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The objective of this paper is twofold: first, to introduce an innovative technique for extracting and exploiting the Electromagnetic (EM) waveguide dispersion of civil engineering materials by means of GPR; and second, to monitor the water ingress front during the absorption process for various concrete mixes. This technique is based on a new inversion procedure that applies the Electromagnetic Waveguide Model (WGM) to invert phase velocity dispersion curves in their modal form. A Parallel homogenization model, derived from the Lichtenecker-Rother equation, has been employed to extend the waveguide from a one-layer to a two-layer medium. The WGM outputs are then used to estimate the geometric parameters of the propagation medium and offer a primary application to water transfer monitoring in concrete through capillarity effects. The initial WGM validation is carried out on FDTD-simulated propagation signals, while the second validation relies on GPR data acquired from homogeneous materials. To achieve the second objective, a broad-based experimental study is conducted for the purpose of correlating electromagnetic waveguide dispersion parameters with both the geometric and hydric characteristics of various concrete mixes. Results obtained using the two-layer WGM serve to monitor the water ingress front during an absorption process. These results are then compared to the moisture gradients generated on cores using gammadensimetry, which is set as the reference. This procedure yields a number of trends, which in turn provide key information on the conditioning state of the studied concretes.

IGARSS 2019, IEEE International Geoscience and Remote Sensing Symposium, Yokohama, JAPON, 28-/07/2019 - 02/08/2019; Ground Penetrating Radar (GPR) is a widely used tool in the management and monitoring of pavement structures. In this paper, we focus on the detection of thin inter-layer debondings between the hot mix asphalt layers of pavement structures. A Stepped-Frequency Radar (SFR) associated with a Support Vector Regression based Linear Prediction (LP-SVR) method is used to detect thin debondings. The performance of SFR with the LP-SVR method is analyzed according to various used frequency bandwidths on the experimental data.

This paper presents a comparative study of two algorithms for detecting and analyzing 29 the characteristic shapes of reflection obtained as a result of Ground-Penetrating Radar (GPR) 30 scanning technology. The first algorithm is a sub-array processing method that uses direction-of31 arrival algorithms and the matched filter technique; this approach is implemented in SPOT-GPR 32 (release 1.0), a new freeware tool for the detection and localization of targets in radargrams. The 33 second algorithm, APEX, is based on machine learning and pattern recognition techniques and it 34 allows finding the coordinates of apexes and further characteristic points of hyperbolas in 35 radargrams. Both software solutions are implemented in MATLAB environment. As a first step, 36 we compare the accuracy of our algorithms when applied to synthetic data, calculated by using 37 the open-source finite-difference time-domain simulator gprMax; the considered scenarios are 38 two concrete cells hosting different metallic and dielectric targets. Then, we compare the 39 accuracy of our algorithms when applied to experimental data, recorded over district heating 40 pipes in a trench, with known geometry and depth of the pipes. For the latter scenario, we have 41 also generated a gprMax radargram, matching the geometry and scanning settings of the real one: 42 both algorithms are tested on this synthetic radargram, as well. Overall, both algorithms perform 43 well and rather uniformly in localizing the targets; the accuracy of the algorithms is at centimeter 44 level, which is sufficient in most applications.

IWAGPR 2017, 9th International Workshop on Advanced Ground Penetrating Radar, EDIMBOURG, ROYAUME-UNI, 28-/06/2017 - 30/06/2017; This paper deals with the effect of concrete carbonation on the propagation and dispersion of EM electromagnetic waves. Capacitive probes working at low frequency (around 33 MHz) and GPR (antenna nominal frequency of 1.5 GHz) could provide useful information for reinforced concrete structure monitoring. So, in order to better understand the phenomena involved by concrete carbonation, the results of 2 complementary experimental campaigns are analyzed. First, the dispersion curves of the complex permittivity are measured for carbonated and non-carbonated samples by an EM cylindrical coaxial cell. Due to carbonation, the permittivity decreases, and the dispersion is slightly reduced. Second, it is confirmed by GPR and capacitive measurements on slabs, that the real part of the permittivity decreases and that the radar signal amplitude increase.

IWAGPR 2017, 9th International Workshop on Advanced Ground Penetrating Radar, EDIMBOURG, ROYAUME-UNI, 28-/06/2017 - 30/06/2017; In the field of civil engineering, Ground Penetrating Radar (GPR) is the most widely used method of Non-Destructive Testing (NDT). Using supervised learning methods or signal processing methods, it is possible to analyze the sub-surface defects in pavement. In this paper, we propose to use a machine learning method called Support Vector Machines (SVM) to detect the presence of debondings within the pavement. Here, the ground-coupled GPR in quasi mono-static configuration along with SVM is used to detect debondings. The experiments are done on bituminous concrete pavements with various material characteristics. The classification results are good and show the efficiency of the detection process.

IWAGPR 2017, 9th International Workshop on Advanced Ground Penetrating Radar, EDIMBOURG, ROYAUME-UNI, 28-/06/2017 - 30/06/2017; The main goal of this paper is to investigate the performance of an algorithm for point extraction from hyperbolic reflections in synthetic and experimental Ground-Penetrating Radar (GPR) data. The real radargrams that we considered contain hyperbolic reflections due to the presence, in the surveyed area, of district heating pipelines DN250. These are buried 88 cm deep in a soil trench, and covered by compacted sand and concrete bricks (behaton pavement). The synthetic radargrams result from the simulation of a model representing the real geometry on the location of interest. The simulation was carried out by using gprMax, version 3.

IWAGPR 2017, 9th International Workshop on Advanced Ground Penetrating Radar, EDIMBOURG, ROYAUME-UNI, 28-/06/2017 - 30/06/2017; The main goal of this paper is to determine the characteristics of an algorithm for point extraction from hyperbolic reflections in Ground-Penetrating Radar (GPR) data with different acquisition settings. Analysis is performed on a series of experimental radargrams that were collected in real conditions, on the same location. Two district heating pipes DN250 in a trench, covered by compacted sand, were scanned and the acquisition was done by using a 900 MHz antenna. The pipe depth and the axial distance were measured when the trench was open. Measured dimensions were then compared with the values obtained by the algorithm.

EGU - European Geosciences Union General Assembly 2017, Vienna, AUTRICHE, 23-/04/2017 - 28/04/2017; Antennas with broadband characteristics have recently found various applications in modern ultra wide band (UWB) communication systems and in ground penetrating radar (GPR). Our applications are focused on imaging the subsurface of a large range of civil engineering structures at several depths using a bistatic GPR positioned on or close to the ground surface. The development of a compact (34´29 cm2) broadband pair of antennas operating in the frequency band from 0.27 to 3.1 GHz, whose radiation characteristics have been preliminary studied theoretically in details in different configurations, is to allow the probing of the subsurface in several frequency sub-bands using a step frequency (SF-GPR) acquisition mode. Microstrip patch antennas (MPAs) are one of the most basic and important types of planar antennas because they offer many advantages such as compact size, low-cost, ease of fabrication, light weight, and various shapes design. However, a low bandwidth and a low gain are the main shortcomings for such planar structure. The microstrip antenna has now reached maturity and many techniques have been suggested for achieving a high bandwidth such as using more complex shapes, parasitic elements, multilayer configurations and the tuning of the feed line. In this paper, an original printed rectangular slot antenna fed by a 50 W CPW (coplanar waveguide) transmission line tuned by a E-shaped patch is presented. Presently, little work has been made to lower the operating frequency band of microstrip antennas at frequencies less than 0.8 MHz and to reduce the antenna size at these frequencies because major applications concern UWB wireless communications. By choosing a relative combination of a E-shaped patch, a linear feed line and a rectangular slot, we have designed an antenna structure on a FR4 substrate ( ) with a very wide operating bandwidth whose nearly half of the spectrum covers frequencies lower than 1 GHz. A partial shield, only opened towards the ground, and coated with an inner layered absorbing material has been added to eliminate undesirable reflections from the upper environment particularly at low frequencies; moreover, in a GPR system, the antenna shielding will allow to reduce the coupling between the transmitting and the receiving units. The proposed rectangular slot antenna has been designed and simulated using the 3D commercial software EMPIRE based on the finite difference time domain (FDTD) technique. A detailed parameter study has allowed to define the several geometrical parameters of the unshielded slot antenna which are the result of a compromise on the frequency bandwidth (S11

Limestone has been a widely used building material for many years. Its degradation process has been strongly linked to its water content, to which the radar waves are sensitive. In this paper, the closed-form, near-field full-wave radar model of Lambot et al. is utilized for monitoring water ingress in limestone. This model is based on planar layered media Green's functions combined with an intrinsic representation of the antenna through global reflection and transmission functions. The Jonscher's model is used to describe the frequency dependence of the limestone electromagnetic properties. Then, an inversion method based on a genetic algorithm is developed and optimized. The method is numerically validated by simulating electromagnetic wave propagation in medias, using a three-dimensional finite element software, namely high-frequency electromagnetic field simulation. Finally, the method is experimentally validated, with a stepped-frequency radar system and an ultra-wide band antenna, during an imbibition process of a limestone slab. Results are compared to gamma densimetry measurements, a nuclear and semi-destructive approach, performed as the reference. Analyses of the results show that the average relative difference between the estimated and the reference water front is 2.5%, thereby demonstrating the performance of the proposed nondestructive method.

Water content, chloride content and carbonation are three durability indicators that affect not only concrete properties and integrity, but also the ground penetrating radar (GPR) response. This article characterizes the effect of water and chloride contents as well as carbonation on the high-frequency electromagnetic (EM) properties of concretes using a coaxial-cylindrical cell operating within the large frequency band from 50 MHz to appprox. 1000 MHz, thus making possible to study dispersion effects on the complex relative permittivity of various concretes. During a second step, three specific designs of experiment (DoE), involving water and chloride contents, and then carbonation, are designed and studied in order to establish the relative sensitivity of these parameters compared to others in describing the mixes at three different frequencies. The complex dielectric properties are evaluated in the laboratory on many concrete specimens (numbering 24, 36 and 24 for the moisture, chloride and carbonation studies respectively). For these evaluations, the composition parameters consist of nature of aggregate, nature of cement, cement content and water-to-cement ratio (W/C) while conditions are described by degree of water saturation, chloride content or carbonation. In the case of the chloride and carbonation DoEs, the mixes are tested under both dry and saturated conditions. The models describing complex relative permittivity, in association with the designs of experiment, are multi-linear polynomials of the 4 or 5 identified engineering parameters, to be chosen depending on the study. The interpretation of datasets entails in independent calculation of model coefficients for the real and imaginary parts of relative permittivity, at the three chosen frequencies. This approach reveals the significant relationships existing between dielectric properties and composition parameters as well as their evolution versus frequency. The major results of this work can be summarized as follow: - The degree of water saturation amounts to about 80% on e′ r variability and 60% to 15% versus frequency on e″ r variability, for the first campaign. - The chloride content, while only visible in saturated mixes, represents approx. 40% and 50% with porosity (via the W/C ratio) accounting for some 30% and 40% on e′ r and e″ r variabilities, respectively. - Lastly, carbonation, while also only visible in saturated mixes, corresponds to a weight of about 14% in low frequencies and vanishes at high frequencies for e′ r variability; this amount rises to roughly 24% for e″ r variability.

EGU - European Geosciences Union General Assembly 2016 , Vienna, AUTRICHE, 17-/04/2016 - 22/04/2016; Sense-City facility is a modeled urban test-bed of 250 m2 (25m×10m) located at University Paris-Est (France) that is dedicated to the validation of measurement technologies in the field of urban sustainability [1]. The novel Ground-Penetrating Radar (GPR) test site falls within the purview of Sense-City smart road topic, as networks usually lie below road structures. This site lies within the actual concern of mapping the underground with a non-destructive technique to retrieve the location of underground pipelines, in order to update urban cadastral databases, to contribute to space saving and to a wise use of land resources when planning for new networks. Thus, the test site designed provides several sources of measurement interest expressed by the presence of a multilayered soil with significant dielectric contrasts, and two distinct areas dedicated to the validation of utility mapping tools, one with buried pipes, and the other with buried blades with various dielectric properties; the objects having a relative small lateral dimension (less than 15 cm) have been buried at several depths (ranging from 14.5 to 64.5 cm ) in trenches filled with a backfill soil different from the natural soil. This paper is focused on the buried pipe area: experimental radargrams have been acquired using several GPR systems (GSSI SIR 3000, UtilityScan DF and a SFCW made of a pair of bowtie slot antennas conceived in our laboratory) operating at frequencies ranging from 300 MHz to 1.5 GHz. At first, the comparison and the interpretation of a few raw Bscans have allowed to characterize the dielectric properties of the soil layers. Afterwards, during the experiments made with the different GPR systems, we have studied the hyperbola signatures of the buried pipes according to several parameters such as central frequency, dielectric contrast of the objects (air filled or water filled), and polarization. The results of this study will help to further evaluate and develop different types of algorithms in signal and image processing (wavelet transform, Hilbert transform, matched filter, mode decomposition, super resolution algorithm, template matching, migration...) in radargrams to finally extract quantitative information. Experimental results highlight that 800 and 900 MHz are the most suited frequencies to obtain radargrams with enough resolution and penetration to characterize the buried objects with relatively small lateral dimension. First measurements have been made in the blade zone and they are currently under interpretation.

This paper presents the design of a novel Ground-Penetrating Radar (GPR) test site that has been integrated into the mini-city demonstrator Sense-City located at University Paris-Est (France). This test site provides several sources of measurement interest expressed by the presence of a multilayered soil with significant dielectric contrasts, and various dielectric pipes and blades buried at various depths in trenches filled with a backfill soil different from the natural soil. This paper presents experimental Bscans associated with the pipe zone acquired by three different GPR systems at frequencies ranging from 300 MHz to 1.5 GHz. The interpretation and comparison of the raw Bscans have allowed to characterize the dielectric properties of the soil layers, and to detect the hyperbola signatures of the buried pipes. The results of this study will help to guide future developments on polarization, operating frequency and signal processing to extract parameters (orientation, dielectric characteristics, position and size) associated with pipes.

This paper aims to present a wide dataset of ground penetrating radar (GPR) profiles recorded on a full-size geophysical test site, in Nantes (France). The geophysical test site was conceived to reproduce objects and obstacles commonly met in the urban subsurface, in a completely controlled environment. Since the design phase, the site was especially adapted to the context of radar-based techniques. The main needs for urban civil engineering, in which the geophysical test site intends to provide an experimental field, relate to the detection, localization and characterization of hidden structures and not to the assessment of soil properties. As a tool accessible to professionals, the site has been used for various needs over the years, such as tests or comparisons of devices, and validation of measurement or modelling methods. After a detailled description of the site and its building process, the GPR profiles included in the dataset are reported and commented on. Overall, the dataset is composed by 67 profiles. They were recorded along eleven parallel lines, crossing the test site in the transverse direction, by using three pulsed radar systems, manufactured by different producers and equipped with various antennas having central frequencies from 200 MHz to 900 MHz. An archive containing all profiles (raw data) is enclosed to this paper as supplementary material. The dataset is the core part of the Open Database of Radargrams initiative of COST (European Cooperation in Science and Technology) Action TU1208 "Civil engineering applications of Ground Penetrating Radar". The idea beyond such initiative is to share with the scientific community a selection of interesting and reliable GPR responses, to enable an effective benchmark for direct and inverse electromagnetic approaches, as well as for imaging and signal processing algorithms. We hope that the dataset presented in this paper will be enriched by the contributions of further users in the future, who will visit the test site and acquire new data with their GPR systems. Moreover, we hope that the dataset will be made alive by researchers who will perform advanced analyses of the profiles, measure the electromagnetic characteristics of the host materials, contribute with synthetic radargrams obtained by modelling the site with electromagnetic simulators, and more in general share results achieved by applying their techniques on the available profiles.

Several NDT methods (ultrasonic surface waves, capacitive method, ground penetrating radar and electrical resistivity probes or tomography (ERT)) were used in similar conditions for the evaluation of the moisture gradients inside concrete. After a long exposure in laboratory conditions to obtain a stabilization of the hygrometry, one face of the tested concrete slabs is put in contact with water. By capillary absorption, water penetrates gradually, and at different time intervals of the process, NDT measurements are performed both on the opposite face and on the face in contact with water. This protocol allows the formation of different water gradient profiles in the concrete slabs during water absorption. At each measurement step, the water gradient profiles are controlled by embedded relative humidity sensors but also by gammadensimetry on a specific sample. The results show that the embedded sensors are able to monitor the water front evolution during water absorption. Phase velocity of ultrasonic surface waves, even-though not significantly affected by moisture variations, can follow up relative modifications within the first concrete centimeters. GPR, electrical resistivity and capacitive measurements are sensitive to the evolution of the water front during absorption. Finally, the ERT provides interesting results for the monitoring of the water front.

NDT-CE 2015, International Symposium Non-Destructive Testing in Civil Engineering , BERLIN, ALLEMAGNE, 15-/09/2015 - 17/09/2015; This paper presents a new method to characterize the change of geometric and dielectric properties inside a material, such as concrete from civil engineering structures, with the application of GPR (ground penetrating radar). The principle of this method is to consider the dielectric medium with changing properties as a waveguide, composed by several layers of media with different thicknesses and dielectric constants. Then we can derive the phase velocity dispersion curve from the guided waves to extract the information of each layer. As we know from some former studies, the penetration of water and chlorides can significantly change the complex permittivity of concrete. Under this condition, the new method using waveguide can be applied to monitor the chloride ingress into concrete. A dielectric mixing homogenization model found by the authors to efficiently implement the multi-layered waveguide is the parallel model. It is originally from the well-known Lichtenecker-Rother equation, combining the dielectric properties from different parts of a composite with its global dielectric. A general procedure of this method starts by a CMP (common mid-point) measurement using GPR on the material. Then the picked dispersion curve describing several propagation modes is used to invert the dielectric constant and thickness of each layer. Our discussion focuses on the monitoring of salty water penetrating into 2 different concretes due to the capillary effect. The concrete slab is considered as an equivalent medium composed by two layers: dry layer and wet layer. The multi-layered waveguide inversion results are compared to the semi-destructive gammadensimetry results, considered as reference. They show that this NDT method makes it possible to monitor the sea water ingress front in concrete over time.

A ground-penetrating radar (GPR) has been developed for civil engineering applications. Ultra-wide band (UWB) bowtie slot antennas operating at frequencies from 460 MHz to beyond 4 GHz have been designed to be integrated in a ground-penetrating radar (GPR) positioned very close to the soil surface. FDTD modeling has allowed to define the optimal geometrical parameters associated with the ground-coupled radar system that has been studied in two polarization configurations TE and TM. The ability of the GPR system in detecting small discontinuities using polarization diversity has been analyzed considering several buried canonical objects with different dielectric characteristics. Measurements in a sand box have been compared to full-wave simulations.

In civil engineering, conventional methods used to estimate the thickness of pavements assume flat interfaces. In contrast, this study uses a rigorous electromagnetic method called propagation-inside-layer-expansion (PILE) to simulate the radar backscattered signal at nadir from a rough pavement made up of two rough interfaces separating homogeneous media. The statistical distribution of the first two echoes is studied by comparison with the default flat case, together with their frequency behaviour. Within the scope of road pavement survey by ground penetrating radar, the scattering model is finally used to assess the performance of the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm, one of the well-known high-resolution time-delay estimation techniques.

Dans le cadre de méthodes de CND de la chaussée par radar, l'ondelette radar est convoluée par la fonction de réflectivité du milieu. Une déconvolution idéale consisterait à restituer la fonction de réflectivité précédente et à améliorer la résolution temporelle. Dans cet article, le modèle convolutif du signal observé est reformulé sous la forme d'un modèle multidimensionnel. Ceci permet d'appliquer la méthode d'analyse en composantes indépendantes (ICA) pour résoudre le problème de déconvolution aveugle. La non-linéarité de la fonction d'optimisation de la méthode est adaptée à la nature creuse/parcimonieuse de la fonction de réflectivité. La méthode est testée sur des données synthétiques puis sur des signaux expérimentaux. Les résultats obtenus démontrent l'amélioration de la résolution temporelle et la précision de mesure de cette méthode.

Le modèle de Jonscher est utilisé depuis une vingtaine d'années par la communauté GPR pour modéliser les variations fréquentielles de la permittivité diélectrique de matériaux naturels tels que les sols. En comparaison des modèles de mélanges, il permet de représenter le phénomène de dispersion sur une large bande de fréquences avec un nombre plus limité de paramètres. A l'instar des travaux récents de Bourdi et al., on souhaite utiliser ce modèle pour caractériser la permittivité du béton hydraulique. En particulier, on souhaiterait corréler les paramètres du modèle à certaines caractéristiques du matériau (rapport Eau/Ciment, teneur en eau, porosité principalement) pour de futures applications en matière de Contrôle Non Destructif (CND). Dans cette perspective, cet article a pour objectif d'évaluer la validité de différentes variantes du modèle de Jonscher, à partir de mesures de permittivité obtenues par une sonde coaxiale développée en collaboration avec l'UBO sur différents échantillons de bétons hydrauliques. Cet article insiste en particulier sur les techniques d'ajustement du modèle aux données. La qualité d'ajustement est illustrée par des mesures, dont l'interprétation est davantage détaillée par ailleurs.

In this paper, we propose a modified matrix pencil method for the problem of time delay estimation in dispersive media obeying a particular frequency power law, namely, the constant-Q model. Being based on a Vandermonde decomposition of the prediction matrix, the matrix pencil method produces biased estimates when applied directly to data of the constant-Q model. The proposed approach allows to compensate for the bias inherent to the classical method by restoring the Vandermonde structure via a spline-interpolation technique. The restoration involves an iterative procedure where each iteration selects a set of interpolated samples depending on the value of the quality factor of the previous iteration. The algorithm is tested on simulated data representing radar acquisitions over a stratified dispersive medium, and its performance is assessed against the Cramer-Rao lower bound.

Blind deconvolution of sparse spikes is a well-known problem in the fields of seismic exploration and ultrasonic nondestructive testing. In measuring thin layer thickness of asphalt pavements using GPR, a similar problem arises; the sparse reflectivity series representing the layered structure of the pavement convolved with the radar wavelet results in masking closely spaced reflections. A successful deconvolution retrieves the reflectivity series and thus improves the time resolution and facilitates quantitative data interpretation. In this paper, we cast the convolutional model as a multidimensional data model which renders blind deconvolution via independent component analysis (ICA) possible. We use a nonlinearity related to the double exponential density whose heavy-tailed nature provides further insight into the sparse nature of the reflectivity series. The method is tested on synthetic and real GPR data from a thin PVC slab. The results attest to the accuracy of the time delay estimates and verify the high resolution of the proposed approach.

Cet article propose quelques améliorations de l'algorithme haute résolution linéaire SWEDE pour l'estimation de retards de propagation dans un contexte de bruit quelconque. La première amélioration consiste à modifier le procédé initial de blanchiment du bruit proposé par Eriksson et al., la nouvelle méthode ainsi obtenue est appelée FBD-SWEDE pour Full Block Diagonalization-SWEDE. La seconde amélioration introduit l'algorithme ESPRIT dans le formalisme de SWEDE, réduisant ainsi le temps de calcul. Nous appelons cette méthode FBD-G-ESPRITWED pour Full Block Diagonalization-Generalized-ESPRIT Without Eigen Decomposition. Les résultats de simulation concernent la mesure d'épaisseur de matériaux de génie civil à l'aide d'un radar en ondes centimétriques. Ils montrent que la résolution temporelle des deux méthodes proposées est supérieure à celle de la méthode HR linéaire initiale, SWEDE.

Two improvements of the linear ESPRIT algorithm in [1] are proposed and applied to the time delay estimation (TDE) from radar data within the microwave range. At first, linear ESPRIT is adapted to the TDE. Then, two new linear subspace algorithms, namely ESPRITWED-UG (ESPRITWithout EigenDecomposition) and AV-ESPRITWED (AVerage ESPRIT Without EigenDecomposition) are proposed. Contrary to [1], both algorithms take the whole bandwidth into account. Computer tests enable to assess the performances of the algorithms on the measurements of the layer thickness of civil engineering materials from GPR data. The new methods show improved noise robustness and smaller standard deviation in comparison with linear ESPRIT [1] and SWEDE [2]

In this paper, we propose a new linear subspace algorithm, called root-OPM, for Time Delay Estimation (TDE)of backscattered radar signals. The proposed algorithm corresponds to the polynomial version of the OPM method. In comparison with OPM, root-OPM allows to improve resolution power, a better noise robustness and a lower computational load. Furthermore, root-OPM enables to afford the same performance as for rootMUSIC at medium SNR and beyond.

In this paper, we employ a blind source separation technique to estimate the thickness of thin pavement layers. The linearity of the convolution operation along with a simple data reorganization permit to formulate a multidimensional signal model in accordance with the model adopted in blind techniques. We use this model to retrieve the reflectivity series and eventually the corresponding time delays and reflection amplitudes without any a priori information. Thus, this technique enables parameter estimation without incorporating a calibration stage which might be difficult in near-field conditions. Numerical simulations indicate the feasibility of the approach.

In the field of civil engineering, sounding the top layer of carriageways, i.e., the pavement layer, is classically performed using standard ground-penetrating radar (GPR), whose resolution is bandwidth dependent. The layer thickness is deduced from both the time delays of backscattered echoes and the known dielectric constant of the medium. This paper focuses on superresolution and high-resolution techniques, which serve to improve the time resolution of GPR signals, and presents a parametric technique and five subspace methods, namely, estimation of signal parameters via rotational invariance techniques (ESPRIT), multiple-signal classification (MUSIC) algorithm, Min-Norm, and their polynomial versions root-MUSIC and root-Min-Norm. The performance of these algorithms will be compared in terms of resolution power as well as root-mean-square error on the estimated thickness. The paper also presents the results of computer tests and radar measurements in the far field.

8th RILEM International Conference on Mechanisms of Cracking and Debonding in Pavements, NANTES, FRANCE, 07-/06/2017 - 09/06/2017; The paper gives an overview of the ongoing experiment to survey debonding areas within pavement structure during accelerated pavement testing on the Ifsttar's fatigue carrousel. Several defects have been embedded during the con- struction phase and have been probed by different NDT techniques. Among them, the paper focuses on radar NDT&E techniques which have been used to detect and locate the artificial defects at the early stage of the experiment and then to perform the survey at different loading cycles. Besides, the test-site has been used to test different GPR materials, including the 3D GPR technology. The experiment has also motivated some related studies in the field of GPR data modelling and data processing, which are summarized in the paper. The experiment is expected to be pursued beyond 300 loading kcycles to reach larger pavement degradations.

Dans le cadre d'application radar à l'auscultation de chaussée, l'impulsion radar est convoluée par la fonction de réflectivité du milieu. Une déconvolution réussit consisterait à restituer la fonction de réflectivité précédente et à améliorer la résolution temporelle. Dans cet article, la convolution est re-formulée sous la forme d'un modèle multidimensionnel. Ceci permet d'appliquer la méthode d'analyse en composantes indépendantes (ICA) pour résoudre le problème de déconvolution aveugle. La non linéarité de la fonction d'optimisation de la méthode est adaptée à la nature creuse de la fonction de réflectivité. La méthode est testée sur des données synthétiques et des signaux expérimentaux. Les résultats obtenus démontrent l'amélioration de la résolution temporelle et la précision de mesure de cette méthode.