Realization of a clock-based global height system: A simulation study for Europe and Brazil

Abstract: Chronometric levelling is a novel technique for the realisation of the International Height Reference System (IHRS). A detailed study of this technique is carried out through closed-loop simulations, aiming to unify regional/local height systems (LHS) in Europe and Brazil. Focusing on a unification accuracy of 1 cm, realistic scenarios with various error parameters/vertical datum parameters in LHS and clock observation uncertainties were analysed. The errors associated with local heights raised from datum offsets, local vertical datum alignment discrepancies in latitude and longitude, accumulated tilts depending on the distance from the reference tide gauge and levelling point elevation-dependent offsets were introduced. Clocks achieving a fractional uncertainty of 10^-18 and 10^-17 were assumed in the simulations, considering temporal correlations of clock intrinsic uncertainties, external effects on clock observations such as tidal effects, propagation delay in terms of link uncertainties and presence of outliers. We determine the preferred distributions of clocks in a network for the best estimation of error parameters. The estimation of the error parameters is related to the spatial distribution of the clocks, hence, an optimal setup of placing clocks at the most distant levelling points, reference tide gauges and elevated points is implemented. Further, a configuration of clock distribution is proposed with master clocks and local clocks with reduced links. Taking into consideration all these realistic constraints, a unification accuracy of 1 cm can be obtained. The unified European and Brazilian height systems are further related to the global geoid such that all geoid-related heights achieve an accuracy of 3 cm.