Ocean tides from harmonic and response analysis on TOPEX/POSEIDON altimetry

Abstract

With the TOPEX/POSEIDON mission having reached the end of its nominal three-year lifetime, a large number of ocean tides models incorporating TOPEX/POSEIDON altimetry data have been released. Because the major part of these models is based on the two classical analysis methods, i.e. harmonic and response analysis, it is interesting to compare and interpret the results of these two methods. Clearly, this requires that the same data are used and moreover that the data are processed with the same scheme. Therefore, both analysis methods have been implemented and three years of TOPEX/POSEIDON altimeter data have been processed to solve the major diurnal and semi-diurnal constituents of the global ocean tides by harmonic and response analysis. The results of both methods are evaluated from the differences with the most recent Grenoble hydrodynamic model and from the fit with the harmonic constants of a globally-distributed set of tide gauges. It was found that the solutions from the harmonic and response methods differ at the millimetre level and that, according to the tide gauges, the harmonic method leads to slightly more accurate results. Also, results from some experiments with the parameters in the response formalism show that the tidal admittance in both the diurnal and semi-diurnal band can be adequately described with a lag interval of two days and a number of lags of three.