Improved Method for Estimating the Ocean Tide Loading Displacement Parameters by GNSS Precise Point Positioning and Harmonic Analysis

Site displacements caused by ocean tide loading (OTL) can reach more than several centimeters vertically, particularly in coastal regions. An ocean tide model typically is used to correct OTL effects, but these model predictions cannot satisfy accuracy requirements because of irregularities. The Global Navigation Satellite System (GNSS) is influenced by OTL and provides a way to measure OTL displacements precisely. This study develops an improved method for estimating OTL-displacement parameters in which the effects of three-dimensional (3D) OTL displacements are estimated as unknown parameters at each epoch by precise point positioning (PPP); then, the amplitudes and phase lags of eight principal constituents are extracted from the time series of the OTL displacements using the harmonic analysis method. 3D OTL displacements of eight constituents at 12 sites in Hong Kong with 8 years of continuous GNSS observations are calculated. The convergence speed of these constituents indicates that the O1, Q1, N2, and M2 constituents are much faster than the K1, P1, K2, and S2 constituents. In addition, the PPP-derived OTL estimates are compared with the predictions from six advanced global ocean tide models, which were modified by the osu.chinasea.2010 local tide model. The results show that the constituents estimated by the improved method are most consistent with the model-predicted values. RMS misfits between the PPP model are small for the N2, M2, Q1, and P1 constituents (less than 1.5 mm in the east component, 2.0 mm in the north component, and 1.9 mm in the vertical component). The S2 and K1 constituents show relatively large misfits of up to 4.3 mm.