Tide gauges

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).

The files of average values

Only the daily, monthly and annual averages calculated from quality controlled (QC’ed) data are provided in the data files. However, the graphs show the averages calculated from QC’ed observations (in blue) and non-QC’ed observations (in red). The averages are calculated from the Demerliac filter and the Doodson filter, with the possibility of a choice for the user. An example is given on the image below, which is taken from the web page of the La Rochelle station.

To obtain further details:
– on the calculation of mean sea levels and the filters;
– on the quality controls carried out by SHOM.

Download

The files of mean values can be downloaded individually from the SONEL Web page of the tide gauge, without authentication, by clicking on the button situated under the graph of the means chosen (filter, data sampling and average type: daily, monthly, annual). An example is given on the image opposite, which is taken from the web page of the La Rochelle station.

However, they are also available on the FTP server (ftp.sonel.org) which is very practical when rapid acces to the data from several stations is required. The FileZilla tool will give you access to the data.

|       
`-- RMSL
    |-- Demerliac          => Name of the filter used
    |   |-- data              -> Files of mean values
    |   `-- graphs            -> Graphs displayed on the Web site 
    `-- Doodson            => Name of the filter used
        |-- data              -> Files of mean values
        `-- graphs            -> Graphs displayed on the Web site