Activities Related to the Materialization of a New Vertical System for Argentina.

The Geodesy Subcommitee of the National Committee of IUGG created the working group "Geopotential Origin" in December 2000 in order to coordinate the national activities, establish and set down a new Vertical Reference System and to interact with Group III of SIRGAS (Geocentric Reference System for the Americas) Project. For that, all the activities were organised in four items. This contribution describes the main results obtained in each of them as well as future tasks for the near future: Tide Gauges: The origin of the Argentine Vertical Reference System, defined by means of tide gauge records, is affected by the sea surface topography at the gauge locations. A project to observe and model the sea level variations using both, tide gauges and satellite altimetry, is being carried out since 1998. Four permanently observing GPS stations have already been installed close to gauges along the Argentine Atlantic coast and integrated in the International GPS Tide Gauge (TIGA) Monitoring Project.Geopotential Numbers: All first order levelling network unadjusted height differences were migrated to digital media and merged with the benchmark positions and gravity values. The resulting database consists of 16,000 level differences distributed along about 3,170 lines. Gravity values are missing for 20 percent of the benchmarks. The data set is currently being checked for consistency.Linking of Altimetric Networks from Neighbour Countries: During 2002 the first link between the altimetric networks of Chile and Argentina was done. The result was a difference of 22 cm, the higher value corresponding to Argentine levelling lines. The border point, where the levelling lines of both countries are connected, is Puesto Monte Aymond, near Estrecho de Magallanes in the south extreme of South America. The corresponding activities in order to make two or three new comparisons along the 5,000 km long borderline between these countries are being coordinated.Recently, the determination of a natural water surface (Fagnano Lake) was used like an equipotential surface to connect the altimetric networks of Chile and Argentina where the classical spirit levelling is not accessible due to the lack of roads.Compensation of Height and Gravity Networks: Adjustment of the national gravity and altimetric networks and their linking with the nets of neighbouring countries are in progress, including both new absolute and relative gravity determinations, which are necessary for the adjustment and optimisation processes. [ABSTRACT FROM AUTHOR]