Abstract
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, M 2 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 M 2 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 M 2 constituent of OTL displacements were compared with the predictions the state-of-the-art ocean tide models, among others, FES2012 [Lyard et al., 2006; Carrere et al., 2012], FES2014 [Carrere 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 M 2 tide at all the sites and in most of the coordinate components. The RMS misfits of the M 2 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.
Highlights
The seafloor pressure variations due to the ocean tide loading (OTL) cause position and tidal frequencydependent harmonic displacements on the Earth crust, the so-called OTL displacements
The daily estimates of tidal constituents and their covariance information are stacked in a combined solution, e.g. using a Kalman Filter as often implemented in Global Navigation Satellite System (GNSS) analysis [e.g., Schenewerk et al, 2001; Dach and Dietrich, 2001; Allinson et al, 2004; King et al, 2005; Thomas et al, 2007; Yuan et al, 2013] and in several very long baseline interferometry (VLBI) analysis [e.g., Schuh and Moehlmann, 1989; Sovers, 1994; Haas and Schuh, 1998; Scherneck et al, 2000; Petrov and Ma, 2003]
The main purpose of this study is to investigate the possibility of estimating M2 constituent of OTL displacements from the VLBI observations carried out during the 15 days long continuous VLBI campaign, CONT14 and investigate the level of agreement of the estimated M2 constituent of OTL displacements with the predictions of the ocean tide models FES2012 [Lyard et al, 2006; Carrère et al, 2012], FES2014 [Carrère et al, 2016] and TPXO8 [Egbert and Erofeeva 2002; Egbert et al, 2010], which were generated from global hydrodynamic simulations that assimilate tide gauge and satellite altimetry data
Summary
The seafloor pressure variations due to the ocean tide loading (OTL) cause position and tidal frequencydependent harmonic displacements on the Earth crust, the so-called OTL displacements. Yuan et al, [2013] estimated OTL displacements 3D components of eight principal harmonics at semi-diurnal and diurnal tidal periods by means of analyzing the observations of globally distributed 456 continuous GPS stations since 1996 till 2011 They used the precise point positioning technique [PPP, Zumberge et al, 1997] on daily GPS batches where the tidal constituents were treated as additional parameters.
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