The South American gravimetric quasi-geoid model, named QGEOID2021, was computed thanks to a collaboration of several institutions, companies and universities of South America. The model covers the area between 15°N and 60°S in latitude and 100°W and 30°W in longitude, with a grid resolution of 5' x 5'. It is based on 959,404 terrestrial gravimetric points, the XGM2019 global geopotential model up to degree and order 200 and the SRTMv3 digital terrain model. The short wavelengths of the solution were estimated via Fast Fourier Transform (FFT) with the modified Stokes kernel proposed by Vaníček and Kleusberg (1987). On the other hand, long and medium wavelengths were removed and replaced in the framework of a remove-compute-restore procedure. Regions without gravimetric observations were completed using XGM2019 to its full degree. The calculation of the geoid model was performed by the Canadian package SHGEO (Stokes-Helmert Geoid Software). The quasi-geoid model was obtained by the classical geoid/quasi-geoid separation term (Heiskanen and Moritz, 1967). The comparison between height anomalies and GPS/levelling data at 1108 points in Brazil shows differences with an RMS of 41 cm.

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.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).