Validating Earth and ocean tide models using tidal gravity measurements

O1 and M2 observations from well-calibrated spring gravimeters and superconducting gravimeters from the Global Geodynamics Project (GGP) are used to test models of the Earthʹs body tide and 10 ocean tide models. It is shown that some of the ocean tide models give anomalous results in various parts of the world. For example, the Schwiderski ocean tide model gives discrepancies in several areas and the FES series of ocean tide models have problems in the western Pacific (China, Japan and Australia). The majority of the high-quality tidal gravity measurements in Europe are in close agreement with the Dehant, Defraigne and Wahr (DDW) elastic and inelastic body tide models. The gravimetric factors for the DDW elastic and inelastic models only differ by 0.12 per cent and the present calibration accuracy does not allow us to distinguish between these models, but does reduce the previous upper bound on inelastic gravimetric factors. The European observations give a phase lag of a few hundredths of a degree for the O1 body gravity tide, which is consistent with the Mathews inelastic body tide model. At some European and worldwide stations the gravimetric factors differ by up to 0.3 per cent from the DDW model and it is suggested that further checks on the gravimeter calibrations are required. Accurate determinations of instrumental phase lags are now easier to achieve and the imaginary (out-of-phase) component of tidal gravity can be used for accurate tests of this component of ocean tide models.