A novel approach to leveraging social media for rapid flood mapping: a case study of the 2015 South Carolina floods

Rapid flood mapping is critical for local authorities and emergency responders to identify areas in need of immediate attention. However, traditional data collection practices such as remote sensing and field surveying often fail to offer timely information during or right after a flooding event. Social media such as Twitter have emerged as a new data source for disaster management and flood mapping. Using the 2015 South Carolina floods as the study case, this paper introduces a novel approach to mapping the flood in near real time by leveraging Twitter data in geospatial processes. Specifically, in this study, we first analyzed the spatiotemporal patterns of flood-related tweets using quantitative methods to better understand how Twitter activity is related to flood phenomena. Then, a kernel-based flood mapping model was developed to map the flooding possibility for the study area based on the water height points derived from tweets and stream gauges. The identified patterns of Twitter activity were used to assign the weights of flood model parameters. The feasibility and accuracy of the model was evaluated by comparing the model output with official inundation maps. Results show that the proposed approach could provide a consistent and comparable estimation of the flood situation in near real time, which is essential for improving the situational awareness during a flooding event to support decision-making.     

Supervised classification of electric power transmission line nominal voltage from high-resolution aerial imagery

For many researchers, government agencies, and emergency responders, access to the geospatial data of US electric power infrastructure is invaluable for analysis, planning, and disaster recovery. Historically, however, access to high quality geospatial energy data has been limited to few agencies because of commercial licenses restrictions, and those resources which are widely accessible have been of poor quality, particularly with respect to reliability. Recent efforts to develop a highly reliable and publicly accessible alternative to the existing datasets were met with numerous challenges – not the least of which was filling the gaps in power transmission line voltage ratings. To address the line voltage rating problem, we developed and tested a basic methodology that fuses knowledge and techniques from power systems, geography, and machine learning domains. Specifically, we identified predictors of nominal voltage that could be extracted from aerial imagery and developed a tree-based classifier to classify nominal line voltage ratings. Overall, we found that line support height, support span, and conductor spacing are the best predictors of voltage ratings, and that the classifier built with these predictors had a reliable predictive accuracy (that is, within one voltage class for four out of the five classes sampled). We applied our approach to a study area in Minnesota.     

EXPERIMENTAL INVESTIGATION AND ANALYSIS OF HEC-6 RIVER MORPHOLOGICAL MODEL

Only comparatively few experimental studies have been carried out to investigate the performance of the HEC-6 river morphological model. The model was developed by the Hydrologic Engineering Center of the US Army Corps of Engineers. In this study, experiments were carried out in a 20 m long concrete flume 0.6 m wide with varying rectangular cross-sections. The channel bed is paved with uniform sand of D₅₀ = 0.9 mm and D₉₀ = 1.2 mm within the test reach of 12 m. Two types of experiments were carried out with sediment transport, one under steady uniform flow and another under steady non-uniform flow conditions. Nine steady uniform flow experiments were carried out to compare the measured equilibrium relationship of flow and sediment transport rate with two bedload formulae, namely, Du Boys and Meyer–Peter and Muller, and with three total load formulae, namely, Toffaleti, Laursen and Yang. It was found that even though the sediment transport consists of a certain portion of bedload, the total load formulae give satisfactory results and better agreement than the two bedload formulae. Five steady non-uniform flow experiments were carried out under various conditions of varying bed profile and channel width and also with sediment addition and withdrawal. The measured transient water surface and bed profiles are compared with the computed results from the HEC-6 model. It was found that the Toffaleti and Yang total load formulae used in the HEC-6 model give the most satisfactory prediction of actual bed profiles under various conditions of non-uniform flow and sediment transport. The effects of Manning's n, variations of sediment inflow, various sediment transport formulae, sediment grain size and the model numerical parameters, i.e. distance interval Δx and numerical weighting factor, on the computed water surface and bed profiles were determined. It was found that the selection of the sediment transport formulae has the most significant effect on the computed results. It can be concluded that the HEC-6 model can predict satisfactorily a long-term average pattern of local scour and deposition along a channel with either a small abrupt change in geometry or gradually varying cross-sections. However, the accuracy of the model prediction is reduced in the regions where highly non-uniform flow occurs.     

Constructing geo-information sharing architecture

IntroductionAlong with the development of computer andInternet technology , GIS applications are be-coming broad increasingly ,geo-information sha-ring are of increasingi mportance ,and geo-infor-mationinteroperabilityis the trend in the futureGIS applica…     

基于GML的WFS研究与实现

网络要素服务(webfeature services, WFS) 是空间数据互操作的一个重要组成部分, 能为不同GIS数据格式提供要素级的交互.基于地理标志语言(geography markup language, GML) 的WFS能够为Web环境下的空间数据互操作技术和空间信息处理互操作技术提供简单而又有效的基本数据访问、要素编辑(包括添加、删除、更新)、要素的组合查询.通过研究开放式GIS联盟(open GIS consortiumInc., OGC) 的标准规范, 使用MAPGIS基础平台和.NET编译环境实现WFS, 使用XML传输和存储地理信息, 其中包括属性和地理要素的几何属性.最后给出了以MAPGIS平台为基础的基于GML的WFS的体系结构和实现方法.WFS只解决了空间数据互操作的一部分, 为了更好的进行空间数据互操作, WCS、WCTS的实现是必不可少的.      

空间位置服务平台的构架设计与服务接口实现

通过空间位置服务平台对位置服务领域中众多复杂的空间信息数据进行有效地整合和资源共享, 可以为用户提供综合性的位置应用和服务.利用基于空间信息网格(spatial information grid, SIG) 的分布式思想对空间位置服务平台的架构进行了模型设计和技术实现, 完成了地图数据和定位查询的分布式存储和检索.平台服务接口满足开放位置服务(openlocation service, OpenLS) 规范, 利用XML进行信息编码, 通过HTTP进行数据传输, 介绍了相应的接口内容和调用示例.针对定位信息的更新和传递提出了一种新的基于Push的主动通知机制, 提供与各种定位接口的数据转换和消息处理能力, 高效地实现了位置应用和服务平台之间的消息传递.最后结合MAPGIS平台和CDMA手机定位技术进行了原型系统的实现, 验证了平台理论模型和服务接口的可用性.      

基于开放大数据的广州市中心城区职住平衡特征研究

以广州市中心城区为例,借助百度热力图、百度实时路况和百度地图POI数据,从中观层面多角度综合分析广州市中心城区就业与居住的空间分布关系。结果显示：1）工作时间段人口聚集的高值区整体呈带状分布,斑块较为细碎,但绝大部分集中在核心地带;人口主要高度集中于各区的商业繁华地段与交通线路周围。而休息时间段的高值区则相对集中分布,用地效率较高,表现出多中心的圈层结构;人口主要高度集中分布在传统的老城居住区和新开发的商业住宅区,与核心商圈相对错开。2）不管是在上班时段还是休息时段,人口聚集程度越高的地区,POI设施密度表现越显著;这意味着人口的聚集具有一定的选择性,主要集中在城市基础设施发展较完备的区域。3）广州市中心城区各街道的职住比介于0.73~1.54,职住相对平衡,区域之间差异较小。其中,分值较高的街道多分布于核心地带（主要集中在越秀区、荔湾区北部和天河区南部）,分值较低的街道多分布于核心地带的外围或边缘地区（主要在海珠区、荔湾区和白云区零散分布）。4）从城市交通响应上看,广州市中心城区工作日内早高峰的拥堵度大于晚高峰,但总体路况变化跨度不大,区内并没有出现特别严重的“潮汐通勤”现象。     

基于多元要素流的珠三角城市群功能联系与空间格局分析

以珠三角城市群9个地级市为研究对象,结合当前热点网络开放大数据,对珠三角城市群内各城市的经济流、交通流、人口流和信息流的联系强度和作用方向进行测算与评价。借助赋值法分别对四种要素流的总量进行打分,以各城市的综合得分作为空间层级划分依据,提出关于“点—线—面”的空间互动格局,进而探索珠三角城市群未来的发展规划。研究结果表明：①从各要素流的联系强度上看,城市间的等级划分具有较高的重合度,说明四种要素流彼此之间相互联系、相互作用。从各要素流的作用方向上看,广州和深圳多作为区域内其它城市的首位空间联系城市,说明各要素流通常指向经济发展水平较高、通达性较好的城市。②从整体来看,珠三角城市群内部功能互动表现极度不平衡,一是中心城市占据了要素流强度的绝大部分,其余城市仅占据极小部分流量,两极分化严重;二是东西两岸发展不平衡,东岸发展水平明显要强于西岸发展水平。③广州、深圳、东莞和佛山等城市虽然在区域内起到了一定的辐射和带动作用,但是针对江门、肇庆等周边城市的辐射和带动强度仍有待提升,说明还需进一步优化珠三角城市群功能分工与产业布局,推进区域经济一体化。     

无人机在露天矿山监测中的应用

在露天矿山开采过程中,对矿山进行实时动态监测很有必要,它不仅能够实时掌握开采进度和开采方案实施的准确性,还有利于数字矿山建设。本文以河北省保定市涞源县某露天矿区为例,利用Pix4Dmapper软件对无人机航拍影像进行数据采集与处理,获取矿区的三维点云数据、数字正射影像和数字地表模型,并利用ArcGIS和Global Mapper软件对生产成果进行矿山开发占地分析,实现露天矿山三维可视化。本文为准确掌握矿山环境治理执行情况,把握矿山开发整体情况给予了有力的参考和借鉴作用。     

开源地理空间情报的搜集方法

在过去的20年,地理空间情报已经由不存在而一跃成为全球情报活动的主要内容主体。基于开源的地理空间情报搜集作为一种低风险、高收益的情报搜集手段,成为各国开展地理空间情报工作的一项重要内容。本文根据开源情报源的主要渠道,分析总结了几种主要的开源地理空间情报搜集方法,重点阐述基于互联网的搜集方法,并给出了具体的分析实践,最后提出开源情报搜集的几点建议。