Aliasing (Altimetry)

Aliasing in altimetry is the folding of a high-frequency ocean signal into a spurious low frequency because the satellite samples any given point only every repeat cycle. TOPEX/Poseidon and the Jason series fly a 9.9156-day repeat, so tidal constituents shorter than about 20 days alias into longer periods: the principal lunar semidiurnal M2 tide aliases to roughly 62 days, S2 to about 59 days, K1 to about 173 days. Tide models such as GOT and FES are removed before the data are used so the residual sea surface height is clean. Get the de-aliasing wrong and a tide leaks into the mesoscale or seasonal signal.