Height systems in Greece and its islands – some experimental results
21/09/2016 | 17:15 | Session 5: Height systems and vertical datum unification
Author(s): Martin Willberg, Thomas Gruber and Gergios S. Vergos
Martin Willberg, Thomas Gruber and Gergios S. Vergos
Height systems in Greece and its islands refer either to the Hellenic vertical datum (for the mainland) or to local tide gauges or other benchmarks (for the islands). GPS/levelling offers a tool to compare the reference equipotential surfaces of these height systems to a GOCE-based global geoid. Offsets between these equipotential surfaces in principle deliver estimates of height system differences between the global and the local systems and consequently also offsets between all local height systems. When applying this approach, a number of systematic effects possibly affecting the resulting height system offsets need to be investigated beforehand. First and most important, the problem of the omission error has to be regarded. From the global GOCE models one gets a spectrally limited geoid signal, while the observed GPS/levelling geoid heights contain the full spectral content of the Earth gravity field. Especially on islands near the resolution of GOCE the omission error can largely exceed average values. Second, height reference surfaces might exhibit systematic distortions, which need to be identified and corrected.
This paper shows some experimental results of height system offset estimates between the Greek mainland and various Greek islands based on the most recent GOCE gravity field models and the available GPS/levelling data. Special emphasis is given to the omission error and to systematic distortions of height reference surfaces and their impact on the estimated height datum differences. Greece with its large number of islands and its mountainous topography is an ideal test area for this kind of analysis. Results and recipes for height system unification obtained from this study later shall be transferred to areas with a less favorable data situation.