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Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics
- Conference date: September 6-10, 2015
- Location: Turin, Italy
- Published: 06 September 2015
161 - 164 of 164 results
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Geophysical Experimental Survey on Flood Protection Dikes - The Case Study of the Loire River Basin
Authors M. Pareilh-Peyrou, P. Labazuy, K. Kelfoun and F. ChalusSummaryAn electromagnetic induction (EMI) survey has been performed along the Loire River protection dikes (France), with a 60 km long, high speed and high resolution, field acquisition campaign. The main aim of this dikes diagnostic mission was to locate and identify potential local weakness or damaged zones inside the engineering structures. We used an EMI device (EM31) and a GPS receiver on board an experimental fiberglass cart support, designed for high yield acquisition surveys. This study allowed to provide the electrical subsurface image (conductivity) of the whole structure and allowed, in addition, for precise detection of the small-scale anomalies. The outputs consist of electrical images of both the inner dike structure and the subsurface geological environment. This fast first-phase study is efficient for detecting decametric local anomalies while giving information about the dike inner structure. Once EMI anomalous zones have been detected, further detailed investigations have been performed on selected areas, including electrical resistivity tomography (ERT) profiles and geotechnical drills. Thus, the objective of our experimental study was to scale down and optimize this second phase of the prospecting campaign, which will considerably reduce the cost and the time spent on the whole survey.
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Application of the DEXP Method to the Streaming Potential Data
Authors M.A. Abbas and M. FediSummaryWe interpret the self-potential data related to groundwater flow by the depth from extreme points (DEXP) method; a multiscale method in which the data are upward-continued and scaled by a scaling law depend on the structural index. The depth to the water table is estimated from extreme points of the DEXP image without a priori estimate of the hydraulic coupling coefficient. The method is tested with a synthetic model of the water table and applied to a real self-potential dataset near a pumping well. The obtained results agree well with the known information.
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Surface-NMR in High Noise Areas
Authors J.J. Larsen and A.A. BehroozmandSummaryOne of the main noise sources in surface-NMR data is the harmonic components of the fundamental 50 Hz powerline signal. In some circumstances, the surface-NMR data are distorted by several unrelated harmonic series. We present surface-NMR data from Ristrup, Denmark, where two harmonic series are present in the data and the noise level is almost an order of magnitude higher than typical Danish surface-NMR data. Noise reduction using standard multichannel Wiener filtering is shown to be inadequate for retrieval of the NMR signal. We show that the NMR signal can be retrieved by sequential fitting and subtraction of the harmonic series using a model-based approach.
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A Waterborne GPR Survey to Estimate Fine Sediments Volume and Find Optimum Core Location in a Rockglacier Lake
Authors L. Sambuelli, N. Colombo, M. Giardino and D. GodoneSummaryRockglaciers are landforms related to ice-rich permafrost creep and represent a substantial reservoir of groundwater in the alpine region. Rockglacier lakes can occur when permafrost-ice meltwater released from rockglaciers, snowmelt, rain and groundwater find the geomorphologic conditions to be collected in an impermeable depression. This depression can be filled with fine-grained sediments (ø<1/16 mm) from at least three sources: 1) the dust contained in the snow covering the lake during winter, 2) the solid fraction of the runoff and meltwater from the rockglacier and 3) the runoff or the wind transport from the surrounding areas. Fine sediment volumes, bedding and typology offer large amount of information for interpreting the past and ongoing biological and abiotic processes in the catchment. In order to estimate the fine sediment volumes and plan a coring campaign in the Col d’Olen Rockglacier Lake (Aosta Valley, Italy) we performed waterborne GPR surveys with both 200 and 500 MHz antennas. After data processing we obtained the bathymetry of the top and the bottom of the fine sediments. Within the fine sediments unit we also found a discontinuity whose meaning will be investigated with a planned coring located in the zone with the maximum sediment thickness.
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