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991.
P.N. Ranasinghe G.W.A.R Fernando C.B. Dissanayake M.S. Rupasinghe D.L. Witter 《Journal of Geochemical Exploration》2009,103(2-3):97-114
Stream sediment geochemistry is extensively used in mineral exploration and environmental studies. However, quantitative assessments of the effectiveness of stream sediment geochemistry for describing upstream lithologies are rare, especially in high-grade metamorphic terrains. This study statistically evaluates whether stream sediment geochemistry can aid in recognizing variations in upstream geology in several high-grade metamorphic lithotectonic units having different metamorphic and tectonic histories, including the Highland Complex, Vijayan Complex, Wanni Complex, and Kadugannawa Complex of Sri Lanka. For this study, concentrations of 21 elements were measured in 2080 stream sediment samples collected from the Walawe River, Maha Oya, Gala Oya basins located on above lithotectonic units and Uma Oya, Belihul Oya, Badulu Oya basins situated adjacent to each other on the Highland Complex. These rivers flow across dry, intermediate and wet zones of Sri Lanka, with river courses having both slope (> 20°) and flat (< 20°) areas. Elemental concentrations, averaged over each river basin, show patterns of enrichment and depletion which may relate to localized mineralization conditions, local lithological changes, anthropogenic activities and environmental factors such as local variations in climate and morphology among river basins. Comparison of element concentrations in sediments from the four different lithotectonic units shows that enrichment – depletion patterns can be partly related to rock geochemistry of the associated lithotectonic unit. However, climate and basin morphology also seem to play an important role. Results of Kruskal–Wallis H tests show that both major and trace element levels in sediments from the four different lithotectonic units, as well as from adjacent Uma Oya, Badulu Oya and Belihul Oya basins, are significantly different. Discriminant function analysis appropriately classifies sediments into the four different lithotectonic units with an accuracy of 91.9%. This method also classifies sediments into river basins which share common lithology being situated adjacent to each other in the same lithotectonic unit with an accuracy of 89.5%. This strongly suggests that stream sediment geochemistry is capable of describing the upstream regional scale as well as local scale lithological changes at a great accuracy in complex high-grade metamorphic terrains. In both cases use of channel slope and basin climatic zone as additional variables does not significantly increase overall or individual accuracy in classification. 相似文献
992.
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
993.
Assessment of different topographic corrections in AWiFS satellite imagery of Himalaya terrain 总被引:2,自引:0,他引:2
V. D. Mishra J. K. Sharma K. K. Singh N. K. Thakur M. Kumar 《Journal of Earth System Science》2009,118(1):11-26
The influence of topographic effects in optical satellite imagery is not investigated very extensively in the Himalayan terrain.
The topographic variability causes a problem of differential illumination due to steep and varying slopes in rugged Himalayan
terrain. Therefore, topographic corrections are essential for qualitative and quantitative analysis of snow cover applications.
The present paper discusses the implementation of different topographic correction models on AWiFS sensor onboard IRS P6 satellite
images and the qualitative and quantitative comparative analysis in detail. Both the Lambertian and non-Lambertian assumptions
have been considered in the present analysis with the aim to explore best suitable empirical model for rugged terrain. The
main topographic methods implemented are:
Lambertian assumptions are found to be very unrealistic over Himalayan terrain as these lead to either underestimation or
overestimation of physical parameters significantly both on sunlit slopes as well as the slopes away from the Sun. This problem
is overcome by considering non-Lambertian assumption. Minneart constant and C-correction coefficients for all AWiFS satellite
bands are estimated using regression analysis. All the results due to topographic effects are investigated qualitatively and
quantitatively using four criteria namely visual analysis, validation with field measurements (in-situ observations), spectral reflectance of training samples of snow on the south and north aspects and graphically. The visual
analysis confirms the minimization of three dimensional relief effects in two-stage normalization and slope matching methods
and retrieves some of the information under mountain shadow. Due to the very bright surface of snow fields there is likely
to be more diffuse reflected light in these areas than over darker vegetated surfaces. The qualitative analysis in other methods
does not extract any information on shady slopes. The quantitative validation of topographic results in satellite imagery
with in-situ observations shows underestimation of spectral reflectance of snow significantly except for slope matching technique. It
is also apparent that although all the topographic methods correct the reflectance of training snow samples on the south and
north aspects but most acceptable values are achieved using slope matching. The results obtained from graphical analysis reveal
that mean reflectance after all topographic corrections are independent of illumination. This study also suggests that the
suitability of topographic models can not be concluded as successful based on single criterion. Slope matching technique is
the only technique which satisfies all the four criteria successfully and produces the best result for Himalayan terrain. 相似文献
• | C-correction |
• | Minneart corrections |
• | Civco’s modified version of cosine correction |
• | two-stage normalization and |
• | slope matching technique. |
994.
YU Zhenshou NI Donghong GAO Shouting MIN Jinzhong REN Hongxiang 《Acta Meteorologica Sinica》2008,22(2):224-238
Typhoons landing in the central and north of Fujian Province often seriously impact Zhejiang Province. Much attention has been given to exceptionally torrential rain in the South/North Yandang mountainous regions in the southeast of Zhejiang Province associated with typhoon-landing. Typhoon Haitang (2005) is a typical case of such a category, which landed in Huangqi Town of Lianjiang County in Fujian Province, and meanwhile greatly impacted Southeast Zhejiang. A numerical simulation has been performed with the PSU/NCAR non-hydrostatic model MM5V3 to study the torrential rain associated with Typhoon Haitang. The comparison of simulated and observed rainfalls shows that the MM5V3 was able to well simulate not only the intensity but also the locations of severe heavy rain of Typhoon Haitang, especially the locations of the south/north heavy rain center areas in the South/North Yandang mountainous regions. Meanwhile, the diagnostic analysis has been also carried out for better understanding of the severe heavy rain mechanism by using the model output data of high resolution. The diagnostic analysis indicates that the westward tilt of the axis of vorticity from lower layer to upper layer over the south heavy rain center area and the coupled structure of convergence in the lower layer and divergence in the upper level over the north heavy rain center area, were both propitious to stronger upward motion in the layers between the mid and upper atmosphere, and the secondary circulation induced by the vertical shear of the ambient winds further strengthened the upward motion in the heavy rain areas. After Haitang passed through Taiwan Island into the Taiwan Strait, the water vapor east of Taiwan Island was continuously transferred by typhoon circulation towards South Wenzhou, leading to the torrential rainfall in the South Yandang mountainous region south of Wenzhou. Subsequently~ Haitang moved northwards, the water vapor belt east of Taiwan Island slowly advanced northwards, the precipitation rate obviously enhanced i 相似文献
995.
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
996.
大光斑激光雷达数据已广泛应用于森林冠层高度提取,但通常仅限于地形坡度小于20°的平缓地区。在地形坡度大于20°的陡峭山区,地形引起的波形展宽使得地面回波和植被回波信息混合在一起,给森林冠层高度提取带来巨大挑战。本文利用激光雷达回波模型和地形信息,提出了一种模型辅助的坡地森林冠层高度反演算法。该方法以激光雷达回波信号截止点为参考,定义了波形高度指数H50和H75,使用激光雷达回波模型与已知地形信息模拟裸地的激光雷达回波,将裸地回波信号截止点与森林激光雷达回波信号截止点对齐,利用裸地回波计算常用的波形相对高度指数RH50和RH75,对森林冠层高度进行反演。并与高斯波形分解法和波形参数法的反演结果进行了比较。研究结果表明:(1)利用所提取的波形指数RH50和RH75对胸高断面积加权平均高(Lorey’s height)进行了估算,在坡度小于20°时,高斯波形分解法、波形参数法和模型辅助法的估算结果与实测值线性拟合的相关系数(R2)分别为0.70,0.78和0.98,对应的均方根误差(RMSE)分别为2.90 m,2.48 m和0.60 m,模型辅助法略优于其他两种方法;(2)在坡度大于20°时,高斯波形分解法、波形参数法和模型辅助法的R2分别为0.14,0.28和0.97,相应的RMSE分别为4.93 m,4.53 m和0.81 m,模型辅助法明显优于其他两种方法;(3)在0°—40°时,模型辅助法对Lorey’s height估算结果与实测值的R2为0.97,RMSE为0.80 m。本研究提出的模型辅助法具有更好的地形适应性,在0°—40°的坡度范围内具备对坡地森林冠层高度反演的潜力。 相似文献
997.
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
998.
999.
矿山的地形测量逐渐引入现代高新技术,GPS的兴起也使矿山地形监测更加方便、准确。详细介绍了GPS卫星定位系统的原理以及在地形控制测量中的优越性,并运用实例探讨了采用GPS定位技术建立矿区地形监测网、监测方法、数据处理等问题。 相似文献
1000.
《The Journal of geography》2012,111(4):164-167
Abstract An Expedition Through the Louisiana Purchase provides a demonstration lesson for American history and Geography, which integrates the five fundamental themes of geography with a roleplaying lesson on Lewis and Clark's exploration of the Louisiana Purchase. The article, aimed at grades 7–12, includes suggested evaluation procedures, extension lessons, as well as materials and resources. Finally, student outcomes will be discussed in order to integrate this lesson into a unit on the theme of exploration. 相似文献