Analysis of the vertical movement of active GNSS stations as a result of semidiurnal tides

Ireland is subject to the constant effects and influence of semidiurnal tides. Western coastal regions are exposed to tidal ranges up to and exceeding five metres, consequentially introducing varied water volumes with temporal intervals. In addition, the Earth is elastic in composition, resulting in morphing and warping at the hands of celestial and oceanic forces.

This study looked at Online Precise Point Positioning (PPP) service to accurately monitor the vertical movement of coastal lands. In addition, GNSS Static Post-processing was conducted to discern which method of the global navigation satellite system (GNSS) processing is best for detecting VLM (vertical land motion). The study took place throughout 2020, focusing on the tidal peaks and troughs of the 21st of each month. Six-hour time windows were created around tidal peaks and troughs using data from the Marine Institute. GNSS data files replicating these time windows were processed using both PPP and manual network adjustment methods. MATLAB Online analysis aided in concluding the study.

Results were inconclusive in determining which method of GNSS processing were best for identifying VLM. Based on the evidence
provided by this study, the influence of semidiurnal tidal peaks and troughs cannot be deemed significant in magnitude to require mitigation. Western Irish coastal zones are therefore not subjected to large scale VLM. Similar studies of coastal zones that experience tidal ranges exceeding five metres would be recommended. An extended study period would also be recommended to better understand semidiurnal tidal influences in Ireland.