UHF bands because more penetration can be achieved at low frequencies. Consequently, large antennas are required, which limits their use for small airborne applications. This thesis explores various GPR antenna designs for a bi-static system that are at least operational from 225 MHz to 255 MHz and suitable for small airborne applications. The 3D electromagnetic simulation software Ansys high-frequency structure simulator (HFSS) was used to simulate various sizes of strip dipole, triangular bowtie, half elliptical bowtie, and elliptical bowtie antennas. Several physical models were constructed to validate the return loss simulation results. Additionally, simulation data is included for a wire dipole and a helical antenna. The helical antenna proved to be too large for small airborne application, so focus was placed on the dipole and bowtie designs. The performance of the dipole and bowtie antenna models are compared by size, weight, return loss (𝑆11), peak gain, and the transmit-to-receive isolation. Out of the fourteen simulated models, twelve meet the bandwidth requirement with an average weight of 0.23 lbs. It is found that the strip dipole exhibited wider bandwidth characteristics than the triangular, elliptical, and half elliptical bowtie models, while maintaining similar weight and size. The smallest strip dipole model is 50 mm x 528 mm x 1 mm, weighs 0.17 lbs, and is operational from 225 MHz to 283 MHz. Two strip dipole test antennas were fabricated and tested. Test results confirm the simulation predictions.

Near field imaging using microwave in medical applications has gain much attention recently as various researches show its high ability and accuracy in illuminating object comparing to the well-known screening tools such as Magnetic Resonance Imaging (MRI), digital mammography, ultrasound etc. This has encourage and motivate scientists continue to exploit the potential of microwave imaging so that a better and more powerful sensing tools can be developed. This thesis documents the development of antenna design for microwave imaging application such as breast cancer detection. The application is similar to the concept of Ground Penetrating Radar (GPR) but operating at higher frequency band. In these systems a short pulse is transmitted from an antenna to the medium and the backscattered response is investigated for diagnose. In order to accommodate such a short pulse, a very wideband antenna with a minimal internal reflection is required. Printed monopole and planar metal plate antenna is implemented to achieve the necessary operating wide bandwidth. The development of new compact printed planar metal plate ultra wide bandwidth antenna is presented. A generalized parametric study is carried out using two well-known software packages to achieve optimum antenna performance. The Prototype antennas are tested and analysed experimentally, in which a reasonable agreement was achieved with the simulations. The antennas present an excellent relative wide bandwidth of 67% with acceptable range of power gain between 3.5 to 7 dBi. A new compact size air-dielectric microstrip patch-antenna designs proposed for breast cancer detection are presented. The antennas consist of a radiating patch mounted on two vertical plates, fed by coaxial cable. The antennas show a wide bandwidth that were verified by the simulations and also confirmed experimentally. The prototype antennas show excellent performance in terms the input impedance and radiation performance over the target range bandwidth from 4 GHz to 8 GHz. A mono-static model with a homogeneous dielectric box having similar properties to human tissue is used to study the interaction of the antenna with tissue. The numerical results in terms the matching required of new optimised antennas were promising. An experimental setup of sensor array for early-stage breast-cancer detection is developed. The arrangement of two elements separated by short distance that confined equivalent medium of breast tissues were modelled and implemented. The operation performances due to several orientations of the antennas locations were performed to determine the sensitivity limits with and without small size equivalent cancer cells model. In addition, a resistively loaded bow tie antenna, intended for applications in breast cancer detection, is adaptively modified through modelling and genetic optimisation is presented. The required wideband operating characteristic is achieved through manipulating the resistive loading of the antenna structure, the number of wires, and their angular separation within the equivalent wire assembly. The results show an acceptable impedance bandwidth of 100.75 %, with a VSWR < 2, over the interval from 3.3 GHz to 10.0 GHz. Feasibility studies were made on the antenna sensitivity for operation in a tissue equivalent dielectric medium. The simulated and measured results are all in close agreement.

This thesis investigates the application of In-Situ Recycling and provides guidelines for localities to aid in the selection of recycling methods, as well as documents a local government's experience with Cold In-Place Recycling. The recycling methods discussed in this study include Cold In-Place Recycling (CIR), Hot In-Place Recycling (HIR), and Full Depth Reclamation (FDR). These methods are performed onsite and in-place in a continuous process of milling, mixing, and placement. The In-Situ Recycling guidelines include suggestions based on: traffic characteristics, existing road condition, distress types, road access, local climate, road geometry, and other road characteristics. The guidelines are based on information from sources including NCHRP Synthesis 421, American Recycling and Reclamation Association (ARRA), FHWA, and state agencies with recycling experience. This study also resulted in documenting obstacles that localities may face when in-situ recycling, as well as the impact of limited experience with recycling. The study also evaluated the construction of Cold In-Place Recycled pavement sections in Christiansburg, VA, using Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR). Additionally, using the FWD and GPR data, alternate recycled designs were proposed in addition to a cost comparison to a conventional design. / Master of Science

Les travaux de cette thèse concernent l'étude d'une méthode d'évaluation des constantes diélectriques du béton d'ouvrage à risque par une approche problème inverse. Pour cela des mesures radar de type GPR et un modèle électromagnétique de ces mêmes mesures seront utilisés. Les deux premiers chapitres de la thèse présentent les concepts clés, le contexte et un historique des travaux déjà réalisés dans le domaine. Le chapitre 2 propose en outre une adaptation des travaux déjà réalisés à la recherche de gradients de propriétés diélectriques dans le béton en profondeur. Cette recherche préliminaire nous a permis de redéfinir le processus de mesures pour le rendre plus adapté à nos besoins. Ainsi le chapitre 3 présente une campagne de mesure réalisée à l'aide d'un nouveau dispositif radar sur des corps d'épreuve conditionnés de telle sorte que la répartition de la teneur en eau soit maîtrisée. Dans ce chapitre, nous détaillons également un nouveau modèle numérique 3D du dispositif qui nous permet de simuler nos mesures de façon réaliste Ces simulations sont nécessaires à l'expression du problème inverse. à partir de ces mesures, dans le quatrième chapitre, nous définissons tout d'abord le problème inverse, puis en utilisant des mesures sur les corps d'épreuves saturés, pouvant être considérés comme homogènes d'un point de vue diélectrique, nous résolvons ce problème inverse par un algorithme d'optimisation basé sur celui de Levenberg-Marquardt. Les résultats obtenus par notre processus d'inversion sont cohérents avec les valeurs physiques que l'on pouvait attendre et sont indépendants des valeurs données à nos inconnues lors de l'initialisation. Ces résultats correspondent effectivement à un minimum de la fonction coût qui mesure la distance entre mesures et simulations. Nous avons ensuite étudié des stratégies pour diminuer le temps de calcul de notre processus d'inversion. Une première approche consiste à utiliser un modèle simplifié en 2D du dispositif, qui permet d'initialiser l'inversion 3D avec un point plus proche de la solution. Une autre idée consiste à utiliser au mieux les performances d'une machine multiprocesseurs en parallélisant le code 3D. Dans le chapitre 5 nous nous intéressons à des mesures sur des corps d'épreuve en béton dont la teneur en eau est une fonction affine de la profondeur. Dans ces conditions nous avons fait l'hypothèse, en première approche, que les constantes diélectriques suivent aussi ce type de loi. Après avoir redéfini les inconnues de notre problème inverse et adapté l'algorithme, nous montrons que le processus d'inversion fourni des résultats cohérents en ce qui concerne la permittivité diélectrique, mais insatisfaisant pour la conductivité. Après analyse de ces résultats nous avons proposé diverses pistes pour améliorer et valider la méthode d'inversion. Finalement en comparant l'ensemble des résultats, il apparaît que notre méthode d'inversion permet de caractériser des gradients de permittivité, mais pas de conductivité. Cela représente néanmoins une avancée significative pour la mesure de la teneur en eau dans les bétons, facteur principal influençant la constante diélectrique de ce matériau, dans le contexte du contrôle non destructif des ouvrages du génie civil. / That thesis aims to propose an assessment method of the concrete electromagnetic properties by using radar measurements in a context of building sustainability, by inverse problem. For that purpose Ground Penetrating Radar (GPR) measurements are used as well as a numerical model of the radar device. The first two chapters of the thesis present the key concepts, the context of the study, as well as the history of the research on that topic in particular in our laboratory. Chapter 2 also expands those early works on the search of electromagnetic properties of concrete in depth. That preliminary work helped us to develop a measurement device that is more fitted to our needs. Chapter 3 presents a measurement campaign that was carried out by using a new measurement device on specially made reinforced concrete slabs whose water content is monitored. In that chapter a 3D model of the device is also described. That model allows us to simulate the measurements very precisely. Those simulations are a critical link on the inverse process. Chapter 4 details the formulation of the inverse problem for the case of concrete slabs saturated with water, which can be therefore considered to have homogeneous electromagnetic properties. The problem is solved by using an optimization algorithm based on Levenberg-Marquardt method. The values obtained by the inverse process are physically acceptable and independent of the values given to the unknowns when initializing the algorithm. Those values are the minimum of the cost function that computes the distance between measured and simulated electromagnetic fields. We then studied some strategies to reduce the computing time of the inverse process. A first approach consists in the use of a 2D simplified model of our device to initialize the 3D inversion with values closer to the searched solution. Another idea is to better take advantage of all the resources of a multiprocessor computer by implementing a parallel version of the 3D code. In chapter 5 we focus on the concrete slab with water content being an affine function of depth. We define the new parameters that represent the unknowns of our problem and we adapt the previous algorithm. Then we show that the inverse process gives satisfying results with regard to the dielectric permittivity only. We suggest some ways to improve the method. Finally we conclude that our method allows to retrieve the permittivity of the concrete, but not its conductivity. Nevertheless that result represents a significant step for the measuring of water content in reinforced concrete in particular when a gradient is present, by using radar measurements.

<div>Pavement drainage systems are one of the key drivers of pavement function and longevity, and effective drain maintenance can significantly extend a pavement's service life. Maintenance of these drains, however, is often hampered by the challenge of locating the drains. Ground Penetrating Radar (GPR) typically offers a rapid and effective method to detect these underground targets. However, typical detection schema that rely upon the observation of the hyperbolic return from a GPR scan of a buried conduit still tend to miss many of the older drains beneath pavements as they may be partially or fully filled with sediment and/or may be fabricated from clay or other earthen materials, yielding a return signal that is convolved with significant background noise. </div><div><br></div><div>To manage this challenge, this work puts forward an improved background noise and clutter reduction method to enhance the target signals in what amounts to a constructed environment that tends to have more consistent subsurface properties than one might encounter in a general setting. Within this technique, two major algorithms are employed. Algorithm 1 is the core of this method, and plays the role of reducing background noise and clutter. Algorithm 2 is supplementary, and helps eliminate anomalous discontinuous returns generated by the equipment itself, which could otherwise lead to false detection indications in the output of Algorithm 1. Instead of traditional 2-D GPR images, the result of the proposed algorithms is a 1-D plot along the survey line, highlighting a set of “points of interest” that could indicate buried drain locations identified at any given GPR operating frequency. Subsurface exploration using two different operating frequencies, 900 MHz and 400 MHz herein, is then employed to further enhance detection confidence. Points of interest are ultimately coded to define the confidence of the detection. Comparing the final result of proposed algorithms with the original GPR images, the improved algorithm is demonstrated to provide significantly improved detection results, and could potentially be applied to similar problems in other contexts.</div><div><br></div><div>Besides the background reduction methods, a group of simulations performed using GPRMAX2D software are examined to explore the influence of road cross-section designs on sub-pavement drainage conduit GPR signatures, and evaluate the effectiveness of alternate GPR antennae configurations in locating these buried conduits in different ground conditions. Two different models were explored to simulate conduit detection. In addition, different pipe and soil conditions were modeled, such as pipe size, pipe material, soil moisture level, and soil type. Four different quantitative measurements are used to analyze GPR performance based on different key factors. The four measurements are 1) signal to background ratio (SBR) in dB; 2) signal to receiver noise ratio (SNR) in dB; 3) signal energy in Volts; and 4) average signal band power in Watts.</div><div><br></div><div>The water and clay content of subsurface soil can significantly influence the detection results obtained from ground penetrating radar (GPR). Due to the variation of the material properties underground, the center frequency of transmitted GPR signals shifts to a lower range as wave attenuation increases. Examination of wave propagation in the subsurface employing an attenuation filter based on a linear system model shows that received GPR signals will be shifted to lower frequencies than those originally transmitted. The amount of the shift is controlled by a wave attenuation factor, which is determined by the dielectric constant, electric conductivity, and magnetic susceptibility of the transmitted medium. This work introduces a receiver-transmitter-receiver dual-frequency configuration for GPR that employs two operational frequencies for a given test - one higher and one slightly lower - to take advantage of this phenomenon to improve subpavement drain detection results. In this configuration, the original signal is transmitted from the higher frequency transmitter. After traveling through underground materials, the signal is received by two receivers with different frequencies. One of the receivers has the same higher center frequency as the transmitter, and the other receiver has a lower center frequency. This configuration can be expressed as Rx(low-frequency)-Tx(high-frequency)-Rx(high-frequency) and was applied in both laboratory experiments and field tests. Results are analyzed in the frequency domain to evaluate and compare the properties of the signal obtained by both receivers. The laboratory experiment used the configuration of Rx(400MHz)-Tx(900MHz)-Rx(900MHz). The field tests, in addition to the configuration used in the lab tests, employed another configuration of Rx(270MHz)-Tx(400MHz)-Rx(400MHz) to obtain more information about this phenomenon. Both lab and field test results illustrate the frequency-shift phenomenon described by theoretical calculations. Based on the power spectrum for each signal, the lower frequency antenna typically received more energy (higher density values) at its peak frequency than the higher frequency antenna.</div>

Les premiers mètres à centaines de mètres de la proche surface terrestre sont le siège de processus naturels dont la compréhension requiert une caractérisation fine de la subsurface, via une estimation quantifiée de ses paramètres. Le géoradar est un outil de prospection indirecte à même d'ausculter les milieux naturels et d'en estimer les propriétés électriques (permittivité et conductivité). Basé sur la propagation d'ondes électromagnétiques à des fréquences allant du MHz à quelques GHz, le géoradar est utilisé à des échelles et pour des applications variées concernant la géologie, l'hydrologie ou le génie civil. Dans ce travail de thèse, je propose une méthode d'imagerie quantitative des propriétés électriques sur des sections 2D de la subsurface, à partir de données radar acquises à la surface du sol. La technique mise en oeuvre est l'inversion des formes d'ondes, qui utilise l'intégralité du champ d'ondes enregistré.Dans une première partie, je présente les principes physiques et l'outil de modélisation numérique utilisés pour simuler la propagation des ondes électromagnétiques dans les milieux hétérogènes à deux dimensions. Pour cela, un algorithme de différences finies en domaine fréquentiel développé dans le cadre des ondes visco-acoustiques est adapté au problème électromagnétique 2D grâce à une analogie mathématique.Dans une deuxième partie, le problème d'imagerie est formulé sous la forme d'une optimisation multi-paramètre puis résolu avec l'algorithme de quasi-Newton L-BFGS. Cet algorithme permet d'estimer l'effet de la matrice Hessienne, dont le rôle est crucial pour la reconstruction de paramètres de différents types comme la permittivité et la conductivité. Des tests numériques montrent toutefois que l'algorithme reste sensible aux échelles utilisées pour définir ces paramètres. Dans un exemple synthétique représentatif de la proche surface, il est cependant possible d'obtenir des cartes 2D de permittivité et de conductivité à partir de données de surface, en faisant intervenir des facteurs d'échelle et de régularisation visant à contraindre les paramètres auxquelles l'inversion est la moins sensible. Ces facteurs peuvent être déterminés en analysant la qualité de l'ajustement aux données, sans hypothèse a priori autre que la contrainte de lissage introduite par la régularisation.Dans une dernière partie, la méthode d'imagerie est confrontée à deux jeux de données réelles. Dans un premier temps, l'examen de données expérimentales permet de tester la précision des simulations numériques vis-à-vis de mesures effectuées en environnement contrôlé. La connaissance des cibles à imager permet en outre de valider la méthodologie proposée pour l'imagerie multiparamètre dans des conditions très favorables puisqu'il est possible de calibrer le signal source et de considérer l'espace libre environnant les cibles comme modèle initial pour l'inversion.Dans un deuxième temps, j'envisage le traitement d'un jeu de données radar multi-offsets acquises au sein d'un massif calcaire. L'interprétation de ces données est rendue beaucoup plus difficile par la complexité du milieu géologique environnant, ainsi que par la méconnaissance des caractéristiques précises des antennes utilisées. L'application de la méthode d'inversion des formes d'ondes à ces données requiert donc une étape préliminaire impliquant une analyse de vitesse plus classique, basée sur les arrivées directes et réfléchies, et des simulations numériques dans des modèles hypothétiques à même d'expliquer une partie des données. L'estimation du signal source est effectuée à partir d'arrivées sélectionnées, simultanément avec des valeurs moyennes de conductivité et de hauteur d'antennes de façon à reproduire au mieux les amplitudes observées. Un premier essai d'inversion montre que l'algorithme est capable d'expliquer les données dans la gamme de fréquences considérée et de reconstruire une ébauche des principaux réflecteurs. / The quantitative characterization of the shallow subsurface of the Earth is a critical issue for many environmental and societal challenges. Ground penetrating radar (GPR) is a geophysical method based on the propagation of electromagnetic waves for the prospection of the near subsurface. With central frequencies between 10~MHz and a few GHz, GPR covers a wide range of applications in geology, hydrology and civil engineering. GPR data are sensitive to variations in the electrical properties of the medium which can be related, for instance, to its water content and bring valuable information on hydrological processes. In this work, I develop a quantitative imaging method for the reconstruction of 2D distributions of permittivity and conductivity from GPR data acquired from the ground surface. The method makes use of the full waveform inversion technique (FWI), originating from seismic exploration, which exploits the entire recorded radargrams and has been proved successful in crosshole GPR applications.In a first time, I present the numerical forward modelling used to simulate the propagation of electromagnetic waves in 2D heterogeneous media and generate the synthetic GPR data that are compared to the recorded radargrams in the inversion process. A frequency-domain finite-difference algorithm originally developed in the visco-acoustic approximation is adapted to the electromagnetic problem in 2D via an acoustic-electromagnetic mathematical analogy.In a second time, the inversion scheme is formulated as a fully multiparameter optimization problem which is solved with the quasi-Newton L-BFGS algorithm. In this formulation, the effect of an approximate inverse Hessian is expected to mitigate the trade-off between the impact of permittivity and conductivity on the data. However, numerical tests on a synthetic benchmark of the literature display a large sensitivity of the method with respect to parameter scaling, showing the limits of the L-BFGS approximation. On a realistic subsurface benchmark with surface-to-surface configuration, it has been shown possible to ally parameter scaling and regularization to reconstruct 2D images of permittivity and conductivity without a priori assumptions.Finally, the imaging method is confronted to two real data sets. The consideration of laboratory-controlled data validates the proposed workflow for multiparameter imaging, as well as the accuracy of the numerical forward solutions. The application to on-ground GPR data acquired in a limestone massif is more challenging and necessitates a thorough investigation involving classical processing techniques and forward simulations. Starting permittivity models are derived from the velocity analysis of the direct arrivals and of the reflected events. The estimation of the source signature is performed together with an evaluation of an average conductivity value and of the unknown antenna height. In spite of this procedure, synthetic data do not reproduce the observed amplitudes, suggesting an effect of the radiation pattern of the shielded antennae. In preliminary tests, the inversion succeeds in fitting the data in the considered frequency range and can reconstruct reflectors from a smooth starting model.

[ES] Los esfuerzos que hacen los países, en conjunto con organizaciones mundiales, tales como IWA (por International Water Association), ONU-Agua y OMS (Organización Mundial de la Salud), para mitigar el impacto ambiental en el campo de la hidráulica urbana son considerados de vital importancia. Sin embargo, la escasez de los recursos hídricos en el mundo aumenta diariamente. Esto viene dado por el aumento constante de la demanda en los sectores industrial, agrícola y urbano, provocado por el aumento poblacional y el cambio climático. Los administradores de los sistemas de abastecimiento de agua (WSSs, por sus siglas en inglés, water supply systems) se han visto desafiados a suplir la creciente demanda de los diferentes sectores con la cantidad, calidad y eficiencia necesarios y, a su vez, reducir el desperdicio y el mal uso del recurso. Desde esta perspectiva, las fugas de agua son el mayor problema que enfrentan los administradores de estas empresas de servicios públicos. Las fugas en una red provocan problemas de salud, de escasez, económicos y medioambientales. El uso de técnicas de inspección no destructivas debe favorecer una rápida identificación de problemas, para realizar acciones posteriores de reparación en la red. Este trabajo hace uso del GPR (siglas en inglés de ground penetrating radar) como técnica de inspección no destructiva porque: favorece la exploración del subsuelo sin causar alteraciones al medio, es de fácil aplicación y, además, permite obtener pseudo imágenes del subsuelo. Uno de los objetivos de este documento es identificar y extraer características de una fuga en un WSS mediante imágenes de GPR, con el fin último de recrear las fugas a través de modelos 3D. Se realizaron ensayos de laboratorio bajo condiciones controladas donde se emuló una parcela en la cual se había enterrado una tubería con una pequeño orifico que simula una fuga de agua; tras introducir agua al sistema, se realizaron prospecciones con el GPR. Una vez finalizada la exploración del subsuelo, dado que las imágenes de GPR en bruto obtenidas no son fácilmente interpretables por personal no experto, tales imágenes fueron sometidas a procesamiento de datos que favorezcan su fácil interpretación. Este documento presenta dos metodologías de procesamiento de datos que permiten obtener imágenes a partir de las cuales es posible identificar tanto los componentes del sistema como la fuga y su alcance. Las metodologías de tratamiento de datos aplicadas en este documento son una metodología basada en sistemas multi-agente y el filtro de varianza, metodología basada en parámetros estadísticos de segundo orden. Posteriormente, tras aplicar estas metodologías de procesamiento a las imágenes, se sometieron los resultados a un análisis que facilitase la mejor elección evitando la subjetividad del experto. Bajo este concepto, este documento propone el uso conjunto de técnicas multicriterio. Se utilizó el Proceso de Jerarquía Analítica Difusa (FAHP, por sus siglas en inglés, Fuzzy Analytical Hierarchy Process), que permite ponderar varios criterios de evaluación, con el propósito de mitigar la incertidumbre que caracterizan los juicios de los expertos, en conjunto con el método ELECTRE III para obtener la clasificación final de alternativas, todo esto de la manera más objetiva posible. Los resultados de este documento son satisfactorios, permitiendo obtener amplio conocimiento de las fugas y su interacción con el subsuelo, proporcionando pautas para desarrollar posteriormente metodologías de automatización que permitan localizar, seguir y predecir problemas en los WSSs. / [CA] Els esforços que fan els països en conjunt amb organitzacions mundials, como ara IWA (per International Water Association), ONU-Agua i OMS (per Organització Mundial de la Salut), per a mitigar l'impacte ambiental en el camp de la hidràulica urbana són considerats de vital importància. No obstant això, l'escassetat dels recursos hídrics en el món augmenta diàriament, donat per l'augment constant de la demanda en els sectors industrial, agrícola i urbà, provocat per l'augment poblacional i el canvi climàtic. Els administradors dels sistemes d'abastiment d'aigua (WSSs, per les seus sigles en anglès, water supply systems) s'han vist desafiats a suplir la creixent demanda dels diferents sectors amb la quantitat, qualitat i eficiència necessaris i, al seu torn, reduir el desaprofitament i el mal ús del recurs. Enfocant aquesta perspectiva, les pèrdues d'aigua són el problema més gran fet front pels directors d'aquestes utilitats. Les pèrdues d'aigua en una xarxa provoquen problemes de salut, d'escassetat, econòmics i mediambientals. L'ús de tècniques d'inspecció no destructives que afavoreixen una ràpida identificació per a realitzar accions de reparació posteriors en la xarxa. Aquest treball fa ús del GPR (sigles en anglès per ground penetrating radar) com a tècnica d'inspecció no destructiva perquè afavoreix l'exploració del subsol sense causar alteracions al entorn, és de fàcil aplicació i a més permet obtenir pseudo imatges del subsol. Un dels objectius d'aquest document és identificar i extraure característiques d'una pèrdua en un WSS mitjançant imatges de GPR, amb la fi última de recrear les pèrdues a través de models 3D. Es van realitzar assajos de laboratori sota condicions controlades on es va emular una parcel¿la en la qual s'ha enterrat una canonada amb una xicotet forat que simula una pèrdua d'aigua; després d'introduir aigua al sistema, s'obtenen prospeccions amb el GPR. Una vegada finalitzada l'exploració del subsol, atès que les imatges de GPR en brut obtingudes no són fàcilment interpretables per personal no expert, són sotmeses a processament de dades que afavorisquen la seua fàcil interpretació. Aquest document presenta dues metodologies de processament de dades que permeten obtenir imatges de les quals és possible identificar tant els components del sistema com la pèrdua i el seu abast. Les metodologies de tractament de dades aplicades en aquest document són una metodologia basada en multi-agents (MABS, per les seves sigles en anglès, multi-agent-based systems) i el filtre de variància, metodologia basada en paràmetres estadístics de segon ordre. Posteriorment, després d'aplicar aquestes metodologies de processament a les imatges se sotmeten els resultats a una anàlisi que faciliti la millor elecció evitant la subjectivitat de l'expert. Sota aquest concepte, aquest document proposa l'ús conjunt de tècniques de decisió multi-criteri (MCDM, per les seves sigles en anglès, multi-criteria decision-making). Es va utilitzar el Procés de Jerarquia Analítica Difusa (FAHP, per les seves sigles en anglès, Fuzzy Analytical Hierarchy Process) el qual s'utilitza per a ponderar diversos criteris d'avaluació, amb el propòsit de mitigar la incertesa que caracteritzen els judicis dels experts, en conjunt amb el mètode ELECTRE III, per a obtenir la classificació final d'alternatives, tot això de la manera més objectiva possible. Els resultats d'aquest document són satisfactoris, permetent obtenir ampli coneixement de les pèrdues d'aigua i la seua interacció amb el subsol, donant-nos la pauta per a desenvolupar posteriorment metodologies d'automatització que permeten localitzar, seguir i predir problemes en els WSSs. / [EN] The efforts made by the countries in collaboration with world organizations, such as IWA (for International Water Association), UN-Water and WHO (for World Health Organization), to mitigate the environmental impact in the field of urban hydraulics are considered of vital importance. However, the scarcity of water resources in the world increases daily, given by the constant increase in demand in the industrial, agricultural and urban sectors, caused by the population increase and the climate change. Managers of water supply systems (WSSs) are challenged to supply the growing demand of different sectors with sufficient quantity, quality and efficiency and, in turn, reduce waste and misuse of the resource. Focusing this perspective, water leaks are the biggest problem faced by the managers of these utilities. Leaks in a network cause health, shortage, economic and environmental problems. The use of non-destructive inspection techniques favors rapid identification to carry out subsequent repair actions on the network. This work makes use of the GPR (ground penetrating radar) as a non-destructive inspection technique because: it favors the exploration of the ground without causing alterations to the environment, it is easy to apply, and also allows to obtain pseudo images of the subsoil. This document presents two data processing methodologies that allow obtaining images from which it is possible to identify both the system components and the leak and its scope. The data treatment methodologies applied in this document are a multi-agent-based system (MABS) methodology and the variance filter, a methodology based on second-order statistical parameters. Subsequently, after applying these processing methodologies to the images, the results are subjected to an analysis that eases the best choice, avoiding expert's subjectivity. Under this concept, this document proposes the joint use of two multi-criteria decision-making (MCDM) methods. The Fuzzy Analytical Hierarchy Process (FAHP) is used first to weight various evaluation criteria, in order to mitigate the uncertainty that characterize the experts' judgments, in conjunction with the ELECTRE III method, to obtain the final classification of alternatives in the most objective way. The results of this document are satisfactory, allowing to obtain extensive knowledge of leaks and their interaction with the subsoil, giving a guideline to subsequently develop automation methodologies that allow locating, monitoring and predicting problems in WSSs. / Part of this work has been developed under the support of Fundación Carolina PhD and short-term scholarship program / Ocaña Levario, SJ. (2021). Análisis, caracterización y modelación 3D de fugas de agua en sistemas de abastecimiento de agua mediante imágenes de GPR [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/163677 / TESIS

The emergence of Ultra-wideband (UWB) technology application has yielded tremendous and vital impacts in the field of microwave wireless communications. These applications include military radar imaging, security screening, and tumour detection, especially for early detection of breast cancer. These indicators have stimulated and inspired many researchers to make the best use of this promising technology. UWB technology challenges such as antenna design, the problem of imaging reconstruction techniques, challenges of severe signal attenuation and dispersion in high loss material. Others are lengthy computational time demand and large computer memory requirements are prevalent constraints that need to be tackled especially in a large scale and complex computational electromagnetic analysis. In this regard, it is necessary to find out recently developed optimisation techniques that can provide solutions to these problems. In this thesis, designing, optimisation, development, measurement, and analysis of UWB antennas for near-field microwave imaging applications are considered. This technology emulates the same concept of surface penetrating radar operating in various forms of the UWB spectrum. The initial design of UWB monopole antennas, including T-slots, rectangular slots, and hexagonal slots on a circular radiating patch, was explicitly implemented for medical imaging applications to cover the UWB frequency ranging from 3.1 GHz to 10.6 GHz. Based on this concept, a new bow-tie and Vivaldi UWB antennas were designed for a through-the-wall imaging application. The new antennas were designed to cover a spectrum on a lower frequency ranging from 1 GHz - 4 GHz to ease the high wall losses that will be encountered when using a higher frequency range and to guarantee deeper penetration of the electromagnetic wave. Finally, both simulated and calculated results of the designed, optimised antennas indicate excellent agreement with improved performance in terms of return loss, gain, radiation pattern, and fidelity over the entire UWB frequency. These breakthroughs provided reduced computational time and computer memory requirement for useful, efficient, reliable, and compact sensors for imaging applications, including security and breast cancer detection, thereby saving more lives. / Tertiary Education Trust Fund (TET Fund) Supported by the Nigerian Defence Academy (NDA)

Humanitarian clearance of minefields is most often carried out by hand, conventionally using a a metal detector and a probe. Detection is a very slow process, as every piece of detected metal must treated as if it were a landmine and carefully probed and excavated, while many of them are not. The process can be safely sped up by use of Ground-Penetrating Radar (GPR) to image the subsurface, to verify metal detection results and safely ignore any objects which could not possibly be a landmine. In this thesis, we explore the possibility of using Full Wave Inversion (FWI) to improve GPR imaging for landmine detection. Posing the imaging task as FWI means solving the large-scale, non-linear and ill-posed optimisation problem of determining the physical parameters of the subsurface (such as electrical permittivity) which would best reproduce the data. This thesis begins by giving an overview of all the mathematical and implementational aspects of FWI, so as to provide an informative text for both mathematicians (perhaps already familiar with other inverse problems) wanting to contribute to the mine detection problem, as well as a wider engineering audience (perhaps already working on GPR or mine detection) interested in the mathematical study of inverse problems and FWI.We present the first numerical 3D FWI results for GPR, and consider only surface measurements from small-scale arrays as these are suitable for our application. The FWI problem requires an accurate forward model to simulate GPR data, for which we use a hybrid finite-element boundary-integral solver utilising first order curl-conforming N\'d\'{e}lec (edge) elements. We present a novel `line search' type algorithm which prioritises inversion of some target parameters in a region of interest (ROI), with the update outside of the area defined implicitly as a function of the target parameters. This is particularly applicable to the mine detection problem, in which we wish to know more about some detected metallic objects, but are not interested in the surrounding medium. We may need to resolve the surrounding area though, in order to account for the target being obscured and multiple scattering in a highly cluttered subsurface. We focus particularly on spatial sensitivity of the inverse problem, using both a singular value decomposition to analyse the Jacobian matrix, as well as an asymptotic expansion involving polarization tensors describing the perturbation of electric field due to small objects. The latter allows us to extend the current theory of sensitivity in for acoustic FWI, based on the Born approximation, to better understand how polarization plays a role in the 3D electromagnetic inverse problem. Based on this asymptotic approximation, we derive a novel approximation to the diagonals of the Hessian matrix which can be used to pre-condition the GPR FWI problem.