Instituto Brasileiro de Geografia e Estatística

About the publication - Gravimetric Network

The gravimetric information takes on critical importance in several areas of the Earth Sciences, such as Geodesy (study of the Earth form – geoid – and dimensions), Geology (investigation of geological structures) and Geophysics (mineral prospection).

In 1956, IBGE started a program in order to establish the horizontal datum (geodetic reference system) for Brazil. During the project, more than 2,000 gravimetric stations were set based on the Chuá vertex, the origin point, located in Minas Gerais. After the end of the activities, IBGE conducted several other gravimetric surveys together with universities and research institutes.

However, gravimetry only acquired a systematic character in 1990, when IBGE installed gravimetric stations aimed at covering the huge information gaps about gravity acceleration, which exist especially in the Northeast, Midwest and North regions of Brazil. Since then, more than 26,000 stations have been installed in these regions.

With GPS technology, geoid determination gains great importance in vertical positioning. Although GPS is a tridimensional system, it provides altitudes in an altimetric system different from the system that includes altitudes obtained by the levelling classical methods (geometrical, trigonometric and barometric). That prevents GPS altitudes from being directly compared with the altitudes and maps provided by IBGE and other Brazilian institutes. The geoidal map represents the conversion of both altitude systems. In order to take profit of this GPS technology, by saving time and resources, a progressively more accurate geoidal map is necessary, since the transformation accuracy is a function of the geoid determination accuracy.

IBGE, in a scientific partnership with the Polytechnic School of USP, has a project aimed at determining and constantly refining the Brazilian geoidal undulation map. Thus, it has provided progressively more accurate and updated versions of the geoidal map; the last version is MAPGEO2004.

The determination of scientific altitudes (orthometric, normal, etc.) requires gravimetric information. As a result, since 2006 gravimetric survey campaigns about the main leveling lines have been conducted with the purpose of helping the estimate of the altitudes and of facilitating the connection of the Brazilian Altimetric Network with the Networks of neighbor countries.