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

Abstract

The "Descartes-Nutation" Project is devoted to the "understanding of the next decimal of precession-nutation, from the theoretical point of view as well as from the observational point of view". In this framework, we made a proposal in order 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 the geophysical fluids on the EOP and (iv) the Nutation observations. We investigate further the links between Earth Orientation and Gravity Field Variations. Indeed, the masses distributions inside the Earth govern the behaviour of the rotation axis in space (precession-nutation) and in the Earth (polar motion), as well as the Earth rotation rate (or equivalently, length of the day). These distributions of masses can be measured by space owing to artificial satellites, the orbitography of which provides the Earth gravity field determination. Then, the temporal variations of the Earth gravity field can be related to the variations of the Earth Orientation Parameters (EOP) (with the Inertia Tensor). Nowadays, the Earth orientation measurements in space, obtained with Very Long Baseline Interferometry (VLBI), have a precision better than the milliarcsecond level. It is then necessary to consider all the geophysical sources that can improve the models precision. The goal of my PhD Thesis was to use the Earth gravity field measurements, as well as its variations, as a tool to improve the Earth orientation modelisation. We present here the results obtained as well as various proposals to extend these investigations (numerical studies, the use of J2 geophysical series, integration of GRACE data ...).