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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
1 - 20 of 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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