The tide gauge observations are heights of sea level expressed with respect to an arbitrary (conventional) and local datum. Hence, the term relative sea level is often used (relative to the land upon which the tide gauge is grounded).
The sea level data available on SONEL are:
daily mean sea levels obtained from different tidal filters (e.g., Doodson, Demerliac);
monthly and annual mean sea levels, which contribute to the world data bank of the PSMSL.
Other kinds of water levels are available too, directly from our partner, the SHOM (REFMAR), whatever the French tide gauge network (RONIM, ROSAME... See news of 16/02/2011). These are:
hourly water levels, available 2-3 months after a thorough quality control;
Higher frequency water levels, available in real-time or near real-time.
Note : SONEL also provides data (meta-data and links to the data) for tide gauges all over the world as long as they are co-located with permanent geodetic GPS stations (white symbols on the map above). Indeed, for this geodetic aspect (continuous GPS at tide gauges) SONEL has been asked to act as a dedicated data assembly center for the GLOSS program from 2011 onwards (the next meeting of the GLOSS group of experts is planned for autumn 2011).