Avalia？？o de modelos globais do geopotencial para os estados do Maranh？o e Piauí

the evaluation of the official geoid model of brazil, mapgeo2010, shows that the lowest model resolutions are in the states of maranh？o and piauí with discrepancies ranging from -1 to +1 m in about 500 km. just for these regions, it is necessary an accurate geoid model in view of the limitations of existing geodetic information. in view of the problem evidenced in the highlighted region we carried out the evaluation of the geoid heights derived from some global geopotential models (ggms). data from the brazilian geodetic system (bgs) comprising bench marks of brazilian fundamental altimetric network (rafb) were gps ellipsoidal heights were determined (eg-gps/niv). the employed ggms came from satellite-only (from grace and goce missions) and the combined ggms egm2008 developed up to the degrees, 360, 720 and 2190 and eigen_05c in the degree and order 360, both with satellite data from grace and lageos missions, as well as altimetry and gravimetry from several data bases. for the study, 47 geodetic stations (eg-gps/niv) of brazilian institute of geography and statistics (ibge) were selected and distributed in the study area comprised among longitude -47,5o ≤ λ ≤ -41o and latitude -10o ≤ φ ≤ -3o. for each station it was calculated the value of the geoid height from the various ggms. based on the analysis presented it follows that there are global models with good fit in the region of studies.