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Amélioration des références massiques de la Terre par synergie entre différentes mesures de géodésie spatiale : Application à l'océanographie par altimétrie spatiale

Abstract : In the context of the overall climate change and the need to analyze the implications of the record ice-sheet melting for the sea level and global fluid mass redistribution budgets, our PhD work focuses on large-scale phenomena impacting the shape of the Earth, its gravity field, and the stability of its rotation pole. We explore strategies for the observation and modeling of subtle variations in geodynamic parameters (lowermost degree coefficients), which are still poorly constrained, despite their importance in determining fundamental terrestrial references. The first part of this PhD is dedicated to the observation of the geocenter motion, using different geodetic technics. The outcomes of this work provided explanations, through a correct handling of the dominant error sources, for the discrepancies between the reference laser-based LAGEOS geocenter time series (defining the origin of the international frame, ITRF) and independent solutions using DORIS/laser/GPS observations from the Jason-2 altimeter satellite. The second part of this PhD presents a self-consistent determination of the degrees 0 (gravitational coefficient GM), 1 (geocenter motion), and 2 (Earth's figure axis orientation) of the geopotential. To this end, we use the available laser data since the 1970s (e.g., the first geodetic satellite Starlette launched by CNES in 1975), as they are the only absolute measurements making possible the monitoring of the first three degree terms. Based on 35 years of satellite laser tracking, an updated value of the geocentric gravitational coefficient was obtained, and a viscoelastic behavior of the Earth's mantle manifesting at decadal time scales was exhibited, combining the derived figure axis variations of the Earth and polar motion observations with the Euler-Liouville equations.
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Alexandre Couhert. Amélioration des références massiques de la Terre par synergie entre différentes mesures de géodésie spatiale : Application à l'océanographie par altimétrie spatiale. Planétologie et astrophysique de la terre [astro-ph.EP]. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30242⟩. ⟨tel-02930229⟩

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