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1.
MRS applicability for a study of glacial sedimentary aquifers in Central Jutland, Denmark 总被引：6，自引：0，他引：6
Konstantinos Chalikakis Mette Ryom Nielsen Anatoly Legchenko 《Journal of Applied Geophysics》2008,66(3-4):176
Intensive geophysical measurements are currently being carried out in Denmark to comply with the Danish Government's environmental plans of dense hydrogeological mapping to ensure high quality non-treated drinking water supply based solely on groundwater. A MRS-TDEM combined geophysical survey was conducted to measure the applicability and the contribution of MRS to running drilling programs.Despite complicated electromagnetic noise conditions, the MRS method proved to be applicable in the Danish context. An example of the practical application of MRS combined with TDEM in two selected areas of the former County of Vejle in Denmark, demonstrates the efficiency of the technique. The MRS results clearly suggest optimal locations for water supply boreholes within subsurface structures with homogeneous resistivity conditions mapped by TDEM. These results reveal the interest of using MRS as a new geophysical tool for the Danish water supply policy, which can provide a foundation for optimising drilling site locations within areas with resistivities in the aquifer range. However, more MRS soundings need to be carried out in order to improve MRS calibration in the Danish context, which will allow quantitative MRS characterization of aquifers. 相似文献
2.
《Journal of Applied Geophysics》2009,67(3-4):176-187
Intensive geophysical measurements are currently being carried out in Denmark to comply with the Danish Government's environmental plans of dense hydrogeological mapping to ensure high quality non-treated drinking water supply based solely on groundwater. A MRS-TDEM combined geophysical survey was conducted to measure the applicability and the contribution of MRS to running drilling programs.Despite complicated electromagnetic noise conditions, the MRS method proved to be applicable in the Danish context. An example of the practical application of MRS combined with TDEM in two selected areas of the former County of Vejle in Denmark, demonstrates the efficiency of the technique. The MRS results clearly suggest optimal locations for water supply boreholes within subsurface structures with homogeneous resistivity conditions mapped by TDEM. These results reveal the interest of using MRS as a new geophysical tool for the Danish water supply policy, which can provide a foundation for optimising drilling site locations within areas with resistivities in the aquifer range. However, more MRS soundings need to be carried out in order to improve MRS calibration in the Danish context, which will allow quantitative MRS characterization of aquifers. 相似文献
3.
Magnetic resonance sounding applied to aquifer characterization 总被引：3，自引：0，他引：3
Legchenko A Baltassat JM Bobachev A Martin C Robain H Vouillamoz JM 《Ground water》2004,42(3):363-373
Magnetic resonance sounding (MRS) is distinguished from other geophysical tools used for ground water investigation by the fact that it measures a magnetic resonance signal generated directly from subsurface water molecules. An alternating current pulse energizes a wire loop on the ground surface and the MRS signal is generated; subsurface water is indicated, with a high degree of reliability, by nonzero amplitude readings. Measurements with varied pulse magnitudes then reveal the depth and thickness of water saturated layers. The hydraulic conductivity of aquifers can also be estimated using boreholes for calibration. MRS can be used for both predicting the yield of water supply wells and for interpolation between boreholes, thereby reducing the number of holes required for hydrogeological modeling. An example of the practical application of MRS combined with two-dimensional electrical imaging, in the Kerbernez and Kerien catchments area of France, demonstrates the efficiency of the technique. 相似文献
4.
David C. Nobes 《Surveys in Geophysics》1996,17(4):393-454
The relatively new subdiscipline of environmental geophysics has grown enormously in the last five years. The size and diversity of the field, and the associated literature, is such that it is extremely difficult to keep up with even a small portion of the field. Electrical and electromagnetic (E & EM) methods, including ground penetrating radar and time-domain reflectometry, play a central role in environmental geophysics. One reason for the utility of E & EM methods in groundwater studies is the similarity in the way that current flow and fluid flow depend on the connectivity and geometry of the pores in soils and rocks. Another reason is the influence of the pore water quality on the geophysical response. More than any other geophysical technique, E & EM methods are directly affected by the presence of conductive pore fluids in the subsurface, such as leachates from landfill sites and sea water invading a coastal groundwater supply that has been placed under stress because of population expansion. The chloride ion is one of the most electrically active of the naturally-occurring ions, and allows us to detect sea water incursion; leachates from landfill sites contain the by-products of organic decay, such as acetic acid, which are generally less conductive than chloride, but nonetheless enhance the pore water and formation electrical conductivities. Landfill leachate plumes are thus easily mapped. The shallow subsurface electrical and dielectric properties exhibit hysteresis due to seasonal changes in water content; the physical properties will be different for the same degree of saturation, depending on whether the water level is rising or falling. Topographic effects are also important; an empirical correction method works well to remove a background trend in the conductivity due to changes in elevation. Heterogeneity and anisotropy of the electric properties may be related to similar effects in the hydraulic properties. New technology and the adaptation of existing technology has lead to the development of fresh instruments, such as electrode arrays towed across the ground, resistivity logging while drilling, fast-rise time TEM, NMR combined with TEM, electric quadripole, et cetera. The applications of E & EM methods cover a wide range of geographic areas and groundwater problems, but have had particularly wide use for groundwater exploration in arid and semi-arid regions, for mapping and monitoring salt-water incursion in susceptible aquifers, and for mapping and monitoring contaminants. 相似文献
5.
The Neogene marine sedimentary rock area in the eastern marginal region of the Japan Sea is an area with some of the highest landslide densities in Japan. Some of the landslides in this area have been known to involve saline groundwater, which can be the cause of these landslides. In order to demonstrate the relationships between landslides and saline water, topographic, geological, groundwater, and electromagnetic surveys were performed in the eastern marginal region of the Japan Sea. Many landslides and gravitational slope deformations with linear depressions and small scarps were recognized in the study area. The resistivity profile obtained by an electromagnetic survey suggests that there is a wide zonal distribution of saline water with salt concentrations equivalent to seawater at depths of 50–100 m or more and that the groundwater shallower than 50 m has an electrical conductivity of less than 100 mS/m. The shallow resistive groundwater is inferred to be meteoric water that replaced the saline groundwater, which likely weakened the bedrock, resulting in landslides. A ridge of competent tuff overlying mudstone has many linear depressions from gravitational slope deformation and low‐resistivity water to a depth of 600 m, which suggests that the mudstone was weakened by water replacement and deformed under the tuff caprock. The saline groundwater is inferred to be fossil seawater trapped in pores during sediment deposition, which is brought near the ground surface along with rocks by tectonic movement in the hills. Thus, the saline water and its fresh water replacement are among the important basic causes of the landslides. The oil well data obtained in the eastern marginal region of the Japan Sea suggest that such saline water replacement has occurred widely and that replacement is likely one of the predispositions for the frequent landslides there. 相似文献
6.
New methods for obtaining and quantifying spatially distributed subsurface moisture are a high research priority in process hydrology. We use simple linear regression analyses to compare terrain electrical conductivity measurements (EC) derived from multiple electromagnetic induction (EMI) frequencies to a distributed grid of water‐table depth and soil‐moisture measurements in a highly instrumented 50 by 50 m hillslope in Putnam County, New York. Two null hypotheses were tested: H0(1), there is no relationship between water table depth and EC; H0(2), there is no relationship between soil moisture levels and EC. We reject both these hypotheses. Regression analysis indicates that EC measurements from the low frequency EM31 meter with a vertical dipole orientation could explain over 80% of the variation in water‐table depth across the test hillslope. Despite zeroing and sensitivity problems encountered with the high frequency EM38, EC measurements could explain over 70% of the gravimetrically determined soil‐moisture variance. The use of simple moisture retrieval algorithms, which combined EC measurements from the EM31 and EM38 meters in both their vertical and horizontal orientations, helped increase the r2 coefficients slightly. This first hillslope hydrological analysis of EMI technology in this way suggests that it may be a promising method for the collection of a large number of distributed soilwater and groundwater depth measurements with a reasonable degree of accuracy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
The use of electrical methods for estimating spatial patterns of groundwater recharge was evaluated at a field site in southeastern Australia. Here, recharge increased from less than 0.2 mm year−1 under native Eucalyptus vegetation, to between 1 and 14 mm year−1 under dryland agriculture. This increase in recharge results in progressive leaching of salts in the soil profile. Differences in recharge can be estimated from differences in depth of leaching. The estimated recharge rates are correlated with soil texture, with higher recharge rates generally occurring through sandier soils. The relationships of recharge to salt content and soil texture both contribute to lower apparent electrical conductivities for higher recharge rates.
The effect of recharge rate on measured apparent electrical conductivities was modelled for various geophysical devices (including frequency-domain (FEM) and time-domain (TEM) electromagnetic instruments and direct current resistivity). The soil-texture effect was shown to have a greater effect than the solute leaching effect in determining the correlation between recharge and apparent electrical conductivity. Analysis of sensitivity to geological noise showed that variations in soil type below 2 m could disguise any correlation.
Correlations between recharge rate, measured at core sites from chloride tracer techniques, and apparent electrical conductivity, measured with FEM electromagnetic devices, supported the conclusions of the model. For DC resistivity and TEM methods, correlations between recharge and apparent electrical conductivity were not significant, although for resistivity this may be due partly to the small number of measurements made. The FEM device most sensitive to variations in recharge had an operating frequency of 9.8 kHz. At lower frequencies the sensitivity is reduced, as the instruments are sensing too deeply. The poor correlations for TEM, as compared with FEM, are due probably to the relatively deeper penetration of the TEM instrument used in the study, rather than any inherent differences between the techniques.
Because the major reason for the correlation between recharge and apparent electrical conductivity is soil texture, in this area the geophysical devices are mostly mapping soil type. 相似文献
8.
Inversion of resistivity in Magnetic Resonance Sounding 总被引：3，自引：0，他引：3
Magnetic Resonance Sounding (MRS, or Surface Nuclear Magnetic Resonance - SNMR) is used for groundwater exploration and aquifer characterization. Since this is an electromagnetic method, the excitation magnetic field depends on the resistivity of the subsurface. Therefore, the resistivity has to be taken into account in the inversion: either as a priori information or as an inversion parameter during the inversion process, as introduced in the presented paper. Studies with synthetic data show that water content and resistivity can be resolved for a low resistive aquifer even using only the amplitude of the MRS signal. However, the inversion result can be significantly improved using amplitude and phase of the MRS signal. The successful implementation of the inversion for field data shows that the resistivities derived from MRS are comparable to those from conventional geoelectric methods such as DC resistivity and transient electromagnetic. By having information about both the resistivity and the water content, MRS inversions give information about the quality of the water in the aquifer. This is of utmost interest in hydrogeological studies as this specific information cannot be determined solely by geoelectric measurements, due to the nonunique dependence of resistivity on water content and salinity. 相似文献
9.
10.
《Journal of Applied Geophysics》2007,61(2):142-154
The productivity and the water quality of coastal aquifers can be highly heterogeneous in a complex environment. The characterization of these aquifers can be improved by hydrogeological and complementary geophysical surveys. Such an integrated approach is developed in a non-consolidated coastal aquifer in Myanmar (previously named Burma).A preliminary hydrogeological survey is conducted to know better the targeted aquifers. Then, 25 sites are selected to characterize aquifers through borehole drillings and pumping tests implementation. In the same sites, magnetic resonance soundings (MRS) and vertical electrical soundings (VES) are carried out. Geophysical results are compared to hydrogeological data, and geophysical parameters are used to characterize aquifers using conversion equations. Finally, combining the analysis of technical and economical impacts of geophysics, a methodology is proposed to characterize non-consolidated coastal aquifers.Depth and thickness of saturated zone is determined by means of MRS in 68% of the sites (evaluated with 34 soundings). The average accuracy of confined storativity estimated with MRS is ± 6% (evaluated over 7 pumping tests) whereas the average accuracy of transmissivity estimation with MRS is ± 45% (evaluated using 15 pumping tests). To reduce uncertainty in VES interpretation, the aquifer geometry estimated with MRS is used as a fixed parameter in VES inversion. The accuracy of groundwater electrical conductivity evaluation from 15 VES is enough to estimate the risk of water salinity. In addition, the maximum depth of penetration of the MRS depends on the rocks' electrical resistivity and is between 20 and 80 m at the study area. 相似文献
11.
大地电阻率分布信息是影响磁共振地下水探测反演结果准确性的重要因素.在众多电磁法勘探技术中,瞬变电磁法具有高分辨率、高效率和大探测深度等优势,能准确探测地下几百米范围内的电阻率分布信息.因此磁共振与瞬变电磁联合解释方法具有重要意义.然而,利用单一测点拼接的磁共振与瞬变电磁联合解释方法进行模拟二维反演时存在解释结果不唯一,容易出现错误异常体等问题,尤其在复杂地质情况下,同一测线上相邻测点探测结果连续性差,解释结果偏离实际.基于此,本文提出磁共振与瞬变电磁横向约束联合反演方法（Laterally Constrained Inversion,简称LCI）,重点引入外推积分法（quadrature with extrapolation,简称QWE）,解决了传统正演过程中基于直接数值积分方法引起的求解效率低的问题,保证了联合反演方法的顺利实施,进而以相邻测点地下结构应具备连续性为依据,引入横向约束反演思想,通过在联合反演目标函数中加入相邻测点间各模型参数约束矩阵,提高磁共振解释结果准确性,加强探测剖面地质结构和含水模型连续性.经过理论模型证实,本文提出的LCI方法能有效提高传统一维反演结果的稳定性和唯一性.最后,对安徽黄山野外实际探测数据进行横向约束联合反演,验证了磁共振与瞬变电磁LCI联合反演方法的实用性.本文的研究成果将为磁共振与瞬变电磁空间约束联合反演奠定基础. 相似文献
12.
Hydrogeological investigations were carried out in an arid area of Inner-Mongolia to determine the locations of future water supply resources. The first geophysical survey was conducted near Baiqi to identify favorable boreholes using magnetic resonance sounding (MRS). The yield capacities of 43 sites were investigated, and the extent of the potential groundwater storage was determined. Previous studies have indicated that a major tectonic structure may have a significant impact on the groundwater flow and well yield in the study area. Therefore, high-resolution seismic surveys were applied in the second stage of the investigation to determine the fault locations. After the regional identification, a major structure was investigated in detail to map the fracture patterns. Based on the assumption that the hydraulic conductivity of this formation is similar along the entire strike of the fracture, we proposed drilling a borehole (BQ3) in the zone. However, this well has a yield of only 0.8 L/s, falling short of the required flow rate of 3.0 L/s. Therefore, the objective of the final stage of exploration was to accurately define the attitude and extension of the aquifer and to select a more favorable borehole site that would meet the required water flow rate. The geophysical exploration was carried out using time-domain electromagnetic (TDEM) and MRS methods. The MRS results suggest optimal locations for water supply boreholes within the subsurface structures mapped by the TDEM inversion method. The data obtained by drilling and coring are in agreement with the predicted aquifer thickness from the TDEM data. Pumping tests indicate that the water discharge of borehole BQ4 was 3.5 L/s. Our results demonstrate that the delineation of the groundwater body using a combined application of three geophysical methods (the MRS, TDEM and 2D seismic methods) was successful. 相似文献
13.
Direct and indirect methods for groundwater investigations: A case-study of MRS and VES in the southern part of Sweden 总被引：1，自引：0，他引：1
Magnetic Resonance Sounding (MRS) has been successfully tested for detecting groundwater in two areas in southern Sweden. Measurements of Schlumberger VES have been conducted in the same place as the MRS and the results are generally consistent. Low resistivity layers interpreted as clay are sometimes identified close to the surface. The MRS result in site 2 is a good example of signals penetrating through the clay and deeper aquifer still being detected. The MRS data suggest aquifers that are not only hosted in soft sediment materials (moraine, sand, and mixed materials), but hosted in basement rocks. Based on the MRS and borehole pumping test data, the results agree with yield, average water content and subsurface geological data. 相似文献
14.
Measurements of electrical resistivity have long been used to find freshwater resources below the earth's surface. Recently, offshore resistivity and electromagnetic techniques have been used to map occurrences of submarine groundwater originating from the offshore extension of terrestrial aquifers. In many cases, observations of a high resistivity (low conductivity) anomaly in the seafloor are sufficient to suggest the presence of fresh (and less conductive) pore waters. Data from offshore Wrightsville Beach, NC show highly variable resistivity structure, with moderately high resistivity at depths of ～20 m subsurface that is at least in part caused by lithologic complexity in an underlying limestone unit, the Castle Hayne. These offshore results suggest caution in the interpretation of resistivity anomalies simply in terms of groundwater volumes. In contrast, low onshore resistivities show evidence for intrusion of saltwater into the subsurface beneath the beach, adjacent to areas of pumping for water supply. 相似文献
15.
16.
磁共振地下水探测(MRS)技术能直接测量水中氢质子的拉莫尔进动,可表征地下水含水量和介质孔隙度等信息,因而获得了广泛应用.然而,MRS信号微弱,实际探测中电磁噪声强度大,若噪声未被有效去除,会导致后续水文参数解释不准确,采用“8”字形线圈或运用带参考线圈的噪声抵消等方法可抑制噪声干扰,但这些方法消噪效果的好坏取决于电磁噪声的空间分布.另外,在强噪声或多噪声源环境下应用MRS方法,选择恰当的探测位置对提高探测效率以及增加探测结果的有效性具有重要意义.因此,本文使用双通道噪声采集装置在实验前记录环境中的电磁噪声,通过双通道参考技术推导同一时刻不同测点的噪声强度,再得到测区电磁噪声分布结果,该噪声分布情况对MRS方法探测方式的选取具有指导性的作用.同时,可根据噪声分布情况为探测线圈选择最佳测点以避开噪声强度大的区域,进而提高采集信号的信噪比.最后,通过采集室外环境下的电磁噪声,验证本文提出的基于双通道参考技术的电磁噪声分布规律研究方法的有效性,为可靠高效地开展磁共振地下水探测提供了新的技术手段. 相似文献
17.
J. DUROUX 《Geophysical Prospecting》1967,15(4):564-583
The electromagnetic field radiated from a magnetic dipole lying on the ground is considered, in the extremely low frequency range (DC to 20 000 Hertz). Theoretical and experimental data are given on the characteristics of the surface wave (vanishing wave) generated at the air-ground interface, in the case of an homogeneous subsurface. The case of a subsurface with electrical resistivity varying with depth is considered. It is shown how the above-mentioned characteristics may be applied in the quantitative investigation of the electrical resistivity of the subsurface as a function of depth, in a method using the measurements on the ground of all the components of the radiated field: horizontal electrical components, vertical and horizontal magnetic components. 相似文献
18.
An attempt to resolve non-uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow-up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non-uniqueness in the determination of the depth to fresh/saline groundwater interface to be resolved. 相似文献
19.
Ashley E. Medin Robert L. Parker Steven Constable 《Physics of the Earth and Planetary Interiors》2007,160(1):51-59
We examine the nonlinear inverse problem of electromagnetic induction to recover electrical conductivity. As this is an ill-posed problem based on inaccurate data, there is a critical need to find the reliable features of the models of electrical conductivity. We present a method for obtaining bounds on Earth’s average conductivity that all conductivity profiles must obey. Our method is based completely on optimization theory for an all-at-once approach to inverting frequency-domain electromagnetic data. The forward modeling equations are constraints in an optimization problem solving for the electric fields and the conductivity simultaneously. There is no regularization required to solve the problem. The computational framework easily allows additional inequality constraints to be imposed, allowing us to further narrow the bounds. We draw conclusions from a global geomagnetic depth sounding data set and compare with laboratory results, inferring temperature and water content through published Boltzmann-Arrhenius conductivity models. If the upper mantle is assumed to be volatile free we find it has an average temperature of 1409-1539 ° C. For the top 1000 km of the lower mantle, we find an average temperature of 1849-2008 ° C. These are in agreement with generally accepted mantle temperatures. Our conclusions about water content of the transition zone disagree with previous research. With our bounds on conductivity, we calculate a transition zone consisting entirely of Wadsleyite has <0.27 wt.% water and as we add in a fraction of Ringwoodite, the upper bound on water content decreases proportionally. This water content is less than the 0.4 wt.% water required for melt or pooling at the 410 km seismic discontinuity. 相似文献
20.
Freezing characteristics were investigated for a sedge covered floating fen and spruce covered swamp located beside a shallow lake in the Western Boreal Forest of Canada. Thermal properties were measured in situ for one freeze‐thaw cycle, and for two freeze‐thaw cycles in laboratory columns. Thermal conductivity and liquid water content were related to a range of subsurface temperatures above and below the freezing thresholds, and clearly illustrate hysteresis between the freezing and thawing process. Thermal hysteresis occurs because of the large change in thermal conductivity between water and ice, high water content of the peat, and wide variation in pore sizes that govern ice formation. Field and laboratory results were combined to develop linear freezing functions, which were tested in a heat transfer model. For surface temperature boundary conditions, subsurface temperatures were simulated for the over‐winter period and compared with field measurements. Replication of the transient subsurface thermal regime required that freezing functions transition gradually from thawed to frozen state (spanning the ?0·25 to ?2 °C range) as opposed to a more abrupt step function. Subsurface temperatures indicate that the floating fen underwent complete phase change (from water to ice) and froze to approximately the same depth as lake ice thickness. Therefore, the floating fen peatland froze as a ‘shelf’ adjacent to the lake, whereas the spruce covered swamp had a higher capacity for thermal buffering, and subsurface freezing was both more gradual and limited in depth. These thermal properties, and the timing and duration of frozen state, are expected to control the interaction of water and nutrients between surface water and groundwater, which will be affected by changes in air temperature associated with global climate change. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献