Error spectrum for the global M-2 ocean tide

The most accurate determinations of the global ocean tides are currently ba sed on altimeter measurements made by the Topex/Poseidon satellite. The err or spectrum corresponding to the Mt tidal solution is here estimated, prima rily by inverse methods and secondarily by simple differencing of several o f the best tidal models. The tidal error spectrum is flatter than the tidal signal spectrum, and it exceeds 10% of the signal at spherical harmonic de gree 15 and above. The tide errors also exceed the anticipated sensitivity of the upcoming GRACE satellite gravity mission for all degrees below 40, a nd possibly below 50.