M₂ constituent of ocean tide loading displacements from VLBI CONT14 hourly sessions

Several studies prove that ocean tide loading (OTL) displacements can be observed with space geodetic techniques. In this study, the amplitudes and Greenwich phase lags for each coordinate component, i.e., radial, west, and south of the principal lunar semidiurnal tide, M₂ of OTL displacements were estimated at the very long baseline interferometry (VLBI) sites of the 15 days long continuous VLBI campaign, CONT14, carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In the estimation of the amplitudes and Greenwich phase lags of the M₂ tidal constituent, hourly VLBI station coordinate time series were used as observations derived through analyzing 1 hour VLBI sessions of the CONT14 campaign. In the analysis of hourly sessions of the CONT14 campaign, to derive accurate hourly station coordinates, troposphere delays estimated from daily sessions were reduced from the observations a priori to the analysis. The estimated amplitudes and Greenwich phase lags of the M₂ constituent of OTL displacements were compared with the predictions the state-of-the-art ocean tide models, among others, FES2012 (Lyard et al. 2006, Carrère et al. 2012), FES2014 (Carrère et al. 2016) and TPXO8 (Egbert and Erofeeva 2002, Egbert et al. 2010). Both the amplitudes and the phases between CONT14 estimates and ocean tide models agree well for the M₂ tide at all the sites and in most of the coordinate components. The RMS misfits of the M₂ tide of OTL displacements in all coordinate components between CONT14 and ocean tide models over coastal sites are found about two times larger than those of inland sites. This result confirms the modeling insufficiencies in shallow waters of ocean tide models which cause an accuracy restriction of OTL displacement predictions around coastal regions.