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3rd EEGS Meeting
- Conference date: 09 Aug 1997 - 11 Aug 1997
- Location: Aarhus, Denmark
- ISBN: 978-94-6282-128-6
- Published: 09 August 1997
1 - 100 of 124 results
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Mapping groundwater areas
Authors T. Valli and A. MattsonThe volume of environmental research has increased in the Geological Survey of Finland (GTK) during the 1990's. The surveys of groundwater areas have played a remarkable role in them, because of the municipal needs for groundwater. The growing risk of pollution, environmental accidents etc. requires information about the flow and storage capacity of groundwater. Geophysical methods have tumed out to be a useful tool in giving regional information of bedrock topography and the thickness of overburden. In these studies GTK has worked as a consult and contractor for cities, municipalities and regional environment centers.
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Large-scale mapping of aquifers in the county of Aarhus using geophysical methods
Authors K. I. Sørensen and V. H. SøndergaardIncreasing problems with water quality have made ground water a very important issue in Denmark. In 1995 the Minister of Environment decided a 10-subjects scheme to improve ground water protection. One of the major issues is that all pesticides that can pollute the ground water should be forbidden. Another major issue is that counties in Denmark by the end of 1997 should be classified into 3 types of recharge areas. The classification includes: - Recharge areas of great drinking water interest, - Recharge areas of drinking water interest and - Recharge areas of limited drinking water interest The clasciffication is based on a comprehensive evaluation of the size and quality of the ground water resource. The new ground water resource plan provides guide-lines for the protection of the ground water in the county.
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Effect of "windows" mapped by geophysical methods on groundwater quality
Authors L. Thorling, K. I. Sørensen and V. ErnstenGeophysical methods turns up to be very useful, when vulnerability of ground waters is mapped in areas with a heterogeneous geological setting. In Denmark groundwater accounts for almost 100 % of the drinking water resource. Only groundwater that satisfy the quality standards of drinking water is used. Thus nitrate becomes a mayor threat in rural areas where nitrate loads generally exceed the quality limit of 50 mg/l. Previous work in Denmark concentrated on nitrate reduction under homogeneous geological condition/1/. In areas with thick day layers above the aquifer nitrate was found to penetrate about 3 - 8 m into the til! and never reached the groundwater /2/. In sandy areas nitrate was reduced in the aquifer by pyrite at the redox boarder where oxygen and nitrate were depleted at the same depth and below reduced conditions with iron and mangese was found. /3/ These homogeneous conditions accounts for about 50 % of the Danish ground waters, but in the rest of the country the geological settings are often very heterogeneous due to disturbance form ice movements during the last glaciation. Therefore both the top layers above the aquifer and the aquifer are very irregular with Iayers of altemating gram size from impermeable sediments with up to 15 % day minerals to coarse gravel deposits. The aim of this work is to study the effect of geological heterogeneity on groundwater quality and redox conditions in the aquifer. This work is part of the Danish Environmental Research programme (1992-1996).
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Borehole logging investigations for planning of remedial actions on water supply wells showing deterioration in groundwater quality
By K. KlittenComprehensive wireline logging investigation is necessary for providing the information needed for the evaluation of the possibility for relief of a deterioration in the quality of the water from a well, and for the choice and design of a remedial solution. Two different techniques are available as remedial solutions both aiming to improve the quality of the water produced from the well. One is a reconstruction of the well in order to close off the inflow of water with unwanted quality.
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Investigation of vadose zone flow mechanisms in unsaturated chalk using cross-borehole ERT
Authors L. Slater, A. M. Binley, M. D. Zaidman and L. J. WestGroundwater resources are vulnerable to surface-derived contaminants resulting from human activity. The vadose zone is a natural barrier between contaminant sources and groundwater stored in aquifers. The fate of contaminants currently in transit within the vadose zone (as determined by operative transport mechanisms) is of political, economic and social concern. Hence techniques are required to investigate solute transport mechanisms within the vadose zone.
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Using imcomplete geophysical datasets to monitor a conductive groundwater tracer experiment
More LessThe tedious and repetative nature of groundwater tracer experiment monitoring using geophysics can result in an incomplete dataset for subsequent interpretation. A fundamental cause is due to the inherent unpredictability of the rate and direction of movement of, and initial geometry of the tracer slug after injection. This problem is inherent to the experiment since if these parameters were accurately known, there would be no need to perform the tracer study. The incompleteness of the geophysical dataset is also directly affected by the balance between collecting enough data to solve the flow problem, and not wanting to collect redundant data due to the high cost of field data acquisition. This paper presents the results of interpreting incomplete geophysical datasets which were obtained to monitor the migration of a conductive saline groundwater tracer through a deltaic sand aquifer in Gray, Maine. In addition to providing a non-intrusive means for monitoring the temporal movement of the conductive tracer, interpretation of these geophysical data has also yielded a more detailed picture of the geologie and hydrogeologic setting explaining observed anisotropy in flow.
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Quantification of hydrogeological parameters by geophysical methods
By S. KomatinaWithin hydrogeological exploration, geophysical methods have a significant role in solving following problems: - possibilities of safe analyses of aquifer geometry and structural properties; - monitoring of aquifer contamination by mineral and organic deposits; - defining relevant indications on a hanging-wail permeability characteristics and aquifer hydrodinamic parameters; - indicating groundwater level; - analysis of groundwater chemistry; - determining clay facii in a complex of hanging-wall sediments; - exploration of velocity transfer for wet front and pollutant within.
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Can K-p relations be estimated through ground water flow model inversion
Authors D. Dam and S. ChristensenIn connection with construction of ground water models an extensive geophysical survey of the area is often made. In Denmark the model area is usually mapped by means of dense geoelectrical surface measurements. The geophysical surface measurements give an area coverage and are relatively inexpensive.
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High resolution travel-time tomography used to delineate a shallow waste disposal site
Authors E. Lanz, H. Maurer, J. Ansorge and A. GreenIn Switzerland, large quantities of waste are buried in glacial and glaciofluvial sediments. These same sedinients comprise two-thirds of the country's aquifers and thus contain important sources of drinking water. To assess the potential for environmental contamination, the boundaries of the buried waste sites (i.e. their lateral extents and depths) must be well known. The depths of the sites are of particular interest for judging if the groundwater table is within or below the waste.
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Laboratory and field results of the use of spectral induced polarization (SIP) method for detecting organic and inorganic contaminants
By H. VanhalaEnvironmental applications of the induced polarization (IP) and the spectral induced polarization (spectral IP or SIP) methods, i.e., the possibility to detect organic and inorganic contaminants in glacial soils, has been studied the Geological Survey of Finland (GTK) for some years. This presentation deals with the IP of natural and contaminated soils (the membrane polarization), and gives two field examples; an area with an organic (hydrocarbon) contamination (Fig. 1), and an area with an inorganic (heavy metal) contarnination.
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Environmental applications of airborne geophysics in Finland
Authors J. Lerssi, M. Kurimo, T. Jokinene, E. Lanne and R. PuranenGeological Survey of Finland (GSF) has carried out systematic airborne geophysical surveys in Finland since 1951. The second program started in 1972 using a flight altitude of 30-40 meters and line spacing of 200(100) meters (Kurimo, et al, 1986; Peltoniemi, 1982; Poikonen, 1991; Vironmäki, et al, 1982). Today 80 % of the country has been measured. The measurements have been made with fixed-wing aircraft The differential GPS is utilised in navigation. In low-altitude measurements the following systems are in use: magnetic, gamma radiation and vertical coplanar EM and VLF eleciromagnetic. Total magnetic field is measured with a wingtip gradiometer. The horizontal spacing between the sensors is 21 meters. Earth's gamma radiation is measured with a spectrometer which utilises a 25 1 NAI crystal detector. In the electromagnetic unit a vertical coplanar coil configuration is used. The frequency is 3112Hz (from 1995 also 14368 Hz) and coil separation is 21.4 m. GSF processes data with in-house software and profile, contour, shaded colour and grey scale maps are drawn (Kurimo, et al. 1986). The survey results are used in mineral exploration and geological mapping, recently also increasingly in environmental applications.
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Quantitative mapping of waste coal tar deposits by EM conductivity and VLF-resistivity surveys
Authors R. D. Ogilvy, P. I. Meldrum and J. NissenThe nature of coal tar deposits presents considerable difficulties for traditional site investigation metliods such as boreholes and cone penelrometer tests. These intrusive methods normally require access by heavy vehicles and would be at risk on a tar surface. However, the low viscosity of tar (in winter) means site characterisation may be undertaken by a geophysicist using lightweight instrumentation.
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Integrating electrical resistivity tomography and soil sampling methods to characterize a solid waste landfill area
Authors G. Morelli, G. Corsini, L. Di Tola, R. Pini, G. Vigna Guidi, M. Miletto, M. Ferguglia, G. Pogliano, G. Catanzariti, F. Franceschini, A. Scozzari and R. CorsiA municipal solid waste Iandfill, located 35 Km east of Pisa (Italy), was selected to experiment the application of Electrical Resistivity Tomography (ERT) to detect and delineate the plume of contamination caused by the absence of any natural or artificial protection for the underlying confined aquifer. ERT resuits have been supported and checked against geochemical data, hydrogeological data and measurements of soil physical properties.
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Identification of shallow targets through integrated 2-D and 3-D multi-fold georadar investigation: A case history
Authors M. Pipan, L. Baradello, I. Finetti, E. Forte and A. PrizzonA 3D multi-fold GPR investigation was carried out in the archaeological park of Aquileia in the framework of a survey proposed by the local superintendency of cultural heritage. Primary objective of the work was the identification of targets of potential archaeological interest in a polygon of approximately 2800 sqm in area, which borders the town cemetery to the north. The comparison of single-fold and multi-fold test profiles encouraged the design of a complete multi-fold grid. The 3-D option was chosen to correlate and map targets of limited dimensions. Targets of possible archaeological interest were identified at estimated depths not exceeding 200 cm in the part of the dataset processed to date.
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Dispersion analysis in radar tomography
Authors S. Tillard, S. Ahr, F. Hollender and F. JullienGround Penetrating Radar and Borehole Radar are commonly used for various applications in civil engineering, archeology, aquifer and soil studies... These prospection methods can also be used to study geological formations for underground waste disposal, for which a set of specifications has been defined by ANDRA. In electrically resistive host rock, for example granite, they allow the localization of discontinuities such as fractures or altered zones.
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Finite-difference ground-penetrating radar modeling in frequency-dependent media
Authors T. Bergmann, J. O. A. Robertsson and K. HolligerRealistic modeling of electromagnetic wave propagation in the radar frequency band requires a full solution of Maxwell's equations as well as a complete description of the material properties. We present a two-dimensional (2-D) flnite-difference time-domain solution of Maxwell's equations that allows to account for the frequency dependence of the dielectric permittivity and electrical conductivity typical of many near-surface materials. In close analogy with the viscoacoustic case, the governing equations are obtained by assuming dielectric and conducting relaxation functions. The finite-difference solution is second-order accurate in time and fourth-order accurate in space, conditionally stable, and computationally only marginally more expensive than its standard equivalent without frequency-dependent material properties. The algorithm is applied to a realistic problem illustrating the respective damping effects of conductivity and frequency-dependent dielectricity.
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Finite-difference modeling of ground-penetrating radar data: The zero-offset approximation
Authors T. Bergmann, K. Holliger and J. LeckebuschMost ground-penetrating radar suveys are acquired in quasi zero-offset mode, Le. source-receiver offsets are small compared to the target depth. The correct way to realistically model such an experiment would be to compute a corresponding sequence of common-offset radargrarns. In finite-difference time domain (FDTD) modeling this approach would be excessively expensive and hence is substituted by initiating a downward travelling plane wave at the earth's surface. However, this method of zero-offset modeling is only realistic for horizontafly layered, one-dimensional media, and thus is unsatisfactory in most realistic situations and defeats the very purpose of finite-difference rnodeling. Therefore, we propose an alternative approach based on the "exploding reflector" concept. This approximation is more realistic, even in highly complex media, and is only marginaily more expensive than the plane wave method.
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Borehole radar surveys in the Borth rock salt mine (FRG)
Authors T. Richter, T. Fechner, L. Corin, L. Halleux, P. Feller, K. Berns, U. Niewianda, R. Maly and G. v. LierdeThe Borth salt deposit (FRG) lies in the Zechstein basin, which covers a large part of Central Europe. The mine is located north-east of Duisburg. Although the deposit is over 150 metres thick, only the lower part is mined here. Mining activity (app. 800 metres below surface) is restricted to a 20 m thick layer of extremely pure white salt.
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Ground penetrating synthetic pulse radar performances
Authors J. Cariou, O. Blondel and E. FerrariFour years ago, the « Ministère de l'Equipement et des Transports », in collaboration with two other French companies (SNCF - Société Nationale des Chemins de Fer; and the RATP - Régie Autonome des Transports Parisiens) presented a paper concerning the development of a synthetic pulse radar. After demonstrating the feasibility of such a system at the end of the eighties, we have recently improved our knowledge and carried out comparisons with the pulse and synthetic radars existing on the market. The main purpose of this research is to try to improve the depth of investigation for the detection of discontinuity or cavities in the ground or in civil engineering structures.
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Forward modeling contribution in the GPR signatures interpretation of urban heterogeneities
Authors G. Grandjean, A. Bitri and J. C. GourryBRGM and the french Projet National Microtunnel funded a research project where Ground Penetrating Radar (GPR) was used to characterize the test-site of the Laboratoire Central des Ponts et Chaussées (France). The objective of this project was to find a method to better interpret the radar signatures by combining data processing to forward modeling, especially in the case of urban heterogeneities. We focused a large part of our work to adapt a sufficient quick and accurate algorithm to be efficient in industrial applications. Modeling algorithm, adapted from radar waves propagation theory in 2D heterogeneous dispersive media, is based on the upward extrapolation of a downgoing field in the frequency-wavenumber domain. Like for other modeling techniques such as ray-tracing (Goodman, 1994; Cai and McMechan, 1995; Powers, 1995), FDTD (Moghaddams et aL, 1991; Roberts, 1994) or pseudospectral methods (Carcione, 1996; Casper and Kung, 1996) some compromises have been introduced and must be kept in mind. In the following, we will first recall the modeling method, and after an example description from the LCPC test site, where real processed data are compared to synthetics, we will insist on the advantages and the weakness of the method.
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Shallow 3-D reflection seismic surveying of glacial sediments in the Swiss molasse basin
Authors F. Büker, H. Horstmeyer and A. C. GreenApplications of geophysical methods to resolve diverse engineering and environmental problems have become increasingly common over the past few years. Investigations of shallow targets in complex heterogeneous geological settings require methods capable of providing high-resolution infonnation. Although seismic reflection profihing has often been applied successfully in nearsurface studies, reliable knowledge of the true dip and lateral extent of structures cannot be obtained from sparse 2-D seismic data sets alone (Lanz et al., 1996). In order to map the stratigraphy and three-dimensional distribution of unconsolidated surficial sediments a 3-D highresolution reflection seismic survey has recently been conciucted within the Suhre Valley, central Switzerland.
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Modelling and imaging within the diffraction limit with application in engineering geophysics
Authors L. -J. Gelius, H. Westerdahl and F. N. KongIn engineering geophysics the task is often to locate and/or image different buried objects or structures. If we consider geotechnical investigations typically targets will be cavities, buried drums, tunnels, pipelines and rock pieces in soil. Correspondingly, in non-destructive testing we aim to characterize structural distortions or to image target objects embedded in a given structure.
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Tau-P mapping" based filtering techniques for linear noise attenuation in reflection data
Authors G. P. Deidda, R. Balia and L. SambuelliOne of the most relevant problems in reflection data processing is related to the suppression of localised coherent noises. In shallow reflection surveys typical examples among these noises are: a) the air-coupled wave, due to the extensive use of low-cost surface energy sources such as dropping weights, hainmers, rifles and so on, which produce, more or less extensively, a wide spectrum, high amplitude air wave; b) other linear noises, such as the direct and refracted waves which, in addition to the fact that their frequency band overlaps significantly that of the signal, are very close to the reflections themselves andlor are spatially undersampled.
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Underground tunnels detection and location by high resolution seismic reflection
Authors B. Piwakowski, J. C. Tricot, C. Leonard, N. Ouarradi and B. DelannoyIn spite of the widespread development of high-resolution seismic reflection techniques during recent years, the detection of underground cavities remains fundamentally unsolved. Except for some general principles, each case requires a particular study. Until now, the successful location of small (in regard to wavelength) cavities has been performed in an indirect way, i.e. by means of the detection of the cavity-induced perturbations of the seismic image of the regular geological structure (which should be known in advance) [1],[2],[3],[4] The direct detection of cavities by means of the reflection originating from the top of a void, though theoretically possible, gives no results in practice. [5]. This paper presents the successful application of the high resolution seisrnic reflection for the indirect detection and location of abandoned old chalk-pits, appearing in the north of France and being now unexploited. Some positions of these voids which form a network of tunnels are mapped, whereas others are unknown and represent a real danger for both population and building activities. The tunnels occur typically in chalk at a depth of 8-15 m and are followed by a water table and a man layer (Fig.1).
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A seismic reflection survey to help determine the ice thickness on the Lobbia Glacier, Adamello Massif, Italy
Authors L. Levato, L. Veronese, A. Lozej, E. Santuliana and E. TabaccoIn the framework of a geophysical study to investigate the ice thickness on the Lobbia Glacier located in the Adamello Massif, Italy, we recorded 1393m of 2D multifold seismic data, in summer 1996, to constrain a joint gravity survey covering an area of about 4 km2, Single fold seismic data (Tabacco, Pettinicchio, and Veronese 1995), and gravity data (Olivier et al., 1996), collected during previous surveys, provided an estimate of the maximum ice thickness. The main processing sequences inciude band-pass filtering, f-k filtering, residual static corrections, stack, deconvolution and migration. The contact between the ice and the granite substratum appears as a strong reflection at a maximum two way time of 105 ms.
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Three dimensional georadar acquisition with a real time positioning system
Authors F. Lehmann, M. van der Veen, A. C. Green, H. Horstmeyer and P. WildFor efficient acquisition of three-dimensional (3-D) subsurface information, quasi-continuous georadar and coordinate data are recorded simultaneously as the georadar antennas are continuously transported across survey areas. A self-tracking laser theodolite with automatic target recognition capabilities has been adapted to serve as a real-time positioning system for the acquisition of the 3-D data. This surveying system provides complete coordinate information with high accuracy. To take advantage of advanced processing procedures the georadar data must be transferred on to a regular grid. A fast two-dimensional Fourier transform technique has been designed for this task. The system has been tested successfully across a number of geological targets in Switzerland. For example, 3-D georadar data were recently collected and processed across a glaciofluvial environment of 25 m x 25 m within a single day. Using the full 3-D information of the data set, channel sediments as well as surface reflections could be clearly identified with the help of time slices.
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The improvement of geotechnical subsurface models through the application of S-wave reflection seismic exploration
Authors J. Brouwer, R. Ghose, K. Helbig and V. NijhofDue to its relatively high sensitivity to the distribution of elastic parameters, the seismic technique is quite suitable for geotechnical subsurface investigations. However, practical implementation of the P-wave exploration technique for soft-soil and shallow-groundwater conditions, as often encountered in the Netherlands, may often prove problematic; the highimpedance contrast at the groundwater table may induce strong reverberations and guided waves, resulting in a distortion of the seismic record at shallow depth. The use of buried sources may be of some advantage, but at the cost of a considerable decrease in the speed of operation.
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An efficient approach to shallow high-resolution seismic data acquisition: Preliminary results
Authors M. van der Veen, F. Lehmann, P. Wild and A. GreenHigh-resolution reflection seismic techniques are powerful tools for mapping shallow geological structures (Steeples and Miller, 1990; Lanz et aL, 1996). During the past decade, the quality of seismic data has improved significantly. This improvement can be ascribed to a better understanding of shallow seismic techniques and significant developments in technology. These advances not only have improved the data quality and increased the ability to record very high-fold data, but they also have increased significantly the logistical complexity of a typical shallow seismic survey; many more geophones now have to be planted and higher shot densities are required.
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The quantification and monitoring of data quality and the design of optimum sweeps
Authors J. Brouwer, P. Bakker, D. Kraaijpoel and K. Roy-ChowdhurryThe application of vibratory sources in seismic exploration principally allows us to tune the source signature to the (changes in) specific (sub-) surface conditions through a proper choice of the pilot signal. Objective design of source signatures is feasible only if we can define how the quality of the dataset is affected by the choice of pilot signal. This requires a description of the quality of the seismic data in terms of the pilot signal.
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Application of proton magnetic resonance for detection of fractured chalk aquifers from the surface
Authors A. V. Legchenko, J. M. Baltassat, A. Beauce and D. ChigotDirect measurement of Proton Magnetic Resonance (PMR) signal from water molecules guarantees a high reliability of the water detection. It is the main distinction of the PMR compared to other geophysical tools. Interpretation of experimental data reveals location of aquifers, theirs depth and water content. A mean size of pores of the water-saturated rocks can also be estimated.
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Small scale correlation between the electrical and the hydraulic conductivity
Authors F. Effersø and K. I. SørensenThere has been an ongoing discussion about the relationship between the hydraulic and the electrical conductivity. In order to test this relationship on a small scale a new method for in situ determination of the hydraulic conductivity has been developed at the Department of Earth Sciences. In a series of field tests in a sandy alluvium, estimates of the hydraulic conductivity were obtained in three closely spaced borings together with gamma and electrical logs. The results indicate that there is no evident relationship between the electrical conductivity and the hydraulic conductivity on a small scale.
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Application of statistical experiment design: Are our data sets "optimal"?
Authors H. Maurer and D. E. BoernerReliable characterization of subsurface targets is the primary objective of every geophysical exploration technique. Regardless of the physical properties being mapped, or the variant of the geophysical method employed, quantifying the resolution of the Earth is a common theme of all field experiments. Inverse theory has proven essential for this task since, for a linear relationship between model parameters and data, it provides an exact mapping between data errors and model uncertainty. In this regard, the amount of information that can be extracted from measured data (i.e. the success or failure of a geophysical experiment) depends explicitly on data quality. Yet measurement accuracy and precision alone do not define data quality. Data independence and sufficiency are also important and illustrate the need for ensuring the collection of appropriate data through experimental design.
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Electromagnetic inversion for environmental site characterization: Data quality versus image resolution
Authors D. L. Alumbaugh and G. A. NewmanNon-linear electromagnetic inversion schemes have been developed to produce 2D and 3D images of subsurface conductivity structure from electromagnetic geophysical data. The solutions are obtained by successive linearized model updates where full forward modeling is employed at each iteration to compute model sensitivities and predicted data. Regularization is applied to the problem to provide stabiity. The use of the inversion is demonstrated on a data set collected with the Apex Parametrics tMaxMin I-8S' over a section of conductive waste at the Idaho National Laboratory's Cold Test Pitt. The out-of phase data are of very good quality while the in-phase are rather noisy due to slight mispositioning errors. A resolution study on synthetic data indicates that the error present in the in-phase data causes images of far lower resolution with more artifacts than if the in-phase and out-of-phase components are of similar quality. Better resolution images result if the data are weighted proportional to frequency; this gives each frequency equal weight. The loss of resolution due to poor quality in-phase data is demonstrated in a 3D inversion of the MaxMin data which shows both artifacts forming outside of the area known to contain the buried waste, as well as an inability to resolve depths.
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Study of configuration dependent resolution of 3-D buried conductors
Authors E. Auken, G. M. Hoversten and H. F. MorrisonThe electromagnetic response of a buried conductor is a complex function of the currents induced and channeled into the conductor from the currents flowing in the background media. The ration between the channeling and induced currents is basically deterrnined by the currents in the background half-space that are available for channeling and on the magnetic fleld on the conductor. In order to "see" the target the secondary fields must exceed some threshold value which is dependent on the layered background response and on the source receiver configuration.
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The pulled array transient electromagnetic method
More LessThe mapping of subsurface resistivity structures using transient electromagnetic soundings, TEM, has gained an important role in hydrogeological investigations in Denmark. Regional mapping with TEM have produced resuits, which leaves no doubt as to the ability of the method to delineate freshwater sandy aquifers in well conducting hosts of Tertiary clays. These results have been achieved measuring in a dense grid and do demonstrated the necessity of estimating the data quality and variation by correlating adjecent data sets to reveal distortion and multidimensionality of the measurements. The fact that these investigations are often carried out in densely populated areas, where the cultural noise level is high, accentuates this necessity even more (Christensen and Sorensen, 1994).
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A combined Gauss-Newton and quasi-Newton inversion method for the interpretation of apparent resistivity pseudosections
Authors M. H. Loke and T. DahlinTwo-dimensional (2D) electrical imaging surveys (Griffiths and Barker 1993) are now widely used to map areas with moderately complex geology where conventional resistivity sounding surveys do not give sufficiently accurate results. In more complex areas threedimensional (3D) surveys (Ellis and Oldenburg 1994, Loke and Barker 1996b), which gives even more accurate results but at a greater cost, have also been used.
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Quasi-3D resistivity imaging - mapping of three dimensional structures using two dimensional DC resistivity techniques
Authors T. Dahlin and M. H. LokeSo far, one dimensional (1D) and two dimensional (2D) techniques have dominated resistivity surveying, and the latter only in recent years, while three dimensional (3D) techniques are still in their infancy. In order to build images of the 3D resistivity distribution of the ground, it is today common practice to merge the result from a number of sections acquired and inverted using 2D resistivity imaging techniques, which may be referred to as a quasi-3D technique.
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Separation of anisotropy and inhomogeneity influence by the spectral analysis of azimuthal resistivity diagrams
Authors D. K. Bolkshakov, I. N. Modin, E. V. Pervago and V. A. ShevninThe first aim of resistivitv survey is a study of any inhomogeneities. Frequently in practice the effect of anisotropy is displayed together with that of layering or inhomogeneities. It complicates data interpretation within the framework of anisotropic models, and distorts results of interpretation in the framework of layered or inhomogeneous media.
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Application of complex resistivity tomography to field data from a kerosene-contaminated site
More LessRecently several investigations on samples in the laboratory have proved the influence of hydrocarbon (HC) contamination on the complex electrical resistivity of soils and rocks (Olhoeft, 1992; Bömer et al., 1993; Vanhala, 1997). Beside the magnitude of resistivity additional information about the contaminant is obtained from the phase angle which may be measured by the frequency domain induced polarization method. However, for environmental HC pollution problems the importance of the complex resistivity method depends on its practical value for the detection, delineation and monitoring of subsurface contamination under field conditions. Here, an application of complex resistivity tomography to field data, collected on a kerosene-contaminated former military jet fuel depot, is presented.
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3D modeling of the Lobbia Glacier bedrock (Adamello Massif, Italy) using gravity and GPS measurements
Authors A. Rosselli, R. Olivier, E. Tabacco, R. Cefalo, B. Dumont, Ph. Logean, Ph. Rosset, M. Manzoni, M. Pavan and S. UrbiniAn important ingredient in establishing climate models for global climatic change studies is the volume of glaciers and its temporal evolution.
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3-D FE-modeling of a mass movement on basis of geophysical investigations
Authors E. Castillo and F. KohlbeckA Iandslide has been modeled by three different models utilizing the FE-Program BMINES. The combination of several geophysical methods provided the information about the 3D-geometry of the slip and the range of some material properties. Seismic refraction surveys, geoelectrical soundings and electromagnetic measurements have been used for the characterization of the slip, location, depth, and physical properties of material.
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Electrostatic measurements in complex artificial (anthropogenic) grounds
Authors C. Panissod, A. Jolivet and A. TabbaghThe electrostatic method constitutes a generalization of the well known electrical method. As the electrostatic poles are located in the air, not far from the ground, the method can be used whatever the type of ground surface (tarmac, slabs, concrete,...).
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An evaluation of electromagnetic methods for waste site assessment
Authors L. Pellerin, D. L. Alumbaugh and M. Cathy PfeiferA baseline study in electromagnetic (EM) exploration of the shallow subsurface (< 10 m) was performed at the Idaho National Engineering Laboratory (INEL) Cold Test Pit (CTP) for the purpose of identifying and evaluating existing commercial and experimental instrumentation, integrating those technologies with multidimensional interpretational algorithms, and identifying gaps in shallow subsurface EM imaging technology.
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Predictive mapping of mechanical properties of alterites through continuous electrical resistivity measurements
Authors J. C. Gourry, R. Wyns and F. LebertBasement rocks constitute 25% of the surface geology of France. Throughout the geological record, and particularly during the Early Cretaceous and Paleogene, these rocks underwent significant weathering to form alterites more than 50 m thick in places. Later erosion incised vaileys in the alterites, which is why, in schistose areas, one may find aggregate quarries very close to day workings (for brick manufacture), the former being in the valley bottoms (minimum weathering) and the latter on the plateaus (maximum weathering). The aim of this research work is to assess the mechanical properties of these surface alterites in order to draw up maps for use in civil engineering sectors, such as excavation work for major communicatjon routes (roads, etc.) and laying underground pipes and cables (gas, electricity, telecommunication lines).
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A high density sampling survey of shallow karst features using EM and magnetic profiling techniques
Authors R. J. Sporry, A. Marquesda Costa, G. Desta, J. Roy and W. A. HugensDuring field experiments on high density sampling shallow EM (Geonics EM31) surveying near Moura, Portugal, it was found that a local shallow terrain depression showed enhanced rainwater infiltration and high apparent conductivity values (Sporry et. al. 1995). Other conductivity anomalies suggested a pattem correlating with the general geological strike direction (NW-SE).
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Flow training dikes for the Wouri estuary in Doula. DC prospection of sand in shallow sea water
Authors S. N‘Seke, B. Bagnérès, R. Lagabrielle and J. -L. MattiuzzoThe Port of Douala, which is located high up the Wouri River Estuary, is reached by means of a 50 km long access channel. The 25 km upper part of this channel currently requires intense and costly maintenance dredging. 20 years of dredging experience gained through three previous programs bas led the Cameroon National Ports Authonty (CNPA) to consider that an altemative solution with higher investment costs (flow training dikes) and reduced maintenance (by more than 60%) is the most appropriate in terms of present benefits.
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Outlook on geophysical evaluation of the ground conditions in the Kruja medieval castle, Albania
Authors A. Frasheri, L. Kapllani, F. Dhima and S. PeçiThe Castle of Kruja is the symbol of the culture and Albanian history. This castie is related with the most glorious epoch of the Albanian National Hero Skanderbeg.
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Relations between hydrogeologic and geoelectric parameters. A case study: The Setúbal peninsula, Portugal
Authors R. M. D. Gonçalves, A. R. Andrade Afonso and L. A. Mendes VictorThe Setubal Peninsula is located southern of Lisbon City, in the midst of Portugal (fig. 1). This belt (area) belongs to the Tejo and Sado river basins and it's located between them. It comprises the most important aquifer system of the country. Geohydrological data from the thousand water extraction wells, and more than one hundred Vertical Electric Sounding (VES) surveys exist from that region (fig. 2). Merging of these different data yields better knowledge about constitution and protection of the system.
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Logging techniques measuring parameters of water flow in wells - a critical review
More LessDuring the prospecting of a hydrogeological structure, a series of boreholes (wells) is usually drilled with the goal to get sufficient information on aquifers, their depth position, and their reservoir properties.
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Lowering of the ground water table - does it affect the fresh/salt water interface, and can we measure it?
Authors T. Vangkilde-Pedersen, H. Olsen and P. M. DuchThe Danish supply of potable water is mainly based on ground water. During construction work in areas with a shallow ground water table, temporary lowering of the water table is often necessary. In coastal regions, if the lowering of the water table is close to existing water abstraction sites, the ground water quality can be threatened by changes in the depth to the freshwater/saltwater interface. With an example from Vestamager near Copenhagen, Denmark a combination of geophysical methods for monitoring the freshwater/saltwater interface is demonstrated. The example ilustrates the advantages of combining geophysical well logging in observation wells with time domain electromagnetic (TDEM) soundings.
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The fresh and salt water distribution in the unconfined aquifer in northern Flanders
Authors W. De Breuck, E. Beeuwsaert and K. WalraevensThe interface between fresh and salt water in the unconfined aquifer of Zealand Flanders (The Netherlands) and the adjacent area in Belgium has been mapped by means of a resistivity survey controlled by many well observations, The interface corresponds with an interpreted formation resistivity equal to or less than 6 Ωm. The distribution pattern of fresh and salt water is tightly linked to the geological evolution of the area. Especially the latest phase of the Dunkirk transgression and the historical inundations have had a thorough influence.
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Seismic investigations of glacial structures in Northern Germany
Authors H. Wiederhold and G. CaspersShallow subsurface structures in Northem Germany and adjacent areas are characterized by glacial erosion and deposition. Thus, a system of up to 400 m deep channels mainly formed during the glaciation of the Elster period and filled with sediments afterwards is known and today of special interest for hydrological questions. Other glacial depressions, especially hollows with no outlet, are excellent sediment traps and afford optimum conditions for the study of stadial and interstadial deposits and thus, the reconstruction of climate and vegetation development during glacial epochs.
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Contribution from EM surveys to a regional groundwater resource quantification project in a hard rock area
Authors J. Roy, M. W. Lubczynski, R. J. Sporry and W. A. HugensThis note is dealing with two key concepts: the quantification of groundwater (GW) resources on one hand and the use of electromagnetic (EM) techniques on the other; these are the objects of this introduction.
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Detection of a volcanic aquifer by TDEM soundings
Authors G. Pagano, A. Menghini and S. FlorisThe purpose of this presentation is to show the great power of resolution of Time Domain Electromagnetics Methods in volcanics areas, in comparison with classic electric methods.
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Hydrogeophysical mapping with the transient electromagnetic sounding method
Authors L. H. Poulsen and N. B. ChristensenThe transient electromagnetic sounding method is an effective reconnaissance exploration tool for mapping good conductors like day and salt water. In the Bredebro area in Southem Jutland, Denrnark, the method has been used for mapping an aquifer situated in a Tertiary valley system eroded out in heavy day. The area was previously mapped with gravity measurements and this investigation indicated the presence of a Tertiary valley system. The transient electromagnetic investigation has confmed the location of the Tertiary valley found in the gravity investigation and added more information about the boundaries of the valley system.
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Hydrogeological investigations in the Bulawayo region, Matabeleland, Zimbabwe
Authors B. Lorentzen, Z. Dladla, P. Gwaze, T. Dahlin and N. B. ChristensenWithin the framework of hydrogeological studies for additional water supply for the city of Bulawayo, Zimbabwe, a cooperation between the University of Zimbabwe, Lund Technical University, Sweden, and the University of Aarhus, Denmark, with support from the Swedish International Development Agency has led to a geophysical survey of the large Kalahari and Karoo sedimentary basins in North Matebeleland, for the purpose of assessing water resources.
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1D joint inversion of radiomagnetotellluric (RMT) and transient-electromagnetic (TEM) data: an application for groundwater prospection in Grundfør, Denmark
Authors W. Schwinn and B. Tezkanin many parts of Europe the resources of ground water are short. A lot of these resources have a risk of contamination through agricultural activity, industry, waste deposits or salt water.
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Joint interpretation of radiomagnetotelluric and CVES measurements in the Grundfør area, Denmark
Authors M. K. Lauridsen and N. B. ChristensenThe radiomagnetotelluric (RMT) method has been used to collect data in the Grunfør area in Denmark to estimate the potential of the method under Danish conditions. The Grundfør area was chosen because it has been intensively mapped with several geophysical methods in connection with the Danish Environmental Research Programme. The results of previous measurements thus form a good basis for comparison.
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Three-dimensional geological model of the complex aquifers in an incised Quaternary valley in Jylland, Denmark
By P. GravesenDeep buried Quatemary valley systems incised into older pre-Quaternaiy deposits exist in many glaciated areas in northern Europe and North America and in the offshore areas of the North Sea basin and the Baltic Sea Basin. The valleys can reach several hundreds of meters below ground surface and they are fihled with diamictons and meltwater deposits. In Denmark the vaileys mainly occur in Jylland where i.e. Lykke-Andersen (1986) has investigated the structures and the formation of the vaileys.
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Statistical modelling of partial clay cover
By M. HansenOne of the major controlling factors for groundwater recharge in area of partial day cover is the distribution of the day bodies. In order to evaluate the distribution of a partial day cover in the Grundfør—Hinnerup area (Figure 1) and to quantify the probable distribution of the day cover a series of statistical simulations of the day distribution has been made.
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The application of geostatistical methods to the hydrological interpretation of geoelectrical soundings
Authors E. Brückl, R. Dutter, A. Schiller, D. Bechtold, J. Dölzmüller and M. LumasseggerDuring the planning of a new railway line through Tirol, Austria comprehensive multidisciplinary hydrological studies were carried out. The goal of these activities was the establishinent of hydrological models to simulate the potential influence of the planned railway line on the existing groundwater regime. One part of these investigations were conventional geoelectrical soundings. In this paper we describe the application of geostatistical methods to the hydrological interpretation of the geoelectrical data and we analyze the impact of the geoelectrical information on the final hydrological model.
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TEM and MEP methods - application examples from Denmark
Authors F. F. Pedersen and M. HalkjærThe TEM and MEP methods are being applied in Denmark. The Danish geology is characterized by thick sedimentary deposits from the quaternary and tertiary period, and in most parts of the country no hard rock is present. The TEM method has been intensively applied for delimitation of aquifers, which often have boundaries of day with low resistivities. The method have also been applied for general hydrogeological mapping, and surveys for deep saltwater in the aquifers.
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Geophysical measurements as efficient tools for hydrogeological investigations
Authors E. Castillo, H. Figdor, K. -H. Roch and R. SpendlingwimmerIn a number of regions the endangering of groundwater reservoirs has been increased considerably by emerging of extensive residential areas in the neighbourhood of big cities or by means of accidents during the transport of dangerous goods. By this for water supply of a region hydrogeological investigations of water resources have become much more significant in recent years. Detailed knowledge of hydrogeological conditions is not only important for estimation of aquifer capacity but also an essential requirement for effective measures of protection and redevelopment.
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Reservoir site selection and monitoring during construction with applied geophysics
By S. PennThe resent period of lower than average rainfall in the United Kingdom, together with changes in commercial factors and land use policy have been contributory aspects to an increased rate of the construction of water reservoirs for agricultural use in Eastern England.
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Below-liner geophysical monitoring at a landfill site in the UK
Authors S. B. Taylor and R. D. BarkerThe UK's first electrical monitoring system to be permanently installed below the geomembrane liner of a landfill site has now been operational for two years. The system, developed jointly by Aspinwall and Company, the University of Birmingham and Campus Geophysical Instruments, is installed at a site operated by Cleanaway Ltd and consists of a basic 20 m grid of electrodes emplaced below a 0.3 m layer of Bentonite enriched sand (BES), underlying a 2.5 mm thick HDPE geomembrane liner. Similar systems have been developed and used in the United States (e.g. Van et. aL, 1991), and elsewhere in Europe (e.g. Frangos, 1994).
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Geophysical measurements as Swedish and Estonian landfills - case studies from four sites
Authors J. Aaltonen and B. OlofssonLandfills have been, and are, the most used solution for waste disposal. There is, though, a growing concern about effects landfills have on the environment. A serious problem occurring is leakage, with its possibility to contaminate nearby aquifers.
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Geostatistical and geophysical modelling of the Oitti DNAPL spill site, Southern Finland
Authors E. Laine and M. PeltoniemiIn the 1950's and 1960's about 10,000 litres of dry cleaning solvent was disposed of in a well or in pits (s1) near the town center at Oitti, southern Finland (Fig. 1). The groundwater was found contarninated in 1992 when a regional groundwater quality survey was done in the region.
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Investigations of oil pollution with electrical prospecting methods
Authors I. N. Modin, V. A. Shevnin, A. A. Bobatchev, D. K. Bolshakov, D. A. Leonov and M. L. VladovThe most widespread source of pollution in Russia is the oil pollution. It occurs at all stages of oil production, transportation and processing. Outflows, proceeding during decades result to formation of oil secondary deposits.
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High-resolution, high-fold seismic reflection profile across a landfill
Authors R. De Iaco, H. Horstmeyer and A. GreenFast and inexpensive methods for exarnining waste disposal sites are becoming increasingly important. We have tested reflection seismic techniques for mapping the depth extent of a landfill.
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Finite-difference modelling of ground-penetrating radar data: antenna radiation patterns
Authors K. Holliger and T. BergmannWe present a FDTD algorithm to model the near-field radiation characteristics of dipole antennas. The antenna is represented as a wire with a small gap in the middle. The initial condition is given by a time-variable voltage pulse fed into the central gap in the wire. The resulting E-field in the gap can be calculated analytically, whereas the E- and H-fields in the vicinity of the wire are evaluated by numerical solution of an integral representation of Maxwell's equations. Integration contours and surfaces are defined by the cells surrounding the wire.
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Ground penetrating radar in pipeline river crossing design. A case study from the jungles of Ecuador
More LessA ground penetrating radar (GPR) survey was conducted to delineate sub-bottom geological strata for a pipeline river crossing project in Ecuador. The primary purpose of this investigation was to map a thick gravel layer underlying sands and silts to a total depth of over 40 metres. Despite significant depth requirements and logistical difficulties, radar data of excellent quality were acquired. This allowed the production of river crossing profiles which were believed to be of greater accuracy and detail than those generated by traditional geotechnical methods.
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Monitoring controlled DNAPL-contaminations using GPR
Authors V. Mayer, K. -J. Sandmeier and H. WilhelmThe Versuchsanstalt für Grundwasser- und Altiastensanierung (VEGAS) in Stuttgart, Germany, provides excellent conditions to test various methods which are designed to monitor, probe and clean aquifers. In December 1996 an experiment was carned out at a water-saturated model aquifer to monitor firstly the infiltration of 100 litres of Trichiorethene (TCE) and secondly the remediation of the model aquifer.
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Planning and constructing gas mains using GPR
By H. WeitzelIn general gas pipes are planned and constructed under strong economical conditions. The more information you get in front of a project the more the economy will increase. According to innovative technologies the planning bas become different and more demanding.
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Precipitation of salts in masonry mapped with georadar
By F. AndreasenThe church at the Christiansborg castle in Copenhagen suffered from a major fire in 1992. The fire was caused by a small emergency flare fired from a boat in the harbour during the local carnival. During the reconstruction of the church an ornamental marble-like mortar used on the inside walls became miscoloured apparently because of a too high water content in the thick masonry.
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Aerial features removing from ground penetrating radar profiles
Authors G. Boutard, C. Camerlynck, M. Dabas, M. Descloîtres and H. RobainThe Ground Penetrating Radar (GPR) has demonstrated its particular ability for many sub-surface investigations. Nevertheless, even in the case of an optimal response from the ground, the image is sometimes disturbed by unwanted features (Sun and Young, 1995). Data processing is then a mandatory way to enhance the useful information inside the radargram. Aerial features are one of the noises encountered using non-shielded antennas.
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Use of seismic refraction method in environmental geophysics
By S. StanicSeismic refraction method is used in environmental geophysics in order to make a precise reconstruction and true interpretation of investigated area. For this, it is neccessary to apply the most modern and very complex procedures and techniques of seismic exploration. One the basic methods within seismic investigations and exploration is seismic refraction method. Without its application it is very difficult to solve problems within geological media, to define precisely investigated area. The method is widely used in environmental geophysics.
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Leaking modes in near-surface seismic surveys
By M. RothIn many seismic surveys the part of the signal following the first break has a multicyclic, 'shingled', and dispersive nature. Particulary in high--resolution seismic surveys these shingled wavetrains limit the offset-time window for observation of refiected waves and therefore are generally treated as source generated noise.
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Soils elastic parameters: A parallel between in-situ and laboratory measurements
More LessMeasuring geotechnical parameters in a borehole and in particular the elastic properties is a goal for niany geophysicists. This technique would have several advantages: it would give valuable information for geotechnical engineering design, such as a continuous set of data with depth, showing soft and stuff zones.
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Landslide assessment with seismic techniques. A case study
Authors R. G. Francese, A. Grespan and V. IlicetoA high resolution P-wave seismic reflection and refraction survey was caried out in the foothill area of the Verona Province - Northern Italy. The objectives of the survey were to investigate structure and stratigraphy of near-surface Tertiary and Quaternary deposits and to develop a working procedure for Iandslide assessment using both refraction and reflection techniques.
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VibroScan - A powerful tool for environmental vibration protection investigations
More LessIt is well known that railway transport is very advantageous with regard to environmental protection. Reduction of air pollution is a typicai example. But railways have their characteristic environmental problems as well. According to an opinion poll in Vienna from 1991 noise imrnissions (41 %) and vibrations (19 %) are considered to be the most important ones by the urban population.
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Frequence domain electromagnetic source polarization investigation in case of a 2-D seafloor trench
Authors G. Petho, P. Kaikkonen and L. L. VanyanIn the course of seafloor EM survey the topographical changes of the seafloor can have influence on the EM components. These topographical inhomogeneities are 3-D ones. However, they are frequently elongated in one direction and can be treated as 2-D inhornogeneties. The aim of this model study is to present a numerical method for frequency domain marine controlled-source electromagnetic measurements using horizontal electric dipole sources on the seafloor and illustrate how the EM responses are affected by a 2-D trench. The horizontal electric dipole source is parallel and perpendicular to the struetural strike and the EM field components are computed along an in-line horizontal seafloor profile perpendicular to the axis of the trench at two frequencies.
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Fast transient electromagnetics: Real device modeling and information analysis
Authors A. B. Cheryauka and S. V. MartakovThe use of methods of alternating electromagnetic field for studying of the nearborehole space in dielectric logging and subsurface layers in shallow depth soundings deals with account of joint influence of conductivity and displacement currents.
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Removing topography influence in VLM-EM data by linear filtering
Authors N. A. Edsen and B. H. JacobsenWhen surveying upon a level homogenous halfspace or over borizontally layered lithologies no anomalies are seen in the conventional VLF-EM method. But in situations where the topography represents a surface with varying relief even upon a homogenous halfspace the terrain itself will generate VLF-EM anomalies which can be misinterpreted as originating from subsurface conductors.
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Main principles of the NPEMFE method employment for decision of different problems of mining geomechanics at mines of Donbass
Authors I. V. Kuznetsov and M. K. OsykinThe Donbass region is characteried by enough complex mining-geomechanic conditions of an underground coal mining, beds of which are subjected to tectonical, plicative dislocations with a break in continuity, complicating a picture of stresses distribution around working. Besides, the long coal nuning during many decades on horizons from 300-400 m to 1 km and more causes the problem of old abandoned underground working revealing, under which cauldrons dangerous for engineering constructions, are formed.
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Site investigation using EKS groundwater flow pathway images
Authors R. H. Clarke and J. W. A. MillarWe report the development and use of equipment which images groundwater distribution and the water flow pathways in aquifers. Aquifer permeability profiles and maps are obtained from electrokinetic signals using algorithms based upon theoretical and laboratory studies (Chandler, 1971, Nourbehecht 1963).
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Improvement in TDEM interpretations by joint inversion of different data sets
Authors S. Krivochieva and M. ChouteauThe TDEM methods are widely used in hydrogeological and environemental problems. Large depth of investigation, expeditive measurements and excellent sounding capabilities in 1D environment are their main advantages. Usually central loop sounding measurements are collected and 1D interpretation is performed at each site.
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Automatic 1D inversion of electrical well logs using the L1-norm and fixed layer-boundaries
By M. HalkjærFor electrical well logs, it is well known that the measured apparent resistivity differs from the true foririation resistivity in a region around boundaries between formations with different electrical resistivity. The apparent resistivity varies with electrode configuration and with resistivity contrast. In this paper, it is shown that inversion of the electrical log leads to a substantial increased resolution of the lithologic sequence. The inversion is performed with a simple one dimensional (1-D) L1-norm inversion routine which can accommodate for a very high number of layers wîth fixed layer boundaries.
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Lithologic inversion of tomographic data
Authors T. Fechner and P. DietrichSubsurface heterogeneity, i.e. the spatial variability of porous rock properties such as porosity or hydraulic conductivity, plays an important role in the spreading of a solute in the subsurface. A few highly-conductive zones may dominate the overall flow regime. Due to drilling costs the number of boreholes drilled to investigate an area is limited leading to uncertainties in determining the hydraulic properties and in resolving structures relevant for subsurface solute movement. A detailed subsurface characterization is however of vital importance for clean up technologies: for instance the efficiency and effectiveness of a "funnel & gate"-systems is dependent on its optimal positioning. It is shown, that high-resolution measurements such as seisinic and electric tomography can be used to identify hydraulic subsurface structures. For the problem of inversion of hydraulic properties and related subsurface structures a new formalism based on multivariate statistics is proposed.
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The location of infinite electrodes in pole-pole electrical surveys and the resulting error for 2D electrical imaging. A practical point of view
Authors H. Robain, Y. Albouy, M. Dabas, M. Descloitres, C. Camerlynck, P. Menchler and A. TabbaghThe improvement of multi-electrode arrays for resistivity measurements has led to an important development of electrical imaging for subsurface surveys. These arrays produce wide apparent resistivity pseudosections, presenting a large set of close data. It allows precise direct or inverse interpretation of 2D ground resistivity at shallow depth.
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Automated gravity terrain corrections using satellite stereo-pairs
Authors R. Davies, M. O‘Neill and R. McDonaldBy using SPOT stereo-pairs it is possible to automate the extraction of conjugate pairs of (matched) image co-ordinates. Propagation of these data through an appropriate sensor model, constrained by at least three ground control points, produces irregularly distributed height estimates which provide the basis of two elevation models. The first is a DEM of orthogonal grid points which is generated by Kriging.
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Filters for fast 2D and 3D pseudo-inversion of the resistivity profiles
Authors P. Cosentino, D. Luzio and R. MartoranaThe aim of the methodological approach here presented is to construct fast pseudosections starting from resistivity data: the pseudo-sections should match as closely as possible the geometry of the investigated structures.
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ELTOMO 97 - a software package for inversion and interpretation of resistivity data
Authors E. Danckwardt, F. Jacobs, S. Kuhn and G. PetzoldA device independent software package was developed for data conversion to an independent data format from any field devices, inversion with selection from some realized algorithms and a comfortable 2D- and 3D interpretation.
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Explorations on the Earth's relativistic gravity field
By W. ShenAccording to Newtonian theory, space and time are absolute, and consequently, once a length measure standard and a time measure standard are chosen, they keep invariant. According to relativity however, the length and time measure standards may vary with different positions and different reference systems. This implies that the observed values at points A and B are not absolute. Hence, we must establish a "common measure standard system", into which all observed values must be transformed.
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IP and resistivity survey at the INEL Cold Test Pit
By W. FrangosInduced polarization ([P) is a technique for detection of diffiise occurrences of metallic material. The Idaho National Laboratory (tNEL) CoId Test Pit (CTP) has been carefiilly constructed to simulate stored hazardous waste occurrences. IP and resistivity surveys of the CTP show a very strong IP response and a modest resistivity response associated with the simulated waste. Several false positive resistivity anomalies are noted.
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A radiomagnetotelluric survey at the Idaho National Engineering Laboratory Cold Test Pit
Authors B. Tezkan, S. Dautel and L. PellerinMany gravel pits have been filled in the last 50 years with household refuse, building debris and industrial waste. They were filled up in an uncontrolled manner with poor or no documentation. Nowadays most of these waste sites are covered by thin gravel and soil layer and are recultivated. however, they bear a huge risk to the environment due to the possible pollution of the aquifers. Therefore the detection of the dimensions of a waste site and especially the determination of different regions inside a waste site are very important for environmental protection studies.
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A test site for geophysical methods
Authors J. -L. Chazelas, D. Leparoux and A. Hollier-LarousseThis conimunication presents a new facility designed to help the development of geophysical rnethods in urban environment, particularly for trenchless technology applications. It is a test site whose dimensions and consistensy have been thought to provide as perfectly known and noiseless conditions as possible for expenments. The different aspects of this site and the care taken to its construction are indicated in order to invite searchers to use It. Some rough results illustrate the quality of measurement conditions and wide range of possibiities.
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Integrated near-surface geophysics applied to clay prospection
Authors H. Matias, J. Carvalho, L. Torres and R. GonçalvesThe area of study is of great importance for day industry. Nevertheless, known day reservoirs have become in the last years close to exhaustion. Also a dear delimitation of day exploration areas, is essential from a land planning perspective, and is one of the major goals of the work of IGM in the area. In fact the area is being studied in a broader programme involving geological reconnaissance, geophysical surveys - mainly EM-34, selective mechanical drilling, day sampling and technological tests on the materials.
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