Testing new geoid models in Tierra del Fuego

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

Buenos Aires

Congreso; Reunión Científica de la International Association of Geodesy, Geodesy for Planet Earth; 2009

Asociación Argentina de Geofísicos y Geodestas, Comité Nacional de la Unión Geodésica y Geofísica Internacional

Tierra del Fuego island is lacated at the southern extreme of the American continent. Its is a very interesting region for several resons, the northern part of the island belongs to the South American plate, while the southern region is part of the Scotia plate. Relative tectonic movements have been reported by several authors. Fagnano lake is a 110 km long lake which extends East West in the zone of the main fault.A local geoid model was first established in Tierra del Fuego using only measurements on the levelling network of the island. however, the levelling points are not well distributed. The lines follow only the main roads.Several years ago, a detailed study of the behaviour of fagnano lake allowed its use as a level surface, thus adding valuable information to the previous model in the South West portion of the island.Recently a new precise geodetic frame was calculated for the region, and the different GPS mesurements were all refered to the GPS frame IGS05 which coincides closely with ITRF.Finally, in 2008 a new levelling line was built and GPS mesasurements were also made in order to improve the data distribution.The observed data at this moment includes 61 GPS/levelling points and 83 GPS determinations on the lake surface. Several global models have been tested using these observations. The standar deviations between the observed and calculated undulations using the 61 points on the land is 0.27 m for EGM96, 0.22 m for EIGEN_GL04c and 0.09 m for EGM2008. The exellent perfomance of the EGM2008 model is clear. Recent gravity data from this zone was included in this model.However, the gravity data do not cover the south west region of the island. The only observations for that region are the GPS data on the Fagnano lake surface. If the geoid undulations estimated from these 83 points are added to the statistics, then the standard deviations become 0.29 m for the EGM96, 0.22 m for the EIGEN_GL04c and 0.33 for the EGM2008. A strong disagreement between the observed values and those calculated using EGM2008 model is clearly seen in the western portion of the lake. This result shows that new efforts should be done to obtain more observations in the extreme Shouth West portion of the island.