Sensitivity of Double-Difference and Precise Point Positioning GNSS Processing Strategies to Determine Ocean Tidal Loading Effect in a Large and Closed Basin Environment

Ocean tidal loading (OTL) induced surface displacements, driven by lunar and solar gravitational forces, present significant challenges in geodetic applications, requiring precise modeling to improve GNSS positioning accuracy. The study conducts a methodological and feasibility assessment of the differential and absolute approaches for detecting and quantifying OTL signals from GNSS coordinate time series. By analyzing GNSS data from selected stations, this research assesses the strengths and limitations of DD and PPP in estimating OTL displacements. Applying the OTL model correction reduced coordinate RMS values by up to 22% in the vertical and 10–15% in the horizontal components, confirming the model’s effectiveness in reproducing dominant tidal displacements. The largest residual after applying the OTL model appears in the PPP-derived vertical component for K1. However, diurnal constituents are particularly sensitive to GNSS-related systematic effects, including satellite orbit mismodelling and constellation repeat periods. Long baselines in DD improved detectability of differential signals but can introduce residual atmospheric biases, whereas shorter baselines were more resilient to noise yet less sensitive to weak tidal components. These results demonstrate that millimeter-level OTL displacements can be reliably detected with GNSS, but the choice of processing strategy and baseline configuration strongly influences the accuracy, resolution, and spectral completeness of the recovered tidal signals. By quantifying these effects across contrasting tidal regimes, this study provides a rigorous assessment framework that can guide the optimal use of DD and PPP in geodetic and geophysical applications.