Preliminary results of GOCE-based height system unification between Greece and Turkey over marine and land areas

Georgios S. Vergos*, Bihter Erol, Dimitrios A. Natsiopoulos, Vassilios N. Grigoriadis, Mustafa Serkan Işık, Ilias N. Tziavos

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


The unification of local vertical datums (LVDs) at a country-wide scale has gained significant attention lately due to the availability of GOCE-based global geopotential models (GGMs) and the unprecedented geoid height accuracies offered. Within a single country, several LVDs may be used, especially in the case of islandic nations. Therefore, the unification of all of them to a single nation-wide LVD is of utmost importance. The same holds for neighboring countries, where the unification of their vertical datums is necessary as a tool of engineering, cross-border collaboration and environmental and risk management projects. The aforementioned set the main scope of the present study, which focuses on the use of GOCE and GOCE/GRACE GGMs in order to investigate the offsets between the Greek and Turkish LVDs. First an evaluation of the latest release 5 GOCE GGMs is carried out, either to their maximum degree or through spectral enhancement with EGM208 and topographic effects. Then, the geopotential value for the Greek and Turkish LVDs is performed, along with different estimates for the marine area of the Aegean Sea where several islands and isles exist with each one realizing its own LVD. The relative offset between the two LVDs was determined and used to provide a direct link between the Greek and Turkish LVDs with the IAG conventional value recently proposed as a global WHS. From the results achieved it was concluded that the spectrally enhanced GOCE GGMs reduce the standard deviation of the differences with GPS/levelling data by 2–4 cm over Turkey and 2 cm for mainland Greece. In terms of the zero-level geopotential determination, the LVD of the Greek mainland is 64.9 cm below the IAG conventional value, while that of Turkey is 9.6 cm above. Finally, it is concluded that in practice each Greek island realizes its own LVD with offsets between them as large as 35 cm. Despite that fact, the spectrally enhanced GOCE GGMs and in particular GOCO05s provides the overall smallest height residuals over the islands, hence the W^oLVD based on that can be recommended as the best estimate. In that way, relative offsets with the LVD of mainland Greece can be computed for each island, ranging between −23.8 and 15.5 cm.

Original languageEnglish
Pages (from-to)61-79
Number of pages19
JournalActa Geodaetica et Geophysica
Issue number1
Publication statusPublished - 1 Mar 2018

Bibliographical note

Publisher Copyright:
© 2017, Akadémiai Kiadó.


The part of this work referring to the zero-level geopotential estimation for mainland Greece and the Greek islands has been funded by the European Space Agency in the frame of the PRODEX funded GOCEproject (CN4000106380C3). The GPS/levelling BMs over Greece are available within a dedicated memorandum between Ktimatologio S.A. and the School of Rural and Surveying Engineering. The TUTGA BMs over Turkey are available with funds by TUBITAK Research Project with contract number 114Y581 and IzJRS network BMs are provided by ITU Geodesy Division. All plots were generated using the Generic Mapping Tools v5.3.1 software (Wessel et al. 2013). All spherical harmonic datasets for the GOCE and GOCE/GRACE GGMs have been accessed through the ICGEM (Barthelmes and Köhler 2016) service of IGFS. The constructive remarks by two anonymous reviewers are gratefully acknowledged, since they evidently improved the initial version of the paper.

FundersFunder number
European Space AgencyCN4000106380C3


    • GOCE
    • Hellenic and Turkish datums
    • Local vertical datum
    • Unification
    • Vertical offsets


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