A preliminary geoid model for the North Sea from gravimetry and altimetry, GPS and levelling

The main goal of the study is to obtain a consistent height and depth reference system in the form of a geoid for the Dutch mainland and marine area. For this purpose a procedure has been developed and tested to combine available gravity data and external data from satellite altimetry, GPS and levelling in an optimal manner. The initial, purely gravimetric geoid is adjusted in longer wavelengths by means of the external geoid data. The preliminary North Sea geoid GEONZ97 has a precision of better than 4 cm at sea and along the Dutch coast. As soon as instantaneous GPS height components in off-shore applications reach a comparable accuracy, tides and meteorological response can be eliminated in an efficient and effective way simply by subtracting the geoid.