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24th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
21 - 40 of 203 results
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Parametric Study of GPR Signals Numerical Model to Analyze Hardened Concrete Response at Different Antenna Positions
Authors I. Rodríguez-Abad, J. Mené-Aparicio, R. Martínez-Sala and Y. BotellaSummaryThe purpose of this paper was to apply a numerical model of a 2 GHz central frequency antenna, to understand the behavior of the waves generated with a GPR, when concrete samples were under study at different antenna positions. The GPR numerical model was created based on the FDTD method and GprMax software was used to provide the 2D numerical modeling. Numerical modeling results and their further parametrical analysis were very clarifying. Arrival times, velocity increments and relative amplitudes presented a pattern according to what it was expected, when the antenna was separated from the concrete sample more than 8 cm. Nevertheless, when this distance was closer than 8 cm, due to the signals overlap the concrete reflection arrival times were altered. Despite that, the relative amplitudes for these distances did present an exponential behaviour, in agreement with what it was expected.
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GPR Prospecting of Fluvial-Eolian Interaction Deposits in the Bermejo Valley, NW Argentina
Authors P. Zabala Medina, N. Bonomo, A.M. Osella, S. Salvo Bernárdez and O. LimarinoSummaryIn this work we present results of a prospecting carried out with GPR and field observations, to determine the composition and geometrical characteristics of an eolic-fluvial interaction environment in Argentina. Three depositional subenvironments were defined and investigated: 1) eolian channel, 2) eolian interchannel and 3) muddy interchannel. In each of them, we acquired GPR data with antennas of different nominal frequencies in order to evaluate their resolutions and penetrations. From the GPR data sections, it was possible to identify numerous reflectors that were interpreted in terms of the field data. The applied methodology resulted very efficient for describing the complex deposits and provided relevant information for later constructing models for reservoir characterization.
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Analysis of GPR Response to Cavities Simulated in the Physical Experiments
More LessSummaryFull-scale physical experiment was conducted to investigate the GPR responses to roadbed cavities using 3-D GPR technique. The experiment employed the testing ground with sandy soil, simulating cavities with dome-shaped structure attributed to old damaged underground facilities such as water supply and sewer pipes made of cast-iron and hume concrete, respectively. The surface of the testing ground was not paved with asphalt concrete at the current stage of the experiments. The GPR responses were investigated using 2-D profile and 3-D volume data obtained with 250 MHz antennas, and with HH and VV antenna orientations. The results of the experiment have shown that the simulated cavities responded with typical hyperbolic shapes reflected from the isolated reflector sources in 2-D and 3-D perspectives. The different antenna orientations have shown the different areal extents of the hyperbolic reflections patterns from the cavities. 3-D GPR volume data has provided better information on the locations and shapes of the cavities in 3-D space. This study is an ongoing project of KIGAM at a second stage of the experiments. More realistic conditions of the road surface with asphalt pavement would be prepared in the testing ground for the next stage of the experiments.
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Automatic Detection of Reflections at Ancient Walls in Simple-Offset GPR Images by Using Cascade Classifiers
Authors P. Bordón, P. Martinelli and N.E. BonomoSummarySimple-offset GPR reflection methodology allows obtaining very precise information in archaeological/historical sites. However, as large amounts of data are usually acquired, their processing, analysis and interpretation can be extremely time-consuming.
In this work, we present three algorithms for the automatic detection of reflections at ancient walls in SO-GPR images, based on cascade classifiers and well-known image feature descriptors: Haar, HOG and LBP. These algorithms were implemented using supervised learning, and experimental data from previous works. The best performances corresponded to the descriptor Haar. With only two cascade stages, remarkably accurate results were attained despite the complex characteristics of the signals of the walls. Almost all of them were detected near their actual positions, and only a few false positive predictions were obtained, mostly without any continuity across the profiles.
The main advantage of these methodologies is that once an accurate and reliable algorithm is implemented using data from an appropriate sector, it can be applied in all the zones of the site with similar characteristics, or even in other site of the same type. Thereby, a precise representation of the target structures is rapidly obtained, and the qualified interpreter only has to examine some parts of particular profiles.
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GPR Survey in Outcropping of the Guarani Aquifer System, Paraná Sedimentary Basin, Brazil - Preliminary Results
Authors J.L. Porsani, J.V. Coutinho, B. Poluha and E. WendlandSummaryThis work shows preliminary results of GPR survey in the Ribeirão da Onça Basin areas, located in outcrops zones of Guarani Aquifer System, in the Parana Sedimentary Basin, São Paulo state, Brazil. Studies had as objective to characterize the subsurface, aiming to obtain saturated and unsaturated layer thickness and other hydrogeological characteristics. Preliminary GPR results obtained with 200 MHz antenna shows strong reflections corresponding to the groundwater level and a subsoil horizon which can be associated with transition from Cenozoic to Mezosoic sediments of the Botucatu Formation. The results are important to improve the understanding about geological characteristics of unsaturated layer, aquifer saturated zone definition, besides of contribute to scientifical improvement in hydrology areas and hydrogeology of outcrops zones of Guarani Aquifer System.
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Eigenimage Filtering on Sudoeksa Field Data to Reduce Clutters
More LessSummaryWe compare the background-removal and eigenimage-filtering techniques in the perspective of suppressing clutters while preserving horizontal subsurface target reflections.
The background-removal technique is a simple but powerful technique to remove laterally invariant clutters. Therefore, it is widely used in GPR image processing softwares. However, in case horizontal subsurface targets exist, the background-removal technique has the risk of damaging the target reflection events.
One of the alternatives to this background-removal technique is the highpass-eigenimage-filtering technique. In some literatures, the effectiveness of the eigenimage-filtering technique has been proven for synthetic data sets. In this study, we compare the eigenimage-filtering technique with the background-removal technique for the field data set acquired at the testbed in Sudeoksa, Korea, for which we already have the information of subsurface target materials and locations. Through this study, we show the effectiveness of the eigenimage-filtering technique in revealing the horizontal subsurface target image.
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Enhancing Stratigraphic and Structural Features in GPR Images of Limestone Karst through Adequate Data Processing
Authors W.E. Medeiros, J. Oliveira Jr., F. Santana, F. Bezerra and C. CazarinSummaryThe demand for detailed understanding of karst formation process in carbonate rocks occasioned an accompanied demand for high quality GPR images. It is necessary to characterize from the images primary strata and to identify fractures, faults, and dissolution features, as an stage to establish spatial and genetic associations among these elements. However, materials infilling karst voids or resulting from carbonate rock weathering might be conductive and, as a result, penetration depth and signal resolution might be greatly reduced due to attenuation. Considerable effort must then be done to improve the image resolution in karst through data processing. We present a GPR processing flow highly tested in the limestone karst environment of the Jandaíra Formation in Potiguar basin, Brazil, composed by the following main steps: static correction, dewow, background removal, spreading and exponential compensation gains, spectral balancing, Kirchhoff migration, band-pass filtering, topographic correction, and amplitude-volume enhancement. The spectral balancing step is of particular importance because, when judiciously applied, it can replace approximately the high frequency content lost by propagation effects. We also exemplify how image improvements obtained in 200 MHz datasets help the interpreter to better visualize the karst geometric elements, thus contributing to a deeper understanding of its formation process.
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A Newly Developed GPR Receiver
Authors P. Annan and N. DiamantiSummaryGround penetrating radar (GPR) signal capture has been a challenge since the method first appeared. The capture of radio frequency signals has required some specialized receiver design and overall more complex system architecture than visible to the normal GPR user. As the field of GPR is evolving and moves towards more quantitative data analysis, there is a need for users to better understand the signal capture process.
We provide a summary of the underpinning aspects of GPR signals and an overview of the principles that have been involved in time-domain signal capture. The capture of wideband transient signals requires considerable hardware ingenuity and the concepts are illustrated with presenting data acquired by an older and new receiver from the same location.
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Analysis of Random Backscattering in Ground-Penetrating Radar Signals to Detect Subterranean Watercourses - Field Results and Laboratory Tests
Authors V. Perez Gracia, Y. Rovira and S. Santos-AssunçaoSummaryThe studies of seismic risk in Barcelona city required nanozonation because measurements of soil response in the plain of Barcelona present sudden changes in small areas, highlighting the importance of a most detailed study to determine the nanozones. The problem lies in the high number of vibration measurement points needed for an appropriate nanozonation that made the analysis time consuming or even unfeasible. Therefore, a previous GPR survey was carried out in relevant zones of the city in order to determine abrupt changes that requires high density of passive seismic measurements. Some previous GPR studies underscore the relation between the noise at consequence of clutter in radar data and the random heterogeneities of the medium. In this paper, GPR is used to detect noise as consequence of clutter due to clusters of materials associated to subterranean streams and paleochannels. In addition, some laboratory test were carried out with the objective of comparing with field survey results.
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Determination of Environmental Vulnerability Using GPR Data
More LessSummaryPluvial floods as a harmful effect of the global climate change process may occur more and more frequently in urban areas. With determination of environmental vulnerability the vulnerability pillar of the impact assessment can be given. The environmental vulnerability depends on three factors: slope, water coverage and the drainage capacity of the earth. Since the drainage capacity of the surface water depends on the soil’s clay content, with a careful calibration of GPR survey the soil factor can be derived from the attenuation of EM waves. This study presents the determination process of environmental vulnerability and with a field example illustrates its applicability where the designation of vulnerable zones was done by using conventional method and the based on GPR survey as well. The field test showed that based on the attenuation of EM waves more precise and reliable vulnerability assessment can be carried out than with the conventional delineation method of the endangered areas.
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Study of Structural Elements in Heritage Buildings with Ground Penetrating Radar Images
Authors S. Santos-Assunçao and V. Perez-GraciaSummaryMaintenance and repairing or ancient buildings requires efforts and a wide knowledge of the structures. However, in many cases, the constructive methods, the distribution of supporting elements and the materials are unknown. There are two main causes of this uncertainty: the lack of information and drawings due to the age of the buildings, and the misinformation about past restorations, damages and alterations of use and structures. This paper presents a GPR assessment of two terraces of ancient buildings, placed in the Eixample neighbourhood of Barcelona city (Spain). Common offset radar data was used to acquire data on the terraces of the buildings, with an 800 MHz centre frequency antenna. In one case, GPR images show structural changes as consequence of rehabilitation. The other case study is characterized by significant variations in the built structural supporting structures, including orientation and material types. In both cases, GPR images allowed to determine the structural supporting structures. The results highlight the capability of the method to determine the position, orientation and shape of structural elements and, also, to differentiate between wooden and metallic members.
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Enhancing Crosshole GPR Data by Analysing Travel Time Differences of Reciprocal Tomographic Measurements
Authors S. Hellmann, P. Giertzuch, M. Grab, A. Bauder and H. MaurerSummaryCross-borehole radar (XBHR) systems have been employed successfully in recent decades in a broad range of geophysical applications from glaciology and hydrogeology to peatland gas development. Especially the high contrast between water and any other material and the high resolution of crosshole measurements allow a detailed investigation of the near subsurface.
During data acquisition the position of the antennas can only be controlled from the surface. While moving the antennas in their boreholes positioning uncertainties are unavoidable. We provide a straightforward algorithm to analyse and correct for depth increment errors by using reciprocal multi-offset gather measurements. Systematic travel time differences due to slightly incorrect depth registration, i.e. due to slip or cable tension while using a common trigger wheel can be analysed and a more realistic depth increment in terms of reciprocal travel times can be determined. Artefacts and velocity errors in the final data can be suppressed. Additionally due to technical reasons randomly occurring zero-time drifts have been investigated. Using a common zero-offset profile and the multi-offset gathers we show how to correct for zero-time drifts in each multi-offset gather individually.
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Development of Drone-Assisted Electromagnetic Prospecting System for Automobiles Buried by Landslides
Authors Y. Mitsuhata, T. Ueda, A. Kamimura, S. Kato, A. Takeuchi and C. AdumaSummaryWe have developed an electromagnetic prospecting system using a drone for searching for automobiles buried by a landslide. The system consists of an drone, an 1.6 m long electromagnetic (EM) sensor with a GPS receiver, an ultrasonic distance sensor for monitoring the height of EM sensor from the ground surface and a WiFi serial transceiver for controlling the EM sensor and monitoring the measured data. The drone suspends the EM sensor and EM data are acquired during the flight. The distance of drone-sensor separation is crucial to avoid EM noise caused from the drone motors and to stabilize the flight of drone On the basis of field experiments, we adopted a separation of 4 m and attached a vertical tail to the aft end of EM sensor witch can stabilize the flight at a speed of at least 2 m/s. The height of EM sensor should be monitored because it affects the EM data significantly. We have tested the system at an experiment site where there are two cars embedded at depths of 1.5 m and 3 m respectively. The close-area search clearly indicated the location of the shallow car, and there was a slight indication of the deep car.
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Electrical Soundings Applied to the Contamination at a Feedlot in Buenos Aires Province, Argentina
Authors C.M. Sainato, P. Zarragoicoechea and B.N. LosinnoSummaryThe cattle fattening in corrals (feedlot) is an activity that has expanded in the last years. These activities may contribute with contaminants to environment through waste water and manure, such as Nitrogen and Phosphorous, pathogens, between others. The aim was to identify and characterize physically, chemically and microbiologically the phreatic aquifer at a feedlot, at the zone of Saladillo, Bs. As. Province, Argentina. A topographic survey was carried out to describe the directions of superficial runoff and to locate the wells. Samples were taken for laboratory analysis. Electrical resistivity tomography was carried out to characterize the extent of the potential contamination. Near the corrals there is a decrease in the resistivity in unsaturated and saturated zone (NSZ, SZ). In the sense of groundwater flow and decreasing topography, an increase of EC of SZ is observed, associated with water salinization. The concentration of nitrates and phosphates increases in the sense of groundwater flow. The Pseudomonas and E coli, in some wells, added to the amount of detected coliforms, demonstrates the deterioration of the groundwater quality. The integration of geophysical survey allowed corroborating the extent of the salinization of the NSZ and SZ by the effect of leachate from the corrals.
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Analysis of Soil Gas and Their Correlation with Seismic Events along Indo-Burmese Subduction Zone
Authors R.C. Tiwari, S. Singh, H.P. Jaishi and R.P. TiwariDespite the fact that no strong earthquake (> M6) occurred during the investigation period in the region, some meaningful relationship between anomalies in radon/thoron concentration and seismic events have been found. It was observed that both soil radon and thoron data seems to be affected by variation in the meteorological parameters. During the investigation period there are two radon peaks (≥ +2SD) and these were correlated with the relevant seismic events. The so-called postquake reduction was observed for radon minimum value during the measuring period. It is interesting to note that most of the seismic events occurred along the Indo-Burmese arc during the investigation period (Fig. 2) suggesting significant disturbance between the plate tectonics along the Indo-Burmese subduction zone. It can be seen that continuous soil radon/thoron measurements at weekly intervals were not frequent enough to obtain a precise interpretation of the data. A long term database is needed for better results for which work is in progress.
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Preliminary Analysis of Strong Motion Data from Nepal Earthquake - An Input for Structural Designing
By M. DagarSummaryStrong ground motion records of an earthquake provide the basic information for evaluation of seismic hazard of an area in order to reduce the considerable loss to life and property. It is an important input for earthquake engineering for perfect designing practices so that the structures can withstand maximum possible shaking. Several earthquake characteristics are studied for qualitative evaluation of seismic hazard of an area. These cover characteristics such as Epicentral distance, Peak ground acceleration and site conditions. Analysing average spectral response on the basis of these characteristics shows three major factors such as strong ground motion source, path and site effects. Further, the comparison of average response spectra with existing BIS code shows the current Indian code is applicable for the entire country is well within the structural limits proposed for the seismic forces at all periods for alluvium sites. If the buildings are designed as per the norms given by the BIS (2002), then a considerable amount of loss in terms of life and property can be reduced.
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Effect of Heterogeneity on Estimation of Permeability Using Lattice Boltzmann
By S. RezaieSummaryIn this study, pore-scale simulation is carried out utilizing the lattice Boltzmann method by taking into account the direct effect of all pores. The smooth profile method [22] is employed for liquid-solid interaction in the pore-scale simulation of the dual porosity porous medium. In REV scale simulation, the effect of micro pores, after homogenization, is combined with the effect of larger pores. In addition to fluid flow simulation, the effects of micro-pore permeation are also examined on the main parameters governing fluid flow.
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2D and 3D Inverse Modeling of the Residual Gravity Field for a Buried Deposit Mass
More LessSummaryGravity surveys have been used in investigations of wide range of scales such as tectonic studies and mineral explorations and in engineering and environmental problems. Geometric shapes and especially prisms are useful in geophysics for modeling two and three dimensional (2D and 3D) underground bodies that produce gravity anomalies. Modeling in 2D and 3D are an important procedures enabling 2D and 3D information about mineralization to be leveraged for the computation or extraction of the key parameters. In this paper, we employ the inversion algorithm of Li and Oldenburg (1998) for 3D inverse modeling and a 2D nonlinear inversion method for a real gravity data set related to metal deposit from Iran.
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Magnetotelluric Responses in Layered Medium
Authors I.V.S. Chanakya and A. KumarSummaryMagnetotellurics, Electromagnetics, Modelling, Synthetic data
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Impact of Small Shear Wave Velocity Variations on Surface Wave Phase Velocity Inversion
Authors A. Wang, M. Le Feuvre, D. Leparoux and O. AbrahamSummarySurface wave methods have attracted a lot of geophysicists’ attention for the purpose of monitoring civil engineering structures, because they represent the most energetic part of the seismic signal, and contain information on shallow media. In order to infer the mechanical properties of the medium as a function of depth, an inverse procedure is required that minimizes a misfit function between observed and modeled data. However, a small change of model parameters can have low effects on observed surface waves data. This study focuses on the inversion of phase velocity dispersion curves of two-layer media with small to moderate variations of shear velocities. We use a simple two-layer model, where the shear velocity and thickness of the top layer are respectively 600 m/s and 8 m, and the shear velocity of bottom layer is 1100 m/s. Results show that it is difficult to distinguish inversion results when variation of shear velocity of the shallower layer is lower than 2%, and 10% for the deeper layer in our study case. These results emphasize the difficulty of estimating small to moderate evolution of medium, especially for deeper layers.
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