Determination of a gravimetric geoid model of Greece using the method of KTH

Abstract: The main purpose of this study is to compute a gravimetric geoid model of Greeceusing the least squares modification method developed at KTH. In regional gravimetricgeoid determination, the modified Stokes’s formula that combines local terrestrial datawith a global geopotential model is often used nowadays.In this study, the optimum modification of Stokes’s formula, introduced by ProfessorSjöberg, is employed so that the expected mean square error (MSE) of all possiblesolutions of the general geoid model is minimized. According to this stochasticmethod, the Stokes’s formula is being used with the original surface gravity anomalywhich combined with a GGM yields an approximate geoid height. The corrected geoidheight is then obtained by adding the topographic, downward continuation,atmospheric and ellipsoidal corrections to the approximate geoid height.The dataset used for the computations, consisted of terrestrial gravimetricmeasurements, a DEM model and GPS/Levelling data for the Greek region. Threeglobal geopotential models (EGM96, EIGEN-GRACE02S, EIGEN-GL04C) weretested for choosing the best GGM to be combined into the final solution. Regarding theevaluation and refinement of the terrestrial gravity measurements, the cross-validationtechnique has been used for detection of outliers.The new Greek gravimetric geoid model was evaluated with 18 GPS/Levelling pointsof the Greek geodetic network. The absolute agreement between the gravimetric andthe GPS/Levelling geoid height was estimated at 27 cm while the relative agreement at0.9 ppm. In a case of study the absolute accuracy of the model was estimated at 14 cm.The geoid model computed in this study was also compared with some previous Greekgeoid models, yielding better external accuracy than them.