Geodetic aspects of long term sea level variations in European seas from altimetry and from tide gauge data

Abstract

The monitoring of the sea level variations at continental margins is traditionally done using tide gauge records of sea level heights with respect to a reference point of the tide gauge station. This method gives the relative sea level changes with respect to the earth crust, but does not allow to distinguish between sea level increase and earth subsidence. The use of tide gauge stations, whose coordinates are known in a geocentric reference frame, along the coast and of altimetry data for the open sea, allows to determine the absolute sea level changes. The regions considered in our study are the European semi-closed basins: the Mediterranean Sea, the Baltic Sea and the North Sea. We investigate the long-term variations of the altimetric sea level heights in a grid of points on sea and of the tide gauge sea level heights along the coast. The sea level heights, at a selected location, are sampled by the satellite altimetry and by the tide gauge stations with different time intervals. The sampling time interval of the altimetric sea level heights depends on the altimetry mission characteristics. Data from the ERS-1, ERS-2 and Topex/Poseidon altimetry missions are used. The agreement between the long-term sea level variations obtained from the tide gauge data and from the altimetry data is studied. The correlation with air temperature and air pressure at the tide gauge stations is investigated. The altimetry data cover a time interval of four years, therefore only the seasonal and the interannual variability over this time can be analysed. The study of sea level variations having longer periods requires altimetry data over a longer time interval.

Keywords: Sea level variation, altimetry, tide gauge

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry