The Role of GNSS Vertical Velocities to Correct Estimates of Sea Level Rise from Tide Gauge Measurements in Greece

ABSTRACT

In this study, we show how the Global Navigation Satellite System (GNSS)-derived vertical velocities contribute to the correction of tide gauge (TG) measurements used for the sea level rise estimation in Greece. Twelve sites with records of local sea level heights are processed in order to estimate their trend. Certain error sources related to TGs, e.g. equipment changes, data noise, may lead to biased or erroneous estimations of the sea level height. Therefore, it would be preferred to follow a robust estimation technique in order to detect and reduce outlier effects. The geocentric sea level rise is estimated by taking into account the land vertical motion of co-located GNSS permanent stations at the Hellenic area. TGs measure the height of the water relative to a monitored geodetic benchmark on land. On the other hand, using GNSS-based methods the vertical land motion can be derived. By means of extended models fitted to the GNSS time-series position, obtained from seven years of continuous data analysis, periodic signals are well described. The synergy of the two co-located techniques results in the correction of TG relative sea level heights taking into account the GNSS vertical velocities and consequently obtaining the conversion to absolute (geocentric) sea level trend.

KEYWORDS:

• GNSS permanent stations
• ITRF2014
• tide gauges
• vertical velocities

Acknowledgements

Prof. Spyridon Spatalas and Prof. Emeritus Dimitrios Arabelos are kindly acknowledged for their contributions supplying some high record TG data. We would like to thank METRICA S.A. and the National Observatory of Athens for providing cGPS data. In particular, we would like to thank the Permanent Service for Mean Sea Level (PSMSL) for their TG data. Last but not least, we thank the Editor and the two anonymous reviewers for their useful suggestions. The figures were created by using the Generic Mapping Tools (Wessel et al. 2013).