SOME RESULTS OF HETEROGENEOUS DATA INVERSIONS FOR OCEANIC TIDES

Many different instruments directly or indirectly observe the oceanic tidal movements. Among them, we consider here the coastal tide gauge and deep-sea pressure recorder which provide at least the principal spectral constituents of the tidal height, the gravimeter which indirectly observes the oceanic tides through the gravitational effect generated by the deformation of the solid Earth under the ocean tidal mass load, and the satellite altimeter which samples the tides in the time domain and over the nearly whole ocean. Our present paper deals with an empirical method for the recovery of the oceanic tides by inversion of heterogeneous data sets. The aim is to take advantage of the different kinds of information coming from the measurement instruments in order to complete more accurate empirical solutions. First, tide gauge and gravity loading data are separately and jointly inverted to provide global charts of the major semidiurnal M2 wave. The results prove that the tide gauge data have a major contribution in the tidal mapping but also suggest that the gravity loading data distort the information. This is certainly due to unmodelled geophysical phenomena and instrumental errors. Second, tide gauge and satellite altimeter data are considered in a separate and a joint inversion computation to provide tidal estimations along a predefined geographical line in the North Atlantic. The results are accurate enough to make provision for the boundary conditions of an hydrodynamical tidal model. As an intrinsic advantage of the inversion method, a posteriori standard deviations and error covariances for all the solutions displayed are provided and analyzed.