Aims and rationale

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Primary objective and rationale of SONEL

SONEL aims to develop in a reasonable and rational manner activities carried out in the field of ‘in situ’ observations of coastal sea level using tide gauges; the exchange of know-how and results; the conservation of historic observations; the scientific exploitation of observations made by organisations which do not always have this vocation.

The motivation of SONEL is to get more from several mono-thematic permanent observing networks, either geodetic or sea-level oriented. This will come from integrating them into an efficient data collection and dissemination scheme, and by combining their measurements in order to provide specific products. This synergy is indeed the only way to get a clear and unambiguous picture of what is actually going on at a specific coastal site: is the sea level rising or is the land sinking over long term time scales?

The ancillary tide gauge or geodetic information frequently requested by users to obtain the expected final results is either unavailable or is obtained by unreliable methods. This stresses the importance of an integrated sea level monitoring system like SONEL. Consequently, SONEL aims to be : (i) an integrated sea level monitoring system (different types of data, sources, time and space scales); (ii) a sea level information system handling the data measured by different observation networks; (iii) a national component of international sea level observing systems (e.g., GLOSS); (iv) a national interface for related European and Global projects and databases (PSMSL, TIGA, etc.); and (v) a service based on long term commitment as most sea level studies on climate change require time series spanning a long period of time.

Specific aims

In order to address the issue of sea-level change along the French coast, and also to contribute to the regional and world observation system, eight major fields of activity have been identified :

- Federate the existing tide gauge networks (RONIM, ROSAME, ...etc.) and oversee the integration of emerging networks (e.g., in French Polynesia, New Caledonia, etc.) into a single system, interoperable with the federation of geodetic GNSS networks (e.g., RGP, RENAG) carried out at the global scale via the service international IGS.

- Collect and archive the observations made by the different tide gauge stations (currently this activity is entrusted to the SHOM partner via REFMAR) and by the co-located GNSS stations (directly performed at SONEL in partnership with IGN); make the data available in a practical way using a single interoperable system.

- Verify the quality of the observations, and the performance of the instruments in the field; provide additional measurements that are needed for them to become useful, for example in geodesy (GPS, absolute gravimetry etc.) in the measurement and monitoring of the geodetic stability of the sites.

- In response to a specific demand made by the world programme GLOSS, elaborate specific products based on the observations, particularly the mean monthly and annual levels for the international service PSMSL, and the vertical movements of tide gauges in a global geocentric reference frame.

- Ensure that the service is run and developed in a manner that meets the needs of the users, while taking into account the technical constraints of the computing equipment and the needs of the data producers.

- Encourage and support research and development based on the observations; conduct our own analyses both on the metrology of sea-level and the scientific exploitation of the data.

- Undertake activities of data archaeology, considering the wealth of French stations and tide gauge records available in non digital form which are interesting to rescue in order to better understand the changes in sea level that occur today.

- Perform data analyses and publish the scientific results.

- Promote the exchange of information between producers and users; share the technical know-how, particularly in the current context of emerging territorial networks; participate in the meetings of the international programs to ensure a full integration of the French in these programs.

The coordination role for tide gauges is entrusted to SHOM (see Prime Minister instruction of 20 April 2010 (fr)->doc316]) in France, whereas that for geodetic stations is traditionally ensured by the IGN.