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In the present work, an improved harmonic analysis method was proposed to examine the time series of vertical coordinates from three global navigation satellite system (GNSS) stations in Hong Kong, aiming to obtain the amplitudes of timevarying ocean tide loading displacement (OTLD). Singular spectrum analysis (SSA) was employed to extract the main components of the time-varying amplitudes, and the fast Fourier transform (FFT) was performed to detect periodic signals in the time-varying amplitude sequences. The results indicate that the mean errors in the vertical coordinates of each station range from 9mm to 13mm, demonstrating satisfactory solution accuracy. Filtering reduced white noise by an average of 60.4% and colored noise by 21.68% across all stations. The four major tidal constituents (M2, S2, O1, K1) all exhibited noticeable seasonal variations. Following SSA processing, these constituents showed reductions in differences between their time-varying amplitudes and static amplitudes by 52.22%, 63.89%, 50%, and 58.33%, respectively. This indicates a remarkable enhancement in the accuracy of time-varying OTLD amplitudes. Additionally, significant annual and semi-annual signals were observed in the four major tidal constituents across all stations. Particularly noteworthy was the M2 tide from the HKOH station, which exhibited a noticeable one-third-year periodic signal, with the annual signal being the most pronounced and the one-third-year signal the least. Overall, this study improves the accuracy of OTLD monitoring and introduces novel methods and data to advance the understanding of dynamic ocean tide processes.
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