey participants are discussed. It is clear from the results of the survey that the geography program at SWT in general has served its graduates well. Results from the survey also clearly indicate that GIS skills are useful in the career development of most geography graduates, particularly for those who have a concentration area in either GIS/Cartography, Resource and Environmental Studies, or Urban and Regional Planning. 相似文献
13.
This study adopts a near real‐time space‐time cube approach to portray a dynamic urban air pollution scenario across space and time. Originating from time geography, space‐time cubes provide an approach to integrate spatial and temporal air pollution information into a 3D space. The base of the cube represents the variation of air pollution in a 2D geographical space while the height represents time. This way, the changes of pollution over time can be described by the different component layers of the cube from the base up. The diurnal ambient ozone (O3) pollution in Houston, Texas is modeled in this study using the space‐time air pollution cube. Two methods, land use regression (LUR) modeling and spatial interpolation, were applied to build the hourly component layers for the air pollution cube. It was found that the LUR modeling performed better than the spatial interpolation in predicting air pollution level. With the availability of real‐time air pollution data, this approach can be extended to produce real‐time air pollution cube is for more accurate air pollution measurement across space and time, which can provide important support to studies in epidemiology, health geography, and environmental regulation. 相似文献
14.
A feasibility study in progress to integrate health and air quality information is presented. The methods of using integrated GIS and air quality dispersion modelling tools to assess the effect of the environment on health are discussed. The main aim is to model human personal exposure to air pollutants and compare the predictions to respiratory health data for asthmatics in a health telematics project. The MEDICATE project develops and tests the feasibility of using a health telematic system for asthmatics. Key to this is the determination of the real-time health (lung function) response to the ambient environment. For this, air quality information is related to respiratory measurements by modelling personal exposure through a GIS. The methods of integrating environmental modelling and assessment tools (GIS) in this case are examined. ESRI's ArcView is used to locate and compile environmental information about the patients' locations and lifestyles in the study areas (London and Barcelona). A dispersion modelling extension to ArcView, ADMS Urban, is used to interrogate the spatial environmental databases (e.g. emission inventories) to model air pollution concentrations. Patients' personal exposure is modelled by time-weighted estimates of their exposure to ambient air quality at each defined location. Lung function data can be compared on a time-wise basis with these air quality indicators to see if there is a relationship on an hourly, daily or lagged-day basis. The aim of this paper is to propose a methodology and discuss the integration and practicalities of using air quality assessment tools (inventories, dispersion modelling and a GIS) in assessing the impacts of the environment on human health. 相似文献
15.
基于GIS方法,对广州市禁摩前和禁摩后两个时间段的抢劫盗窃犯罪案件数据,进行点模式描述和点模式分析。分析结果表明:禁摩前后广州市抢劫盗窃犯罪的案发地点在空间位置和空间范围上发生了很大变化。空间位置整体向东北方向移动,空间范围进一步扩张,由禁摩前的东西走向变为向西北和东南两个方向延伸;同时,禁摩后的空间聚集程度也有所降低。这些变化都进一步说明了,新时期下,这类犯罪呈现出了新的时空变化特征。 相似文献
16.
应用“3S”技术进行北京市森林立地分类和立地质量评价的研究 总被引：33，自引：0，他引：33
本文针对目的森林立地分类和立地质量评价研究中存在的问题。试图从立地分类和评价的方法进行技术上新的探讨。研究中以生态学和景观生态学理论为基础,以遥感（ＲＳ）、地理信息系统（ＧＩＳ）和专家系统（ＥＳ）作为主要的技术手段,借助相关数学分析,对北京市森林进行立地类型划分和在此基础上的立地质量评价及多目标动态决策。通过对北京地区景观特征及其气候、地貌、地形、土壤、植被等各种因子的定性分析,以及一、二类调查数据的定性定量分析,结合实际应用,确定分类原则和分类系统。应用ＧＩＳ建立各级分类的各因子专题数据库和图形库,通过各分类层次的主导因子及辅助因子的专题图叠加完成初分类。在此基础上,应用知识库中的专家知识及ＥＳ的推理机制对初分类结果进行综合,根据可信度理论,得出各级符合生产、造林规划和经营实际的立地类型图。对于最低一级的分类结果,采用专家打分的方法进行各类型立地质量的多因子综合评价,并编制立地质量评价图。在分类和评价的基础上,可以根据森林的生态效益、经济效益、环境效益和社会效益的综合考虑选择目标集,进行面向目标的动态决策。 相似文献
17.
利用遥感和GIS研究内蒙古中西部地区环境变化 总被引：22，自引：1，他引：22
利用TM和MSS卫星遥感数据提取反映生态环境的植被、土壤亮度、湿度、热度指数，结合气候数据和其它地学辅助信息，在GIS的支持下建立环境质量评价模型；利用该模型评价了内蒙古中西部地区19876、1987、1996年跨越20年的环境变化，从区域平均环境质量指数的变化和各级指数分布的区域面积变化两方面说明了研究区20年来的环境退化；分析了气候因子对环境质量变化的影响，定量说明了半干旱地区影响环境变化的气候因子主要是湿润度，指出20年来人为因素对环境质量的影响呈现越来越大的趋势。 相似文献
18.
Applied Research Laboratories, The University of Texas at Austin (ARL:UT) has established a cross platform open source software
project called the GPSTk or the GPS Toolkit. The GPSTk consists of a library and collection of applications that support GPS
research, analysis, and development. The code is released under the terms of the Lesser GNU Public License. The GPSTk supports
a broad range of functionality. This includes reading and writing observations in standard formats, such as RINEX, BINEX,
and SP3, ephemeris evaluation, position determination, receiver autonomous integrity monitoring (RAIM), atmospheric delay
modeling, cycle slip detection and correction, and P-code generation. The GPSTk provides the core set of functionality that
is used for GPS research and development at ARL:UT. ARL:UT has been involved with satellite navigation since Transit (the
precursor to GPS) in the 1960s and is currently conducting research in a wide variety of GPS-related fields, including precise
surveys, monitor station networks, and ionospheric studies. The GPSTk is a community-wide resource for all users of GPS and
GNSS technology. Participation is welcomed in all areas including: bug reports, new algorithms, suggestions for improvement,
and contributions of additional functionality or applications. ARL:UT continually improves the library, shepherds community
participation, and is committed to the project’s development and maintenance.
The GPS Toolbox is a column dedicated to highlighting algorithms and source code utilized by GPS Engineers and scientists.
If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail
it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to download source code, visit
our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic
Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada. 相似文献
19.
测绘质量问题是一个受多方面影响因素作用的复杂问题,其中大量的影响因素都难以量化。运用层次分析法（AHP）定量分析各个影响因素的重要度,按影响程度进行排序,可确定影响测绘质量的主要因素。研究发现,质量体系是影响测绘质量的首要因素,生产工期、人员培训、过程控制和技术设计等是影响测绘质量的相对重要因素,建议测绘单位可就此建立... 相似文献
20.
采用时空同现模式分析方法挖掘多元犯罪事件之间的关联关系,可为犯罪事件防控问题提供科学指导。现有方法依赖人为设置的频繁度阈值,应用部门若缺乏先验知识则可能导致决策错误。因此,基于非参数统计思想,提出一种面向城市犯罪的时空同现模式显著性检验方法。首先通过重建每类犯罪事件的时空分布,构建多元犯罪事件分布独立的零模型;然后根据零模型下多元犯罪事件同现频率的试验分布,判别候选时空同现模式的显著性。最后设计具有预设模式的模拟数据实验验证该方法的有效性;在多个分析尺度（时空半径）下识别S市2016年13种犯罪事件间时空同现模式,并以时空同现模式{扰乱治安,盗窃电动自行车,扒窃}为例,结合公共设施空间分布,对该模式形成机理进行深入分析。结果表明:①该方法充分顾及了单元犯罪事件自相关特征的影响,能够有效识别具有统计特性的时空同现模式;②犯罪事件时空同现模式随分析尺度的变化而存在差异;③具有相似建成环境和社会环境的犯罪事件容易形成时空同现模式。 相似文献