Weathering and Geochemical Processes Controlling Solute Acquisition in Ganga Headwater–Bhagirathi River, Garhwal Himalaya, India     

Shiv Kumar Pandey  Abhay Kumar Singh  S. I. Hasnain 《Aquatic Geochemistry》1999,5(4):357-379

Water and suspended sediment samples were collected along a longitudinal transect of the Bhagirathi – a headwater stream of the river Ganga, during the premonsoon and postmonsoon seasons, in order to assess the solute acquisition processes and sediment transfer in a high elevation river basin. Study results show that surface waters were dominated by HCO₃ and SO₄ in anionic abundance and Ca in cationic concentrations. A high concentration of sulphate in the source region indicates oxidative weathering of sulphide bearing minerals in the drainage basin. The combination of high concentrations of calcium, bicarbonate and sulphate in river water suggests that coupled reaction involving sulphide oxidation and carbonate dissolution are mainly controlling the solute acquisition processes in the drainage basin. The sediment transfer reveals that glacial weathering and erosion is the major influence on sediment production and transfer. The seasonal and spatial variation in ionic concentration, in general, is related to discharge and lithology. The sediment mineralogy and water mineral equilibrium indicate that water composition is in equilibrium with kaolinite. The river Bhagirathi annually delivers 0.74 M.tons of dissolved and 7.88 M.tons of suspended load to the river Ganga at Devprayag. The chemical and physical denudation rate of the Bhagirathi is 95 and 1010 tons/km²/yr, higher than the Indian and global average.  相似文献   

LGY-Ⅲ型智能测沙颗分仪   总被引：10，自引：0，他引：10  

蔡守允  魏延文  雷学锋 《海洋工程》1999,17(4)

介绍了应用于多项国家重点科技攻关项目——泥沙河工模型试验的ＬＧＹ－Ⅲ型智能测沙颗分仪的工作原理和应用方法。  相似文献   

High‐resolution multi‐component distributed acoustic sensing          下载免费PDF全文

Ivan Lim Chen Ning  Paul Sava 《Geophysical Prospecting》2018,66(6):1111-1122

Distributed acoustic sensing uses an optical fibre together with an interrogator unit to perform strain measurements. The usage of distributed acoustic sensing in geophysics is attractive due to its dense spatial sampling and low operation cost if the optical fibre is freely accessible. In the borehole environment, optical fibres for distributed acoustic sensing are often readily available as a part of other sensing tools, such as for temperature and pressure. Although the distributed acoustic sensing system promises great potential for reservoir monitoring and surface seismic acquisition, the single axial strain measurement of distributed acoustic sensing along the fibre is inadequate to fully characterise the different wave modes, thus making reservoir characterisation challenging. We propose an acquisition system using five equally spaced helical optical fibres and a straight optical fibre to obtain six different strain projections. This system allows us to reconstruct all components of the 3D strain tensor at any location along the fibre. Analysing the condition number associated with the geometry of the optical fibre, we can systematically search for the optimum design parameters for our configuration. Numerical examples demonstrate the effectiveness of our proposed method to successful reconstruction of the full strain tensor from elastic wavefields of arbitrary complexity.  相似文献   

一种多波宽频地震数据采集设计与仪器实现关键技术   总被引：1，自引：1，他引：0       下载免费PDF全文

刘勇  庹先国  李怀良  沈统  陆景 《地球物理学报》2017,60(11):4302-4312

随着多波多分量技术的发展,宽频数据采集逐渐成为地震勘探的发展趋势.通过高保真获取全波场信息,并尽可能保留高频有效成分,进而利用多种波场信息相互验证和补充,是提高地震勘探精度的有效方法.受仪器带宽限制,常规设备在高频段很难同时保持高分辨率和大动态范围特征,在多波地震采集时,极容易出现分辨率不足和限幅失真等现象,极大影响多波多分量方法的实际应用效果.鉴于此,本文给出一种利用积分器、高频ADC、DAC和抽取滤波器构成的低成本宽频数据采集方法.通过构造环路滤波器(调制器),对高频ADC输出数据中的量化噪声二次整形,并配合抽取滤波,对带外噪声进行有效压制.实际测试表明,通过精细电路结构设计,采集站有效分辨率可达24位(采样率为2 kHz),动态范围超过140 dB,SNR达142 dB.相比传统设备,其采集数据在5～25 Hz的低频段和100 Hz以上的高频段都具有更加丰富的有效信息,非常适合多波多分量数据采集.  相似文献   

基于WSN的分布式节点地震仪分层通信网络   总被引：1，自引：1，他引：0       下载免费PDF全文

宾康成  张晓普  佟训乾  林君 《地球物理学报》2017,60(11):4313-4320

针对深部探测对节点地震仪器提出的质量监控和数据现场回收要求,本文设计了基于WSN的三维地震勘探分层通信网络.分层网络由骨干网和多跳网两个网络层构成:骨干网使用LTE技术与监控中心进行数据交换,并实现了链路带宽的合理分配与大范围的信号覆盖;多跳网结合地震勘探的特点,使用私有路由协议和数据传输协议完成了仪器的组网与数据的接力式传输.测试结果验证了组网协议的设计正确性与数据传输的稳定性,且网络总体性能满足实际应用的需求.数据多跳传输实现了无线局域网技术的远程访问,从而提高了勘探作业效率.  相似文献   

随钻四极源声波测井多模式采集测量TTI地层各向异性的研究          下载免费PDF全文

卫建清  何晓  陈浩  王秀明 《地球物理学报》2018,61(2):792-802

本文应用三维柱坐标时域有限差分方法模拟了多极子随钻声波测井的波场,提出了在横向各向同性（TI）慢速地层倾斜井中,使用四极源激发、多模式采集进行各向异性参数反演的方法.模拟结果表明：在强各向异性地层大角度倾斜井中使用四极源能够激发出多极模式波,并且井孔内的声场会随着声源方向角β（声源方向和快横波偏振方向的夹角）的改变而发生变化.使用四极子采集方式记录时,可以发现波形会分裂成快慢两种波;并且在声源方向与地层快横波偏振方向成45°时,分裂的两种波形的速度更趋近于地层快慢横波波速,用此可反演地层各向异性值大小.使用单极子采集方式记录时,其波形能量与声源方向角β大致成cos²2β的关系,在声源方向角为45°时,其波形幅度最小,用此可判断与快横波偏振方向成45°角的方向.使用AC方向（与声源同方向）偶极子采集方式记录时,当声源方向与快横波偏振方向一致时,采集到的波形幅度最小;而与快横波偏振方向垂直时,波形幅度最大,所以通过偶极子采集方式记录的波形可以判断快横波偏振方向.因此,在强各向异性倾斜井中进行随钻四极子测量时,可以使用多模式采集方式来进行地层各向异性的反演.  相似文献   

Patch‐scale representation of vegetation within hydraulic models          下载免费PDF全文

Timothy I. Marjoribanks  Richard J. Hardy  Stuart N. Lane  Matthew J. Tancock 《地球表面变化过程与地形》2017,42(5):699-710

Submerged aquatic vegetation affects flow, sediment and ecological processes within rivers. Quantifying these effects is key to effective river management. Despite a wealth of research into vegetated flows, the detailed flow characteristics around real plants in natural channels are still poorly understood. Here we present a new methodology for representing vegetation patches within computational fluid dynamics (CFD) models of vegetated channels. Vegetation is represented using a Mass Flux Scaling Algorithm (MFSA) and drag term within the Reynolds‐averaged Navier–Stokes Equations, which account for the mass and momentum effects of the vegetation, respectively. The model is applied using three different grid resolutions (0.2, 0.1 and 0.05 m) using time‐averaged solution methods and compared to field data. The results show that the model reproduces the complex spatial flow heterogeneity within the channel and that increasing the resolution leads to enhanced model accuracy. Future applications of the model to the prediction of channel roughness, sedimentation and key eco‐hydraulic variables are presented, likely to be valuable for informing effective river management. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

The construction of a simple portable electromagnetic vibrator from commercially available components     

Timothy Dean  Hoang Nguyen  Anton Kepic  David Halliday 《Geophysical Prospecting》2019,67(6):1686-1697

Since its introduction in the late 1950s, hydraulic vibrators have become the dominant source for land seismic surveys. The hydraulic vibrators typically used for commercial land seismic acquisition, however, are large, costly to operate and expensive to purchase. This inhibits their use for small-scale and short-duration surveys as well as Vibroseis research. In this paper we describe, in detail, the construction of a portable vibrator from commercially available components for a cost of less than $US2,000. Data shows that the vibrator is able to successfully transmit sweeps from 15 to 180 Hz with different spectral contents. The vibrator produces a stronger signal than a sledgehammer and we estimate its output to be around 1 kN. The frequency content of the data was concentrated at lower frequencies (<100 Hz) and the ground-roll was far more energetic than that produced using a sledgehammer.  相似文献   

Seismic on floating ice: data acquisition versus flexural wave noise     

Tor Arne Johansen  Bent Ole Ruud  Ronny Tømmerbakke  Kristian Jensen 《Geophysical Prospecting》2019,67(3):532-549

Geophysical surveying of the Arctic will become increasingly important in future prospecting and monitoring of the terrestrial and adjacent areas in this hemisphere. Seismic data acquired on floating ice are hampered with extensive noise due to ice vibrations related to highly dispersive ice flexural waves generated by the seismic source. Several experiments have been conducted on floating ice in van Mijenfjorden in Svalbard in the Norwegian Arctic to specifically analyse the extent of flexural waves recorded with various seismic receivers and sources deployed both on top of ice and in the water below. The data show that flexural waves are severely damped at 5 m or deeper below the ice and hydrophone data suffer less from these vibrations compared with data recorded on the ice. Aliasing of single receiver hydrophone data can to some extent be suppressed using an in-line line source of detonating cord. Experiments on ice on shallow water show prominent guided wave modes often referred to as Scholte waves propagating along the seabed. In this case, both flexural and Scholte waves interfere and make a complicated pattern of coherent noise. On shallow water, the positioning and type of the seismic source must be evaluated with respect to the coherent noise generated by these waves. Geophone strings of 25 m effectively suppress both flexural and Scholte waves due to their relative short wavelengths. An airgun generates relative more low-frequency energy than a surface source of detonating cord. Accordingly, seismic mapping of deep seismic horizons seem to be best achieved using geophone strings of such length and an airgun source. For shallow targets, the use of hydrophones in combination with detonating cord is an appropriate solution. Seismic surveying in the Arctic always have to follow environmental restrictions of not disturbing or harming wildlife and not causing permanent footprints into the vulnerable tundra, which implies that the choice of seismic acquisition strategy might occur as a trade-off between optimum data quality and environmental constraints.  相似文献   

空间信息系统原理（二）:空间信息系统数据的获取   总被引：1，自引：0，他引：1  

王家耀  苗国强  成毅 《海洋测绘》2004,24(2):1-4

简要介绍了空间信息系统(SIS)获取空间信息数据的三种最主要的方法：地图数据采集、遥感(RS)数据采集和GPS数据采集,并介绍了RS与GIS、GPS与GIS的集成。  相似文献