IBGE makes available new version of Brazil's geoid undulation model (MAPGEO2015)

The IBGE makes available today (11/30/2015), in partnership with the Polytechnic School of the University of São Paulo – EPUSP, a new version of the Brazilian geoid undulation model, MAPGEO2015. With the interpolation system, made available together with the model, users can obtain the geoid height in a point of set of points in the national territory based on their planimetric coordinates. The MAPGEO2015 System is available for download on the following link, where further information on the model can be obtained:

www.ibge.gov.br/home/geociencias/geodesia/modelo_geoidal.shtm.

New Brazilian Geiod Model

The new version of MAPGEO2015 uses the global geopotential model EIGEN-6C4, coupled with nearly 950,000 terrestrial gravimetric stations (points where gravity acceleration is set) in South America, of which, 450,000 are inside Brazil. Among them, 18,485 correspond to new stations monitored in the Brazilian territory since the previous version, MAPGEO2010, was released.

MAPGEO2015 was assessed by means of the geoid heights obtained through the difference between the orthometric heights (those above the sea level) taken from the geometric leveling considering 592 references of level together with points whose ellipsoidal heights were gotten through satellite positioning techniques. The points were chosen through a detailed study carried out in the Brazilian Altimetric Network, identifying the connections belonging to the closed leveling lines with adjusted height values. The consistency between the geoid heights obtained through the interpolation with the model and the direct values obtained from the connections presented an enhancement of nearly 20% in relation to the previous model, with a mean square error of ±0,17 m.

MAPGEO2015 allows determining with more accuracy heights in relation to mean sea level

Due to its speed and precision obtaining coordinates, the Global Navigation Satellite Systems (GNSS) have revolutionized the activities which demand positioning.

However, the height established using a GNSS receptor is not related to the mean sea level (or, more rigorously, to the geoid, which is the equipotential surface of the gravity field of the Earth that coincides with the mean still water level) but  to an ellipsoidal reference with specific dimensions, adopted as the geometric shape of the Earth. As a result, it is necessary to tell the difference between the geoid surfaces and the ellipsoidal ones, i. e., the geoid height or undulation, in order to obtain the orthometric height (above the mean sea level). The undulation geoid model is used for applications in the areas of mapping and engineering, and the IBGE, together with EDUSP, have been working in the last decades to set even more precise models.