THE USE OF GPS DATA FOR IMPROVING LOCAL GEOID DETERMINATION

The ellipsoidal heights of selected stations at Port Island in Japan were determined using Global Positioning System (GPS). By using geoidal height values derived both from the GPS ellipsoid heights h GPS and orthometric height of the levelling h levelling, and from gravimetry we have tested the capacity of GPS and gravimetry to derive orthometric heights at the sites to evaluate sea surface topography later. The gravimetric solution over the region covered 6241 of 0.1° × 0.1° point free-air gravity anomalies, ∆g and have been collected from the Japan Gravity Data Base, selected within the region 34.651° ≤ ϕ ≤ 34.661°, 135.212° ≤ λ ≤ 135.227°, where sufficient data existed to evaluate ΔN. The poor gravity data coverage in parts of Port Island produced results of ≤ 10 p.p.m. accuracy, but they are not sufficient for high precision applications, such as sea surface topography determinations.Comparisons of the full gravimetric determinations using different geopotential models of OSU89A, OSU89B and GPM2F, available at the department at the time of computations, were made. When using the OSU89A as the reference model, the gravimetric ∆N, which ranged from −2.2 cm to 16.7 cm, compared well with the control ∆N GPS/levelling.