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101.
以正确提取城区Li DAR点云中建筑物为目标,综合利用不同类别目标点云的回波特征以及地形信息,提出了一种基于区域多次回波密度分析的Li DAR点云建筑物提取方法。首先,将点云构建不规则三角网(triangulated irregular network,TIN),获取封闭的等高线;然后,利用等高线间的拓扑关系得到等高线族区域;最后,统计每一区域的多次回波点云密度信息,通过建筑物和树木区域多次回波点云在区域密度上的巨大差异来识别建筑物点云和树木点云。研究结果表明:该方法既充分利用了建筑物表面与植被间多次回波特性的差异,又不否定建筑物边缘同样存在多次回波的现象;通过封闭的等高线自适应地检测出地物目标的轮廓,弥补了传统Li DAR建筑物提取方法的不足;该方法能够较其他方法更准确地提取建筑物。 相似文献
102.
H. M. Habersack 《水文研究》2001,15(3):377-391
Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio‐tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain‐diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain‐diameters and 6·1 m or 120 grain‐diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
103.
Lederer Susan M. Campins Humberto Osip David J. Schleicher David G. 《Earth, Moon, and Planets》1997,78(1-3):131-136
We report the identification of gas jets in comet Hale-Bopp in OH, NH, CN, C2 and C3. This is the first time OH and NH jets without an obvious optical dust jet counterpart have been identified in narrowband
comet images. We also confirm the existence of CN jets as reported by Larson et al. (1997) and Mueller et al. (1998). Jet
features can be seen in the March and April 1997 datasets, approximately a month before and after perihelion. Our results
contribute to the understanding of both the chemical properties of the comet as well as the physical mechanisms necessary
to produce these features.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
104.
The gastric shield and underlying stomach epithelium of Chlymas ffarreri were examined at the light and ultrastructural levels.The results showed that the gastric shield consisted of two different size lobes joined together by a narrow middle piece,the thicker lobe was shaped like a funnel,but unclosed at the lateral side;the other lobe was irregularly triangular-shaped.The transverse section of the thicker lobe was obviously laminated and gradually decreased in thickness from the peak to the margins of the shield.The underlying epithelium bore numerous about 3μm diameter spherical processes formed by the apical plasmalemma of the epithelial cells becoming blunt pseudopodia.Microvilli and some interspersed cilia were present in the areas among the spherical processes regions where only microvilli existed.Rough endoplasmic reticulum,Golgi apparatus,different-sized electron-dense secretory granules and electron-lucent vacuoles as well las abundant mitochondria were present in the underlying epithelial cells.Fused droplets of the secretion from the underlying epithelial cells formed the gastric shield. 相似文献
105.
Characterisation of Soot Emitted by Domestic Heating,Aircraft and Cars Using Diesel or Biodiesel 总被引:1,自引:0,他引:1
Anne?Smekens Ricardo?Henrique?Moreton?Godoi Patrick?Berghmans René?Van?GriekenEmail author 《Journal of Atmospheric Chemistry》2005,52(1):45-62
The characterisation of aggregates, like soot, firstly requires the determination of the size distribution of the primary
particles. The primary particle size of combustion generated aggregates depends upon the combustion environment and the formation
conditions, such as temperature, pressure and fuel-to-air ratio, among others. Since the combustion characteristics are different
in the different types of burners, the characterisation of primary particles may offer the possibility to distinguish soot
from different sources. In this paper, we present the signature of the primary particles and the aggregates of soot emitted
by cars using diesel or biodiesel, by domestic heating, and by aircraft exhausts, which can be considered as the major sources
as derived from measurements on transmission electron micrographs. The size distributions of all aggregates types with different
aerodynamic diameter were log-normal and quasi-monodisperse. The size distribution of the primary particles for soot emitted
by different sources showed minor differences. However, a comparison between the diameter of the primary particles and those
obtained using a standard method for carbon black revealed discrepancies. The median diameter of the primary particles was
combined with the median number of primary particles in an aggregate to calculate the relative particle surface area available
for adsorption. In a similar way, the relative specific surface area was determined. The surface area was measured using the
Brunauer-Emmett-Teller (B.E.T.) nitrogen adsorption method and the relative surface area available for adsorption was calculated. 相似文献
106.
根据高分辨率遥感影像中城镇道路的特点,提出了一种基于特征点的道路信息提取方法。首先,对影像进行增强处理并选取感兴趣的子区域,利用改进的分水岭分割理论和阈值选择算法,结合八邻域检测方法得到道路的特征点;然后,利用回归分析方法在一定的坐标系统下得到每条道路的回归方程,根据端点坐标信息得到道路信息图;最后,利用数学形态学算法获取道路骨架图。结果表明,本方法能够精确有效地提取高分辨率遥感影像的城镇道路信息。 相似文献
107.
108.
正确认识天山北坡城市群的空间组织结构以及空间发展形态,对于完善绿洲城市群的发展理论和规划具有重要意义。以天山北坡城市群为研究对象,通过资源环境承载力的分析,总结出未来城市群发展面临的客观制约因素;通过中心性分析、断裂点理论修正的Voronoi多边形等方法识别出城市群的中心城市及各自的辐射范围城市;通过引力模型识别出城市之间的社会经济联系强度。据此,利用多维尺度分析的方法,可视化地展现了天山北坡城市群发展的空间组织形态。经调查了解:(1)乌鲁木齐市与克拉玛依市是未来城市群发展的两个中心城市,五家渠市、阜康市、昌吉市、石河子市周边目前属于乌鲁木齐市的辐射范围城市,奎屯市,乌苏市属于克拉玛依市的辐射范围城市;(2)城市群内部的城市之间的联系比较松散,特别是两个中心城市之间联系较弱;(3)城市群的空间发展形态为串珠式,是一种特殊的走廊式空间形态。 相似文献
109.
Mark D. Green 《Applied geography (Sevenoaks, England)》2012,32(2):335-349
Tourism accounts for 15% of Greece’s gross domestic product. In the wake of a struggling economy many of Greece’s coastal villages have turned to tourism to supplement local economies. Preliminary analysis of structural and cultural materials recovered from an excavation on Mitrou, a small islet near the coastal village Tragana located 140 km north of Athens has established the site’s contribution to a fuller understanding of settlement practices in Central Greece from the end of the Bronze Age through the Early Iron Age. The site’s historic importance combined with its scenic coastal setting has considerable potential to be developed into an important tourist site. The physical geography of the region is the product of the complex interaction of coastal, alluvial, fluvial, and seismic processes. This investigation integrates the archaeological material with a geographical analysis employing a variety of geographical techniques (soil and sediment analysis, past climatic data, environmental surveys, and geospatial modeling) to reconstruct the geomorphological history of the site and to evaluate the area as a potential tourist site. 相似文献
110.
近60年洞庭湖泊形态与水沙过程的互动响应 总被引:2,自引:0,他引:2
以历史文献、图件及1951~2009年长系水沙等资料为依据,对比分析洞庭湖形态与水沙过程的互动响应,结果表明:由于湖泊形态与水沙过程存在着相互作用的关系,近60年间,水沙过程以多种形式改变湖泊形态特征值,如湖盆结构破碎、解体,水深变浅以及湖面﹑湖容依次减少1840km2及130×108m3;同时湖泊形态特征值改变也引起水沙特性变异,在1951~2002年间湖盆蓄水量呈明显的增减波动,但同流量下汛期水位普遍抬高1.2~1.90m,西﹑南﹑东洞庭湖水位变幅依次增大1.61m、1.39m和1.35m,各主要水文站前5位最高洪水位排序的年份均出现在湖面积(容积)历史最低值,泥沙淤积率为70%以上;2003年6月三峡水库蓄水及"退田还湖"后,高、中水位下湖盆调蓄量有所减少,城陵矶丰、枯水位分别降低1.12m及0.35m,西湖区与东南湖区的泥沙输出比均呈增大趋势,泥沙淤积率减至35.9%。其互动响应机制,可概化为泥沙淤积循环→湖盆结构破碎、解体,湖面湖容缩小→水沙特性异变→改变湖泊形态→水沙特性变异的互动响应动态演进模式。 相似文献