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The "Descartes-Nutation" Project is devoted to the "understanding of the nextdecimal of precession-nutation, from the theoretical point of view as well asfrom the observational point of view". In this framework, we made a proposal inorder to contribute to the study of (i) the dynamical flattening of the Earth,(ii) the coupling effects of the lunisolar forcing, (iii) the effect of thegeophysical fluids on the EOP and (iv) the Nutation observations. Weinvestigate further the links between Earth Orientation and Gravity FieldVariations. Indeed, the masses distributions inside the Earth govern thebehaviour of the rotation axis in space (precession-nutation) and in the Earth(polar motion), as well as the Earth rotation rate (or equivalently, length ofthe day). These distributions of masses can be measured by space owing toartificial satellites, the orbitography of which provides the Earth gravityfield determination. Then, the temporal variations of the Earth gravity fieldcan be related to the variations of the Earth Orientation Parameters (EOP)(with the Inertia Tensor). Nowadays, the Earth orientation measurements inspace, obtained with Very Long Baseline Interferometry (VLBI), have a precisionbetter than the milliarcsecond level. It is then necessary to consider all thegeophysical sources that can improve the models precision. The goal of my PhDThesis was to use the Earth gravity field measurements, as well as itsvariations, as a tool to improve the Earth orientation modelisation. We presenthere the results obtained as well as various proposals to extend theseinvestigations (numerical studies, the use of J2 geophysical series,integration of GRACE data ...).

Earth rotation and variations of the gravity field, in the framework of the "Descartes-nutation" project