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冠状动脉数字图像造影（CCTA）是一种有效的无创评估冠脉血管狭窄等病变情况的成像技术，对CCTA的自动筛查评估依赖于冠脉管腔的高精度分割。为探索能够分割出高质量的冠脉官腔的算法，本文进行基于深度学习的端到端分割实验以及基于中心线先验信息结合CCTA灰度特征的冠脉管腔分割实验，其中基于深度学习回归方法的Polar1DMLP模型能够结合中心线先验信息得到较好的分割效果。基于公开数据集Coronary Artery Stenoses Detection and Quantification Evaluation Framework中的78组冠脉截段数据进行训练与验证，在16段数据的验证集上得到MSD （mean surface distance）为0.169 mm，DICE为0.796。结果表明本文提出的以中心线为导向信息的Polar1DMLP模型能够较好地整合血管CCTA灰度特征，回归出较为准确的冠脉血管内壁管腔轮廓半径，得到较为平滑的冠脉管腔表面模型，本方法有着较大的潜力以及拓展空间。 相似文献
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城市海量手机用户停留时空分异分析——以深圳市为例 总被引：1，自引：0，他引：1
识别海量手机数据中蕴含的行为模式,是地理学的一个研究热点与难点。目前,较多研究针对手机用户移动特征开展,而对停留及其模式的研究则相对较少;其时空分异规律对理解城市人群动态,甚至优化城市系统至关重要。本文根据人们日常时空约束条件定义了手机用户停留,提出了基于海量手机位置数据的手机用户停留模式的提取方法,以深圳市约790万个匿名手机用户一天的海量手机位置数据为例,识别出了覆盖约98%用户的典型停留模式,并结合该城市土地利用的空间分布与分异特征,剖析不同停留模式的手机用户空间分异特征和城市不同区域停留次数的时段分异特征。研究发现:(1)15种停留模式可覆盖约98%的手机用户,而且其一天不同的停留位置数量不超过4个;(2)15种停留模式手机用户在城市区域空间上的分布存在分异现象,严重受制于土地利用的空间分布;(3)城市不同区域停留次数的时段分异特征与该区域常住人口、人口密度,以及区域主要职能和性质存在较强的相关性。研究结论对理解城市手机用户行为模式的群体特征有积极的意义,对城市土地利用的科学决策和城市交通规划与预测有重要参考价值。 相似文献
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蝗虫遥感监测预警研究现状与展望 总被引：3，自引：0，他引：3
气候变化背景下全球蝗灾日益肆虐，为支撑虫害及时精准防控，迫切需要开展大面积蝗虫动态监测预警研究。本文从蝗虫生境遥感监测、蝗虫发生动态遥感预警，以及蝗灾遥感损失评估3个方面介绍了当前研究现状，并指出当前存在的问题主要包括3个方面：蝗虫监测预警的时空分辨率较粗，无法精准定位虫害热点发生区和重点危害区；遥感虫害响应机制与虫害生物学扩散模型耦合度较低，导致模型时空普适性较差；缺乏高时空精度的虫害监测预警空间信息服务产品。因此，当前急需发展面向全球、洲际、全国、区域的多尺度、长时序、高精度虫害精准监测预警平台。通过建立时空精细尺度的虫害监测预警指标体系，研制遥感机制与虫害生物学机理深度耦合的高精度预测预报模型，发布多尺度高时频的虫害监测预警空间信息产品和服务，以实现海量数据的自动入库和智能存储、多层次模型的快速调用和高性能计算、虫害测报产品的在线生产和可视化服务。建立从数据到模型到产品服务的全链路，从而切实提升全球应对重大迁飞性虫害的智能化水平，为保障粮食安全、维护区域稳定和可持续发展提供科技支撑。 相似文献
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Jun?NiuEmail author Ji?ChenEmail author Liqun?Sun Bellie?Sivakumar 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2423-2432
The time-lag effects of droughts on vegetation responses vary significantly across a large-scale river basin. The spatio-temporal response characteristics obtained are important for decision making processes on the allocation and transportation of regional water resources in mitigating drought impacts. Here we consider the Xijiang (West River) basin in South China as a case study, which has experienced severe drought events since the beginning of the 21st century. A threshold level approach is employed to identify the major drought events over the basin in the first decade of this century. The vegetation responses to land soil water evolution are examined, particularly for the severe drought events occurred. The time-lag effects of the vegetation responses within the basin range within 0–96 days. The lower reaches of the headwater sub-basins in the west part of the Xijiang basin are identified as the regions with short time-lag effects. The enhanced vegetation index (EVI) shows consistent responses to the soil water evolution in conjunction with the climate aridity in this area, which is the drought-vulnerable area in the Xijiang basin. 相似文献
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An enhanced approach for surface flow routing over drainage‐constrained triangulated irregular networks 
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下载免费PDF全文 The accuracy and efficiency of the simulations in distributed hydrological models must depend on the proper estimation of flow directions and paths. Numerous studies have been carried out to delineate the drainage patterns based on gridded digital elevation models (DEMs). The triangulated irregular network (TIN) has been increasingly applied in hydrological applications due to the advantages of high storage efficiency and multi‐scale adaptive performance. Much of the previous literature focuses mainly on filling the depressions on gridded DEMs rather than treating the special cases in TIN structures, which has hampered its applications to hydrological models. This study proposes a triangulation‐based solution for the removal of flat areas and pits to enhance the simulation of flow routing on triangulated facet networks. Based on the drainage‐constrained TIN generated from only a gridded DEM by the compound point extraction (CPE) method, the inconsistent situations including flat triangles, V‐shape flat edges and sink nodes are respectively identified and rectified. The optimization algorithm is an iterative process of TIN reconstruction, in which the flat areas are generalized into their center points and the pits are rectified by embedding break lines. To verify the proposed algorithm and investigate the potential for flow routing, flow paths of steepest descent are derived by the vector‐based tracking algorithm based on the optimized TIN. A case study of TIN optimization and flow path tracking was performed on a real‐world DEM. The outcomes indicate that the proposed approach can effectively solve the problem of inconsistencies without a significant loss in accuracy of the terrain model. 相似文献
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卫星CCD图像的去云处理对遥感信息的增强与提取有重要的意义,尤其是在云覆盖严重的低纬度地区。为去除CBERS-02B卫星CCD图像中薄云的影响,分别使用Mallat和à trous 2种小波变换对图像进行分解;利用同态滤波对2种小波分解图像的低频系数进行处理,衰减其低频信息;将处理后的小波低频系数与分解的高频系数进行小波重构,从而达到去云的目的。定量分析基于Mallat和à trous小波变换结合同态滤波法的去云结果表明,经à trous小波变换结合同态滤波法的去云影像所包含信息量大,细节信息丰富,去云效果较好。 相似文献
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Water management practices and access to safe water supplies have major implications for human health. While a range of assessments has been developed to assess water vulnerability, limited work has extended these concepts to health and wellbeing. Water-associated disease cycles are characterized by complex linkages between social and ecological determinants, thus conceptualizing vulnerability in the context of health offers a useful framework for analysis. This paper applies a water associated disease index (WADI) as a tool to deepen understanding of changing vulnerability to dengue, comparing conditions in 2000 and 2010 in Pernambuco, Northeast Brazil. Multi-dimensional data were integrated into indicators of exposure and susceptibility using the WADI approach, including water access, land cover, climate, and solid waste collection, and outputs were validated and visualized in map form. The findings illustrate heterogeneous patterns of vulnerability to dengue in the region, and highlight trends of seasonal and long-term changes. Highest vulnerability was observed in densely populated Recife and the surrounding coastal region in both time periods, with climate conditions creating seasonal trends in exposure to dengue. While more remote areas in the semi-arid Sertão showed low vulnerability overall, increases were observed in some areas between 2000 and 2010 due to land use intensification and growing population densities. These findings suggest that interventions should consider the dynamic nature of social and ecological factors that contribute to health outcomes and address current as well as future populations vulnerable to dengue transmission. This vulnerability mapping approach can be applied to other water-associated diseases impacted by global environmental change to highlight priority areas for further investigation and contribute towards improving interventions. 相似文献
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多时相遥感影像辐射归一化方法综述 总被引：2，自引：0，他引：2
多时相遥感影像的辐射归一化是进行变化检测或拼接不可缺少的步骤。本文从绝对辐射归一化和相对辐射归一化两个方面对现有的多时相遥感影像辐射归一化方法进行了总结。对各种辐射归一化方法进行了剖析,并指出了这些方法的优缺点和适应性。最后对多时相遥感影像辐射归一化方法未来的发展进行了展望。 相似文献
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《Geoforum》2017
This article explores the effects of people's digital coexistence on the construction of difference and feelings of aversion to or recognition of “others”. It seeks to make a theoretical contribution to works on the geographies of difference and encounter, Internet or digital geography, as well as on migration and digital media, by highlighting the relevance of indirect and fleeting digital encounters and the dialectical process in which encounters play out in intertwined, specific and multiple digital and physical spaces that we define as “cON/FFlating situational places of encounter”. Based on a qualitative study with Chinese, Filipino and German migrant professionals in Singapore, it shows how fleeting digital encounters take an ambivalent role through challenging but also producing new “temporary fixings of difference”. As such they can engender new sensibilities for and openness toward the host society but also breed new, or aggravate existing, cultural stereotypes and prejudices. The findings show that inherited and instituted classificatory practices that people use to structure and make sense of their fleeting interactions with others in offline space are, where possible, transferred and imposed on encounters in digital space. At the same time, they are inflected or replaced with new markers of difference where ingrained sorting mechanisms applied in offline space did not help them make sense of encounters in digital space. 相似文献