Ocean tides from T/P, ERS-1, and GEOSAT altimetry

Abstract

Aliasing of the diurnal and semi-diurnal tides is a major problem when estimating the ocean tides from satellite altimetry. As a result of aliasing, the tides become correlated and many years of altimeter observations may be needed to seperate them. For the three major satellite altimetry missions to date i.e., GEOSAT, ERS-1, and TOPEX/POSEIDON (T/P), the alias periods as well as the Rayleigh periods over which the tides decorrelate can be identified. Especially in case of GEOSAT and ERS-1, severe correlation problems arise. However, it is shown by means of covariance analyses that the tidal phase advance differences on crossing satellite groundtracks can significantly reduce the correlations among the diurnal and semi-diurnal tides and among these tides and the seasonal cycles of ocean variability. Therefore, it has been attempted to solve a multi-satellite response tidal solution for the diurnal and semi-diurnal bands from a total of 7 years of altimetry. Unfortunately, it could be shown that the GEOSAT and ERS-1 orbit errors are too large to improve a 3-year T/P tidal solution with about 2 years of GEOSAT and 2 years of ERS-1 altimeter observations. However, these results are preliminary and it is expected that more accurate orbits, which have become available recently for ERS-1, and additional altimeter data from ERS-2 and the GEOSAT Follow-On (GFO) should lead to an improved T/P tidal model.