Evaluation of GOCE/GRACE GGMs Over Attica and Thessaloniki, Greece, and Wo Determination for Height System Unification

Within the frame of the Elevation project, recently acquired collocated GPS/Leveling observations over trigonometric benchmarks (BMs) have been used for the evaluation of the recent GOCE/GRACE Global Geopotential Models (GGMs) and the unification of the Greek Local Vertical Datum (LVD). To this extent all available satellite-only and combined GOCE/GRACE GGMs were evaluated to conclude on the possible improvement brought by GOCE in the determination of the geoid over Greece. At a second stage, the present work focuses on the determination of the zero-level geopotential value W0LVD for the Greek LVD. The estimation of W0LVD was carried out using a least squares adjustment of Helmert orthometric heights, surface gravity disturbances and geopotential values computed from EGM2008 and GOCE/GRACE GGMs over the available GPS/Levelling BMs. Moreover, given that the BMs used belong to two distinct areas, i.e., one over Attica and another in Thessaloniki, the W0LVD determination was carried out for each region separately, to conclude on the possible biases of the Hellenic LVD itself. From the evaluation of the GOCE/GRACE models it was concluded that the latest releases provide a significant, compared to EGM2008, improvement in the comparisons with the GPS/Levelling data, by as much as 3 cm, in terms of the standard deviation. Furthermore, the W0LVD determined for the Greek LVD indicates a bias of about −4.95 m2/s2 compared to the conventional value of 62,636,856.0 m2/s2.