Towards 0.1mm/yr stability over decades for measuring sea level using tide gauges together with GNSS-based instruments?

Precise and stable measurements of sea level are critical for understanding long-term climate trends. This study investigates the stability of sea level measurements using tide gauges and GNSS-based instruments at the Corsica calibration site. The calibration and validation of satellite altimetry missions require an uncertainty of ± 0.3 mm/yr at a global scale and ± 1 mm/yr at a regional scale. The study also evaluates the vertical land motion (VLM) of the reference GNSS site (RG00) and its impact on long-term sea level trends. The study assesses the reliability of sea level measurements provided by advanced GNSS processing methods, including differential positioning and Precise Point Positioning (PPP). The analysis demonstrates that the stability of tide gauges, as confirmed by GNSS-based measurements, is better than 0.1 mm/yr. Furthermore, the study examined the long-term sea level trend at the Senetosa site, revealing an average increase of +4.4 mm/yr over a 26-year period (1998–2024), with a possible acceleration of +0.18 mm/yr2. This rate exceeds global estimates, potentially due to regional oceanographic effects. The findings emphasize the necessity for high-precision monitoring and underscore the importance of GNSS-based systems in validating tide gauge records for accurate sea level assessments.