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991.
The release of a digital elevation model (DEM) for Australia on a 9″ (~250 m) grid has enabled the computation of gravimetric terrain corrections thus allowing the computation of complete Bouguer anomalies across the continent. The terrain correction was calculated through a two‐dimensional fast Fourier transform algorithm applied to a linear, planar approximation of the terrain‐correction formula, and with a constant topographic density of 2670 kg.m‐3. The technique was applied to two datasets in order to test for instabilities in the terrain‐correction algorithm: the original 9″ DEM, and a 27″ DEM averaged from the 9″ data. The 27″ terrain corrections were compared with values supplied by the Australian Geological Survey Organisation in Tasmania: 86% of these data were found to agree within 3.91 μm.s‐2; 98% agreed to within 5.32 μm.s‐2 (1σ). 相似文献
992.
The unique topography of the pothole region of the North American prairies creates challenges for properly determining basin contributing area. Numerous depressions or potholes within the landscape impound runoff. However, potholes can ‘fill‐spill’ resulting in surface water connections between the potholes. Surface water connectivity between potholes ultimately influences basin contributing area. Currently, automated methods, such as landscape analysis tools, treat depressions in the landscape as artifacts and simply fill the depressions to delineate a drainage basin. Using this method to calculate contributing area assumes that all surface storage has been satisfied (threshold) and the drainage basin will contribute 100% of its area for all runoff events. However, most runoff events in the prairie pothole region are pre‐threshold events that contribute only a portion of surface runoff to the outlet. These pre‐threshold events have surface storage that varies because of antecedent water levels and have a variable or dynamic potential to store further runoff in the basin. Government agencies have developed methodologies for determining pre‐threshold contributing areas, but these methodologies do not incorporate current technologies and, as a result, have limitations. We propose an automated method for determining contributing area that incorporates the fill‐spill of prairie potholes. The algorithm, which uses the D‐8 drainage direction method, automates a methodology for identifying and quantifying runoff contributing area. Any algorithm that determines pre‐threshold contributing area, must allow the DEM to be filled in an incremental manner. This will simulate increasing pond levels, and the resulting decrease in available storage in the basin, in response to runoff events. The SPILL algorithm is an iterative solution that increases the magnitude of input runoff events and records the decreasing change in available surface storage and the increase in contributing area until the storage threshold is reached and the contributing area reaches 100%. Through application of the algorithm on prairie pothole region basins, we test proposed conceptual curves that describe a hypothesized non‐linear relationship between decreasing potential storage in the landscape and contributing area. Results indicate that the proposed conceptual curves represent the relationship between potential surface storage and contributing area in the test basins very well. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
993.
全球虚拟地形环境中Mipmap纹理技术研究 总被引:4,自引:0,他引:4
Mipmap纹理技术是目前解决纹理分辨率与视点距离关系的最有效途径.将Mipmap纹理引入全球虚拟地形环境的金字塔模型中,在分析现有Mipmap纹理生成技术不足的基础上,提出了一种新的Mipmap纹理生成技术,并针对Mipmap纹理以多级形式存储会使数据量增加的问题,提出了Mipmap纹理压缩算法,以提高实时渲染中Mipmap纹理的装载速度和创建速度,并用实验结果验证了算法的可行性.最后给出了全球金字塔模型中Mipmap压缩纹理的存储结构. 相似文献
994.
虚拟地形环境中道路与地形模型融合算法研究及精度评价 总被引:1,自引:0,他引:1
以大比例尺地图构建的虚拟地形环境,由于观察视点的接近以及应用中对各种查询和分析的需要,所以要求构建的环境既能准确地表现地形特征又能使地物与地形精确融合,准确地查询出地物的属性,以满足目视及精确定位的要求.然而,实际应用中往往忽视地形与地物的密切关系,从而导致在目视比例尺条件下出现地物飘在空中或钻入地下等失真现象.为此,本文以道路为例提出了道路模型与地形模型的融合算法,同时对融合后道路与地形模型的精度进行了评估,为构建逼真的地理环境提供了基础.也为河流、岛屿、湖泊等地物与地形模型的融合提供参考. 相似文献
995.
检波距是浅层折射地震勘探中的一个重要参数,检波距的合理选择是资料解释结果可靠性的重要保证。特别是在二元和多元地形条件下的折射地震勘探资料解释中,选择平距或斜距来计算检波距在不同行业和单位是不统一的。这里从理论上探讨了在二元地形条件下,浅层折射地震资料解释中用平距和斜距二种方法计算检波距对表层有效速度的影响和误差大小,明晰了实际工作中二元或多元地形条件下,不同检波距计算方法所引起折射地震勘探资料解释结果的差异和误差大小及其合理性。 相似文献
996.
复杂山地近地层强风特性分析 总被引:10,自引:2,他引:8
利用在贵州省西南部复杂山地上获取的近地层梯度风观测资料和三维超声测风仪观测资料,从中筛选出具有该地气候特征的强风样本,利用数量统计和谱分析等方法,计算分析了由于复杂地形影响而导致的局地低层强风的平均和脉动特征.平均风场主要表现在受当地主要特征地形(西北-东南走向的深切峡谷)影响,其全年的主导风向和最大风速出现的方向几乎完全转为沿峡谷走向,即使在符合中性大气层结条件下,风的垂直廓线也完全不满足幂指数分布,风攻角远远大于规范推荐的值,并且不同风向的强风攻角因地形影响其差异可达20°;强风条件下脉动风场的主要特征是:不同风向强风的湍流强度有所不同,在纵、横和垂直方向的湍流强度比值与现行设计规范给出的三维湍流强度比值有明显差异,其中垂直方向的湍流强度显著偏大是突出特征;湍流积分尺度偏大,其中纵向值偏大20%-60%,横向值在某些风向上可偏大3倍以上,垂直方向则普遍较平坦地形偏大一个量级左右;在桥梁结构较为敏感的频域范围内,各风向的湍流谱密度值有显著差异,其中不同风向在纵向上最大差值可达8倍,横向和垂直向可相差6倍,但无论哪个方向的湍流谱密度值均比台风中心要小1-2个量级. 相似文献
997.
998.
S. M. Hamilton 《Journal of Geochemical Exploration》1998,63(3):155-172
Recent studies have reported the presence of geochemical anomalies spatially related to mineralisation but which overlie thick glacial overburden. Existing models developed to account for similar anomalies over thin overburden do not adequately explain their presence in thick, young overburden, and to date no new model has been advanced that does. Problems with the existing models are discussed and a new theory is advanced that proposes electrochemically induced mass transport to account for the presence of geochemical anomalies over thick glacial drift. An upward increasing redox gradient exists in most surficial geological materials. Sub-vertical electronic conductors such as graphite or metallic sulphides in bedrock can provide a ‘short-circuit' route across this redox field between reducing agents abundant at depth and oxidising agents abundant in shallower areas. As electrons move up the conductor, oxidising agents in overlying overburden are consumed and a negative redox anomaly develops above the conductor relative to surrounding overburden. High redox gradients in this area induce the rapid migration of reduced anions away from the top of the conductor resulting in the development of a redox-front between reduced and oxidised areas. This front continues to migrate outward and upward at a quantifiable rate that far exceeds that of chemical diffusion until it encounters a continuous source of oxidising agents. The final result may be the propagation of the redox anisotropy to ground surface and the development of a permanently reduced ‘column' between bedrock mineralisation and surface. Higher redox gradients between mineralisation and the ground surface at the edges of the ‘column' relative to its centre result in the focusing of ionic current at the edges. ‘Rabbit-ear' anomalies in surface materials could result from both upward movement of reduced anions to the flanks and inward movement of oxidised cations. Depletions in soil media for iron and manganese and co-precipitating elements are expected in the centre of the column due to their higher mobility in reduced environments. 相似文献
999.
GEOLOGICAL EVOLUTION AND OROGENY OF EAST KUNLUN TERRAIN ON THE NORTHERN QINGHAI—TIBET PLATEAU 总被引:1,自引:0,他引:1
GEOLOGICAL EVOLUTION AND OROGENY OF EAST KUNLUN TERRAIN ON THE NORTHERN QINGHAI—TIBET PLATEAU1 XuZQ ,YangJS ,ZhangJX ,etal.AcomparisonbetweenthetectonicunitsonthesidesoftheAltunsinistralstrike slipfaultandthemechanismoflithosphericshearing[J] :ActaGeologicaSinica,1999,73:193~ 2 0 5(inChinesewithEnglishabstract) .
2 YangJS ,XuZQ ,LiHB ,Wu ,etal.DiscoveryofeclogiteatthenorthernmarginofQaidambasin,NWChina[J] .Chi neseScienceBulletin,1998,4 3… 相似文献
1000.
Dhruba Mukhopadhyay Krishnapriya Basak 《Journal of the Geological Society of India》2009,73(4):489-518
The Eastern Ghats Belt is a polycyclic granulite terrain along the east coast of India whose western boundary is marked by
a shear zone along which the granulites are thrusted over the cratonic units of the Indian shield, and its northern margin
is marked by the presence of a number of fault-bounded blocks. Recent work has convincingly brought out that there are domains
within the belt having different evolutionary histories. The segment south of the Godavari Rift went through a high grade
thermo-tectonic event at ∼1.6–1.7 Ga. North of the Godavari Rift in a narrow zone along the western boundary the last high-grade
metamorphic event is of late Archaean age. A series of alkaline plutons along the western boundary zone testifies to a rifting
episode at ∼1.3–1.5 Ga. In the major part of the EGB the metamorphism is broadly of Grenvillian age, with two major thermo-tectonic
pulses at ∼1.1–1.2 Ga and ∼0.95–1.0 Ga. But high grade conditions persisted for a long period and younger thermal events of
∼0.65 Ga to ∼0.80 Ga are locally recorded. There are differences in the tectonometamorphic histories of different domains,
but the tectonic significance of these differences remains uncertain. Pan-African (0.50–0.55) thermal overprints are common
and become conspicuous along the western boundary zone. The thrusting of the Eastern Ghats granulites in a hot state over
the cratons to the west is of Pan-African age. In the Rodinia assembly (∼0.9 Ga) the Eastern Ghats and the Rayner-Napier Complexes
of Antarctica were contiguous, but the pre-Rodinia configuration of these terrains remains unclear. At ∼0.8 Ga during the
Rodinia break up Greater India rifted apart from East Antarctica, and only later it docked with Australia-East Antarctica
at 530–550 Ma. The continuation of the East Antarctic Pan-African orogenic belts into the Eastern Ghats is yet to be ascertained. 相似文献