Impact of PPP Ambiguity Resolution on Antarctic Glacier GNSS Time Series: Comparison with Network-Based and PPP Ambiguity-Float Solutions

Geodetic observations play a key role in quantifying glacier dynamics and long-term vertical surface changes in Antarctica, where Global Navigation Satellite System (GNSS) techniques are widely used under challenging environmental and logistical conditions. This study investigates the impact of ambiguity resolution in Precise Point Positioning (PPP) processing for glaciological applications through comparisons with both network-based solutions and earlier PPP implementations relying on float ambiguity estimation. Two complementary datasets collected within the Italian National Antarctic Research Program are analyzed: a short-term kinematic GNSS campaign on the rapidly flowing Drygalski Ice Tongue and a long-term continuous time series from the permanent GNSS station DCRU installed at Station Concordia (Dome C, East Antarctic Plateau). The analysis focuses on the consistency of displacement time series, stochastic noise characteristics and long-term velocity estimates derived from different processing strategies. Results indicate that ambiguity-fixed PPP solutions provide displacement and velocity estimates consistent with network-based and float PPP processing, while generally exhibiting reduced short-term scatter and improved temporal stability. This behaviour is particularly evident for the kinematic observations at Drygalski, where the improved signal-to-noise ratio enhances the resolution of small-amplitude glacier motions associated with ocean-tide forcing. Spectral analysis further confirms the tidal origin of the dominant periodic components, with peaks at approximately 25.6 h and 23.4 h. At Dome C, the long time-span observation record confirms the robustness of three-dimensional velocity estimates over more than a decade, with only minor differences between processing approaches. These findings highlight the overall consistency of glacier motion estimates with respect to the adopted processing strategy and demonstrate the benefits of ambiguity-resolved PPP for improving the interpretation and long-term reliability of Antarctic GNSS time series.