Une technique de tomographie micro-onde appliquee entre forages, visant a la detection 2D d' heterogeneites enfouies, a ete mise au point. Fondee sur une inversion lineaire d' un probleme de diffraction electromagnetique dans le domaine spectral, elle fournit des representations qualitatives de contrastes de courants induits par le champ incident dans la zone exploree. L' etude theorique puis la validation experimentale en mode d' illumination transverse-magnetique (TM), definie par la propagation d' un champ electrique scalaire, est d' abord traitee. Une deuxieme approche, fondee sur l' illumination en mode transverse-electrique (TE), qui prend mieux en compte les contraintes de forages, a ete developpee en exploitant l' aspect vectoriel du champ electrique ; des hypotheses fortes, imposees par les configurations geometriques, entrainent toutefois une resolution spatiale de moins bonne qualite. Enfin, de facon plus prospective, l' utilisation d' antennes-boucles est evoquee dans le but d' adapter aux forages reels la technique du mode TM, moins restrictive numeriquement. (A). (Titre en anglais : Performance of 2D microwave imaging applied to inter-borehole tomography). PERFORMANCE OF 2D MICROWAVE IMAGING APPLIED TO INTER-BOREHOLE TOMOGRAPHY. A microwave tomography technique applied between boreholes and intended for the 2D detection of embedded heterogeneities has been developed. Based on the linear inversion of an electromagnetic diffraction problem lying in the spectral domain, this technique yields qualitative representations of contrasts in currents induced by the incident field within the investigated zone. The theoretical study followed by experimental validation in transverse-magnetic (TM) illumination mode, as defined by the propagation of a scalar electric field, will first be discussed. A second approach, derived from illumination while in transverse-electric (TE) mode to better incorporate borehole constraints, was then produced by utilizing the vectorial aspect of the electric field; a set of strong hypotheses, imposed by geometrical configurations, nonetheless cause a drop in spatial resolution quality. In looking forward, the use of loop antennas will be examined in the aim of adapting the technique running in TM mode to actual boreholes; this proves less restrictive from a numerical standpoint.
Samenvatting