Precise determination of geoid height and free-air gravity anomaly at Syowa Station, Antarctica

From the International Terrestrial Reference Frame 1994 (ITRF94) coordinates of the Doppler Orbitography Radiopositioning Integrated by Satellites (DORIS) beacon marker at Syowa Station (69.0°S, 39.6°E), Antarctica, we derived the ellipsoidal height of the Scientific Committee on Antarctic Research (SCAR) Global Positioning System (GPS) point as 42.240 m on the World Geodetic System 1984 (WGS84) associated ellipsoid of a tide free Earth at the epoch of 1993.0. Because the SCAR GPS reference mark was 21.165 m above the local mean sea level at the epoch of 1993.0, and because the sea surface topography is estimated as −1.29 m, the ground data of geoid height can be estimated as 22.37 m on the WGS84 ellipsoid. As for error estimate of the above value, 20–30 cm formal error can be assigned including 3 cm error from the DORIS determination, 1 cm error from the local geodetic tie, and the dominant 20–30 cm error from uncertain modeling of sea surface topography, etc. The EGM96 geoid model gives the synthetic geoid height of 22.10 m at Syowa Station; the discrepancy of 27 cm from the observed value is within the 36 cm cumulative (to the degree 360) rms (root-mean-square) error of the model. We retried similar determination at Breid Bay (70.2°S, 23.8°E) and made a tie to the inland outcropped Seal Rock; the obtained value of 21.4 m has an overall error of 1.8 m. These ground data can be used as test data for generating higher-order (n, m ≥360) geopotential models. With the establishment of the International Absolute Gravity Basestation Network (IAGBN) standard value at Syowa Station and gravimetric connection to the Seal Rock, ground data of free-air gravity anomalies of 0.05 mgal accuracy at Syowa Station and 1 mgal accuracy at Seal Rock were obtained. These gravity ground data will also serve as test data for adjusting the satellite- and/or shipborne-derived gravity anomaly maps in the region concerned.