The Uruguayan hybrid geoid: UruGeoide2000

UruGeoide2000 is a hybrid geoid model for Uruguay computed in 2000. The extent is from 29° S to 36° S in latitude and 52° W to 60° W in longitude, however the model is valid in the Uruguayan territory only. The grid resolution is 1´ × 1´. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). A gravimetric model was initially computed through the remove-restore procedure, using 5873 ground gravity observations, 9987 marine free-air gravity anomalies from the GMGA9706 model and the EGM96 geopotential model. The topographic data were compiled from the 2 km × 2 km SGM digital terrain model, the 2.5' × 2.5' USP model and from the GTOPO30 global topographic model. The external masses to the geoid was considered with the second Helmert condensation method, taking in account the indirect effect. The gravimetric contribution was calculated using residual free-air anomalies in the spherical Stokes formula, evaluated with 1D-FFT. The resulting gravimetric geoid was finally adapted by a bias and a tilt to the national vertical system, Cabildo 1948, by fitting GPS/levelling observations, with a resulting accuracy of 13 cm. The UruGeoide2000 model was adopted by the Military Geographic Service (SGM) and it was the official Uruguayan geoid model for height conversion until the computation of an updated model in 2007.

The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.