The acquisition of precise soil data representative of the entire survey area, is a critical issue for many treatments such as irrigation or fertilization in precision agriculture. The aim of this study was to investi...The acquisition of precise soil data representative of the entire survey area, is a critical issue for many treatments such as irrigation or fertilization in precision agriculture. The aim of this study was to investigate the spatial variability of soil bulk electrical conductivity （ECb） in a coastal saline field and design an optimized spatial sampling scheme of ECb based on a sampling design algorithm, the variance quad-tree （VQT） method. Soil ECb data were collected from the field at 20 m interval in a regular grid scheme. The smooth contour map of the whole field was obtained by ordinary kriging interpolation, VQT algorithm was then used to split the smooth contour map into strata of different number desired, the sampling locations can be selected within each stratum in subsequent sampling. The result indicated that the probability of choosing representative sampling sites was increased significantly by using VQT method with the sampling number being greatly reduced compared to grid sampling design while retaining the same prediction accuracy. The advantage of the VQT method is that this scheme samples sparsely in fields where the spatial variability is relatively uniform and more intensive where the variability is large. Thus the sampling efficiency can be improved, hence facilitate an assessment methodology that can be applied in a rapid, practical and cost-effective manner.展开更多
With the need in the global change research project for the land -use/land-cover change information, most international and regional research organization or groups have put amounts of efforts to improve of the dynami...With the need in the global change research project for the land -use/land-cover change information, most international and regional research organization or groups have put amounts of efforts to improve of the dynamics monitoring and database updating techniques. With the pressure on nature environment from increasing population and decreasing farmland be- coming significant more and more in China, the farmland urban dynamics in historical and current times, even the change trends in the future, should be monitored and analyzed serving for regional and national social, economic and environmental sustain- able development in the long future. Based on spatial and temporal series of land -use/land-cover database resources, Chinese Academy of Sciences designed a sampling framework for monitoring farmland and urban area dynamics in regional and national level. In order to test the accuracy of the sampling schema for national and regional level, we took two provinces area into overall covered change detecting process with TM images data through being inter’Preted by digitalization on the screen. The result shows that our stratified random sampling schema is suitable for monitoring land -use/land-cover change at national and regional level with quick response, high accuracy and low expenses. The land-use/land-cover change (LUCC) information can update the LUTEA database for global change research during certain period so that the forecasting process and evaluating analysis on land resources and environment under human and natural driving force will get essential data and produce valuable conclusions.展开更多
Since 1990s,the spatial data warehouse technology has rapidly been developing, but due to the complexity of multi-dimensional analysis, extensive application of the spatial data warehouse technology is affected. In th...Since 1990s,the spatial data warehouse technology has rapidly been developing, but due to the complexity of multi-dimensional analysis, extensive application of the spatial data warehouse technology is affected. In the light of the characteristics of the flood control and disaster mitigation in the Yangtze river basin, it is proposed to design a scheme about the subjects and data distribution of the spatial data warehouse of the flood control and disaster mitigation in Yangtze river basin, i.e., to adopt a distributed scheme. The creation and development of the spatial data warehouse of the flood control and disaster mitigation in Yangtze river basin is presented .The necessity and urgency of establishing the spatial data warehouse is expounded from the viewpoint of the present situation being short of available information for the flood control and disaster mitigation in Yangtze river basin.展开更多
The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based ...The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based on an in-house solver.This solver is developed on an in-house platform HRAPIF based on the finite volume method(FVM)with the elemental velocity vector transformation(EVVT)approach.The present solver adopts the density-based method with a low Mach preconditioning technique.The turbulence models are the Spalart-Allmaras(SA)model and the k-ωshear stress transport(SST)model.The inviscid spatial discretization schemes are the third-order monotone upstream-centered schemes for conservation laws(MUSCL)scheme and the fifth-order modified weighted essentially non-oscillatory(WENO-Z)scheme.The power coefficient,instantaneous torque of blades,blade wake,and turbine wake are compared and analyzed at different tip speed ratios.The extensive analysis reveals that the density-based method can be applied in VAWT numerical simulation;the SST models perform better than the SA models in power coefficient prediction;the rotation-curvature correction is not necessary and the third-order MUSCL is enough for power coefficient prediction,the high-order WENO-Z scheme can capture more flow field details,the rotation-curvature correction and high-order WENO-Z scheme reduce the length of the velocity deficit region in the turbine wake.展开更多
为有效地解决当前相关标准和标准数据匮乏的问题,通过分析中文文本中地理空间关系描述的语言特点,提出中文文本的地理空间关系标注体系,并以GATE(General Architecture for Text Engineering)为标注工具,以《中国大百科全书中国地理》...为有效地解决当前相关标准和标准数据匮乏的问题,通过分析中文文本中地理空间关系描述的语言特点,提出中文文本的地理空间关系标注体系,并以GATE(General Architecture for Text Engineering)为标注工具,以《中国大百科全书中国地理》为文本数据源,采用交叉校验方式建立了地理空间关系标注语料库。实现了中文文本中地理空间关系描述的结构化表达,提供了地理空间关系信息抽取的标准化测试数据。展开更多
基金We thank the financial support from the National Natural Science Foundation of China(40701007,40571066)the Postdoctoral Science Foundation of China(20060401048).
文摘The acquisition of precise soil data representative of the entire survey area, is a critical issue for many treatments such as irrigation or fertilization in precision agriculture. The aim of this study was to investigate the spatial variability of soil bulk electrical conductivity （ECb） in a coastal saline field and design an optimized spatial sampling scheme of ECb based on a sampling design algorithm, the variance quad-tree （VQT） method. Soil ECb data were collected from the field at 20 m interval in a regular grid scheme. The smooth contour map of the whole field was obtained by ordinary kriging interpolation, VQT algorithm was then used to split the smooth contour map into strata of different number desired, the sampling locations can be selected within each stratum in subsequent sampling. The result indicated that the probability of choosing representative sampling sites was increased significantly by using VQT method with the sampling number being greatly reduced compared to grid sampling design while retaining the same prediction accuracy. The advantage of the VQT method is that this scheme samples sparsely in fields where the spatial variability is relatively uniform and more intensive where the variability is large. Thus the sampling efficiency can be improved, hence facilitate an assessment methodology that can be applied in a rapid, practical and cost-effective manner.
基金the auspices of the national key project(96-802-01).
文摘With the need in the global change research project for the land -use/land-cover change information, most international and regional research organization or groups have put amounts of efforts to improve of the dynamics monitoring and database updating techniques. With the pressure on nature environment from increasing population and decreasing farmland be- coming significant more and more in China, the farmland urban dynamics in historical and current times, even the change trends in the future, should be monitored and analyzed serving for regional and national social, economic and environmental sustain- able development in the long future. Based on spatial and temporal series of land -use/land-cover database resources, Chinese Academy of Sciences designed a sampling framework for monitoring farmland and urban area dynamics in regional and national level. In order to test the accuracy of the sampling schema for national and regional level, we took two provinces area into overall covered change detecting process with TM images data through being inter’Preted by digitalization on the screen. The result shows that our stratified random sampling schema is suitable for monitoring land -use/land-cover change at national and regional level with quick response, high accuracy and low expenses. The land-use/land-cover change (LUCC) information can update the LUTEA database for global change research during certain period so that the forecasting process and evaluating analysis on land resources and environment under human and natural driving force will get essential data and produce valuable conclusions.
文摘Since 1990s,the spatial data warehouse technology has rapidly been developing, but due to the complexity of multi-dimensional analysis, extensive application of the spatial data warehouse technology is affected. In the light of the characteristics of the flood control and disaster mitigation in the Yangtze river basin, it is proposed to design a scheme about the subjects and data distribution of the spatial data warehouse of the flood control and disaster mitigation in Yangtze river basin, i.e., to adopt a distributed scheme. The creation and development of the spatial data warehouse of the flood control and disaster mitigation in Yangtze river basin is presented .The necessity and urgency of establishing the spatial data warehouse is expounded from the viewpoint of the present situation being short of available information for the flood control and disaster mitigation in Yangtze river basin.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2806300).
文摘The effect of rotation-curvature correction and inviscid spatial discretization scheme on the aerodynamic performance and flow characteristics of Darrieus H-type vertical axis wind turbine(VAWT)are investigated based on an in-house solver.This solver is developed on an in-house platform HRAPIF based on the finite volume method(FVM)with the elemental velocity vector transformation(EVVT)approach.The present solver adopts the density-based method with a low Mach preconditioning technique.The turbulence models are the Spalart-Allmaras(SA)model and the k-ωshear stress transport(SST)model.The inviscid spatial discretization schemes are the third-order monotone upstream-centered schemes for conservation laws(MUSCL)scheme and the fifth-order modified weighted essentially non-oscillatory(WENO-Z)scheme.The power coefficient,instantaneous torque of blades,blade wake,and turbine wake are compared and analyzed at different tip speed ratios.The extensive analysis reveals that the density-based method can be applied in VAWT numerical simulation;the SST models perform better than the SA models in power coefficient prediction;the rotation-curvature correction is not necessary and the third-order MUSCL is enough for power coefficient prediction,the high-order WENO-Z scheme can capture more flow field details,the rotation-curvature correction and high-order WENO-Z scheme reduce the length of the velocity deficit region in the turbine wake.
文摘为有效地解决当前相关标准和标准数据匮乏的问题,通过分析中文文本中地理空间关系描述的语言特点,提出中文文本的地理空间关系标注体系,并以GATE(General Architecture for Text Engineering)为标注工具,以《中国大百科全书中国地理》为文本数据源,采用交叉校验方式建立了地理空间关系标注语料库。实现了中文文本中地理空间关系描述的结构化表达,提供了地理空间关系信息抽取的标准化测试数据。
