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Near Surface Geoscience 2012 – 18th European Meeting of Environmental and Engineering Geophysics
- Conference date: 03 Sep 2012 - 05 Sep 2012
- Location: Paris, France
- ISBN: 978-90-73834-34-7
- Published: 03 September 2012
61 - 80 of 194 results
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Evaluation of the GPR Effectiveness from the Results of Measurement of Dielectric Properties of Soils
Authors Z.B. Khakiev, K.Y. Kislitca, Z.B. Khakiev and V.A. YavnaThe work considers the depth evaluation of Ground Penetrating Radar (GPR) surveys using the attenuation factor of electromagnetic radiation in a medium. A method of determining the attenuation factor of low-conductive non-magnetic soils is developed based on the results of direct measurements of permittivity and conductivity of soils in the range of frequencies used in the practice of GPR. The method relies on measuring the shift and width of the resonance line after a soil sample is placed into a tunable cavity resonator. The advantage of this method is the preservation of soil structure during the measurement.
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GPR Method for Determining the Electrical Properties of Soils
Authors Z.B. Khakiev, A.V. Morozov, V.L. Shapovalov and V.A. YavnaThe paper studies the possibility of quantitative processing the GPR data obtained in a laboratory, and determining the dielectric permittivity and conductivity of a medium. Experimental studies are made using radargrams of soil samples with specified values of moisture and conductivity. The methods of quantitative processing of radargrams are proposed to determine dielectric permittivity and conductivity of soils. The results of theoretical studies and experimental measurements are in good agreement and presented in the paper.
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Geophysical Investigations of Early Middle-ages Turkic Fortresses
Authors S.A. Erokhin, I. Modin, A. Pavlova and M. KatsThe investigation of early middle-ages Turkic sites Is a very complicated task because of the shortage of written sources, huge amount of archaeological excavations needed and the low contrast between the physical properties of buildings and virgin layer. The paper presents the capabilities of integrated geophysical researches for the investigation of early middle-ages Turkic sites. The paper describes the investigations of mud brick-made Djankent site (Kyzyl-Orda region, Kazahstan) and Semikarakorsk site (Rostov region, Russia). The results of integrated geophysical surveys enable to determine the planning of the site, the construction of buildings made of filled soil and mud brick, and to achieve valuable information for historical and paleogeographic reconstructions.
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Use of Geophysics Methods to Characterize the Hydrology of Assateague Island National Seashore, Worcester County, Maryland
Authors C. Johnson, J. Masterson, E. White, E. Voytek, P. Joeston, B. Fleming and J. LaneA suite of borehole and surface geophysical methods was used to characterize the lithology and salinity of the subsurface of Assateague Island, a barrier island on the Atlantic Coast of Maryland and Virginia. The U.S. Geological Survey, as part of its Climate and Land Use Change Research and Development Program, is conducting a multi-year investigation to assess potential impacts to the natural resources of Assateague Island National Seashore that may result from changes in the hydrologic system in response to projected sea-level rise. The geophysical data collected as part of the characterization phase of this investigation will serve as the foundation for development of numerical groundwater-flow models to assess the potential effects of climate change on the coastal groundwater system of Assateague Island. Geophysical data were collected along five transects across the island. Methods used included borehole electromagnetic induction and gamma, and surface time-domain electromagnetics, frequency-domain electromagnetics, ground-penetrating radar, and coupled-capacitance resistivity. Two of the transects were in areas subjected to frequent and periodic overland wash and two of the transects were in the oldest, most stable part of the island where there is no overland wash. Based on an integrated interpretation of the geophysical data, it was concluded that the geophysical methods used are effective for determining the following: approximate location of the freshwater/salt-water interface, the distribution of fresh and brackish water in the shallow aquifer, the geometry of the fresh groundwater lens beneath the island, and the distribution and thickness of fine-grained lagoonal and peat deposits in the subsurface throughout the Island.
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ALIS - GPR 3-D Imaging for Humanitarian Demining
Authors M. Sato, K. Takahashi and Y. YokotaMore than 10 years has passed since the Ottawa Treaty or the Anti-personnel Mine Ban Treaty became effective in 1997, humanitarian demining is still important and unsolved problems in may mine affected courtiers. Antipersonnel mines have been left buried in many of regions where conflicts have occurred, and after many years, the land has to be returned to the local people.
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Gravity-measured Water Storage Change and Subsurface Hydraulic Properties at a Managed Recharge Facility in Tuscon, AZ, USA
Authors J. Kennedy, B. Creutzfeldt, T. Ferre and A. GuntnerThe storage of subsurface water is central to Arizona’s future sustainable water supplies. Presently large amounts of water delivered from the Colorado River by Central Arizona Project canals (over 400,000 acre-feet/year permitted capacity) are stored underground at artificial recharge facilities to augment future water supplies. As the demand for Colorado River water increases and the energy required to transport, store, and recover this water becomes more costly, the importance of proper management and siting of recharge facilities increases. In this study, we combine different gravimeters (superconducting, absolute, and spring gravimeters) and advanced analysis methods to improve monitoring of subsurface storage and the characterization of subsurface hydraulic properties at Tucson Water’s Southern Avra Valley Storage and Recovery Project (SAVSARP) infiltration basins. Waterstorage changes will be monitored continuously with two iGrav™ superconducting gravimeters. These observations will be supported by time-lapse monitoring of spatial gravity variations with an A-10 absolute gravimeter and spring gravimeters. We will test novel approaches to gravity monitoring network design that make intelligent use of different gravimeter types for hydrological applications. These data will be analyzed in a coupled hydrogeophysical inverse framework to estimate groundwater-storage changes and to constrain effective hydraulic properties at the field scale. Here we will present the study concept, preliminary measurements, and modelling results.
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A Novel Surface NMR Pulse Sequence for Improved Estimation of Longitudinal T1 Relaxation Times
Authors E. Grunewald and D. WalshObtaining estimates of permeability from NMR methods requires the ability to measure relaxation time parameters that are most sensitive to pore geometry. While surface-NMR (SNMR) measurements can reliably quantify the effective transverse relaxation time T2*, transverse relaxation times are sometimes dominated by the influence of magnetic geology. The longitudinal relaxation time T1 is known to provide a more robust link to pore geometry, but previous attempts to measure T1 by SNMR, have shown mixed success due to fundamental limitations the commonly applied “pseudo-saturation recovery” (PSR)experiment. Recognizing a need for improved measurements, we have developed a new paradigm of experiments for quantifying T1, which we refer to as the “crush recovery” (CR)sequence. The CR sequence utilizes two pulses: a first pulse of fixed amplitude and a second smaller pulse with an amplitude that is varied between measurements. The first pulse of the CR sequence is not intended to generate saturation with 90 degree tip angles, as in the PSR sequence; rather, the initial pulse acts to crush or decoherently scatter the magnetization orientation, leaving an effectively saturated condition of zero net longitudinal magnetization over a range of shallow to intermediate depths. A second pulse, applied after a short delay, is then used to probe the magnetization that recovers by T1 between the two pulses. The amplitude of the second pulse is varied to provide depth resolution of T1 recovery within the “crushed” zone. Fixing the amplitude of the initial pulse provides constant initial conditions, such that the data measured after the second pulse can be inverted using the standard SNMR imaging kernel. Inversion of a CR dataset for a single delay time yields depth-separated free induction decay signals where the amplitude of the signal components are linearly weighted by the observed T1 recovery at each depth. Given a complete set of CR data acquired with multiple delay times, the inversion provides estimates of both T1 and T2* as a function of depth. Further, the covariance of the observed signal with T2* and T1, provides the opportunity to estimate a two-dimensional distributions of T2* versus T1 at each depth. We illustrate the success and advantages of this new approach though a combination of synthetic and real field data examples.
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Mapping Seismically Masked Seabed Structures with a New DC Resistivity Streamer
More LessWe developed an underwater electromagnetic-based streamer to image the near-shore marine substratum. The system was tested to assess its feasibility to map the electrical resistivity of the near-surface geological seabed. The results are very encouraging to characterise heterogeneities in areas with seismic masks. We present results in two regions, one with submerged karstic structures and the other with shallow free gas
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A Bayesian-based Methodology to Detect Suspicious Electrodes for Long-term Permanent ERT Monitoring Experiments
Authors J. Deceuster, O. Kaufmann and M. Van CampDuring long-term ERT monitoring experiments, the data quality may reveal time-dependent mainly due to changes in galvanic contact resistance between buried electrodes and soil. Identifying suspicious electrodes in a permanent spread is of major importance as a faulty electrode may affect the quality of tens to hundreds of measurements on each time-slice. An automated methodology was developed to detect suspicious electrodes based on a Bayesian approach. This methodology allows pointing out faulty electrodes based on the analyses of temporal sets of measurements, each one containing multiple electrode arrays. Standard and studentized estimators of the influence of each electrode in the global data quality are computed for each time-slice based on the measurement quality factor Q given as a coefficient of variation of repeated measures. The automated detection of faulty electrodes is obtained by comparing the computed studentized estimators to values expected when every electrode can be considered as good for the given data set. These expected values are computed by Monte Carlo simulations using a distribution of Q factor values of quadripoles selected as good based on reciprocal errors. The efficiency of the proposed methodology is assessed on a field experiment.
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A Method to Detect Displacements of Borehole Electrodes through Electrical Resistivity Tomography
Authors P. Tsourlos, I. Giannakis, N. Papadopoulos and A. GiannopoulosIn this work a new geophysical methodology is presented which is able to detect any displacements of buried electrodes that are permanently installed in boreholes. These displacements can seriously affect the quality of the measurements and the subsequent resistivity inversion image. The exact knowledge of the electrode displacements will either help in correcting the electrode coordinates and the geometric factors of the measurements associated with these electrodes or just to reject all corresponding erroneous measurements. During this method pole-pole type measurements are conducted, where the current is injected in every buried electrode in the borehole and the potential is measured on a number of electrodes that are spread out along a line on the ground surface. A finite-difference least-squares non-linear inversion algorithm with damping constraints has been developed in an effort to recover the accurate coordinates of the borehole electrodes. Although a priori resistivity model resulted by a surface ERT or by any other geological and geophysical information can be used to constrain the optimization algorithm it is also shown that that the lack of this knowledge does not affect the resulting electrode positioning. The validity and effectiveness of the approach was tested through synthetic modeling and real data.
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Optimizing Surface-to-tunnel ERT Measurements
Authors K. Simyrdanis, P. Tsourlos, P. Soupios and J.H. KimThe applicability of tunnel-to-surface electrical resistance tomography (ERT) measurements for imaging subsurface targets is studied in this work. Various issues of this special arrangement are discussed and explored by means of synthetic, simulation tank and real data examples. In particular different electrode arrays including experimentally chooses optimum ones are examined and compared for various targets. Further, the significance of the tunnel effect as well as the accuracy of the electrode positioning in relation to the measured arrays is examined. Ways for taking tunnel effect as well as electrode positioning errors into account while selecting optimum electrode arrays are proposed.
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Data Quality Quantification for Time Domain IP Data Acquired at a Former Waste Deposit in Lund
Authors T. Dahlin and T. SandströmTests were done measuring resistivity and time domain induced polarisation using standard multi-core cable spreads and a special layout with separate cable spreads for transmitting current and measuring potentials. For both types of cables spreads both normal and reciprocal measurements were done in order to estimate the measurement errors. The tests were done on a former landfill in Lund in Sweden. The electrode contact was favourable with resistances of some hundred ohm. The results gave low average error levels for both types of cable spreads, but the single cable spread showed a larger variation with more scatter in the IP data. Data for both types of spreads gave very consistent models that delineate the lateral distribution of waste as well as the contaminant leachate flow path. The results agree well with observations of contaminant outflow and test pit results. It is concluded that the standard approach with a single cable spread is adequate for a site with favourable characteristics as the one studied here.
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Determining Background Variations to Identify Significant Changes in Resistivity and IP for Time-lapse Experiments
Authors A. Etienne, J. Deceuster and O. KaufmannElectrical Resistivity Tomography conducted in time-lapse mode is frequently used for the monitoring of time-varying processes. Nevertheless, it is tricky to identify significant changes in resistivity and chargeability when monitored processes vary slowly in time. Moreover, the errors on acquired measurement might not be negligible as well as the uncertainties on the blocks of the reconstructed models. The uncertainty distribution depends especially on selected arrays, resistivity and chargeability distributions and model blocks sensitivities. An estimate of the background variations for every block of the models is thus required prior to the mapping of resistivity and IP changes during the monitoring experiment. A new methodology is proposed to estimate these background variations and to point out significant changes in resistivity and chargeability. This methodology is based on a two steps approach. The first step consists in determining a sensitivity cut-off value to estimate the depth of investigation. The second step aims to estimate resistivity and chargeability confidence intervals of each model block based on Monte-Carlo simulations. This methodology was applied to a field monitoring experiment conducted on a site contaminated with chlorinated solvents where biodegradation remediation is performed to assess its efficiency.
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Simultaneous Mapping of the Soil Electrical Conductivity and Dielectric Permittivity using a Medium Frequency EM Device
Authors P. Kessouri, S. Buvat and A. TabbaghElectrical conductivity and dielectric permittivity are two useful tools to characterize the soil state parameters such as its water or clay content. A new EM device working in the medium frequency range has been developed to simultaneously measure these parameters. The prototype, working between 1 and 5 MHz with an inter-coil spacing of 1.2m has been tested on a clay loam plot at INRA Estrée-Mons (ORE-ACBB) during the spring dry period. As only half of the plot was covered with growing wheat, significant water content variations were expected. The prototype detected these variations and electrical conductivity and dielectric permittivity were mapped. These first results are in good agreement with the spatial distribution observed by d.c. electrical profiling and by mass water content direct measurements.
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Application Results of Compact EM Tool at the Geoelectric Test Site of Institute of Petroleum Geology and Geophysics
By E.V. BalkovA geoelectric prospecting test site was constructed within the area of Kluchi geophysical station (Novosibirsk, IPGG SB RAS). The aim of the test site is to study resolution of the near surface geophysical equipment and to improve methodical base of field works. The ten squares of 100 m2 were used test site design, in which 33 targets simulating various real objects were organized. The following objects were laid down: plastic and metal pipes with different length and diameter, aluminum flasks, plastic jerry cans, etc. In the course of our work the distinctive features of every measured component of the signal were identified. Various targets are identified either in real or imaginary components of the signal. The imaginary component describes the position of the test object more clearly. The phase of signal appears to be an efficient way to display the field data. Targets with different shapes and depths can appear as form of one to five images. It can lead to difficulties connected with the interpretation of this material without prior accumulated methodical information.
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Pseudo-3D Characterization of a Geothermal Field through Magneto Telluric
Authors C. Comina, L.V. Socco and A. ManzellaThe use of Magneto Telluric (MT) data for geothermal resource assessment is widely documented in scientific literature. Full 3D inversions are however seldom performed since they are time consuming and provide, in most situations, smoothed models which are not suitable for accurate prospection of local anomalies. To overcome these limitations, an algorithm for the pseudo-3D interpretation of MT data based on a spatially constrained inversion is applied. An application to a real dataset is presented to show the potentialities of the selected approach. Data from an extensive MT survey carried out in the geothermal system of Travale (Tuscany, Italy) are presented. Geological constrains from a 3D seismic reflection survey, from geological data and from available stratigraphic logs were used as a-priori information for the inversion and for a correct tuning of the spatial constraints.
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Radiomagnetotelluric Measurements on the Lake Mälaren along a Planned New Motorway in Stockholm, Sweden
Authors L. Persson, M. Bastani, A. Vass and C. MellqvistIn this study we have tested a new technique with RMT measurements on water which we call Marine Tensor RMT. The measurements were performed on the Lake Mälaren close to the city of Stockholm along a planned new motorway “E4 The Stockholm bypass”. The RMT system was slightly modified to be adapted for marine applications and part of the equipment was placed on a float that was dragged behind a small motorboat. The first results from the two test profiles on the Lake Mälaren are very promising. It was possible to make the measurements in a continuous way with an approximate speed of 2 km/hour. This makes it ten times faster compared to measurements on land. With this technique large areas can be covered with parallel profiles within a short period of time. The results from the 2D inversions show a good correlation with the results from the refraction seismic investigations in the same area. Moreover the resolution is fairly good even at greater depth and the resistivity models can give additional quantitative information about the bedrock quality at depth down to 60 m which is the depth for the planned road tunnel.
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Experience of Application of the Radiomagnetotelluric Sounding Method for the Solution of Environmental Tasks
Authors A. Saraev, A. Simakov, A. Shlykov and B. TezkanProspects of application of the radiomagnetotelluric (RMT) sounding method at the solution of environmental tasks are considered. Features of the foot, mobile and controlled source modifications of the RMT method are described. Results of surveys using the RMT method for the investigations of landfills of industrial and domestic wastes and subsurface structure at a gas station are analyzed.
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The TEM Method in Studies of Near-surface Magnetically Viscous Rocks
Authors N.O. Kozhevnikov and E.Y. AntonovThe paper discusses the effect of magnetically viscous near-surface rocks on the TEM response. In geological materials magnetic viscosity is caused predominantly by relaxation of magnetization of superparamagnetic mineral grains. Magnetic viscosity is shown to have a pronounced effect on the TEM data. More often than not it is regarded as a noise hampering the interpretation of TEM data in terms of conductivity. By contrast, we show, through forward calculation of TEM responses and inversion of the field TEM data in terms of time-dependant magnetic susceptibility, how magnetic viscosity effects can be used as a source of important information on the near-surface geology.
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Magnetic Properties of the French Soil Monitoring Network: First Results
Authors J. Thiesson, L. Boulonne, S. Buvat, C. Jolivet, B. Ortolland and N. SabyThe magnetic properties of the French soil Monitoring Network have been measured. This presentation show the first results obtained and especially maps of the magnetic properties at the country scale for France. Relationships between geology and the magnetic properties are clearly shown by the maps. Advanced statistics and geostatistics have applied to evaluate the possibility for magnetic properties to be used in pedotransfer function for assessing some soil chemical or physical properties.
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