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.
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.
The format adopted is that of the PSMSL, as are the calculation criteria for the monthly and annual means, in particular for the issue of observation gaps. The data files are presented in the form of a two-column matrix.
The dates are in decimal years (centered on the 15th day of the month for the monthly values and at noon for the daily values).
The daily, monthly and annual sea-level heights are expressed in millimetres.
This is how the names of the data files are defined:
The first letter in lower case :
"d" for the daily means, "m" for the monthly means and "y" for the yearly means
The acronym of the station, in capital letters, is made up of 5 letters (the internal identifier of the SONEL data base)
The extension ".slv", for the type of quantity "sea level".
Example: the daily means file of La Rochelle is called dLROCH.slv
Structure of the file system in the FTP server
|-- 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