The use of MRS in the determination of hydraulic transmissivity: The case of alluvial aquifers     

Juan L. Plata  Flix M. Rubio 《Journal of Applied Geophysics》2008,66(3-4):128

Magnetic Resonance Sounding (MRS) is nowadays accepted as a new geophysical method that can be used for a reliable determination of the ground water content distribution in the top 150 m. A great effort has also been made in MRS development to deduce the hydraulic transmissivity, based on empiric relationships of the permeability with a factor F which is calculated with NMR parameters measured at laboratory scale. To use this relationship under field conditions a calibration coefficient C_T = T_pt / F has to be previously established, which demands the knowledge of the transmissivity T_pt evaluated in the pumping test. The transmissivity can then be calculated at any other site of the same aquifer using the relation T_mrs = C_TF. The C_T values reported suggest a certain relationship with the lithology, but with a great dispersion and contradictory results. MRS surveys carried out in alluvial aquifers in Spain have shown that the value of C_T evaluated at one site may not be valid at another place of the same aquifer, because of the great heterogeneity of this kind of geological environment. The demand of a pumping test at each site where a MRS is measured invalidates the method actually used for MRS transmissivity evaluation. More than 50 MRS have been used to propose a new methodology. The aquifers visited cover a great range of transmissivities (from 2 × 10^− 6 to 9 × 10^− 3 m²/s). The MRS signal amplitude varies between 20 and 1400 nV, the signal/noise ratio is in the range from 0.6 to 42, and the value of the decay time constant varies from 200 to 800 ms. It has been demonstrated that when the transmissivity increases, the value of F decreases, and C_T increases, except for certain groups of MRS taken at the same aquifer or part of one aquifer, for which F increases with T_pt, keeping C_T constant. A function C_T(F) of the type C_T = mF^− n has been obtained that allows the transmissivity evaluation without the need of T_pt. Considering that both values of transmissivity, T_pt and T_mrs, are subjected to deviations due to the experimental errors as well as due to evaluation errors, the prediction achieved by the proposed equation is rather good. To perform a better evaluation of the values of the coefficients m and n it is necessary to have a greater number of MR soundings of good quality and with a trustworthy inversion at locations where a really comparable and good performed pumping test is available, covering a sufficient range of transmissivities. Though the data we have used do not always fulfil these conditions, the result is promising. Once a trustable function is available, the forecast of the transmissivity using MRS will not need the existence of any pumping test in the area. The general extension of this methodology demands the availability of MRS taken at all kinds of geological and hydrogeological environments, which is impossible without the existence of a universal MRS data base.  相似文献   

银川台石英摆倾斜仪格值变化的分析     

李国斌 《高原地震》2008,20(2):26-29

对银川台所使用的SQ－70型石英摆倾斜仪的格值变化作了较深入的分析。一年中该台南北向格值平均变化0．160×10^-3″／mm,东西向格值平均变化0．133×10^-3″／mm,2个测向的格值变化与其倾斜量、洞体室温之间存在显著相关性。同时还将格值变化对γ值的影响作了分析。  相似文献   

智利高地震烈度区高压瓷瓶隔离开关的高等级抗震考核试验     

王军丽  吉堂付  翁萱  杨辉  朱云龙 《震灾防御技术》2019,14(2):314-327

为获取户外高压隔离开关的动态特性、研究瓷瓶破断力与地震载荷的关系以及验证隔离开关的抗震性能,开展了相关的考核试验。依据IEEE 693—2005标准的要求,试验前进行了应变计的校准试验、瓷瓶的弯曲破断试验和隔离开关的抗震性能试验。经过抗震试验,隔离开关完好无损且在抗震试验前后其共振频率变化不大,瓷瓶破断力大于地震载荷的2倍。结果表明隔离开关结构稳定,通过了抗震考核。  相似文献   

四分量钻孔应变观测的实地绝对标定   总被引：17，自引：1，他引：16  

邱泽华  石耀霖  欧阳祖熙 《地震》2005,25(3):27-34

钻孔应变观测的实地标定问题有二层涵义: 在第一个层面上, 可以认为实地标定是相对室内标定而言的, 是对仪器(元件)灵敏度的标定, 称为相对标定; 在第二个层面上, 由测值换算出孔径相对变化以后, 还要利用理论固体潮等依据对与钻孔周围介质的弹性有关的参数进行标定, 从而给出应变变化, 称为绝对标定。 文中提出了四分量钻孔应变观测的绝对标定的新方法, 并以昌平台RZB-1型钻孔应变观测为例进行实际应用, 取得了相当好的结果。  相似文献   

Radiometric calibration of small-footprint full-waveform airborne laser scanner measurements: Basic physical concepts   总被引：4，自引：0，他引：4  

Wolfgang Wagner   《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(6):505-513

  相似文献   

Sustainable management of Mogan and Eymir Lakes in Central Turkey   总被引：2，自引：0，他引：2  

Ozlem Yagbasan  Hasan Yazicigil 《Environmental Geology》2009,56(6):1029-1040

Mogan and Eymir Lakes, located 20 km south of Ankara in Central Turkey, are important aesthetic, recreational, and ecological resources. Dikilitas and Ikizce reservoirs, constructed on upstream surface waters, are two man-made structures in the basin encompassing an area of 985 km². The purpose of this study is to quantify groundwater components in lakes’ budgets and to assess the potential impacts of upstream reservoirs on lake levels for sustainable management of the system. Available data have been used to develop a conceptual model of the system. A three-dimensional groundwater model, incorporating a lake component, has been developed for the system. The model has been calibrated successfully under transient conditions over a period of 6 years using monthly periods. The results show that groundwater inflows and outflows have the lowest contribution to the overall lakes’ budget. The model has been subsequently used to evaluate the impacts of upstream reservoirs. The results show that these reservoirs have a significant effect on lake stages but not on groundwater levels. A trade-off curve between the quantum of water released and the average stage in Lake Mogan has been developed to enhance decision makers’ ability for sustainable management of the system in the long term.  相似文献   

An approach to the radiometric aerotriangulation of photogrammetric images     

David Hernández López  Beatriz Felipe García  José González Piqueras  Guillermo Villa Alcázar 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):883-893

Harnessing the radiometric information provided by photogrammetric flights could be useful in increasing the thematic applications of aerial images. The aim of this paper is to improve relative and absolute homogenization in aerial images by applying atmospheric correction and treatment of bidirectional effects. We propose combining remote sensing methodologies based on radiative transfer models and photogrammetry models, taking into account the three-dimensional geometry of the images (external orientation and Digital Elevation Model). The photogrammetric flight was done with a Z/I Digital Mapping Camera (DMC) with a Ground Sample Distance (GSD) of 45 cm. Spectral field data were acquired by defining radiometric control points in order to apply atmospheric correction models, obtaining calibration parameters from the camera and surface reflectance images. Kernel-driven models were applied to correct the anisotropy caused by the bidirectional reflectance distribution function (BRDF) of surfaces viewed under large observation angles with constant illumination, using the overlapping area between images and the establishment of radiometric tie points. Two case studies were used: 8-bit images with applied Lookup Tables (LUTs) resulting from the conventional photogrammetric workflow for BRDF studies and original 12-bit images (Low Resolution Color, LRC) for the correction of atmospheric and bidirectional effects. The proposed methodology shows promising results in the different phases of the process. The geometric kernel that shows the best performance is the Lidense kernel. The homogenization factor in 8-bit images ranged from 6% to 25% relative to the range of digital numbers (0–255), and from 18% to 35% relative to levels of reflectance (0–100) in the 12-bit images, representing a relative improvement of approximately 1–30%, depending on the band analyzed.  相似文献   

Pre-processing of a sample of multi-scene and multi-date Landsat imagery used to monitor forest cover changes over the tropics   总被引：1，自引：0，他引：1  

Catherine BodartHugh Eva  René Beuchle  Rastislav RašiDario Simonetti  Hans-Jürgen StibigAndreas Brink  Erik LindquistFrédéric Achard 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):555-563

In support to the Remote Sensing Survey of the global Forest Resource Assessment 2010, the TREES-3 project has processed more than 12,000 Landsat TM and ETM+ data subsets systematically distributed over the tropics. The project aims at deriving area estimates of tropical forest cover change for the periods 1990-2000-2005. The paper presents the pre-processing steps applied in an operational and robust manner to this large amount of multi-date and multi-scene imagery: conversion to top-of-atmosphere reflectance, cloud and cloud shadow detection, haze correction and image radiometric normalization. The results show that the haze correction algorithm has improved the visual appearance of the image and significantly corrected the digital numbers for Landsat visible bands, especially the red band. The impact of the normalization procedures (forest normalization and relative normalization) was assessed on 210 image pairs: in all cases the correlation between the spectral values of the same land cover in both images was improved. The developed automatic pre-processing chain provided a consistent multi-temporal data set across the tropics that will constitute the basis for an automatic object-based supervised classification.  相似文献   

Slingram EMI prospection: Are vertical orientated devices a suitable solution in archaeological and pedological prospection?     

Julien Thiesson  Gabrielle RousselleFrançois Xavier Simon  Alain Tabbagh 《Journal of Applied Geophysics》2011,75(4):731-737

Electromagnetic induction (EMI) is one of the geophysical techniques widely used in soil studies, the slingram devices being held horizontally over the soil surface, i.e. with the coils located at the same height above the ground surface. Our study aims assessing the abilities of slingram devices when held vertically. 1D and 3D modelling have been achieved in order to compare the theoretical responses of vertical devices to the horizontal ones. Some comparative surveys were also undertaken in archaeological contexts to confirm the reliability of theoretical conclusions. Both approaches show that vertical slingram devices are suitable for survey and can constitute an alternative to the usual horizontal orientation. We give a table in Appendix A which contains the calibration coefficient allowing transforming of the values given by some of commercially available devices which would be advantageous to use in vertical orientation  相似文献   

中国东西重力潮汐剖面   总被引：5，自引：0，他引：5       下载免费PDF全文

毛慧琴  许厚泽 《地球物理学报》1989,32(1):62-69

为了检验体潮与海潮的理论模型,分析了中国东西重力潮汐剖面（1981年9月-1985年1月）。同时,为研究LaCoste ET-20和ET-21重力仪的格值系统,建立了一条由17台LaCoste G型和2台LaCoste D型重力仪观测的重力垂直基线。在基线上标定的结果表明,ET-21重力仪的格值大了1％。由标定得到的格值计算剖面上各测站的潮汐因子,经海潮改正后,接近Wahr模型值,振幅因子的残差:O₁波小于0.3μGal,M₂波小于0.4μGal。但是上海和拉萨的观测经海潮改正后,相位迟后有很大的改善,振幅因子却更偏离于模型值,其潮汐异常主要是近海的海潮模型不完善,以及在海潮计算中,所采用的地球模型未考虑地壳与上地幔的横向不均匀性所引起。  相似文献