Geoid undulation accuracy

For use in oceanographic applications the geoid is ideally needed to a high accuracy and to a high resolution. In 1979 the cumulative geoid undulation error to spherical harmonic degree 20 was ±1.4 m for the GEM10 potential coefficient model. Today the corresponding value has been reduced to ±25 cm for GEM-T3 or ±11 cm for the OSU91A model. Similar improvements are noted in harmonic degree (wavelength) and in resolution. The accuracy of the determination of the geoid is discussed from several points of views. Some comparisons are made with information available 12 years ago and that now available in the time framework of the TOPEX launch. It is noted that the accuracies described are subject to constant improvement. This is especially true as new satellite tracking data (e.g. DORIS data) are used in the potential coefficient models and more satellite altimeter data become available from the ERS-1 and TOPEX/Poseidon missions