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排序方式: 共有232条查询结果,搜索用时 125 毫秒
61.
地图扫描影像中的文字、符号注记与图形目标的分离是实现地图符号注记诱导自动识别的重要前提和基础,文中提出一种基于影像行的连接影像目标整体及交互的提取算法。借助该算法不仅可以有效地实现地图扫描影像中文字、符号注记与图形线划目标的分离,而且可以实现其它一些二值铁处理及分析。 相似文献
62.
南极地区的大气环流流体物理实验 总被引:2,自引:1,他引:2
通过流体物理实验,研究南极地形及冷源对大气环流的影响。正压流体实验表明,由于地形动力强迫,在南极大陆沿岸及以北地区生成气旋性涡旋带,有3个低压中心。在地形上空生成巨大的反气旋。斜压流体实验表明,东移“行星波”的波数及波形有准周期低频振荡,其振荡周期相当于地球大气系统中的21d。东移的槽在110°E以东逐渐发展,在160°W的罗斯海附近发展得最深,再往东则逐渐减弱 相似文献
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简要介绍了将差分GPS技术用于水下地形测绘的方法,重点研究了平面坐标转换和水深数据修正两个关键技术,给出了平面定位的坐标转换方法和考虑水温、含盐度等对声速的影响,以及海水潮位变化等因素后的水深测量修正方法。 相似文献
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为推进大地电磁三维反演的实用化,本文实现了基于L-BFGS算法的带地形大地电磁三维反演.首先推导了大地电磁法三维反演的Tikhonov正则化目标函数以及Hessian矩阵逆矩阵近似表达式和计算方法,然后设计了一种既能保证空气电阻率固定不变又能保证模型平滑约束的协方差矩阵统一表达式,解决带地形反演问题.在反演算法中采用正则化因子冷却法以及基于Wolf条件的步长搜索策略,提升了反演的稳定性.利用开发的算法对多个带地形地电模型(山峰地形下的单个异常模型、峰-谷地形下的棋盘模型)的合成数据进行了三维反演,并与已有大地电磁三维反演程序(ModEM)进行对比,验证了本文开发的三维反演算法的正确性和可靠性.最后,利用该算法反演了华南某山区大地电磁实测数据,得到该区三维电性结构,揭示了研究区以高阻介质为基底,中间以低阻不整合面和相对低阻介质连续分布,浅部覆盖高阻介质的电性结构特征,进一步验证了本文算法的实用性. 相似文献
67.
《地学前缘(英文版)》2020,11(5):1695-1709
The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the Mongol-Okhotsk Ocean that separated Siberia from Mongolia-North China continents.Following the oceanic closure,the tectonic evolution of that region was characterized by collisional uplift and subsequent extension that gave rise to the formation of metamorphic core complexes.This complex tectonic setting prevailed simultaneously between 150 Ma and 110 Ma both in Transbaikalia,North Mongolia,and within the North China Craton.Published paleobotanical and paleontological data show that the oldest Mesozoic basins had formed in western Transbaikalia before the estimated age of extension onset.However no precise geochronological age is available for the onset of extension in Transbaikalia.The Tugnuy Basin,as probably the oldest Mesozoic basin in western Transbaikalia,is a key obj ect to date the onset of extension and following changes in tectonic setting.In this study,U-Pb(LA-ICP-MS) dating of detrital zircons from three key Jurassic sediment formations of the Tugnuy Basin are used to identify the potential source areas of the sediments,understand the changes in sediment routing and provide insights on the topographic evolution of western Transbaikalia.Our results show several significant changes in tectonic regime after the closure of the Mongol-Okhotsk Ocean.A wide uplifted plateau formed during the closure of the Mongol-Okhotsk Ocean,determining the Early Jurassic drainage system reaching the AngaraVitim batholith to the north and shedding sediments to the continental margin to the South.The following collisional event at the end of the Early Jurassic led to the uplift of the collision zone,which partially inverted the drainage system toward the North.A strike-slip displacement induced by the oblique collision initiated some of the early Transbaikalian depressions,such as the Tugnuy Basin at about 168 Ma.A phase of basin inversion,marked by folding and erosion of the Upper Jurassic sediments,could correspond to the short-term collision event that took place during the latest Jurassic-earliest Cretaceous in the eastern Central Asian Orogenic Belt.The following inversion in tectonic regime from compression to extension is consistent with the mid-lower-crustal extension that led to the formation of the numerous metamorphic core complexes throughout northeastern continental Asia during the Early Cretaceous. 相似文献
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Manel Grifoll Almudena Fontán Luis Ferrer Julien Mader Manuel González Manuel Espino 《Coastal Engineering》2009
A background knowledge of marine dynamics helps harbour managers to control pollution and to manage dredging and traffic operations. This contribution studies the hydrodynamic conditions within Bilbao Harbour, which is enclosed by the Nervión Estuary (in the Basque Country, Spain). The results obtained from hydrographical surveys are compared with numerical simulations obtained using the Regional Ocean Modelling System (ROMS). Hydrodynamic modelling was carried out to determine the inner harbour currents for a specific period in which data were available. Then, numerical experiments were designed in order to quantify the importance of different driving mechanisms in the harbour hydrodynamics. The results show that, in addition to the strong tidal influence on water circulation, the wind forcing and freshwater discharge also have a non-negligible influence on the currents. The computational domain is complex due to the presence of harbour infrastructures (i.e. breakwaters and piers). As a result, topographic eddies are therefore observed in the results. The freshwater influence of the Nervión river can also be observed in residual currents. This paper presents an improvement to the application of numerical modelling to a complex geometry domain, contributing to our understanding of the behaviour of the marine systems in meso-tidal harbours. This can be used to deal with harbour engineering and management problems. 相似文献
70.
Data from National Centre for Atmospheric Research (NCAR) Queen Air boundary-layer flights over the Nebraska Sandhills are analyzed to investigate the effects of these low hills on boundary-layer turbulence. The Sandhills are an area of anisotropic rolling terrain with characteristic wavelengths of order 2km and rms height variations of order 25m. The biggest impact is found in early morning flight data where horizontal velocity perturbations appear at the same wavelengths as the terrain and variances (normalised by u
2
, where u is the local friction velocity) are significantly enhanced relative to standard flat terrain values. By contrast the vertical velocity variance seems less affected and terrain effects are much less evident in data from the afternoon convective boundary layer. 相似文献