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Solid Earth and ocean tides estimated from satellite orbit analyses
Author(s) -
Lambeck Kurt,
Cazenave Anny,
Balmino Georges
Publication year - 1974
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg012i003p00421
Subject(s) - ocean tide , satellite , geology , phase lag , orbit (dynamics) , geodesy , earth's orbit , geophysics , physics , astronomy , aerospace engineering , engineering , mathematics , spacecraft
The earth's tidal deformations cause perturbations in the motions of close earth satellites, observations of which give estimates of the Love number k 2 and phase lag δ. The contribution of the ocean tides has generally been considered unimportant, but this is not so. These ocean tides cause the same spectrum of orbital perturbations as the solid tide, and a complete separation, by analyzing satellite orbits of different elements, is not possible. Neglect of the ocean tide will introduce errors in k 2 of as much as 15% and in phase angle of as much as 10° depending on the orbit. This explains the low values for k 2 near 0.25 that have been obtained recently from orbital analyses. Comparison of several models for the principal lunar tide ( M 2 ) of the ocean indicates that these models are insufficient for making precise orbital corrections. For the other tidal frequencies that often have important effects on satellite orbits, no satisfactory tide models exist. The equilibrium theory does not suffice for these corrections, and improved values for k 2 and particularly for the phase lag δ can only come from a concomitant improvement in our knowledge of the ocean tides. It is possible to extract some information on the ocean tides from the orbital analyses, and this could be used as a constraint in numerical ocean tide computations. We have analyzed the orbit of the satellite Geos 2 for the lunar M 2 tide. After correcting for the ocean tides the value found for k 2 varies between 0.27 and 0.30, depending on which ocean tide model is used. The solutions for the phase angles are quite unsatisfactory, and this condition stems from insufficiently precise tracking data and inadequate coverage as well as from inadequate tide models. We have applied approximate ocean tide corrections to the tide parameters determined by several authors to give a mean value of k 2 =0.31 and δ2=0.5°. This phase lag corresponds to a mantle Q of about 60.