Search

The concept of volume of influence (VoI) for electromagnetic induction (EMI) sensors is introduced and accurately defined. It enables one to better understand the response of a magnetic soil to an EMI sensor, as well as the effect of soil inhomogeneity on soil compensation. The VoI is first defined as the volume producing a fraction a of the total response of a homogeneous half-space. As this basic definition is not appropriate for sensor heads with intrinsic soil compensation, a generalized definition is then proposed. These definitions still do not yield a unique VoI, and a constraint must be introduced to reach uniqueness. Two constraints are investigated: one yielding the smallest VoI and the other one the layer of influence. Those two specific volumes of influence have a number of practical applications which are discussed. The smallest VoI is illustrated for typical head geometries, and we prove that, apart from differential heads such as the quad head, the shape of the smallest VoI is independent of the head geometry and can be computed from the far-field approximation. In addition, quantitative head characteristics are provided and show-among others-that double-D heads allow for a good soil compensation, assuming, however, approximate homogeneity over a larger volume of soil. The effect of soil inhomogeneity is further discussed, and a worst case VoI is defined for inhomogeneous soils.

The problem of wind statistics measurements in the planetary boundary layer using a coherent Doppler LIDAR is addressed. More specifically, it focuses on the design of efficient algorithms in the time-frequency space dedicated to the detection and the characterization of atmospheric hazards, such as aircraft wake vortices or wind shears. To support this study, a simulation program has been developed which combines the numerical simulation of LASER beam propagation in a turbulent medium with state-of-the-art Large Eddy Simulation (LES) of wake vortex in atmospheric turbulence or in ground effect. This tool constitutes a complete framework for optimizing the LASER source while developing and evaluating the performance of the whole estimation process. Moreover, an analytical formulation of the coherent LIDAR Wigner-Ville spectrum has been derived along with its associated Cohen’s class of time-frequency estimators. This theoretical basis leads to explicit equations of the wind statistics that are actually retrievable, depending on the measurement conditions and the laser pulse parameters. It also yields to an adaptive spectral modeling algorithm which is used to detect the wake vortices and then estimate their wind speed probability density function as well as their extremum radial velocity profiles, related to the vortex maximum tangential velocity. Another major achievement of this thesis is the development and the validation of a fast inversion method dedicated to wake vortex characterization, e.g. the estimation of its position and intensity. In this method, a Burnham-Hallock model, transformed by a new measurement model integrating the effects of the estimation process, is directly matched to the retrieved radial velocity map. Monte Carlo simulations have been carried out on both analytical models and LES to confirm its good performance. Finally, the validation of the axial detection of vortices with a fiber-based LIDAR has been performed during a test campaign co, (FSA 3) -- UCL, 2010

A general model to compute the response of an electromagnetic induction sensor to a magnetic soil, in both time and frequency domains, is developed. The model requires modest computational resources and can be applied to arbitrary soil inhomogeneities and relief, and to arbitrary sensor coil shapes, orientations, and positions. Central to the model is the concept of a head sensitivity map, which can be used to characterize the sensor head as a function of the shape, size, and position of the sensor coils. Two further concepts related to the head sensitivity are presented, which are the zero equisensitivity surface and the volume of influence. We demonstrate that these concepts aid the understanding of the detector behavior. The general model is based on the Born approximation, which is valid if the soil magnetic susceptibility is sufficiently small. A simpler model, which is only valid for homogeneous half-space soils but does not require the Born approximation, is also developed. The responses predicted by both models are shown to be in good agreement with each other and also with available analytic solutions. Comparing the two models also enabled an expression for the error incurred when using the Born approximation to be established. We shown that, for most soils of relevance to mine clearance, the corresponding error is negligible.

SCOPUS: ar.j, info:eu-repo/semantics/published

Chaque année, d'innombrables collisions se produisent entre des avions en vol et des oiseaux. L'impact aviaire, menace redoutée par les pilotes, concerne tant l'aviation civile que son pendant militaire. Les statistiques démontrent que, même si fort heureusement le nombre d'accidents graves reste limité, les incidents sont de plus en plus nombreux.Parmi les acteurs qui luttent contre ce danger, les constructeurs d'avions jouent un rôle prépondérant. Contraints par des réglementations internationales, ils s'attachent à produire des éléments de structure qui résistent à l'impact d'oiseaux.Dans la mise au point de leur produits, les avionneurs démontrent cette résistance à l'aide d'essais d'impact :on accélère un simulant d'oiseau jusqu'à la vitesse voulue -- de l'ordre de la vitesse de croisière nominale de l'avion -- et on le projette sur un aileron ou un morceau de fuselage. La présente thèse doctorale, co-dirigée par les professeurs Philippe Bouillard de l'ULB et Marc Pirlot de l'ERM, contribue doublement à l'amélioration de ces techniques d'essais dynamiques.D'une part, elle réalise la mise au point et la validation d'un lanceur pyrotechnique à double étage pour l'accélération du simulant d'oiseau. Un canon de calibre 20 mm est combiné avec un accélérateur de calibre 160 mm. La combustion d'un mélange de poudre propulsive contenu dans une douille adaptée génère les gaz à haute température et à haute pression nécessaires à l'accélération d'un simulant d'oiseau dûment confiné dans un conteneur de protection. Un dispositif de séparation arrête le conteneur afin que seul le simulant d'oiseau percute l'élément d'avion à l'essai. La solution pyrotechnique à double étage mise au point est validée par de nombreux tirs instrumentés en vitesse, en accélération et en pression ;elle se révèle conforme aux exigences de sécurité et de reproductibilité. Le lanceur pyrotechnique présente par rapport aux solutions pneumatiques, utilisées à notre connaissance d, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Ground-penetrating radar (GPR) proves to be a very valuable tool in the field of humanitarian demining, especially for the detection of plastic land-mines. Recently, a monostatic stepped-frequency continuous-wave (SFCW) GPR, together with a conceptual model of the radar-antenna-soil system, has been developed for the characterization of the electromagnetic parameters of soil, i.e. dielectric permittivity (epsilon), magnetic permeability (mu) and electric conductivity (sigma). This approach is extended here to the extraction of the GPR signal and to modelling the signatures of buried targets. The equivalence principle is used to decompose the GPR signal into its soil and target-in-soil components, as well as to model the radar-soil-target system. It permits the soil contribution to be subtracted from the total GPR signal to provide the signature of the buried target. This signature is compared to simulations. For a proof of the concept, the GPR return signal from a buried metal sphere has been simulated using the Method of Moments and it shows good agreement with its measured counterpart. We also have extracted clean frequency- and time-domain signatures of a PMN-2 plastic mine embedded in a multilayered medium, subject to various water contents. The method is also applied to a B-scan above a buried conducting cylinder. Finally, a study of the main sources of errors in the extraction of the signature of a buried target shows that mistakes in antenna height measurement lead to errors more important than those due to misestimating the relative dielectric permittivity of the soil.

This paper presents an accurate model of a monostatic stepped-frequency continuous-wave (SFCW) ground-penetrating radar (GPR). The model takes into account the multiple reflections occurring between the soil, target and antenna, which are a transverse electromagnetic (TEM) ultra-wide band (UWB) horn. The antenna radiation pattern is accounted for by a Huyghens cosinusoidal distribution of electric and magnetic current located on the aperture. The model is validated by experiments, involving dielectric targets embedded in a sandbox. These experiments validate altogether the radar modeling, as well as the MoM and the dyadic Green's functions (DGFs) used in the numerical algorithms., Anglais

This paper presents an accurate model of a monostatic stepped-frequency continuous-wave (SFCW) ground-penetrating radar (GPR). The model takes into account the multiple reflections occurring between the soil, target and antenna, which are a transverse electromagnetic (TEM) ultra-wide band (UWB) horn. Two equivalent current distributions representing the antenna radiation pattern are considered: a dipole of electric current located at the phase center of the antenna, and a Huyghens cosinusoidal distribution of electric and magnetic current located on the aperture. The model is validated by experiments, for which the targets are embedded within increasingly complex backgrounds: in free space, above a metal plane, and finally buried in a sandbox. These experiments validate altogether the radar modeling, as well as the MoM and the dyadic Green's functions (DGFs) used in the numerical algorithms., Anglais

Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Final Report, info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published