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25th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 8-12, 2019
- Location: The Hague, Netherlands
- Published: 08 September 2019
41 - 60 of 141 results
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Identification and Recognition of Landmine Internal Structure Scattering Contribution from GPR Data
Authors F. Lombardi, M. Lualdi, F. Picetti and P. BestaginiSummaryThe aim of the study was to quantify the potential increase in the information level produced by an increase in the data dimensionality, i.e. from analysing a 1D signature to the investigation of a 3D GPR volume. The experimental campaign was carried out employing two different neutralised landmines, characterised by a different internal structure and buried in controlled conditions. Obviously, the acquisition of a single monodimensional signature of the target has the advantage of being almost effortless, but shows significant limitations in achieving adequate performance, in particular for landmines showing an irregular internal structure. This is a consequence of the impossibility of effectively separating the different scattering contribution. As well, despite producing a clearer and more intuitive image of the target, a single 2D profile is not able to provide reliable performance, hence there is little benefit in acquiring a 2D profile as it still suffers from not producing unambiguous results. The analysis of a 3D volume, instead, allows for an accurate delineation of the internal structure of the target, providing a reliable solution to the complex target design critical issue.
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Tree Inspection by GPR Reflection and Transmission Measurements
Authors K.Takahashi Takahashi, K. Aoike, K.Kajino Kajino, Y. Ashiba, K.Kaneko Kaneko and N. IshizawaSummaryTree trunk inspection has been conducted to assess the risk of the collapse and maintain the safety of pedestrians. Conventional methods often involve invasive measurements that may cause further damages to trees. Radar can be used as a tool to non-invasively image the inside structure of tree trunk for the inspection. We developed a workflow of the inspection that combines reflection and transmission measurements. It makes inspection work efficient; the quick assessment by transmission measurement and detailed inspection by reflection imaging. In addition the permittivity of tree trunk, which is required for reflection imaging, can be estimated from the transmission measurement data. Consequently, we can improve the quality of reflection imaging by using the estimated permittivity. In the present paper, our workflow for the tree inspection by radar is illustrated and demonstrated with data collected for old trees in a shrine.
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Integrating Resistivity and GPR Data for Plant Root Study in Indoor Agricultural Environments
Authors A.G. Gerea, A.E. Mihai and P. AtkinsSummaryThe use of two geophysical methods is presented, the electrical resistivity tomography and GPR. Integrating these methods in agricultural environments posses significant advantages in water and fertilizer consumption representing a very fast and useful tool in the area of precision agriculture as well. The results are promising, achieving a level of precision by implementing various IoT (internet of things) devices and adaptations of the method and data processing.
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The Use of Resistivity to Complement GPR Surveys on Tree Roots in Urban Areas
More LessSummaryUrban areas are not usually favourable sites for geophysical surveys. However, GPR has shown promise in different environments, particularly in the mapping of coarse roots. Given its functionality on multiple urban surfaces, speed of data acquisition, and overall suitability for tree root detection, we find that in most scenarios, GPR is the most well-suited geophysical method for tree root detection. GPR is not a panacea, though. It has fundamental limitations when it comes to tree root detection , and given the variability of environmental parameters in urban areas, as well as the numerous sources of noise, the extent to which GPR can detect tree roots (and thinner roots in particular) remains site-specific and not fully clear.
In this case, resistivity surveys and ERT in particular can serve as a complementary or potentially even self-sufficient method of detecting tree roots.
Here, we use four different antennas covering a broad range of central frequencies (250 MHz, 750 MHz, 1.5 GHz, and 4 GHz) to showcase the potential and limitations of GPR in this scenario, as well as a hybrid between a commercial resistivity meter and lab-developed equipment to implement both conventional and non-conventional arrays.
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Recording Longer for Higher-Resolution Near-Surface Imaging - Shear-Wave Reflections from Vertical Sources and Receivers
By A. MalehmirSummaryMode-converted reflections have long been recognized in field seismic data and have been used for improved imaging and targeting. However, their use for near-surface imaging and characterization have only been limited to dedicated SH-SH data acquisition setups. In a quick-clay landslide prone area in southwest Sweden, collocated SH-SH using 1 m source and receiver spacing, and a conventional P-wave line using 2 m source and receiver spacing were separately acquired using different instruments and setups. Both datasets have so far been the subject of several studies, however, only recently after recovering longer records of the P-wave data, clear hyperbolic events with slow moveouts were observed at 0.5 second and later times. Thanks to the long record and available SH-SH dataset, these reflections are interpreted to have pure shear-wave origin. Confirmed by downhole logging data and core observations and to some extent other independent geophysical datasets, the shear-wave reflection imaging of the perceived vertical component data, allowed two sets of coarse-grained layer materials and extremely undulating bedrock to be resolved. The P-wave reflection imaging of the dataset did not provide such a high-resolution image as obtained by the shear-wave reflection imaging given the strong source-generated noise at the very early arrivals.
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High-Resolution Seismic Imaging Using a 2C Land Streamer System
Authors T. Szabþ, T. Toth, Z. Hamori, V. Németh and P. FilipszkiSummaryLand streamers are often used for seismic surveys in urban areas and paved surfaces, where conventional spike geophones can not be planted.
With development of shear-wave seismic methods, land streamers recording S-component also gained more importance. Due to their low velocity, shear-waves give us the opportunity to investigate the shallow (0-20 m) subsurface with high resolution, using the reflection seismic method. Worldwide published examples of land streamer surveys and a novel P- and S-wave vibroseis source for engineering applications initiated the development of a modular 2-C land streamer system. Our goal was to develop a seismic land streamer which enables fast data acquisition on varying surfaces for different types of data processing, such as multichannel analysis of surface waves, turning ray tomography, reflection and refraction processing.
Several surveys were carried out with the newly developed land streamer in noisy urban areas, on paved surfaces in order to investigate the applicability of the instrument. P and SH waves were generated simultaneously and the recorded data were processed with different methods Real data example will be shown demonstrating the data quality and productivity of the developed 2-C land streamer.
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Comparison of Site H/V Spectral Ratio and Predominant Frequency by Using Microtremor and Earthquake Data
Authors K.H. Coban and N.Sayil SayilSummaryThe determination of the predominant frequency and H/V ratio is an essential part of dynamic site characteristics. In the present study, we aim to evaluate the site effects of the Marmara region by calculating horizontal-vertical spectral (H/V) ratio and predominant frequency from microtremors and earthquakes data. We selected 5 earthquakes (M ≤ 4.5), which occurred in the Marmara region and recorded by 14 broadband seismometer stations. Also, we determined 1-hour microtremor records according to earthquakes date and time. The H/V ratio and predominant frequency were calculated by Nakamura method with Geopsy program and Seaseme criteria. Besides, the same parameter was estimated from S-waves and Coda waves of selected earthquakes. The results were compared with each other. According to the results, the H/V ratio and predominant frequency values vary according to the direction of earthquakes. In some stations, the microtremors and earthquakes results give close results. However, for reliable H/V ratios and predominant frequency values, we think that earthquake records and microtremors records should be compared. The study results will contribute to the Marmara region seismic risk assessment.
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Seismic Imaging Using Electromagnetic Vibrators - Storm versus Lightning
Authors B. Brodic, R. De Kunder, P. Ras, J. Van den Berg and A. MalehmirSummarySeismic imaging using two electromagnetic (EM) vibrators (E-vibes) based on linear synchronous motor principle was evaluated via a seismic survey in central Netherlands. The sources, Storm and Lightning, weigh 1650 kg and 90 kg, respectively. Storm is a vertical-type vibrator with full drive frequency 2-200 Hz and peak force of 7 kN. Depending on the orientation, Lightning can be used either as P- or S-wave vibrator with full drive frequency 8-400 Hz and peak forces of 1.7 kN (S-wave) and 1.2 kN (P-wave). Data were acquired using a 100-unit-long three-component microelectro-mechanical (MEMS-based) seismic landstreamer and 253 wireless seismic nodes. We analyze and compare data recorded using both sources and vertical components of different seismic receivers (MEMS versus geophones), along with different acquisition strategies in terms of signal quality, maximum penetration depth and offsets. Shot gathers and stacked sections indicate great potential of both sources for broadband (2-200 Hz) seismic imaging with excellent quality data from 50 ms to 1.6 s (~2000 m depth) using the Storm and comparable, but of lower quality and resolution, using the Lightning source. Bellow 1.6 s, coherent events are absent on the Lightning data while the Storm shows weaker events down to 2.2 s.
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Detection of Near-Surface Heterogeneities at Archaeological Sites Using Seismic Diffractions
Authors J. Liu, Q.Bourgeois Bourgeois, R. Ghose and D. DraganovSummaryWe develop a new approach to locate very shallow subsurface objects using seismic diffractions of low signal-to-noise ratio. In our approach we use the diffraction arrivals recorded from the subsurface objects. To image the objects, we apply spatial instantaneous-phase-coherency summation along diffraction hyperbolae. We demonstrate the performance of our method using synthetic and field data.
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Integrated Analysis of Geophysical Data Using a Data Mining Approach
Authors K. Sabor, D. Jougnot, R. Guerin, L. Apffel and B. SteckSummaryA data mining algorithm was tested in order to jointly interpret electrical tomography and seismic refraction profiles. As a first step, the geophysical profiles used are numerical ones before applying this approach to real measurements data in further studies.
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An Optimal Combination of Geophysical Methods to Image Geological Structures
Authors B. Owoc, A. Marciniak, S. Kowalczyk, J. Dzierzek and M. MajdanskiSummaryNowadays seismic methods are commonly used in geological research because they give a clear image of the structure at various depths. The resolution of the seismic image depends on the amount of data. Therefore to maximize the use of recorded seismic data the combination of a few seismic methods is proposed. In this paper, an optimal combination of geophysical methods is suggested to study the near-surface geological problems. A standard reflection seismic imaging is supported by multi-channel analysis of surface waves, first breaks traveltime tomography and Ground Penetrating Radar. All these methods are cost-efficient and easy to perform. Using all recorded wavefield, high-quality images are obtained down to 200 m with small additional processing. The Mesozoic bedrock is clearly visible in the seismic imaging as a very strong reflector. Its depression is probably connected to erosion or structure (syncline). Under this horizon, it is possible to find one or two detachments related to the nearby fault. Moreover, the field work was an opportunity to test in-house modifications to seismic source and GPS based timing device, and both systems worked correctly.
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Enhancing Time-Lapse Geoelectrical Models of Soil Moisture Dynamics with a-priori X-Ray CT Derived Information
Authors M. Cimpoiasu, O. Kuras, T. Pridmore and S. MooneySummaryDeveloping a better understanding of soil hydraulic properties is of significant importance for such diverse fields as agriculture, soil and ecosystems management, civil engineering and geotechnics. Electrical Resistivity Tomography (ERT) and X-ray Computed Tomography (CT) are two state-of-the-art methodologies with great potential for applications in soil science. ERT allows time-lapse monitoring of solute transport. X-ray CT is sensitive to bulk density changes at high resolution.
We monitored the infiltration of a KCl solution through a partly deionized water saturated undisturbed cylindrical soil column using ERT. Prior the infiltration, we scanned our sample and segmented the pore architecture out of the resulting X-ray radiograms. Based on pore characteristics such as size and connectivity, we split the pore volume into two distinct zones, percolating and non-percolating pores. Afterwards, we reconstructed non-percolating pore features within the ERT model mesh. By comparing the ERT inversion result, with or without the pore architectural information, we noticed a sensible improvement in how the electrical model is able to represent the fluid flow path. This result sets the scene for a new joint methodology, which constrains the geoelectrical interpretation of the subsoil moisture with soil structural information and its contribution to solution infiltration.
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Co-Operative Inversion of Multi-Channel Analysis of Surface Waves and Electrical Resistivity Tomography Using Fuzzy Clustering Approach
More LessSummarySeismic and electrical resistivity tomography methods are recognized as powerful tools to investigate landslides. The effectiveness of the investigation significantly increases if we can exploit the strength of the each method and complement this information in a combinative model. In this study, we performed co-operative inversion of two datasets (multi-channel analysis of surface waves and electrical resistivity tomography) via a fuzzy clustering technique. Our results demonstrate the robustness of our routine. In our single data inversion process, this method can construct models that include zones relating similar parameters. A conventional inversion process uses smoothing criteria to find a final solution, but this approach cannot image a subsurface with highly variable physical properties due to faults and groundwater seeps present in our survey area. The co-operative inversion of the seismic and geo-electrical data exploits the advantages of the both methods, to build a better model than models inverted from the single datasets. Our inversion model provides a more reasonable subsurface model than conventional inversion results. Finally, our process can provide the clustering image, namely pseudo-lithology, from the co-operative inversion models of the two methods. This makes interpretation much easier than using the inverted models.
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Identifying Sedimentary Facies in Mediterranean Ephemeral Channels (MEC) by Using of Electrical Resistivity Tomography
SummaryThe effects of Climate Change and the intensification of land use on the territory show the importance of Mediterranean ephemeral channels. The morphological adjustments of this type of system are mainly controlled by the magnitude and frequency of hydrological events.
The primary objective of this case of study is to analyse the morphological and systemic adjustments produced in the MECs, as a consequence of Climate Change and new environmental scenarios. To analyse these effects, a small semi-arid Mediterranean basin located in the Southeastern Iberian Peninsula, has been chosen. The analysis of geomorphological evolution carried out in several narrowing of this basin has been made from the identification of the structure and sedimentary facies associated with the geoformations of the fluvial bed. For each cross-section of the bed chosen as the control section, geoelectric profiles will be made to be correlated with stratigraphic data of shallow depth mechanical boreholes, from which the tomographies can be calibrated. The use of both techniques will allow knowing the texture and sedimentary structure of the bed, which will help to detect changes in the processes of erosion, transport and sedimentation produced in recent periods, as well as determine the depth of the rocky substrate.
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Geometrical Characterisation of a Marine Intrusion by Utilising Electrical Resistivity Tomography
Authors M.D. Vásconez-Maza, M.A. Martínez-Segura and M.C. Garcîa-NietoSummaryIn semiarid zones, agricultural activity exerts much pressure on the aquifers. Every year much water is utilised in crops; wells are overexploiting the aquifers which do not have enough recuperation time. In this study, the “Minor Sea” baths all the coast of the overexploited aquifer what is promoting the intrusion of the seawater in the continent. The principal aim of the paper is to characterise the underground layers of an agricultural terrain located near to the cost and determine the geometry of the marine intrusion by using Electrical Resistivity Tomography and boreholes.
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Electrical Resistivity Tomography (ERT) Applied to the Characterization of Fractured and Weathered Zones in Subsurface Granites
Authors R. Garcia, M. Himi, L. Rivero, L. Camarero, A. Urruela, R. Lovera, A. Sendrós and A. CasasSummaryTwo ERT campaigns were carried out to characterize the subsurface geology and the possible infiltration and flow pathways of the water through the granites (fractured and weathered zones) from the Barranc de Contraix area (Aiguestortes i Estany de Sant Maurici National Park, Catalonia, NE Iberian Peninsula). Three types of geoelectric levels were defined: high resistivity levels (>15.000 Ω-m), medium resistivity levels (between 6.000 and 15.000 Q-m) and low resistivity levels (<6.000 Ω-m). The ERT profiles have been shown highly resolutive to identify the existence of these fractured and/or weathered zones on the granites, represented by relatively low resistivities in comparison with the high resistivities associated to fresh granites. This fractured or weathered zones on the granites may allow the flow of water from the high mountain lakes Estanys Gelats (>2700 m.a.s.l.) to the actual fluvial system (1900 m.a.s.l.).
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Numerical Estimation of Geoelectrical Data Errors -Comparison with the Method of Reciprocal Measurements
Authors P. Martinelli, V. Grunhut, P. Bordon, F.E. Robledo, M.E. Franzoni and A.M. OsellaSummaryIt is well-known that considering appropriate estimations of geoelectrical data errors improves inversion results, especially in the presence of data with atypical values. In these cases, other option is to apply some procedure for removing the outliers from the datasets, and then perform inversions without considering data errors. However, these data are not always easily identifiable.
In this work, we present four numerical methods for estimating data errors, alternative to reciprocal measurements. They are based on the analysis of the differences among the data corresponding to neighboring measurement points. They are computationally cheap, and present two important advantages: they do not increase survey times because they do not require any additional measurements, and they can be used with any electrode configuration. Using a representative experimental example, we demonstrate their effectiveness for reducing the effects of outlier data on the inversion results. The subsoil models obtained considering the proposed error estimations are, in general, similar to that obtained considering the errors estimated from direct and reciprocal measurements. These models are also in agreement with the results obtained without considering data errors, after removing the outlier data.
The formulations presented are 2D, but can easily be generalized to three dimensions.
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Modular Resistivity Device for Physical Model Studies
Authors M. De la Vega, V. Bongiovanni and A.M. OsellaSummaryA programmable automated resistivity device was designed and constructed using an open-source electronic platform. In this work we present a low power version of the device that was implemented for physical model laboratory studies.The low power version of the device for physical model measurements use a 24V battery system to generate the A-B current flow. A resistance of 560Ω limits the current flow to less than 40mA. We present results obtained in a simple physical model to verify the performance of the automated resistivity device developed. We program the electrodes positions to make in line dipole-dipole, Schlumberger-Wenner, and Y11n configuration surveys. The tomography obtained from the D-D and S-W data show an excellent agreement with the physical model, the convergence is of 1% for these configurations. Y11n configuration give a convergence of 12%.
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Simultaneous Inversion of Multi-Channel IP Data with Structural Simliarities
More LessSummaryTime-domain spectral induced polarization data can be inverted by using the concept of four dimensional (4-D) inversion method. In this approach, the entire multi-channel data set is simultaneously inverted, where the apparent chargeability and model chargeability at entire time-channels are composed into a single data and model vectors in the space and channel domains. Regularizations not only in the space domain but also in the channel domain is applied to reflect the characteristic of chargeability curves. Furthermore, we introduce the concept of structural similarity between resistivity and chargeability models by using minimal cross-gradient constraints. Developed inversion algorithm was successfully applied to several simple subsurface models to obtain reasonable chargeability distribution. Through the structural simlarity constraint, more reasonable IP data distribution can be obtained since noisy IP data can resort to resistivity distribution which more robust and stable due to higher S/N ratio.
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Theoretical Fundaments to Obtain Complex Permittivity and Resistivity in CR Method
Authors A. Lucuy, M.V. Bongiovanni, V. Grünhut and A.M. OsellaSummaryThe resistive capacitive contact (CR) method is a non-intrusive geophysical technique that allows to characterize the subsoil, by means of electrical images. There are several models that interpret how the electromagnetic signal propagates in terms of the conductivity and polarization of the charges under the action of an electric field. In general, most of the works focus on the phenomenon of polarization. When a time-varying electric field is applied on a surface with a sufficiently high frequency for there to be a considerable relaxation time, not only a complex susceptibility but also a complex conductivity are generated and therefore, a complex resistivity. The purpose of this work is to analyze the behavior of the electromagnetic signal on a soil, with relatively high frequencies, and to link the complex conductivity and resistivity through the tangent of losses, as a function of a scale factor and a phase shift between the emitted and received signal. Through an adequate description of the physical principles involved, a theoretical formulation will be developed. It could be obtain through experimentally measuring the amplitudes and the phase shift, both the usual information of the apparent resistivity of the subsoil, and also information about its apparent permittivity.
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