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9th EAGE/EEGS Meeting
- Conference date: 31 Aug 2003 - 04 Sep 2003
- Location: Prague, Czech Republic
- ISBN: 978-94-6282-116-3
- Published: 01 September 2003
41 - 60 of 180 results
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Non linear inversion of noise array measurements for determining S-wave velocity vertical profiles
Authors M. Wathelet, M. Ohrnberger, D. Jongmans, T. Camelbeeck and F. ScherbaumThe knowledge of the shear wave velocity (VS) profile at a given site is of major importance in earthquake engineering. The geophysical techniques generally used in soil dynamics to obtain shear wave velocity as a function of depth are the borehole tests (Jongmans, 1992), which are expensive and limited to shallow depths.
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Wavefield composition and decomposition for the electro-kinetic reflection
Authors A. Ranada, E. Slob and C. P. A. WapenaarThe electro-kinetic effect represents a class of processes in which there is a conversion from electromagnetic to kinetic energy and vice versa. In the case of this transfer taking place in a saturated porous medium we name the effect electro-seismic for the transfer from electromagnetic to kinetic energy, and seismo-electric for the transfer from kinetic to electromagnetic energy.
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Using a lattice solid model for vertical seismic profiles
Authors N. Fillipidou, S. Abe and G. G. DrijkoningenThe transmission of seismic energy through a sequence of layers consisting of unconsolidated material is by itself a challenging problem. The seismic pulse is known to broaden slightly with propagating distance, often described with a damping factor Q. In shallow sediments damping is very high compared to rocks, and should therefore show more pronounced effects of energy loss. One part of the losses can be described by viscoelastic losses, although viscosity is not the reality but is a way of giving a phenomenological description of damping. From a physical point of view, particles that can move in relation to each other seems to be more evident in unconsolidated or partly consolidated mediums like soils and other soft sedimentary formations.
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Airborne geophysics for shallow object detection: Technology update 2003 - electromagnetics
Authors T. J. Gamey, W. E. Doll, L. P. Beard and D. T. BellORNL has been developing helicopter-mounted geophysical systems for detection of shallow buried objects since 1997. In collaboration with the U.S. Army Engineering Support Center - Huntsville and private sector partners we have focused our efforts on UXO detection and characterization, but the system is equally well adapted to any large area shallow mapping project such as utility locating, brownfield studies, hazardous waste sites and archeological sites.
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Airborne geophysical surveys assessing the general scale quaternary mapping project in Finland
Authors E. Hyvönen, J. Lerssi and T. VäänänenGeological Survey of Finland has mapped surficial Quatemary deposits mainly at a scale 1:20000. These large scale maps cover only part of Finland. To fulfil the needs of the customers and the authorities a new mapping program begin in 2003 to produce maps and database at scale 1:250 000, covering whole Finland by the year 2007. The new database will contain geospatial distribution of sediment polygons and related attribute information. It will be produced by interpreting, modifying and generalising existing spatial data using GIS- and image processing techniques with minimum amount of field work (Nevalainen et al., 2002).
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A detailed inversion scheme for helicopter-borne electromagnetic frequency-domain data
Authors R. J. Tølbøll and N. B. ChristensenGround-based electromagnetic methods have for many years successfully been employed for hydrogeological investigations in Denmark. A wish for higher efficiency has led to a growing interest in the possibility of using airborne electromagnetic methods in the mapping campaign, and lately the helicopterborne electromagnetic frequency-domain (HEM) method has been in focus.
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SkyTEM - new development in high-resolution airborne TEM
Authors K. I. Sørensen and E. AukenIn Denmark, 99% of the water supply is based on groundwater abstraction. Increasing problems with the groundwater quality, due to urban growth and agricultural contamination, have caused the Danish Minister of Environment to approve a plan for improving ground water protection.
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Ground penetrating radar modelling of rough underground interfaces
Authors A. Giannopoulos and N. DiamandiIn many electromagnetic scattering problems, the Earth's surface as well as subsurface interfaces are often modeled as planar dielectric boundaries (Cui and Chew, 1999). However, this assumption is not always valid and roughness in the Earth's subsurface can potentially be a major source of variability in the obsewed GPR signals. In some applications where shallow targets have constitutive properties very close to those of the background medium clutter due to the rough interface may introduce severe constraints on target localization and identification. As a result the detection of a buried object under a rough subsurface interface, using ground penetrating radar (GPR) could become problematic.
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Mineral detection by a new approach to the compact inversion of gravity data
More LessA new approach for computing the regularization parameter in compact gravity inversion (Last and Kubik,1983) is presented. Neyman (1979) procedure for discrete data is used for the regularization parameter. A field example is demonstrated . Key words: Compact inversion, regularization parameter, mineral detection.
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Polarization and acquisition in GPR surveys: tests on physical models
Authors P. Capizzi, P. L. Cosentino and L. RomanoIn most cases GPR surveys are carried out using co-pole data, because cross-pole data are generally not acquired. However, in the planning of GPR survey it is important to consider the antenna polarization, as the sensitivity of cross-pole and co-pole configurations is connected with the type of target as well as with the subsurface conditions.
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Increase in measurement capacity of low frequency GPR investigations
By J. AaltonenTo carry out fieldwork with unshielded low frequency GPR systems with the aim to investigate groundwater and geological conditions requires today a comparable large work effort. This paper will show how using a new bistatic one-unit in-line antenna of 50 MHz can ease these types of investigations.
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Test of the MRS technique in Southern Africa
Authors J. Roy and M. LubczynskiITC, together with ten collaborating agencies from seven countries is involved in a research project on the MRS (magnetic resonance sounding) technology since 1996, when IRIS Instruments introduced the NUMIS instrument. Thanks to regional collaboration, MRS tests were made in Botswana, Namibia and South Africa. The fieldtests were carried-out under a combination of low earth's magnetic field and high ambient noise conditions. The test sites included different aquifers from the point of view of lithology, depth and porosity thickness product. MRS field results and operational constraints are discussed.
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On the inversion of complex magnetic resonance signals
By A. LegchenkoIt is known that the phase shift caused by electrically conductive subsurface makes the magnetic resonance signal complex (Legchenko, et al., 1990). Obviously, inversion of the complex signal may provide more information about the subsurface in comparison with inversion of only amplitudes currently available (Legchenko and Shushakov, 1998). Recently, an effort was made to improve the mathematical model used for interpreting MRS measurements.
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Inversions of surface-NMR signals using complex kernels
Authors M. Braun and U. YaramanciSurface Nuclear Magnetic Resonance (SNMR) is used for groundwater exploration and aquifer characterization (e.g. [1]). The NMR-Experiment is conducted by a coincident transmitter and receiver loop at the surface exciting the protons of water molecules underground with the Larmor frequency of the earth's magnetic field. Performing a SNMR measurement with increasing excitation intensity (pulse moment) yields a complex sounding curve, where the amplitude of the relaxation signal is determined by the numbers of protons i.e. the water content. The subsurface electrical conductivity affects both the amplitude and especially the phase [2,3].
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Correlation of remote sensing data and 2-D resistivity imaging method for evaluating paddy yields in Kedah, Malaysia - a preliminary study
Authors A. B. Saiful Bahari, M. S. Safid, M. N. M. Nawawi and K. AbdullahA preliminary study was conducted to investigate the feasibility of integrating remote sensing and 2-D resistivity imaging technique for evaluating paddy yield. The selected study site was a rice growing area in Kedah, Malaysia, developed by the Muda Agricultural Development Authority (MADA) as shown in Fig. 1(a).
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Sampo - Frequency domain wide-band EM system for deep hydrogeological and environmental studies
Authors T. Valli, T. Jokinen, J. Lehtimäki and H. VanhalaSampo is a frequency domain wide-band electromagnetic (EM) sounding system constructed by Outokumpu co. and GTK. It consists of a magnetic dipole as a transmitter and a threecomponent receiver. The transmitter-receiver spacing (coil spacing) varies between 50 meters and 1500 meters, the latter being also the maximum depth of investigation.
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Site conditions requiring extra precautions for induced polarisation measurements
More LessIn a precedent paper we compared sections acquired either with separated multicore cables and non-polarisable potential electrodes or with only one multicore cable and current and potential electrodes both in stainless steel. From the results obtained at two sites in Southern Sweden, we could conclude that it was possible to obtain good quality time-domain induced polarisation data with the simplified logistics. Consequently, we have applied the method to other sites, and could occasionally verify that it was justified. But in some cases, when the grounding resistances were very high, the quality of the induced polarisation data was very poor.
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A 3D seismic survey applied to the study of an aquifer
Authors S. Picotti, G. Rossi and G. Böhm3D seismic survey is proven to be a very efficient tool for underground exploration, but up to now it has been used almost only for hydrocarbon production. In fact, the high costs of acquisition limited the use of this technology for other purposes, as for example hydrology applications. Today, however, the decreasing costs of equipment and the increasing water request are making this technology suitable in such a field too.
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Geometrical description of an aquifer for the NAME project
Authors B. Ludovic and D. ChapellierThe NAME project (Nitrate from Aquifers and influence on carbon cycling in Marine Ecosystems) is a European research project which gathers hydro geologist, geophysicist, geochemist and marine biologist belonging to different institutions.
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Resistivity surveying applied to hydrogeological characterisation of Quaternary paleo-valleys
Authors L. Marescot and D. ChapellierThe understanding of complex Quaternary structures has always been a major endeavour for geologists. Identifiing Quaternary paleo-valleys incised into the bedrock is important for understanding groundwater circulations and pollutants migration. Cost effective resistivity surveys may provide the fundamental information required by engineers for hydrogeologic modelling.
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