Quasi-Geoid of New Caledonia: Computation, Results and Analysis

Abstract

The archipelago of New Caledonia is located in the Pacific Ocean, near the New Hebrides Trench. The gravity field is extremely rough in this area, free-air gravity anomalies varying from -230 to +200 mgal. Two vain attempts to compute a geoid model in 2000 and 2004 led the Territorial Government of New Caledonia to put IGN (French National Geographic Institute) in charge of a new calculation. Gravity data were provided by several institutions (Bureau Gravimétrique International, Institut de Recherches pour le Développement, Genavire, IGN) and were of various quality, so that data cleaning has been an important stage. Using the GRAVSOFT package, height anomalies have been computed by the residual terrain method combined with Stokes integration. By comparison of the quasi-geoid with levelled GPS points on the main island, accuracy has been estimated to be better than 9 cm, which shows a significant improvement with previous solutions. A grid to convert ellipsoidal heights into heights above mean sea level has been derived from the quasi-geoid and levelled GPS points. Its accuracy is about 4.5 cm. The shifts between vertical reference systems of principal islands of the archipelago have been determined. Differences between the geoid and the mean sea level at tide gauges, and their correlation with oceanic currents have also been studied and discussed in the paper. © Springer-Verlag Berlin Heidelberg 2010.