Inversion of oceanic tidal currents from measured elevations

The problem of deducing tidal current velocities from measured tidal elevations is considered. Emphasis is given to global scales for which accurate cotidal charts based on satellite altimetry are readily available. Barotropic tidal currents are deduced from a recent altimetric tide solution by solving the two-dimensional momentum equations and the continuity equation in a least squares fashion. This approach represents a middle ground between commonly used data assimilation schemes and simple local solutions of the momentum equations. The estimated velocities are compared with those of other available global models, with acoustic velocity measurements, and with current meter measurements. Agreement with acoustic measurements is especially good; RMS discrepancies are consistently less than 2 mm s−1. The method appears to be a useful tool for investigating various aspects of tidal dynamics.