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Modélisation de la diffraction électromagnétique des surfaces végétalisées avec prise en compte de la topographie : application à l'étude des forêts tropicales et à la présence d'hydrocarbure sur le sol

Abstract : This work is in the general frame of coherent modelling of interaction between electromagnetic waves and surfaces with vegetation. Our objective is to develop an approach of the electromagnetic simulation taking into account topography and vegetation heterogeneities. Simulation results have been validated using numerous in-situ measurements. The corresponding code is then used for two issues. First one is the study of tropical forests to retrieve bio-geophysical properties (biomass, moisture). Second one is the consideration of hydrocarbons with short vegetation in a context of hydrocarbons characterization and exploration. This work is part of a program of research and innovation in remote sensing conducted jointly by ONERA and Total. The first step consisted in writing the coherent electromagnetic simulation code, taking into account the relief and the heterogeneity of the vegetation. For this purpose, the forest is represented by a variable stacking of pentahedral volume elements (voxels) to match the triangular mesh of the ground and to follow the irregularity of the canopy. After validating our code on theoretical examples, we have been able to study the effects of the relief on radar backscattering. Then, a vegetation description model for tropical forests was developed based on in-situ measurements and direct observations. This model generates the input data for our electromagnetic simulation code and it permitted to compare simulations with airborne and proximity measurements acquired by ONERA on two sites in Africa. Sensitivity studies on the input parameters of both the electromagnetic simulation code and the growth code are presented. In parallel, substitution models for the numerical code have been developed to perform the inversion of the bio-geophysical features versus the polarimetric radar data. These models are much faster while remaining accurate. An application to retrieval is presented: it is possible to retrieve some bio-geophysical characteristics of one forest (moisture, biomass ...) from a radar image set. Finally, a study on the effects of hydrocarbons on radar backscatter with short vegetation is presented.[...]
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  • HAL Id : tel-02316023, version 1

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Jean-Pascal Monvoisin. Modélisation de la diffraction électromagnétique des surfaces végétalisées avec prise en compte de la topographie : application à l'étude des forêts tropicales et à la présence d'hydrocarbure sur le sol. Géophysique [physics.geo-ph]. Université Paul Sabatier - Toulouse III, 2018. Français. ⟨NNT : 2018TOU30177⟩. ⟨tel-02316023⟩

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