一种基于格网的快速等值线充填算法   总被引：16，自引：0，他引：16  

吴自银  高金耀 《测绘学报》1999,28(4):350-354

本文提出一种基于格网的等值线跟踪,适用于任意边界分割的快速充填算法,实现充填的 量化效果。根据边界线与非封闭等值线间的关系,建立等值线间的拓扑关系,并以树结构方式存储,以准确快速地实现边界线、非封闭等值线之间的封闭和封闭等值线间的嵌套。该算法已成功应用于海量多波束地形数据的成图,克服了常用多波束后处理成图软件栅格充与等值线之间的失配。  相似文献   

根据地性线绘制等高线的研究   总被引：8，自引：2，他引：6  

赵夫来  郝向阳 《测绘学报》1999,28(4):2

根据地形特征点和地性线绘制等高线是测绘大比例尺地形图等高线的主要方法,本文在分析现有自动绘制等高线方法的基础上,提出了一种根据地性线及其拓扑关系直接求取和跟踪等高线的方法。针对利用各种传统曲线光滑算法所绘相邻等高线间常常出现不协调现象的缺点,首次提出并详细讨论了相邻等高线通过点间的抛物线双向加权平均光滑算法。大量实践表明,利用本文所提出的跟踪和光滑方法所绘等高线的光滑性和协调性是令人满意的。  相似文献   

三维复杂地壳结构非线性走时反演   总被引：2，自引：1，他引：1       下载免费PDF全文

俞贵平  徐涛  张明辉  白志明  刘有山  武澄泷  滕吉文 《地球物理学报》2017,60(4):1398-1410

中国大陆中西部乃至全球造山带普遍具有复杂地壳结构.随着矿产资源勘探和深部探测研究的深入,探测造山带及盆山耦合区下方地壳精细结构正逐渐成为当前面临的巨大挑战.人工源深地震测深方法正越来越清晰地揭示出不同构造域地壳速度结构的基本特征,然而传统的层状结构模型参数化方法难以准确描述复杂地质模型,通常情况下多忽略速度结构的精细间断面且采用层边界平滑处理,难以满足地壳精细结构成像的发展要求.针对上述困难,本文采用最近发展的块状结构建模方案构建三维复杂地壳模型,基于逐段迭代射线追踪正演走时计算方法,推导了走时对三角形界面深度以及网格速度的偏导数,开展了非线性共轭梯度走时反演方法研究.发展了利用直达波和反射波等多震相走时数据对界面深度和网格速度的多参数联合反演方法,并引人不同种类震相数据的权系数和不同类型参数偏导数归一化的方法.数值算例表明,基于块状结构的非线性共轭梯度走时反演方法适用于复杂地壳结构模型,在利用人工源走时数据反演复杂地壳精细结构领域具有良好的应用前景.  相似文献   

模拟退火方法在三维速度模型地震波走时反演中的应用   总被引：5，自引：3，他引：2  

李飞  张雪梅  陈宏峰  何少林 《中国地震》2017,33(3):355-364

采用块状建模以及三角形拼接的界面描述方式,并通过立方体速度网格线性插值获得块体内部的速度分布。正演过程中采用逐段迭代射线追踪方法计算三维复杂地质模型中的射线走时,并采用模拟退火方法进行了三维模型中的地震波走时反演研究。模型测试结果表明,使用的射线追踪和走时反演算法有效。  相似文献   

Travel time computations using a compact eikonal equation for vertical transverse isotropic media          下载免费PDF全文

Peyman Moghaddam  Reza Khajavi  Henk Keers 《Geophysical Prospecting》2018,66(8):1475-1484

Eikonal solvers often have stability problems if the velocity model is mildly heterogeneous. We derive a stable and compact form of the eikonal equation for P‐wave propagation in vertical transverse isotropic media. The obtained formulation is more compact than other formulations and therefore computationally attractive. We implemented ray shooting for this new equation through a Hamiltonian formalism. Ray tracing based on this new equation is tested on both simple as well as more realistic mildly heterogeneous velocity models. We show through examples that the new equation gives travel times that coincide with the travel time picks from wave equation modelling for anisotropic wave propagation.  相似文献   

Near-bankfull floods in an Alpine stream: Effects on the sediment mobility and bedload magnitude   总被引：1，自引：0，他引：1  

Riccardo Rainato  Luca Mao  Lorenzo Picco 《国际泥沙研究》2018,33(1):27-34

In a mountain environment, the transport of coarse material is a key factor for many fields such as geomorphology, ecology, hazard assessment, and reservoir management. Despite this, there have been only a few field investigations of bedload, in particular using multiple monitoring methods. In this sense, attention has frequently focused on the effects of “high magnitude/low frequency floods” rather than on “ordinary events”. This study aims to analyze the sediment dynamics triggered by three high-frequency floods (recurrence interval “RI” between 1.1 and 1.7 yr) that occurred in the Rio Cordon basin during 2014. The flood events were investigated in terms of both sediment mobility and bedload magnitude. The Rio Cordon is an Alpine basin located in northeastern Italy. The catchment has a surface area of 5 km², ranging between 1763 and 2763 m above sea level. The Rio Cordon flows on an armored streambed layer, with a stable step-pool configuration and large boulders. Since 1986, the basin has been equipped with a permanent station to continuously monitor water discharge and sediment flux. To investigate sediment mobility, 250 PIT-tags were installed in the streambed in 2012. The 2014 floods showed a clear difference in terms of tracer displacement. The near-bankfull events showed equal mobility conditions, with mean travel distance one order of magnitude higher than the below-bankfull event. Furthermore, only the near-bankfull events transported coarse material to the monitoring station. Both events had a peak discharge up to 2.06 m³ s^-1, but the bedload transport rates differed by more than one order of magnitude, proving that under the current supply-limited condition, the bedload appears more related to the sediment supply than to the magnitude of the hydrological features. In this sense, the results demonstrated that near-bankfull events can mobilize large amounts of material for long distances, and that floods of apparently similar magnitude may lead to different sediment dynamics, depending on the type and amount of sediment supply.  相似文献   

三维地质模型中地震波共轭梯度非线性走时反演   总被引：2，自引：0，他引：2  

李飞  张雪梅  姬运达  何少林 《地震地磁观测与研究》2018,39(4):33-37

地震体波走时层析成像是探测地球内部速度结构的重要方法之一。基于三维块状建模以及三角形拼接的界面描述方式,结合快速高效的逐段迭代射线追踪方法,获得三维复杂地质模型中的地震射线路径与走时信息,采用共轭梯度非线性反演算法,进行地震波走时反演。实验结果表明共轭梯度反演算法在三维层状模型中具有较高的有效性。  相似文献   

蒸发波导对GNSS海面反射信号有效散射区域的影响          下载免费PDF全文

刘黎军  夏俊明  白伟华  孙越强  杜起飞  骆黎明 《地球物理学报》2019,62(2):499-507

蒸发波导在海洋低空的发生概率高达90%,对舰船雷达、通信等电磁系统具有重要影响.为了分析利用GNSS卫星海面反射信号的时延-相关功率波形反演蒸发波导的可行性,本文提出了GNSS卫星海面反射信号的有效散射区域的概念,并将有效散射区域内的GNSS反射信号区分为GNSS标准反射信号和GNSS波导反射信号;然后,利用射线追踪方法,仿真分析了GNSS卫星海面反射信号的有效散射区域大小对蒸发波导的关键参数——波导高度的敏感性,并分析了在时延-相关功率波形上利用反射信号的传播时延将二者分离开的可行性.结果表明,GNSS卫星海面反射信号的有效散射区域对蒸发波导高度非常敏感,对于2～25m高的GNSS反射信号接收天线,当蒸发波导的高度由0m增加至20m时,GNSS反射信号有效散射区域半径的均值可由约14km迅速扩展至约160km;采用高度角足够大的GNSS卫星可以将有效散射区内的GNSS标准反射信号与GNSS波导反射信号在时延-相关功率波形上分离开.  相似文献   

西准噶尔红山地区晚古生代赞岐岩锆石U Pb年代学、地球化学特征及其地质意义   总被引：1，自引：0，他引：1  

马飞宙  陈宣华  徐盛林  马芬  韩乐乐  丁伟翠  王叶 《地质学报》2020,94(5):1462-1481

中亚造山带西部西准噶尔地区红山花岗岩体内部发育多期似岩墙状安山质暗色条带,LA-ICP-MS锆石U-Pb同位素定年和岩石化学与同位素分析表明,它们具有不同的形成年龄、相同的源区和相似的形成过程。其中,具有不规则状或环状形态的暗色条带,其锆石U-Pb年龄为319.1±2.9 Ma和313.3±2.4 Ma,远大于红山岩体花岗岩锆石结晶年龄(305～301Ma),可能是红山岩体侵位过程中所捕掳的围岩;具有线性展布特征的安山质暗色条带,其锆石U-Pb年龄为295±2Ma,形成于红山岩体侵位之后,构成伸展岩墙群。红山岩体中的安山质暗色条带和线状岩墙群具有相似的岩石化学组成,富SiO_2(56.48%～63.09%)、MgO(3.56%～6.31%),具有高的Mg#值(51.74～62.40)及Na_2O/K_2O值(1.34～3.43);球粒陨石标准化稀土元素(REE)配分模式呈明显的右倾型,富集轻稀土元素(LREE)和大离子亲石元素(LILE)Rb、K、Ba、U、Sr,亏损高场强元素(HFSE)Th、Nb、Ce、P和重稀土元素,具较弱的负铕异常;其同位素组成特征为(~(87 )Sr/~(86 )Sr)i=0.703295～0.703620,(~(143) Nd/~(144) Nd)i=0.512612～0.512618,εNd(t)=6.91～7.62,(~(206) Pb/~(204) Pb)t为17.6883～17.9876,(~(207) Pb/~(204) Pb)t为15.5313～15.5686,(~(208)Pb/~(204)Pb)t为37.4460～38.0581。它们具有与赞岐岩类似的地球化学特征,总体表现出与弧岩浆作用相关的地球化学特征,可能具有共同的物质来源,为准噶尔洋板片俯冲消减后同一地幔源区在不同阶段的产物。其中,形成于弧岩浆作用时期的赞岐岩(319～313 Ma),构成与岛弧花岗岩类伴生的环状似岩墙状安山质暗色条带;形成于后造山伸展岩浆作用晚期的赞岐岩(～295Ma),构成与达拉布特左行走滑作用相关的陆内伸展岩墙群。安山质暗色条带(岛弧火山作用)、红山岩体(后造山伸展)和线状岩墙群(陆内伸展)记录了西准噶尔红山地区洋陆转换的全过程。  相似文献   

Bedrock erosion due to hoeing as tillage technique in a hilly agricultural landscape,southwest China     

Haichao Xu  Jianhui Zhang  Yuhang Wei  Jiadong Dai  Yong Wang 《地球表面变化过程与地形》2020,45(6):1418-1429

Tillage on hillslopes may not only induce severe soil erosion, but may also cause bedrock erosion under certain conditions. Yet, little is known about bedrock erosion by tillage in a hilly agricultural landscape, southwest China. The aim of this study is to quantify the translocation of rock fragments derived from bedrock fragmentation by hoeing under different conditions, including slope gradient, hoeing depth and soil-covered thickness using a gravel tracing method. The reliability of the gravel tracing method was confirmed by the bedrock dyeing tracing method. Hoeing depth is a significant factor affecting the translocation rate of rock fragments (Q_r ). Meanwhile, under the condition of overlying soil layers (0.06−0.10 m thick), the values of Q_r were significantly smaller with a reduction of 20.7−25.6%, compared with rock fragmentation by hoeing for bare bedrock. However, slope gradient was found to have insignificant effects on Q_r . Fractured bedrock moved as individual small fragments, which was mainly controlled by the hitting force of the hoe, while soil moved in the shape of lumps, which was dominated by both drag force of the hoe and gravity. This study suggests that hoeing into soil-covered bedrock can diminish bedrock erosion while providing soil matrix for shallow soil layers. Our work presents a quantitative assessment of bedrock erosion by hoeing and an underlying insight into characteristics of bedrock erosion by tillage operations in hilly agricultural regions with mudstone and shale, southwest China. © 2020 John Wiley & Sons, Ltd.  相似文献