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Theses

Analyse et modélisation de haute précision pour l'orientation de la Terre

Abstract : The increase of accuracy of the space and geodetic techniques giving access to the Earth orientation, as well as the improvement of the terrestrial and celestial reference systems, require, for a best scientific benefit, a more precise modelling of the Earth rotation. With this aim, the International Astronomical Union recommended, in August 2000, a new parametrization in the Earth orientation. The first part of this thesis is devoted to the implementation of these recommendations, which became effective on 1 January 2003, and to the computation of the models adapted to the new astrometric representation based on the Non-Rotating Origin. These models concern the celestial coordinates of the Celestial Intermediate Pole (CIP), and the quantity providing the position of the CEO. Such developments are based on the new precession-nutation model IAU2000A and on the recent estimates of the connexion parameters between reference frames. We present also a model for the quantity giving the displacement of the origin of the longitudes in the terrestrial frame, derived from the observed polar motion. External fluid layers (atmosphere and oceans) play a prominent part in the non-predictible part of the Earth rotation. In the second part of this thesis, we present an overall evaluation of these effects on the Earth Orientation Parameters, based on the more recent meteorological data. Besides the mean contribution of atmosphere and oceans during the time spans covered by the series, we study the temporal variability of the periodic terms and we show its strong correlation with the corresponding observed variations in the polar motion and the length of day. Estimating the excitation of nutations by fluid layers remains a delicate operation because of the lack of data in the diurnal frequency band, the small size of these effects and the strong variability of the excitation. We show also that the Atmospheric Angular Momentum is modified by the lunisolar torque giving an effect on the precession in longitude and on the 18.6-year nutation. In the framework of the recent implementation of the IAU2000A precession-nutation model, it has become necessary to compute all the effects of which amplitudes are of the order of tens of microarcseconds. One of these effects is the coupling between the variations in the Earth's rotation rate due to zonal tides and the precession-nutation. These variations are taken into account in the computation of the Universal Time (UT1) and are modeled. Their effect on nutation has recently been evaluated by different approaches with disparete results. In the third part of this thesis, we investigate the differences and we determine an exhaustive model for a real Earth allowing to correct the nutation angle. The major effect is on the 18.6-year nutation and on the precession in longitude.
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https://tel.archives-ouvertes.fr/tel-00008856
Contributor : Sebastien Lambert <>
Submitted on : Wednesday, March 23, 2005 - 4:53:23 PM
Last modification on : Monday, December 14, 2020 - 9:45:56 AM
Long-term archiving on: : Friday, April 2, 2010 - 9:21:59 PM

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  • HAL Id : tel-00008856, version 1

Citation

Sebastien Lambert. Analyse et modélisation de haute précision pour l'orientation de la Terre. Sciences de la Terre. Observatoire de Paris, 2003. Français. ⟨tel-00008856⟩

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