Decimetric Geoid for Buenos Aires Province Based on Gps and Global Models
A precise GPS network was measured directly on the existing high precision leveling network of the Buenos Aires Province. The surveyed region is a North-South transect of about 400 km long, crossed at its southern border by an East-West transect 600 km long. Typical distances between adjacent points are 50 km excepting four densification areas where the distances are 5 to 10 km. The GPS network included 3 control points from the GFZ SAGA network. One of them is La Plata IGS permanent station. The observations were made with Ashtech Z12 and Trimble 4000 SSE receivers. IGS precise ephemeris were used. The baselines solutions were obtained with the GPPS software and the compensation of redundant observations and final adjustment to the SAGA datum (close to the ITRF94), with the Fillnet software. The estimated accuracy of the three components is about 1 to 2 cm. Similar accuracy is estimated for the orthometric heights, so the “observed” geoid undulations are accurate to only a few cm.
Comparisons of these results with the calculated undulations obtained with OSU91A global model show a mean difference of about -70 cm (in the sense observed — model) with standard deviation (SD) of 20 cm. A slightly bigger SD is obtained when using the GFZ96R global model but in this case the mean difference is only about -30 cm. In the case of the model EGM96, the SD is 25 cm and the mean difference, -20 cm. Several functions are being tested to adjust the global models to the observed undulations, however, with very simple interpolation functions, an accuracy of only a few centimeters is possible in the flat regions, while one to two decimeters accuracy is obtained in mountainous areas.
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