Comparison of Various GPS Processing Solutions toward an Efficient Validation of the Hellenic Vertical Network: The ELEVATION Project

A research project called ELEVATION (Evaluation of the HelLEnic Vertical Network in the FrAme of the European SysTems and Control Networks InterconnectiONApplication in the Areas of Attica and Thessaloniki) for the validation of the Hellenic vertical network is currently in progress. Two investigation areas in central and northern Greece were chosen for the project. The areas include several benchmarks of the national trigonometric and leveling networks. In the current research, static global positioning system (GPS) observations as well as classical terrestrial leveling were performed to assess the internal accuracy of the two networks. This paper presents some of the numerical tests based on GPS and leveling measurements and outlines the goals of the project. The strategies followed in the processing of GPS data are presented, with emphasis on their future use within this project. GPS observations were processed using various commercial as well as scientific software packages to examine the influence of the processing algorithms on the final results. Significant differences between the results of the various software packages were revealed, particularly in the case of challenging observation conditions. Finally, comparisons of the estimated geoid heights at GPS benchmarks (BMs) to Earth Gravitational Model 2008 (EGM2008) geoid information are presented as a first step toward the evaluation of the Hellenic vertical network. These comparisons indicate that the two investigation areas are of different internal accuracy, namely, 8.3 and 15.8 cm in terms of the standard deviation of the differences at the Attica and Thessaloniki test areas.