Unification of vertical datums by GPS and gravimetric geoid models with application to Fennoscandia

The second Baltic Sea Level (BSL) GPS campaign was run for one week in June 1993. Data from 35 tide gauge sites and five fiducial stations were analysed, for three fiducial stations (Onsala, Metsahovi and Wettzell) fixed at the ITRF93 system. On a timescale of 5 days, precision was several parts in 10(9) for the horizontal and vertical components. Accuracies were about 1 cm in comparison with the International GPS Geodynamical Service (IGS) coordinates in three directions. To connect the Swedish and the Finnish height systems, our numerical application utilises three approaches: a rigorous approach, a bias tit and a three-parameter fit. The results between the Swedish RH70 and the Finnish N 60 systems are estimated to -19.3 +/- 6.5, -17 +/- 6 and -15 +/- 6 cm, respectively, by the three approaches. The results of the three indirect methods are in an agreement with those of a direct approach from levelling and gravity measurements.