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• W3023742007 abstract "The subject of this PhD thesis is « Electromagnetic propagation modeling in inhomogeneous media with refractive index gradients based on Gaussian beams – Application to realistic atmospheric propagation and radio occultation between satellites ». The study started on december 2nd, 2013 at the DEMR (Departement Electromagnetisme et Radar) department of the ONERA research laboratory, in Toulouse, France. It was funded both by the ONERA and Region Midi-Pyrenees. It was supervised by Jerome Sokoloff (LAPLACE/UPS, thesis director), Alexandre Chabory (ENAC, thesis co-director) and Vincent Fabbro (ONERA). The doctoral school was «Ecole Doctorale Genie Electrique, Electronique, Telecommunications : du systeme au nanosysteme ».The Gaussian beam was mostly used in scientific investigations to study optical systems such as lasers. Rarer and more recent works suggested the use of the Gaussian beam formalism in order to model the propagation of seismic waves. The properties of the Gaussian beam also led some authors to develop models for atmospheric propagation. In this thesis a model based on Gaussian beams called GBAR (Gaussian Beam for Atmospheric Refraction) was developped for tropospheric propagation in realistic and deterministic conditions.The scientific approach consisted in rewritting the fundamental equations introduced by Cerveny and Popov describing iteratively the propagation of a Gaussian beam in inhomogeneous media, under the high-frequency assumption (asymptotic model). New equations were derived from them in order to get analytical equations of the propagation of a Gaussian beam in inhomogeneous media described by the variations of the refractive index. The basic assumption under to get the analytical equations is to consider that the refractive index gradient is vertical and constant around the beam axis.The analytical equations that describe the propagation of a Gaussian beam were extended to model the propagation of an arbitrary field in a tropospheric medium with strong variations and inversions of the refractive index. This was done by coupling the analytical equations with the multibeam expansion procedure developped by Alexandre Chabory in his PhD thesis. The GBAR model was validated in tropospheric conditions, using refractive index grids from the WRF (Weather Research and Forecasting) mesoscale meteorological model.In the third and final phase, the GBAR model was used to simulate Radio Occultation data inversions. Tools exist to allow for interpretations of Radio Occultation data in order to estimate the physical properties of the atmosphere from measured phased, amplitude, Doppler shift and delay of GNSS signals transmitted between satellites orbiting around the Earth. Those models suggest that both the Earth the its atmosphere are spherically symmetric. The GBAR model was used to simulate the refrative effects of the troposphere on the propagation of the GNSS signals, and to process the amplitude of the field to give inverted profiles of the refractive index in the atmosphere. The impact of the spherical symmetry on the inverted profiles was also evaluated.The work of the PhD thesis was presented in the French conference Journees Nationales Microondes in June 2015, in Bordeaux, and in the international conference The 10th European Conference on Antennas and Propagation, in April 2016, in Davos, Swiss. Two papers are in final phase of redaction and should be submitted to IEEE Antennas and Propagation in Spring 2017. Furthermore, the results brought by this PhD thesis led to discussions with the CNES (Centre National d'Etudes Spatiales) in order to continue the investigations." @default.
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• W3023742007 date "2017-04-19" @default.
• W3023742007 modified "2023-09-23" @default.
• W3023742007 title "Electromagnetic propagation modeling in inhomogeneous media with refractive index gradients based on Gaussian beams – Application to realistic atmospheric propagation and radio occultation between satellites" @default.
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