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This paper introduces PTrees, a multi-scale dynamic point cloud segmentation dedicated to forest tree extraction from lidar point clouds. The method process the point data using the raw elevation values (Z) and compute height (H = Z − ground elevation) during post-processing using an innovative procedure allowing to preserve the geometry of crown points. Multiple segmentations are done at different scales. Segmentation criteria are then applied to dynamically select the best set of apices from the tree segments extracted at the various scales. The selected set of apices is then used to generate a final segmentation. PTrees has been tested in 3 different forest types, allowing to detect 82% of the trees with under 10% of false detection rate. Future development will integrate crown profile estimation during the segmentation process in order to both maximize the detection of suppressed trees and minimize false detections. 相似文献
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基于多种探测资料对武汉一次短时暴雪天气的监测分析 总被引:2,自引:0,他引:2
利用Thies Clima激光雨滴谱仪、MP3000A微波辐射仪、多普勒雷达和人工加密观测资料,分析了2011年2月12日武汉一次暴雪天气过程的演变特征。结果表明:(1)在这次短时暴雪过程中,先后出现了降雨、雨夹雪和纯降雪3个阶段,激光雨滴谱仪监测到该降雨阶段的雨滴谱较宽,最大直径达4.5mm,数浓度比较小,为2~5 429个.m-3.mm-1,雨滴谱型呈双峰型分布特点;(2)微波辐射仪对水汽相态监测显示,08:12-09:34(世界时)期间在1.5~3.5km过冷层比湿维持14~16g.kg-1大值区,之后迅速由雨夹雪过程(仅16min)过渡到纯降雪阶段,在65min内武汉站降雪量达到5.035mm,占整个降雪量的80%以上;(3)雷达反射率因子与粒子谱宽和数浓度密切相关,若后两者越大则对应的雷达回波强度也越大;同时还发现,与微波辐射仪反演的水汽密度、激光雨滴谱仪测得的降水强度也有较好的对应关系,若将这些结合起来对降水的相态变化、强度、量级和持续时间有很好的监测能力。 相似文献
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Based on the dynamic analysis and research of pollution risk of groundwater sources, this paper creates the dynamic assessment method of pollution risk of groundwater source area under the theory of “source-pathway-receptor”, and applies this method to one typical fissure karst groundwater source area in northern China. Following the 30-year petroleum pollutant migration simulation and pollution risk assessment of groundwater source area, this study finds that the very high risk zone is mainly located in Q Petrochemical Company and the surrounding area and the area adjacent to River Z. Within this period of thirty years, the pollution risk of groundwater source area has showed a dynamic trend that features an inverted “V” shape. The ratio of very high risk zone to the total area will be 18.1%, 17.47% and 16.62% during the tenth year, the twentieth year and the thirtieth year separately, and will reach the highest level of 19.45% during the fifteenth year. Meanwhile, the vertical migration distance of pollutant centre concentration changed from the surface soil at the outset to the deepest point of about 250 meters underground during the tenth year. The results of this risk assessment indicate the dynamic feature of pollution risk. The dilution, degradation and migration of petroleum pollutants in groundwater system contribute to an ultimate decline in pollution risk. 相似文献
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常德张家界高速公路某大桥桥基砂土液化评价 总被引:2,自引:0,他引:2
结合常德张家界高速公路某大桥桥基工程,在DSD160型电磁式振动三轴试验仪上,通过往返加荷三轴试验,对饱和砂土进行了液化试验研究,探讨了基于动三轴液化试验结果判断饱和砂土液化的方法。并尝试了这种室内研究反应分析的液化可能性估计方法与地震剪应力时程相结合的综合判断方法。在该高速公路大桥桥基的饱和砂土液化评价中,采用这种综合判断方法,对大桥桥基砂土液化进行了判断。在判断场地是否液化后,对其液化危害程度进行了等级划分,给出了该工程场地在未来遭受到不同超越概率下的地震作用时发生液化的危害程度,得到了一些有工程实用意义的结果。 相似文献
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Simulating coseismic deformation of quartz in the middle crust and fabric evolution during postseismic stress relaxation — An experimental study 总被引:3,自引:0,他引:3
Claudia A. Trepmann Bernhard Stckhert Dorothe Dorner Rasoul Hamidzadeh Moghadam Martina Küster Klaus Rller 《Tectonophysics》2007,442(1-4):83-104
Non-steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake-driven episodic deformation in the middle crust. Three types of experiments were carried out using a modified Griggs-type solid medium deformation apparatus. All three start with high stress deformation at a temperature of 400 °C and a constant strain rate of 10− 4 s− 1 (type A), some are followed by annealing in the stability field of α-quartz for 14–15 h at zero nominal differential stress and temperatures of 800–1000 °C (type A + B), or by annealing for 15 h at 900 °C and at a residual stress (type A + C).The quartz samples reveal a very high strength > 2 GPa at a few percent of permanent strain. The microstructures after short-term high stress deformation (type A) record localized brittle and plastic deformation. Statisc annealing (type A + B) results in recrystallisation restricted to the highly damaged zones. The new grains aligned in strings and without crystallographic preferred orientation, indicate nucleation and growth. Annealing at non-hydrostatic conditions (type A + C) results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation. In this case, however, the recrystallised zone is several grain diameters wide, the grains are elongate, and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation. Quartz microstructures identical to those produced in type A + B experiments are observed in cores recovered from Long Valley Exploratory Well in the Quaternary Long Valley Caldera, California, with considerable seismic activity.The experiments demonstrate the behaviour of quartz at coseismic loading (type A) and subsequent static annealing (type A + B) or creep at decaying stress (type A + C) in the middle crust. The experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks. 相似文献
118.
地形对门头沟一次大暴雨动力作用的数值研究 总被引:5,自引:2,他引:5
2002年6月24—25日,北京门头沟附近发生了一次大暴雨过程。为探讨地形在本次过程中的动力作用,采用美国俄克拉荷马大学风暴分析预测中心开发的ARPS模式,对大暴雨过程进行了数值试验。控制试验采用27、9 km双重单向嵌套网格,网格覆盖范围约为3000 km×3000 km、900 km×900 km。两层网格均采用全物理过程,使用的都是全球30″的地形资料。在控制试验的基础上,进行了3组敏感性试验:第1组试验采用干过程模拟,即不考虑凝结潜热的作用;第2组试验将地形整体向东/西平移1°;第3组试验是将门头沟西部的局地地形抠除一部分。试验结果表明,在不考虑凝结潜热作用时,东南风气流仍然可以爬升到2 km以上,超过了大气的抬升凝结高度,证实了地形的动力作用是本次大暴雨的触发机制;将地形向东/西平移1°后,由于大气的对流稳定度发生了改变,模拟的降水强度和落区也发生了变化,表明山坡和山顶的对流不稳定大气是导致本次大暴雨的必要条件;抠除局地地形后,模拟的降水量也发生了不同程度的改变,再次证明大暴雨是在多尺度地形以及一定的天气系统配置下产生的。 相似文献
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