Multi-constellation GNSS estimation of ocean tide loading displacement

Abstract

For geodetic stations in proximity to intricate coastlines and shallow seas, the ocean tide loading (OTL) displacement, with up to decimetre level sub-daily peak-to-peak variations, is imperfectly modelled by the procedures recommended in the International Earth Rotation and Reference System Service (IERS) conventions. GPS Precise Point Positioning provides a means to measure OTL displacement, and about 0.3 mm accuracy for the GPS-estimated main lunar semidiurnal OTL displacement (M2) has been reported. Nonetheless, the GPS orbital and satellite constellation repeat periods are identical to those of the lunisolar K2 and K1 tidal constituents, respectively, which makes these constituents inseparable from the GPS orbit modelling and multipath errors. To help overcome the GPS problem of estimating K2 and K1 OTL displacement, the use of GLONASS data is investigated. After processing GPS-only, GLONASS-only and combined GPS+GLONASS observations for 49 globally-distributed stations, which are affected marginally by OTL displacement forward modelling error, similar accuracy for the M2, N2, and O1 OTL displacement constituents estimated by GPS-only and GLONASS-only float ambiguity PPP is demonstrated. Combined GPS+GLONASS float ambiguity solutions show comparable precision to GPS-only fixed ambiguity solutions, and better accuracy than GPS-only and GLONASS-only for the aforementioned signals. The use of GLONASS data leads to about 2.0–2.5 mm accuracy improvement for the K2 and K1 OTL displacement estimation, compared with GPS-only estimates. Finally, geophysical inferences of the OTL displacement in Alaska were investigated. The GPSestimated OTL displacement at 87 stations in Alaska shows that FES2014b is the most accurate global ocean tide model in the region. It is also shown that including asthenosphere anelastic dispersion may improve OTL vertical displacement forward modelling in Alaska by up to 1–2 mm. Multi-GNSS OTL displacement investigation in Alaska also confirms the GLONASS data benefits which were found at the globally-distributed stations.