Regional geoid determination in Tierra del Fuego. The use of Fagnano Lake to improve data distribution

D. DEL COGLIANO; R. DIETRICH; A. RICHTER; R. PERDOMO; J. L. HORMAECHEA; G. LIEBSCH; M. FRITSCHE; M. E. GOMEZ; D. BAGÚ; L. MENDOZA

Kiel

Congreso; 20 Lateinamerika Kolloquium der Geowisenschaften; 2007

Christian-Albrechts University

A regional geoid model for the Argentine portion of the Tierra del Fuego Island was established in previous works on the base of GPS determinations on levelling lines. This first approach suffers for the lack of data in the remote south-west region of Tierra del Fuego. There are no levelling lines reaching that zone. This fact increases the local interest in getting a geoid model to transform ellipsoidal heights into mean sea level heights. In order to improve the data distribution inthis region, the mean lake level of Fagnano Lake has been studied to use it as a first approximation of the local geoid. This narrow but long lake extends for more than 100 km in the east west direction. Using a GPS buoy and pressure tide gauges, a method to determine the mean lake surface topography with respect to the ellipsoid has been developed. A specific paper on this topic is also presented in this meeting. It is shown that the obtained mean lake level is essentially controlled by the regional gravity field. It isimportant to note that even when the use of the lake surface as an equipotential is only an approximation, the inclusion of this information in the local geoid model produces an important benefit due to the improvement on the data distribution. These results are compared with global models (EGM96, Eigen series) to conclude that none of them fits this region properly. Inthis sense, new efforts will be made to improve the local research.For the future, gravity measurements, observed geoid undulations and vertical deviations will be combined using the equivalent sources technique in order to produce a detailed geoid model in areas with sparse information. The equivalent masses are located under the observation stations at a depth related to the sources gravitational effect (the deepest masses correspond to points where the geoidundulations are known). The effect of the equivalent masses has to fit simultaneously, the anomalous potential related to the geoid and its vertical gradient or gravity anomaly.