Comparison between Altimetric and Gravimetric Geoid in the South — West Mediterranean Basin
The processing of altimetric data collected by the Topex-Poseidon satellite on the Western Mediterranean sea, based on the Barrick-85 model, permitted the extraction of the instantaneous sea surface height. The analysis of 76 passes distributed over 8 orbital arcs, after correction of the disturbing effects (troposphere, ionosphere,…), the reduction of the instantaneous measurements and elimination of the weak periodic variable phenomena, allowed us to give a mean altimetric profile.
The processing of the mean arcs on the crossing points by the least squares method allowed us to get a mean level on the western Mediterranean sea with a precision of a centimeter. The results confirm the dominance of an East-West current along the Algerian coast and the existence of localized eddies off the North African coasts (Bernard & al, 1993).
The sea surface obtained from Topex data were compared to the global geoid deducted from the OSU91A potential model. The metric difference obtained shows insufficient adequacy of the global solutions for geodetic applications. The comparison of the solution above with a gravimetric geoid provided by the collocation method (using Gravsoft software and a set of BGI free air gravity anomalies surrounding the region) near the Algerian coasts, improves the results appreciably and shows the importance and the influence of the inshore quality data.
The introduction of exhaustive and precise altimetric data, and of gravimetric measurements with sufficient density, will permit to define a more precise altimetric surface of the geoid by the intergration of the existing tidegauge measurements.
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