Comparison of high precision geoid models in Switzerland

Abstract

The recently released national geoid model CHGeo2004 of Switzerland was determined by combining gravity, vertical deflections and GPS/leveling. Its accuracy is in the order of 2-3 cm as could be verified by comparison with independent data. In addition to the standard models (topography and global geopotential model), a simple 3D density model of the Earth's crust has been introduced for the reduction of the observations. The method for the calculation was basically least squares collocation with a slight modification in the way that the parameters of the covariance function have been chosen to minimize the resulting residuals between the astrogeodetic, the gravimetric and the GPS/leveling geoid model. Although CHGeo2004 is the result of a combination of different data sets, individual pure astrogeodetic, gravimetric and GPS/leveling solutions have been calculated as well. This gave us the opportunity to investigate the systematic discrepancies. With a pure astrogeodetic solution, we obtained a global accuracy of about 6 cm with some larger systematic differences to the combined solution of up to 20 cm. The deflections of the vertical are the most sensitive data set with respect to the variation of the covariance model. Gravity and GPS/leveling are less sensitive to changing the covariance function. Nevertheless, especially GPS/leveling shows rather large differences to the solutions of the other data sets in some areas. The official geoid model that has been released to the surveyor community is strongly based on GPS/leveling, since their principal use of the geoid model is GPS height determination, which should be in agreement with leveling. © Springer-Verlag Berlin Heidelberg 2007.