Diurnal rainfall variability over the Upper Blue Nile Basin: A remote sensing based approach

In this study we aim to assess the diurnal cycle of rainfall across the Upper Blue Nile (UBN) basin using satellite observations from Tropical Rainfall Measuring Mission (TRMM). Seven years (2002–2008) of Precipitation Radar (PR) and TRMM Microwave Imager (TMI) data are used and analyses are based on GIS operations and simple statistical techniques. Observations from PR and TMI reveal that over most parts of the basin area, the rainfall occurrence and conditional mean rain rate are highest between mid- and late-afternoon (15:00–18:00 LST). Exceptions to this are the south-west and south-eastern parts of the basin area and the Lake Tana basin where midnight and early morning maxima are observed. Along the Blue Nile River gorge the rainfall occurrence and the conditional mean rain rate are highest during the night (20:00–23:00 LST). Orographic effects by large scale variation of topography, elevation and the presence of the UBN river gorge were assessed taking two transects across the basin. Along transects from north to south and from east to west results indicate increased rainfall with increase of elevation whereas areas on the windward side of the high mountain ranges receive higher amount of rainfall than areas on the leeward side. As such, mountain ranges and elevation affect the rainfall distribution resulting in rain shadow effect in the north-eastern parts of Choke-mountain and the ridges in the north-east of the basin. Moreover, a direct relation between rainfall occurrence and elevation is observed specifically for 17:00–18:00 LST. Further, results indicate that the rainfall distribution in the deeply incised and wide river gorge is affected with relatively low rainfall occurrence and low mean rainfall rates in the gorge areas. Seasonal mean rainfall depth is highest in the south-west area and central highlands of the basin while areas in the north, north-east and along the Blue Nile gorge receive the least amount of rainfall. Statistical results of this work show that the diurnal cycle of rainfall occurrence from TRMM estimates show significant correlation with the ground observations at 95% confidence level. In the UBN basin, the PR conditional mean rain rate estimates are closer to the ground observations than the TMI. Analysis on mean wet season rainfall amount indicates that PR generally underestimates and TMI overestimates the ground observed rainfall.     

Enhancing a GIS Cellular Automata Model of Land Use Change: Bayesian Networks, Influence Diagrams and Causality

Cellular Automata (CA) models at present do not adequately take into account the relationship and interactions between variables. However, land use change is influenced by multiple variables and their relationships. The objective of this study is to develop a novel CA model within a geographic information system (GIS) that consists of Bayesian Network (BN) and Influence Diagram (ID) sub‐models. Further, the proposed model is intended to simplify the definition of parameter values, transition rules and model structure. Multiple GIS layers provide inputs and the CA defines the transition rules by running the two sub‐models. In the BN sub‐model, land use drivers are encoded with conditional probabilities extracted from historical data to represent inter‐dependencies between the drivers. Using the ID sub‐model, the decision of changing from one land use state to another is made based on utility theory. The model was applied to simulate future land use changes in the Greater Vancouver Regional District (GVRD), Canada from 2001 to 2031. The results indicate that the model is able to detect spatio‐temporal drivers and generate various scenarios of land use change making it a useful tool for exploring complex planning scenarios.     

A GIS‐Based Procedure for Downscaling Climate Data for West Africa

Local studies aimed at assessing the impact of climate variability on crop yield at the individual farm level require the use of weather and climate data. These are often collected at points known as meteorological stations. In West Africa, meteorological stations are sparsely distributed and as a result, are often unable to satisfy the data requirements for such studies. One major problem arising from this is how to estimate values for locations where primary data is not available. General Circulation Models (GCMs) have recently been deployed for weather forecasting and climate change projections but the resolution of their outputs is low requiring downscaling. This article describes a GIS‐based procedure for downscaling GCMs’ outputs for use in studies assessing the impacts of climate variability on crop yield at the farm level. The procedure is implemented with the Hadley Centre's GCM (HadCM2) data, although any other GCM can be used. Results in this study show that the model works best when representing drier months as compared to wet months in all three domains tested. For example, it estimated the rainfall for January (the driest month) better than that of July which is the peak of the rainy season in West Africa. There is also a north‐south pattern influencing the accuracy of estimated rainfall distribution, with stations in the south better represented than those in the north. For the greater part of West Africa where similar climatic conditions persist as in Nigeria, this procedure can be considered suitable for interpolation and downscaling.     

面向防汛应急的重庆市洼地积涝预测模型研究

针对重庆市城市防汛应急的需要,在传统内涝模型的基础上,结合GIS空间分析与可视化技术,建立了一个运算快、实时性强的洼地积涝分析预测模型.该模型首先利用空间分析方法建立数字高程模型、城市洼地模型等数据模型,然后采用数值计算方法构建降雨模型、汇水模型、排水模型等分析模型,最后预测出洼地的积水面积、深度等.采用重庆市主城区的...     

基于ArcEngine的林火监测云图坐标转换及配准功能的研发

采用二次开发语言VB,通过基于ArcEngine的组件开发模式,对林火监测云图进行配准及坐标转换,使其能够与基础地理信息数据叠加显示,准确判断火点的属地信息等相关地理信息以及相关防火、扑火信息,并且可以依托地理信息系统对火点信息进行管理。使林火监测云图与地理信息系统高度融合,增加了地理信息系统数据的来源,提高了云图的使用效率。最终促进了森林防火工作的信息化和现代化。     

Soil,landuse and land evaluation studies of Patna area Bihar

The soil and landuse surveys have been conducted in Patna area, Bihar, using aerial photos of 1:25,000 scale. Three major systems, Ganges Gandak and interfluvial plain, have been identified in the area. These were further sub-divided into levees plains and channels etc. The soils were classified according to Soil axonomy. The major land use of the area is cultivation (62.2%) (Upland, lowland and wet land crops) plantation (1.8%) habitation (16.0%), water bodies (8.8%), barren lands (9.4%) and miscellaneous (1.8%). The soils of the area have been evaluated for different land utilization types-upland crops, lowland crops, and habitation. For paddy 75.:%, upland crops 8.2% and for habitation 57%, area was found suitable.     

The Geography,Structure, and Evolution of the GIS Research Community in the US: A Network Analysis from 1992 to 2011

The research community of Geographic Information Systems and Science (GIS) has been growing rapidly during the last two decades. Little attention has been paid to understanding its geography, structure and evolution. Taking a new organizational perspective, this article aims to fill the knowledge gap by analyzing collaboration and citation networks between GIS research organizations, including academic institutions, government agencies, businesses, and others. These two networks are analyzed in geographical and bibliographical spaces, respectively, to discover characteristic distributions and structures. The results show an uneven geographic distribution of GIS research organizations, and clustered spatial interactions between them. Both collaboration and citation networks exhibit typical “scale‐free” structures, which came into being around the year 2000 and have remained to the present. Further, the GIS research community is composed of 11 cohesive sub‐groups, with each having a clear hub‐spoke structure and a few highly connected organizations as leaders. These results shed light on the overall picture of the GIS research community, and offer a reference system that stimulates further exploration.     

Machine learning innovations in address matching: A practical comparison of word2vec and CRFs

Record linkage is a frequent obstacle to unlocking the benefits of integrated (spatial) data sources. In the absence of unique identifiers to directly join records, practitioners often rely on text‐based approaches for resolving candidate pairs of records to a match. In geographic information science, spatial record linkage is a form of geocoding that pertains to the resolution of text‐based linkage between pairs of addresses into matches and non‐matches. These approaches link text‐based address sequences, integrating sources of data that would otherwise remain in isolation. While recent innovations in machine learning have been introduced in the wider record linkage literature, there is significant potential to apply machine learning to the address matching sub‐field of geographic information science. As a response, this paper introduces two recent developments in text‐based machine learning—conditional random fields and word2vec—that have not been applied to address matching, evaluating their comparative strengths and drawbacks.     

面向行业深度耦合的专业级云GIS服务平台设计

针对行业具体需求定制开发专业级地理信息服务平台,是将地理信息资源和技术优势与具体行业深度耦合,充分挖掘地理信息潜在应用价值的重要步骤。本研究立足专业级地理信息服务平台建设,以云GIS架构为基础开展研究,重点就复杂业务环境下系统高效运行问题、多层级平台架构下各地区信息化发展不均衡问题、平台优势资源灵活复用问题等展开探讨。期望研究成果为相关行业专业级地理信息云服务平台建设提供借鉴。     

当代地理信息系统进展综述

综述当代地理信息技术的发展现状与趋势,涉及地理信息的获取与处理,地理空间数据的管理,地理信息应用服务,地理信息共享技术以及新型GIS如WebGIS、组件GIS、三维GIS和移动GIS等方面的内容。     

Vertical accuracy of the SRTM DTED level 1 of Crete

A reference digital elevation model (DEM), produced from contour lines digitization, from topographic maps at scale 1:250.000 is used in order to assess the vertical accuracy of the SRTM DTED level 1 in Crete Island in Southern Greece. The error image interpretation revealed three types of systematic errors: (a) stripping, (b) large voids and (c) those errors resulted from the mis-registration of the Shuttle Radar Topography Mission (SRTM) imagery to the local datum. Terrain was segmented to plane regions and sloping regions. Sloping regions were segmented to aspect regions (aspect being standardized to the eight geographic directions defined in a raster/grid image). Error statistics was computed for the study area as well as the individual terrain classes. Vertical accuracy was found to be terrain class dependent. Sloping regions present greater mean error than the plane ones. Statistical tests verified that the difference in mean error between aspect regions that slope in opposite geographic directions is statistically significant. The greater mean error is observed for SW, W and NW aspect regions. The additional finishing steps applied to the SRTM dataset were not sufficient enough for the systematic errors and the terrain class dependency of the error to be corrected. The observed root-mean-square error (RMSE) for the SRTM DTED-1 of Crete do not fulfil the 16 m RMSE specification for the SRTM mission while the USA national map accuracy standards for the scale 1:250.000 are satisfied.     

基于ArcGIS的中温带不同天气类型点太阳辐射分析——以佳木斯市辖区为例

考虑天气情况对入射太阳辐射的影响,研究和分析日照时数、天气类型和辐射参数的关系,并将散射模型、透射率和散射比例与4种常用天气类型相对应。以佳木斯市辖区为例,采用ArcGIS的点太阳辐射分析批处理工具,对佳木斯辐射台站进行日入射太阳辐射分析。通过将默认情况和天气类型两种模拟结果与辐射台站的实测值进行分析和验证,获得两者的相关性R2分别为0.573 4和0.899 5。研究结果表明按不同天气类型进行中温带地区点太阳辐射分析的方法切实可行,并获得更好的点日太阳辐射模拟效果,其有利于研究不同天气类型下物理和生物过程模型所受到的太阳辐射影响。     

Loose programming of GIS workflows with geo‐analytical concepts

Loose programming enables analysts to program with concepts instead of procedural code. Data transformations are left underspecified, leaving out procedural details and exploiting knowledge about the applicability of functions to data types. To synthesize workflows of high quality for a geo‐analytical task, the semantic type system needs to reflect knowledge of geographic information systems (GIS) at a level that is deep enough to capture geo‐analytical concepts and intentions, yet shallow enough to generalize over GIS implementations. Recently, core concepts of spatial information and related geo‐analytical concepts were proposed as a way to add the required abstraction level to current geodata models. The core concept data types (CCD) ontology is a semantic type system that can be used to constrain GIS functions for workflow synthesis. However, to date, it is unknown what gain in precision and workflow quality can be expected. In this article we synthesize workflows by annotating GIS tools with these types, specifying a range of common analytical tasks taken from an urban livability scenario. We measure the quality of automatically synthesized workflows against a benchmark generated from common data types. Results show that CCD concepts significantly improve the precision of workflow synthesis.     

WaterNet: A GIS Application for the Analysis of Hydrologic Networks Using Vector Spatial Data

Traditionally, stream and sub‐watershed characterization in GIS has been accom‐ plished using a DEM‐based terrain analysis approach; however, there is a large amount of existing vector hydrographic data difficult to accurately reproduce using DEMs. WaterNet is a GIS/hydrologic application for the integration and analysis of stream and sub‐watershed networks in vector format. Even with vector data, hydrologic inconsistencies between streams and sub‐watersheds do exist, and are revealed in the form of streams crossing drainage divides and sub‐watersheds with more than one outlet. WaterNet rectifies these inconsistencies and couples the two datasets. Most algorithms involving traces of dendritic networks employ a form of tree traversal which requires topologic information to be organized into specialized data structures. On the contrary, WaterNet develops topologic relationships from GIS attribute tables, which, in combination with sorting and querying algorithms, make the calculation process efficient and easy to implement. With the topologic relationships of the streams and sub‐watersheds, WaterNet can perform traces to calculate cumulative network parameters, such as flow lengths and drainage areas. WaterNet was applied to the catchment of the Texas Gulf coast for a total of 100 cataloging units (411,603 km²) and 60,145 stream lines (183,228 km).     

Writing Geospatial Concepts: Assessing Student Knowledge Accrued Through Both Writing‐Intensive and Methods‐Oriented Coursework

While writing is touted as a way to learn, little has been written about the use of writing in courses focused on the geospatial technologies: geographic information systems (GIS), remote sensing, and the Global Positioning System (GPS). This study, therefore, aimed to assess student knowledge gained through two types of coursework, writing‐intensive and methods‐oriented. The study used a pre‐/post‐test strategy to measure gains in student knowledge. Results illustrate that student learning took place in both types of courses. The results, while encouraging, point to the need for more refined study of the use of writing in courses on geospatial technologies.     

基于三维GIS的天气雷达组网信息平台的构建

采用基于三维GIS的全球展示模型,结合雷达站点建设信息,全方位立体化的展示了全国天气雷达的总体布局;采用气象行业专用的以雷达站点为中心的极坐标参考系,建立起单个雷达站点的局部三维探测模型;采用雷达组网拼图技术,实现了全球模型下指定高度的雷达探测范围自动制图。     

网络众筹和用户自助相结合的新型地理信息共享应用平台研发

针对常规GIS应用系统存在阻碍地理信息进一步社会化共享应用的问题,本文提出并研发了一套网络众筹和用户自助相结合的新型地理信息共享应用平台。该平台结合互联网开放性与参与性的特点,借助网络众筹等思想,通过管理激励机制,让网络中地理信息供需双方精准对接与众筹互助。同时通过组合搭建方式,让地理信息需求方在获取地理信息资源后对其进行自助式组合应用。应用实践表明,该平台具备常规GIS无法比拟的诸多优点,能降低地理信息共享应用的专业门槛,促进地理信息跨部门、跨地区的社会化共享应用。     

基于GIS的主要农作物病虫害气象等级预报系统研究

为了将农作物病虫害气象等级预报能力扩展到更大空间尺度,根据相邻和相近农作物种植区域的一致性,进行农作物病虫害预报模型区域化应用和拓展。建立了气象等级划分标准,在Oracle农业气象数据库和地理空间数据库的支持下,采用Visual Basic.NET和GIS组件,设计并实现了基于地理空间信息的主要农作物病虫害气象等级预报系统。该系统可对北方草原蝗虫、东北玉米螟、江南稻飞虱、黄淮棉铃虫、黄淮小麦条锈病、江淮江汉小麦赤霉病和西南地区水稻稻瘟病7大类主要作物病虫害发生发展气象等级进行实时预报,取得了较好效果。     

Multi‐temporal transport network models for accessibility studies

Vehicle tracking is a spatio‐temporal source of high‐granularity travel time information that can be used for transportation planning. However, it is still a challenge to combine data from heterogeneous sources into a dynamic transport network, while allowing for network modifications over time. This article uses conceptual modeling to develop multi‐temporal transport networks in geographic information systems (GIS) for accessibility studies. The proposed multi‐temporal network enables accessibility studies with different temporal granularities and from any location inside the city, resulting in a flexible tool for transport and urban planning. The implemented network is tested in two case studies that focus on socially excluded people in a large global city, São Paulo, Brazil, including accessibility analyses from slum areas. It explores variations within a day and differences between transport modes across time. Case study results indicate how the accessibility is heterogeneous in low‐income regions.     

Change of geographic information service model in mobile context

IntroductionGreat progress of scientific and technologicalcivilization dramatically i mproves the interactivemethods between people and world. At the sameti me various intelligent mobile terminals spreadInternet over anywhere in human’s life . Mobilecomputing and mobility of computational toolswill reform traditional geographic informationservice model ,combine seamlessly people ,real-ity and digital world through networks each oth-er ,achieve interoperability without li mitation ofti me and …