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Imagerie radar basse fréquence pour l'exploration des zones arides terrestres et martiennes : détection de l'humidité du sous-sol et cartographie de la paléohydrologie.

Abstract : These research tasks propose an experimental approach to study the capabilities of low frequency radar imagery for the detection of moisture in the first few meters of the terrestrial and Martian arid areas and the geological cartography of their close subsurface. In particular, the phasimetric analysis of L-band SAR images of the Pyla Dune (France) made it possible to highlight a particular behaviour of the copolarized phase difference, related to the presence of buried wet structures in the subsurface. In order to interpret and to model this phenomenon, we developed an analytical single-scattering model based on the IEM, supplemented by an analytical expression of the multiple scattering term. Simulating successfully the studied phenomenon, our model confirms the phase signal being generated by the moisture profile of hidden structures because of the multiple scattering component. It was also shown that this particular phase signature allows the detection of wet interfaces at depths more significant than those authorized by the analysis of the traditional radiometric indicators. Taking part in the program Terrestrial Analog to Mars of NASA, we also worked with the definition of the performances of an orbital P-band SAR system for detecting moisture in the upper few meters of the planet Mars, by means of the copolarized phase difference. Including a volume scattering term, our preceding IEM model shows that the presence of heterogeneities in the first meters of the Martian crust could deteriorate the performances of the copolar phase signal for the detection of moisture in term of depth of investigation. Nevertheless, our results of simulations indicate that such a SAR system, exploiting the copolar radar phase, would authorize the detection of moisture and its follow-up on a seasonal scale until some 3 meters depths in the areas presenting a favourable geological context i.e. a weak concentration of surface and subsurface scatterers. Beyond the soil moisture detection, we also sought to highlight the contribution of the radar imagery for the cartography of geological interfaces on a large scale by means of spaceborne SAR systems. The polarimetric analysis of SIR-C/X-SAR data for Mauritania made it possible to show the potential of the low frequency radar imagery for the detection of geological structures of surface like for the cartography of the subsurface paleohydrology in arid context. In particular, our results showed that the polarimetric data provide not only informations on the scattering mechanisms brought into play, but also make it possible to differentiate the superficial structures by the roughness which they cause, of the structures of subsurface by the diffusion of volume that they generate.
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https://tel.archives-ouvertes.fr/tel-00262275
Contributor : Marie-Paule Pomies <>
Submitted on : Tuesday, March 11, 2008 - 11:52:52 AM
Last modification on : Monday, November 23, 2020 - 2:38:10 PM
Long-term archiving on: : Friday, May 21, 2010 - 12:09:33 AM

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  • HAL Id : tel-00262275, version 1

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Citation

Y. Lasne. Imagerie radar basse fréquence pour l'exploration des zones arides terrestres et martiennes : détection de l'humidité du sous-sol et cartographie de la paléohydrologie.. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2005. Français. ⟨tel-00262275⟩

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