Imagerie microonde: influence de la polarimétrie du champ diffracté

This thesis is devoted to the study of bidimensional polarimetric microwave imaging and consists of two parts. The first is dedicated on experimental studies for buried objects detection while the second presents the development of quantitative imaging algorithm. The work carried out in the first part deals with the realization of ultra-wide band antennas and the determination of their behaviour during polarimetric measurement. In the last case, many tests have been carried out and allow us to conclude on their qualities. In a second stage, we present a bidimensional imaging algorithm which is taking into account 2D-TM and 2D-TE polarizations. First, the development of an electromagnetic scattering algorithm is exposed. Its association with an inverse problem algorithm allows to generate the quantitative imaging algorithm. Then, many reconstruction configurations with isotropic or anisotropic homogeneous objects highlight its abilities.Le travail présenté dans ce mémoire de thèse s'intéresse au problème de l'imagerie microonde bidimensionnelle polarimétrique. Il est scindé en deux parties, la première est dédiée aux études expérimentales liées à la détection d'objets enfouis tandis que la seconde présente le développement d'un algorithme d'imagerie quantitative. Ainsi le travail effectué dans la première partie du manuscrit porte sur la réalisation d'antennes ultra-large bande et la détermination de leur comportement lors de mesures polarimétriques sur sites. Dans ce dernier cas, plusieurs tests ont été réalisés et permettent de conclure sur les qualités des capteurs développés. Dans une deuxième phase, un code d'imagerie bidimensionnelle prenant en compte à la fois la polarisation 2D-TM et 2D-TE est présenté. Le développement d'un algorithme de diffraction électromagnétique est tout d'abord exposé. Son association avec un algorithme de problème inverse existant déjà au laboratoire permet alors de générer le code d'imagerie quantitative. Plusieurs configurations de reconstruction d'objet homogène, isotrope ou non, permettent ensuite de mettre en évidence ses capacités

Step-frequency radar applied on thin road layers

International audienceIn the field of road construction and maintenance, the need for information on the thickness of very thin road layers is not satisfied by means of commercial pulse GPR, due to the inability of such devices to operate over ranges of several gigahertz. As a result, research has focused on the design of a step-frequency radar technique, able to work with very high-frequency synthetic pulses.An ultrawide band antenna, belonging to the family of Vivaldi antennas, has been developed for road applications. It has been created using stripline technology and yields a band width greater than one decade. During an initial step, this antenna was tested on various bituminous concrete samples with a network analyzer. Different parameters were studied, including band width, offset between antennas, and height and shape of the frequency-dependent pulse.A second step involved GPR dynamic measurements. A customized software program enabled recording data from the network analyzer. Several radar profiles were developed from selected road construction and maintenance test sites (e.g. the Circular Pavement Fatigue Test Track, composed of a number of known structures). Results show improved resolution when compared to a commercial impulse GPR system

Step-frequency radar applied on bituminous concrete

International audienceIn the road field, the need to get information on the thickness of very thin road layers is not solved by GPR. The reason is that the devices are not able to work over several gigahertz. That is why, a research has focused on the conception of a step frequency radar technique, enable to work with very high central frequency synthetic pulses. In collaboration with the LCPC (Central Laboratory of Bridges and Roads), an ultra wide band antenna has been developed at the LEAT (Electronic, Antennas and Telecommunication Laboratory). The ultra wide band antenna, developed for roads application, forms parts of the family of the Vivaldi antennas. It has been realized in stripline technology and one obtains a bandwidth greater than one decade. In a first step, this antenna has been tested on various bituminous concrete samples, with a network analyzer. Different parameters were studied like the bandwidth, the off-set between antennas, the height, and the shape of the pulse depending to the frequencies. A second step concerns GPR dynamic measurements. An homemade software enables to record data from the network analyzer. As LCPC has large testing facilities in the road field, such as a circular Pavement Fatigue Test Track, composed of different known structures, several radar profiles have been done. Results are compared with classical GPR profiles