GOCE Variance and Covariance Contribution to Height System Unification

The definition and realization of vertical datum is a key concept in support of not only geodetic works but also for surveying and hydraulic studies to name a few. In the GOCE era, this is customarily done by estimating height and/or geopotential offsets with respect to a conventional reference geopotential value or to available GNSS/Leveling observations on trigonometric BMs and a GOCE-based geoid. This work investigates the influence of GOCE errors in the determination of the Hellenic Local Vertical Datum. This is facilitated through a least-squares adjustment of collocated GNSS/Leveling and GOCE geoid heights over a network of 1,542 BMs. TIM-R5, GOCO05s and GOCO05c Global Geopotential Models (GGMs) are used for representing the contribution of GOCE and GRACE to the Earth’s gravity field. First, a weighted adjustment is carried out employing the GGMs commission error as indicative of the geoid height variance for all stations. Then, full variance-covariance matrices of the GGMs are employed for utilizing realistic GOCE error information and investigating their influence on the adjustment results. Using the available GNSS/Leveling formal errors, a Variance Component Estimation (VCE) is performed to evaluate height (h, H, N) error matrices and assess the stochastic model for the corresponding observational noise. VCE is used to address the impact of a simplified uniform variance assumption for all geoid height data on the final prediction variances in contrast to using the full covariance matrices. Finally, zero-level geopotential values are estimated for the Greek mainland following weighting schemes as the ones described above.