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10th International Workshop on Advanced Ground Penetrating Radar
- Conference date: September 8-12, 2019
- Location: The Hague, Netherlands
- Published: 08 September 2019
39 results
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Using GPR on a problematic agricultural field for groundwater protection in a karst environment
Authors Marjana Zajc and Janko UrbancSummaryDue to the extreme heterogeneity and increasing importance of karst aquifers as water supply sources and their often inadequate protection strategies, the knowledge of subsurface conditions in such areas is vital for the accurate groundwater vulnerability assessments. The presence of agricultural activity can increase the risk of groundwater pollution, therefore a GPR study was conducted on a problematic agricultural field within a karst aquifer. The use of two different antenna frequencies (250 and 500 MHz) proved useful for detecting different features at different depths. The results show a very thin top soil layer as well as multiple discontinuities and karst features in the shallow subsurface. The combination of both allows for rapid drainage, reduced crop growth as well as increased groundwater pollution risk.
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A Novel Processing Framework for Tree Root Mapping and Density Estimation using Ground Penetrating Radar
Authors Livia Lantini, Fabio Tosti, Iraklis Giannakis, Daniel Egyir, Andrea Benedetto and Amir M. AlaniSummaryEstimating the root density of mature trees is of high importance as the root system is a robust indicator of both the health status and the structural integrity of a tree. With this in mind, a multi-stage data processing scheme is proposed using Ground Penetrating Radar (GPR) to achieve an effective estimation of the root density of trees. The proposed framework is divided into three main chronological steps. Initially, ringing noise is removed using a Singular Value Decomposition (SVD) filter prior to a frequency-wavenumber (F-K) migration. Subsequently, a tracking algorithm is applied to the processed data in an effort to identify patterns associated with roots. Lastly, the found patterns are expressed as continuous and differentiable functions from which the root density is derived. To demonstrate the viability of the proposed approach, a case study is presented in order to identify the root system and map the overall density of the roots of a mature tree. The algorithm is commercially appealing with minimum computational and operational requirements for large-scale forestry applications.
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Using Ground Penetrating Radar (GPR) To Detect Water Leakage From a Buried Pipeline
Authors Khaled F. Almutairi, Yasir A. Almutairi and Majed A. AlmalkiSummaryThis paper discusses conducting GPR surveys with different frequencies to detect a suspected water leakage from a buried pipeline at a gas platform. Due to the difficulty in accessing the area above the pipeline because of the fill nature of the pipeline area, the survey had to be conducted a long lines that are 1.5 meters way from the pipe line on both sides. The high-resolution 250 MHz antenna needed to identify the leakage could not provide reliable information on the location of the potential leakage due to the distance. However, the low-resolution 25 MHz antenna acquired over two lines on both sides of the pipeline captured the pipeline, in spite of the distance. At a certain location, a dimmed pipeline reflectivity is remarkable due to a regional geology, or related to leakage. Based on analysis, this location is the most probable location for leakage, however with high uncertainty. Generally, GPR managed to detect the pipeline and the host material, soil and limestone, however, confidence in its ability to capture the leakage is not that high for many reasons. This paper provides recommendations of survey designs to detect a considerable water leakage from a pipeline at similar site conditions.
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Assessment of a stepped-frequency GPR for subsurface drainage mapping for different survey configurations and site conditions
SummarySubsurface drainage systems (popularly known as “tile drains”) are installed in poorly drained agricultural fields to remove excess water and enhance crop yields. Knowledge of the precise location of drainage pipes is important for both economic and environmental reasons. Conventional methods of locating drainage pipes involve the use of tile probes and trenching equipment, which are not only laborious in use, but also entail a high risk of damaging the drainage pipes. In this study, we evaluate the alternative of a stepped-frequency continuous wave (SFCW) ground penetrating radar (GPR) system mounted in two survey configurations and employed in wet and dry field conditions for subsurface drainage mapping. Three different combinations were tested on an organic soil of an intensively tile-drained lowland area. The evaluated test combinations include a ground- and air-coupled antenna array on a dry soil and a ground-coupled antenna array on a relatively wet soil with a snow cover and possible frozen topsoil layer. Although wet soil conditions provided more strongly contrasting anomalies for deep drain lines, our results suggested that dry soil conditions are more generally suitable for drainage mapping, i.e. for a variation of soil textures and drain line depths. Complementarily, average electrical conductivity (EC) estimates obtained from a spatially constrained inversion of apparent electrical conductivity (ECa) measurements from a multi-receiver electromagnetic induction (EMI) instrument were used to provide insight in soil variability and to evaluate the suitability of soil conditions for drain line mapping with GPR.
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A Tomographic Inversion Approach for the Detection of Decay and Cavities in Tree Trunks using Ground Penetrating Radar
Authors A.M. Alani, F. Soldovieri, G. Gennarelli, I. Giannakis, I. Catapano, L. Lantini, G. Ludeno and F. TostiSummaryA variety of tree species, such as ash and oak trees, are nowadays under serious threat in the United Kingdom and European territories as a result of the action of aggressive fungal diseases. To this effect, Ground Penetrating Radar (GPR) is an effective geophysical tool capable of collecting information on the internal structure of trees. Nevertheless, traditional processing methods can provide only limited indications for health monitoring purposes. In this study, a demonstration of the GPR potential and the use of a tomographic inversion approach in detecting decay and cavities is provided. In that context, a set of finite-difference time-domain (FDTD) simulations of different complexity (i.e. internal trunk configurations and dimensions of the targets) were used to assess the performance of the proposed strategy. The results prove the viability of the proposed approach in identifying the position of cavities and decay in tree trunks.
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Mutually Constrained Inversion of Common Offset GPR Reflection and Surface Wave Dispersion Data in Layered Media
Authors Shufan Hu, Yonghui Zhao and Shuangcheng GeSummaryGround penetrating radar (GPR) and seismic surface wave methods (SWMs) are widely used in near-surface surveys. For the most frequently used common offset GPR reflection data, a key requirement for proper imaging of subsurface reflectors is an accurate velocity model, especially when dipping layers are present in the subsurface. For the inversion of surface wave data in a layered system, the model parameterization is critical if a priori information is not available. Here, we presented a possible way for mutually constrained inversion of the common offset GPR reflection traveltime and surface wave dispersion data. We used the depth of interfaces to link the model parameters of GPR and the surface wave method based on structural similarity. The parameterization problem of the surface wave data inversion is mitigated by using interface constraints from GPR profile, we then inverted the layered model parameters including thickness and velocities of EM wave and shear wave simultaneously by using the alternate coupling strategy. Test on a synthetic example showed that the estimation of depth and EM velocity in GPR result is significantly improved, while, the simultaneous use of both datasets could provide a reliable parametrization for the surface wave inversion.
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Critical verification of the underground cartography of the municipality using a high performance Ground Penetrating Radar
Authors Massimiliano Pieraccini, Lapo Miccinesi and Heidi Garcia CanizaresSummaryThe city of Florence, Italy has a modern and continuously updated underground map archive. After the construction of a new parking area in a terrain of the University of Florence, the area has been mapped using a high performance Step Frequency Continuous Wave Ground Penetrating Radar. The images acquired by the GPR have been compared with the official cartography. We noted important features not reported in the map. This confirm the necessity of GPR survey also in city provided with modern and updated underground cartography.
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Signal Artifacts in GPR Engineering Surveys
By Davide CampoSummaryGround Penetrating Radar (GPR) data may include not only signal events originated by real features present within the investigated materials, but also some artifacts caused by additional and not easy to predict travel paths or by elements located adjacent or above the scan line. A good understanding of the wave behavior and accurate observations on site are therefore necessary and mandatory for a correct interpretation. This paper presents five case-studies where unwanted and unexpected signatures produced by structural and non-structural metal elements and overhead objects are discussed and analyzed.
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Laboratory and field GPR measurements to detect qanats
Authors Azadeh Hojat, Luigi Zanzi, Saeed Karimi-Nasab, Hojjatollah Ranjbar and Meng Heng LokeSummaryDetection of qanats is one of the main geotechnical concerns in the development of cities in most parts of Iran. Using old aerial photos, we have tracked eight qanat systems at Shahid Bahonar University of Kerman (SBUK). To map qanats in detail, integration of ground penetrating radar (GPR) and electrical resistivity tomography (ERT) techniques was proposed. In this paper, we present the results of laboratory and field GPR measurements to detect qanats at the main campus of the university. Laboratory measurements were performed using an IDS 3GHz antenna on a sand box simulating qanats at different scale and equivalent depths. GPR investigations using Mala antenna with the frequency of 250MHz were performed near the buildings that are located on or close to the qanats tracked at the first phase of this research. GPR method has the required resolution to detect qanats, but the problem becomes challenging for deep qanats in radar absorbing soils. ERT technique could be considered as an alternative to map qanats for soils where GPR penetration is poor. We suggest a perspective idea of using drone technology to be integrated with the defined methods to overcome the limitations of geophysical methods.
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Preliminary development of a workflow for processing multi-concurrent receiver GPR data
Authors Dimitrios Angelis, Craig Warren and Nectaria DiamantiSummaryRecent advances in timing and control technology have allowed the development of multi-concurrent receiver Ground Penetrating Radar (GPR) systems. These types of system enable rapid acquisition of Wide-Angle Reflection and Refraction (WARR) data and have the potential to provide a wide range of benefits, including improved velocity models. However, the high volume of data that can be generated, as well as the fact that these systems are new and continually being developed, demands research and automation of new processing workflows.
Numerical modeling is gradually becoming a standard approach in GPR for testing new processing schemes/algorithms and guiding interpretation of real data. Nevertheless, simulations can require detailed models of antennas, targets, and structures, which can be time-consuming to create programmatically.
In this work, we demonstrate a graphical user interface (GUI) tool for rapidly designing and building complex geometries that can be used in numerical simulations for GPR. We then use this toolset to generate realistic WARR data to test automatic first break/time-offset correction algorithms we have developed. These algorithms form the initial steps of our workflow for processing WARR data.
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Measuring Asphalt Pavement Density with a GPR-based Sensor: A Case Study
Authors Nectaria Diamanti, A. Peter Annan and Steven R. JacksonSummaryDuring the construction of asphalt pavements, one of the most important parameters critical to pavement longevity is its density. Pavements need to contain enough air voids to allow some plastic deformation and at the same time, have low enough air voids to prevent water ingress and moisture damage. Being able to map density during emplacement can help control asphalt installation leading to greater pavement life.
We have recently presented a new instrument, the Pavement Density Profiler (PDP), which is designed to be a simple, easy-to-use instrument that enables the pavement industry to rapidly assess the compaction of hot mix asphalt (HMA) pavements. In this paper, we present PDP test results performed in cooperation with the Minnesota Department of Transportation on a newly paved section of road. The main conclusions of this testing are that the current PDP is far simpler to use, that instrument factory calibration is reliable, and that the translation to density still needs serious industry assessment.
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Advances in the Prediction of the Bearing Capacity of Road Flexible Pavements using GPR
Authors Fabio Tosti, Luca Bianchini Ciampoli, Fabrizio D’Amico and Amir M. AlaniSummaryThis work proposes an experimental-based model for the assessment of the bearing capacity of road-flexible pavements using ground-penetrating radar (GPR - 2 GHz horn antenna) and the Curviameter non-destructive testing (NDT) methods. It is known that the identification of early decay and loss of bearing capacity is a major challenge for effective maintenance of roads and the implementation of pavement management systems (PMSs). To this effect, a time-efficient methodology based on a quantitative modelling of road bearing capacity is developed in this study. The viability of using a GPR system in combination with the Curviameter NDT equipment is also proven.
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Laboratory tests in rigid pavement
SummaryDeterioration of concrete structure is consequence of aging, applied loads and weathering. In this paper, several laboratory tests were presented, compared to computational models and a field test case study. The purpose of the laboratory measurements is the analysis of the results in the case of different size cracks in concrete beams, filled with several materials
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Analytic GPR data processing for surface layer thickness assessment
Authors Vânia Marecos, José Pedro Figueiredo, Simona Fontul and Mercedes SollaSummaryThis paper presents the ongoing research as part of a master thesis on the analytic handling of GPR data for the quick assessment of road surface layer thickness. Equations were developed and then validated with test data. It was verified that the method is valid for layer thickness determination as the errors obtained are well within an acceptable threshold when comparing to the real thickness obtained from core drills.
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GPR for preventive conservation and valorisation of buried archaeology
Authors Luca Bianchini Ciampoli, Roberta Santarelli, Fabio Tosti and Andrea BenedettoSummaryThis paper deals with a geophysical experimental activity carried out in Maxenxius Complex, an archaeological site located in Rome, Italy. The objective of the study was to evaluate the feasiblity of GPR for the structural detailing of buried archaeological remains, in view of its future valorisation through three-dimensional reconstruction. As a result, GPR allowed to confirm the literature-based information, i.e. to precisely locate the tanks of the thermal area which was known to be buried in the inspected area. In addition, the tomographic analysis highlighted the presence of two further tanks, thereby suggesting the possibility of further rooms to be located close to the excavated ones. This assumption was also confirmed by tomographic analysis, which stressed out a wall pattern that seems to suggest the presence of further rooms in the top-right side of the area. In general terms, GPR demonstrated a great applicability to archaeological purposes, despite the reliability and productivity of the data interpretation are strongly influenced by the expertise of both the geophysicists and the archaeologists involved.
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Mathematic Physical Equivalency of 2D Pure Waves in Seismics and Electromagnetics
Authors Tan Qin and Thomas BohlenSummaryFor a long time people tried to find the inner connection between the seismic waves and electromagnetic (EM) waves to explain their similarity. For example, the acoustic wave and Shear Horizontal (SH) wave possess the similar mathematic expression with the Transversal Electric (TE) and Transversal Magnetic (TM) wave, respectly. In this paper, we summarize those waves into an uniform wave equation based on a concept we termed the “wave operator”. The spartial matrix derived from the wave operator consists of four parts in three directions: the direction component, the volume component, the shear component and the rotation component. We then proved the equivalency of different pure waves in 2D case using this uniform expression. Therefore the forward solver developed for the longitudinal, shear and rotation wave can be converted to each other with a simple substitution. The two numerical tests verified our proposition.
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Quasi-Measurement Pitch Change: A New Framework for Machine Learning on GPR
Authors Rei Ogura and Takamichi MiyataSummaryGround-penetrating radar (GPR) is a geophysical method for non-destructive inspection of underground infrastructure. The main impediment to machine-learning-based classification of GPR data is gathering enough labeled data. Previous work done to solve this problem generated pseudo-GPR data through the numerical simulations done with expensive GPU clusters.
In this paper, we propose a simple yet effective framework for machine learning with GPR data without enormous computational cost. The key idea of our method is quasi-measurement pitch changes (QMPC) that can obtain several times the amount of pseudo-data from real measurements. QMPCs are based on a simple sub-sampling procedure from real data, and no interpolation is applied for the pseudo-data. Thus, special hardware like GPU clusters are not required and no artifacts are produced by such an interpolation. Moreover, using QMPCs for test data allows us to apply ensemble learning at the inference phase of machine learning.
The experimental results for the classification problem of buried objects clearly show that our framework can drastically improve accuracy with additional labeled data and without significantly increasing computational cost.
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Investigation of the characteristics of the soil by means of TDR probes: a preliminary work on some future perspectives
Authors Raffaele Persico, Iman Farhat, Lourdes Farrugia and Charles SammutSummaryIn this contribution, a technique that can be employed by a TDR probe for the measurements of the electromagnetic characteristics of a soil is presented. In particular, the proposed approach aims to characterise the dispersion law of a soil (in general, of the probed propagated medium), which by itself is a relevant piece of information or it can be exploited within an advanced data processing scheme related to GPR data.
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Field Experiments to Investigate Cross-polarization Characteristics of a Dipole Array Antenna in a Water-filled Borehole
Authors S. Ebihara, K. Toyozawa and T. HasegawaSummaryWe investigated cross-polarization characteristics of a dipole array antenna in a water-filled borehole. We theoretically determined the electromagnetic fields when a plane wave is incident to multiple cylindrical layers. According to our analysis, the dipole array antenna may be characterized by a spatial frequency spectrum of the dipole array signals. If a cross-polarized wave is incident on the antenna, the absolute value of the spectrum is maximized to the first order. Furthermore, there is a phase difference of 90 deg. between the co-polarization and cross-polarization incidence angles at the first order spatial frequency. Numerical simulations confirmed that the cross-polarization characteristics in the spatial frequency spectrum may be observed as suggested in the theoretical analysis. Field experiments in soil were carried out at a test site. Data equivalent to signals of a dipole array in a borehole were obtained using a transmitting loop in another borehole. In the experimental data, cross-polarization characteristics were observed similar to those deduced from the theoretical and numerical analyses.
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Reconfigurable GPR systems: achievements, errors and perspectives
More LessSummaryA reconfigurable stepped frequency GPR system is a GPR system that can change in a programmable way some parameters. The reconfigurability, as a general idea, was patented at Italian level, and then a prototypal stepped frequency reconfigurable GPR system was implemented in 2010. Here, we describe some studies and activities performed with this system, outlining some achieved results but also some errors. Finally, also some perspective hypotheses that, hopefully, might become future research activities, will be outlined.
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Badger project: GPR system design on board on a underground drilling robot
Authors Alessandro Simi, Davide Pasculli and Guido ManacordaSummaryThe present paper presents some results of EU founded project called Badger, the first underground robotic system that can drill, maneuver, localize, map and navigate in the underground space, and which will be equipped with tools for constructing complex geometry networks of stable boreholes. The proposed robotic system will enable the execution of tasks that cut across different applications including trenchless constructions, cabling and pipe installations, geotechnical investigations. The robot will integrate technology for perception, localization and mapping, in order to sense, map and interpret the surrounding underground environment; the system will merge collected underground data with digital maps to plan and track the motion of the robot with respect to the environment. Finally, the robotic system will be capable to manage and intelligently combine the massive data gathered during underground operation, to continuously improve its perception and cognition abilities. In particular, with reference to the cognition system, in this paper is reported the design of an on-board integrated GPR system, whose purposes is collision avoidance as well to provide input to Simultaneous Locating And Mapping (SLAM) system. Innovative design and resulting performance are reported, where miniaturization of radiating elements without decrease bandwidth and working frequency represents the main challenge.
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The Gopher antenna: A new efficient design for ground penetrating radar
By Veli VoipioSummaryIn this article, we propose a new design we call the “Gopher antenna”: a patch antenna structure which does not require a resistive load and is therefore more efficient than the current ground-penetrating radar (GPR) antennas. When tested, it works well in a GPR application as low as approximately -25 dB of the application’s original transmit power. The Gopher antenna also meets the general requirements for the GPR antennas: a received wide spectrum and a good impulse response. Departing from the common designs (bow-tie dipoles and horn/Vivaldi structures), the Gopher antenna is a patch-antenna structure consisting of a quarter-wave feeder and a parasitic half-wave patch with no resistive load. The Gopher antenna has a directive radiation pattern, a good impulse response without distortion, a reasonable cross-polarization ratio, and a good radiated spectrum also when placed on the ground.
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A New Drone-Borne GPR for Soil Moisture Mapping
SummaryWe present a new drone-borne ground-penetrating radar (GPR) for soil moisture mapping. The GPR system is lightweight, <1.5 kg, and consists of a vector network analyzer (VNA) as frequency-domain radar, a hybrid horn-dipole antenna operating in the range 250–2800 MHz, a microcomputer for controlling the radar, a smartphone or tablet for remote control, and a GPS for positioning. Radar data processing is performed using full-wave inversion based on the method of Lambot et al. As a proof of concept, we present the results of a data acquisition over an agricultural field in Saint-Denis, Belgium. For this example, we used the 500–700 MHz frequency range and inversion was performed in the time domain, focusing on the soil surface reflection. The retrieved permittivity was converted into soil moisture values using Topp’s equation. The soil moisture map was constructed using kriging. The obtained results were very consistent with the soil topography map, with higher soil moisture values observed in the talwegs and lower values observed in the highest slopes. Although the method still requires a few improvements before being routinely applicable, the method appears to be very flexible and promising for a series of drone applications, including precision agriculture and environmental engineering.
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GPR survey of “Bellariva” swimming pool complex with a continous wave step frequency GPR radar
Authors Lapo Miccinesi, Massimiliano Pieraccini, Gloria Terenzi and Giulia MazzieriSummaryThis paper presents the results of a Ground Penetrating Radar survey on a historical building taking part of the “Bellariva” sport Centre, designed and built in Florence (Italy) in 1957-1960 years by the Word-famous Italian engineer Pier Luigi Nervi. The building under survey hosts the locker rooms of the swimming pool and a bar at the first floor, a restaurant at the second where an evident crack was observed. A Ground Penetrating Radar survey was performed in order to determinate the internal structure of the floor, dimensions and disposition of steel bars, and to gather information about the connections between perimeter beams and balcony at the level of the restaurant. The survey confirmed what were reported on the original drawings of the building. The results of the survey will be used for defining a numerical model and to design possible retrofit interventions.
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Detecting rebar corrosion through complementary GPR and IRT methodologies
Authors M. Solla, N. Fernández, S. Lagüela and F.J. VidatSummaryCorrosion is one of the pathologies that most affects the resistance of reinforced concrete. There are numerous ancient structures still in use affected by corrosion that need proper evaluation and remedial treatment for their maintenance. This work presents a combined methodology by using Ground-Penetrating Radar (GPR) and Infrared Thermograpy (IRT) techniques for the detection and evaluation of corrosion. The combination of these complementary techniques allowed for the identification of corroded areas and moisture, along with inner damages such as cracking and debonding.
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A Multidisciplinary Study on the Roman Amphitheatre of Lecce, Southern Italy
SummaryIn this contribution, a multidisciplinary investigation regarding the Roman Amphitheatre in Lecce, southern Italy, is be proposed. In particular, GPR prospecting combined to passive seismic measurements and with a virtual reconstruction of the monument allows deducing some important features of the monument, unknown before. In particular, this is a monument only partially brought to light, and part of it lies under the current Saint Oronzo’s Square. We have investigated about the part still undiscovered of the amphitheatre.
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Using GPR to Evaluate the Stratigraphic Condition of the Mosaic of the Dolphins in Delos Island, Greece, in order to Adopt the necessary Conservation measures
Authors Meropi Manataki, Christos Maris, Apostolos Sarris and Antonis VafidisSummaryThe mosaics of Delos island are a significant body of the ancient Greek art of the Hellenistic period that are inscribed to UNESCO’s World Heritage List. In this study, GPR systems with frequencies of 1600MHz, 500MHz and 250MHz are used to evaluate the stratigraphic condition of the mosaic at house of the Dolphins that decorates the peristyle impluvium. All the obtained data were processed in MATLAB and both Bscans and depth slices were used for the interpretation. The 1600MHz system performed the best and it was possible to identify the boundaries of the mosaic layers as well as problematic areas, such as bulges and high levels of moisture that may cause deterioration. The results obtained from the 500MHz and 250MHz are complimentary to the ones obtained from the high frequency system as the emitted signals can reach deeper levels. Structural characteristics of the cistern below the main mosaic floor were mapped in some detail including five stone arches. The overall performance of the GPR was satisfactory and the resulted information will be taken into account for the upcoming conservation plans.
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Anisotropie matrix-free tomography using discontinuous Galerkin of GPR data acquired between boreholes in Rustrel carbonates
Authors Marco Salcedo, Stéphane Garambois, Philippe Le Bouteiller and Jean VirieuxSummaryAn increasing number of Ground-Penetrating Radar (GPR) studies takes benefit from illumination capabilities provided by dense acquisitions between boreholes. Traveltime tomography, migration and full waveform inversion provide high-resolution images to be interpreted. Tomography is often performed under an isotropic assumption, although anisotropy may exist at different scales. A new tomography approach is investigated based on an anisotropic Eikonal solver for the forward problem and an adjoint formulation for inverse problem. The misfit gradient is computed directly without expressing the sensitivity matrix, leading to explicit contribution of anisotropic parameters. The parametrization of elliptical anisotropy based on vertical and horizontal velocities is preferred to a parametrization based on Thomsen parameters for a realistic synthetic example, inspired from a real example of GPR transmission tomography between two boreholes in a carbonate environment where an old gallery exists. The vertical velocity is nicely recovered while the anisotropy contribution stays small. However, the real application provides similar results either through a layered isotropic model or through a smoother anisotropic model. Geological information is, therefore, needed for further specific interpretation.
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Associating borehole radar logging data with petrophysical properties in a mud-contaminated reservoir: Can we converse disadvantage to advantage?
Authors Feng Zhou, Iraklis Giannakis, Antonios Giannopoulos and Evert SlobSummaryIn the phase of oil drilling, mud filtrate penetrates into porous formations and alters the pore fluid properties. This complicates well logging exploration, and inevitably gives rise to shift in reservoir estimation. Logging engineers deem mud invasion a harm and attempt to eliminate its impact on logging data exploration. However, from our point of view, the mud-contaminated parts of the formation do also carry some valuable information, notably with regard to the key hydraulic properties. Therefore, if adequately characterized, mud invasion effects, in turn, could be utilized for reservoir estimation. Typically, the invasion depth critically depends on the formation porosity and permeability. To achieve this objective, we propose to use borehole radar to determine the mud invasion depth considering a high spatial resolution of ground-penetrating radar (GPR) compared with the conventional logging tools. We implement numerical investigations on the feasibility of this approach by coupling electromagnetic (EM) modelling with fluid flow modelling in an oil-bearing formation disturbed by mud invasion effects. The simulations imply that a time-lapse radar logging is able to extract EM reflection signals from mud invasion front, and the invasion depth and EM velocity can be obtained by a downhole antenna displacement of one source and two receivers. We find that there exists a positive correlation between the estimated invasion depth and permeability curves, and a negative correlation between the estimated velocity and porosity curves. We suggest that borehole radar has potential to estimate permeability and porosity of oil reservoirs, wherein the mud invasion effect is positively utilized. The study demonstrates a potential method of oil reservoir estimation and a novel application of GPR in oil fields.
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3D Reconstruction of Tree Roots under Heterogeneous Soil Conditions using Ground Penetrating Radar
Authors A. Aboudourib, M. Serhir and D. LesselierSummaryCoarse roots can cause damage to pipes, pavements and building foundations. Hence, reconstructing tree root system in its three dimensions is of paramount importance to understand and reduce interactions between trees and urban infrastructures. Ground Penetrating Radar (GPR) is a promising non-invasive technique for the study of tree roots. In this contribution, a 3D GPR simulation was carried out on two roots having elemental architectures in order to be reconstructed. The simulation was performed with GprMax software under heterogeneous soil conditions. Considering a heterogeneous soil not only provided a realistic soil model, but also enabled us to test the robustness of our post-processing techniques. We mainly used a Singular Value Decomposition (SVD) combined with the matched filter technique.
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Full 3D Ground Penetrating Radar Imaging of Vertical Structures
Authors G. Gennarelli, G. Ludeno, C. Noviello, F. Soldovieri and I. CatapanoSummaryThis work deals with the application of ground penetrating radar (GPR) for imaging the inner of vertical elements, which is of interest for the diagnostics of columns or pillars as well as tree trunks. The structure is probed along its surface by means of vertical GPR scans. The imaging is tackled as an electromagnetic inverse scattering problem by accounting for the 3D vectorial nature of the scattering phenomenon. A linearized inversion algorithm based on the Truncated Singular Value Decomposition (TSVD) is adopted to achieve stable and accurate results. The performance of the solution approach is assessed by means of a study regarding the resolution limits also devoted to investigate how the density of measurement data affects the image quality. Furthermore, experimental results are reported to highlight the feasibility of the approach in preliminary controlled laboratory conditions.
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GPR Method as an Efficient NDT Tool to Characterize Carbonate Rocks during Different Production Stages (Winner Best Oral EAGE-GMS Meeting)
Authors A. Hojat, M. Izadi-Yazdanabadi, S. Karimi-Nasab, D. Arosio and L. ZanziSummaryIran and Italy have a great potential in stone production relying on a variety of dimension stone quarries, especially carbonate rocks. To survive in the modern challenging international market, it is crucial to have products without defects. Ground Penetrating Radar (GPR) method as a rapid and efficient non-destructive technique (NDT) can be used to characterize carbonate rocks during different production stages. In this paper, we present the results of GPR measurements to monitor the quality of marble and limestone rocks at different scales. Considering the availability of GPR antennas in a wide range of frequencies, providing different resolutions, GPR method is very encouraging to detect the desired discontinuities of carbonate rocks at different production stages. Lower frequency antennas can detect major discontinuities to optimize the extraction design. Higher frequency antennas can later detect smaller fractures of the extracted blocks to optimize slab production. Our research is under progress to explore the efficiency of GPR method in mapping the quality of resin injection in fractured rocks. As an auxiliary NDT method to be integrated with GPR measurements, ultrasonic pulse velocity tests are also performed. The results show that changes in the velocity can be a good indication of the stone quality.
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Structural health monitoring of civil engineering structures using GPR detection of patch antenna resonance frequency changes
SummaryWireless and inexpensive sensors present a great attractiveness and are of growing interest in such fields as civil engineering. In this study, the feasibility of a wireless sensing system, which consists of a patch antenna sensor and an external wireless interrogator, has been investigated. The patch antenna is designed to operate at two fundamental radiation modes (TM010 & TM001) in the L Radar-frequency band according to the IEEE standard. The ground penetrating radar (GPR) interrogator consists of a printed Ultra-wide band Vivaldi antenna which is connected to a network analyzer. In order to evaluate its ability to monitor civil engineering structures, the performed patch antenna is placed behind various controlled slabs and its resonance frequency is varied artificially. The outside GPR interrogator permits to follow the frequency shift by measuring the reflected signal of the patch antenna. A series of preliminary experimental tests were carried out in order to demonstrate the principle.
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Effect of the tide on permittivity values obtained on a reinforced concrete bridge in marine environment
Authors X. Dérobert, L. Bourreau, W. L. Lai, V. Bourreau, Y. S. Chan and F. C. J. ShamSummaryMain damage occurring on reinforced concrete (RC) structures can be attributed to the corrosion of the rebar. When dealing with structures in marine environment, chloride ion penetration and water content must be considered, as the different exposure zones (tidal, splash and atmospheric) will have a significant influence.
GPR survey were performed on several piles and processed to evaluate the evolution of the surface permitivity vs. elevation in the tidal and splash areas. For that, a in-house software by HK Polytechnic university was used to estimate the local radar wave velocity for each location of rebar. The objective herein is to estimate if any vertical gradient of water/chloride content in the surface content. GPR results show a notable decrease of water content between the tidal and the atmospheric area, and no significant information on any gradient of chloride content vs. elevation.
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Signal Processing For Tree-Trunk Investigation Using Ground Penetrating Radar
Authors Iraklis Giannakis, Fabio Tosti, Livia Lantini, Daniel Egyir and Amir M. AlaniSummaryInvasive fungi diseases are considered one the biggest threats for the ash and oak forests in United Kingdom. To that extend, Ground Penetrating Radar (GPR) can provide a powerful diagnostic tool for assessing the health status of tree trunks based on their internal dielectric distribution. GPR acquisitions in tree-trunks is a unique problem that can not be approached with traditional GPR processing approaches. Typical interpretation tools like hyperbola fitting and migration should be adjusted and fine-tuned in order to be applicable for irregular measurements in a closed curve. The purpose of this paper is to provide GPR practitioners with a set of interpretation tools that can be applied in the field using commercial GPR antennas. In that context, a novel processing framework is presented that is fine-tuned for the current problem. The suggested scheme is successfully tested using both numerical and real data indicating the capabilities of GPR as a diagnostic tool for early detection of tree diseases.
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Numerical Modelling of Ground Penetrating Radar for Potash Mine Safety
Authors Victor Okonkwo, Tokini Briggs, Raman Paranjape and Matthew van den BergheSummaryThis paper presents a software tool which simulates the geological stratigraphy of a potash mine which is then used with gprMax (public domain Ground Penetrating Radar (GPR) simulation software) to examine and evaluate the effectiveness of auto-picking algorithms. The system is used to simulate the GPR response from clay seams in the roof of potash mining rooms. As it is extremely onerous to obtain in-situ data that captures all possible normal and anomalous geological conditions present in the mine roof, earth models are generated which accurately represents the geology of the mine. In particular, random clays in the mine roof can negatively affect the performance of auto-picking algorithms. These earth model simulations can be used to present these random clays accurately.
gprMax is an open source software that simulates Electro-Magnetic (EM) wave propagation in materials in order to support a better understanding of the use of GPR in various applications. Currently, GPR systems are in use in potash mines to assist with monitoring of the roof status of mining rooms. The goal of this paper is to validate the ability of using gprMax with effective earth models to generate realistic GPR signals that are used to test and evaluate auto-picking algorithms. The use of simulated data in comparison to the experimental (actual physical) data and generation of test bed models for an auto-picking algorithm has many benefits. Synthetic data is generated by gprMax using the Finite Difference Time Domain (FDTD) methodology. An effective methodology to develop and test robust auto-picking algorithms is created using simulated GPR signals because the ground truth is known from the earth models.
Additionally, in this work results from both an industry standard auto-picking algorithm and a newly developed auto-picking algorithm, called Clustered Ratio Derivative (CRD), are presented for this mine roof monitoring application. Finally, in this work we take advantage of cloud computing resources in order to execute this work.
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Estimating the Permittivity of Soil Using Common-Mode Currents on a Coaxial Transmission Line
Authors Wouter van Verre, Frank JW Podd, Xianyang Gao and Anthony J PeytonSummaryKnowing the value of the permittivity of the soil is important when using ground-penetrating radar (GPR) systems in outdoor conditions. Soil permittivity can be estimated by a variety of techniques, from destructive methods that require soil sampling though to non-contact methods using the GPR system.
This paper introduces a novel method for estimating the permittivity of soils, based on measuring the travel time of common-mode currents on coaxial transmission lines such as semi-rigid coax cables. The common-mode current concept was validated using finite-difference time-domain simulations of dielectric half-spaces. Experimental measurements were taken of air and deionised water as reference materials. The estimated value of the permittivity of these materials was within 3% of the expected value.
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Data Augmentation in feature-space with Generative Adversarial Networks, applied to GPR-based Buried Threat Detection
Authors Jordan M. Malof, Daniël Reichman and Leslie M. CollinsSummaryIn this work we consider the problem of developing algorithms for automatic buried threat detection (BTD) in ground penetrating radar (GPR) data. Many such algorithms are supervised, and perform best when they can be trained on large quantities of labeled threat and non-threat GPR data, respectively. Unfortunately, such data is costly to collect, and therefore relatively scarce. One approach to mitigate this problem is data augmentation, in which novel training data is created by applying transformations to existing data. Prior work has shown that augmentation can indeed improve the training of GPR-based BTD algorithms. In this work, we explore the use of Generative Adversarial Networks (GANs) for data augmentation. GANs can be trained to generate novel, but highly realistic, data after training on a real-world dataset. GANs have yielded impressive results on many types of data, but they are notoriously difficult to train. In this work, we propose an approach, entitled featureGAN, that mitigates some of the challenges training GANs. We show that augmentation using featureGAN yields improved detection performance, and yields better performance than some naïve alternative augmentation strategies. We also propose a metric for quantifying the success of GAN training, called the q-metric, which was crucial to achieving good results.
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Estimation of False Alarms Rates for GPR Detection using the Euler characteristic of Gaussian Random Fields
Authors Christian Bräu and F. I. RialSummaryThresholds for GPR anomaly detection are often chosen offline and experimentally after data processing. For a real-time operation, especially for mine and IED detection, it is desirable to choose a threshold according to a certain false alarm rate. Because of spatial correlations caused for example by the detection algorithm and heterogeneous soils it is not enough to use only statistics of individual pixels in the decision map. In this work we present a method for estimating the number of false alarms. For this we apply techniques based on the Euler-Poincare characteristic of stationary Gaussian random fields to an exemplary detection scheme. The necessary parameters are estimated from only a small target free area in the data.
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