Oceanographic Real-Time Measurement on Buoyancy Beacon Feedback in the Rhône Delta and Gulf of Fos Fruce France Pierre Gaufrès, B. Andres, and F. Dufois
Abstract The instrumentation implanted since 2003 on two buoyancy beacons (BFI) in the Gulf of Fossur-Mer and in the delta margin provides local oceanographic and meteorological real-time data. The device is based on Doppler technology sensors fixed on the beacon pipe. Meteorological sensors, acquisition, and data transmission systems are clamped to the emerged structure close to Aide to Navigation (AtoN) and their energy systems. The monitoring of this device and analysis of recorded observations for nearly 4 years allows specifying uncertainties linked to this kind of measurement and provides a reliable feedback on the exploitation of the observatory. A database of simultaneous measurements of beacons structure behavior (tilting measurement) and oceanographic and meteorological parameters has been used to design new BFIs for future projects (Lavezzi in Bonifacio Strait, Corsica, Port of Marseilles Authority, etc.). Analysis of the current measurement enables one to characterize the current profiles on the water column located above sensors, and to distinguish flow stratification effects and wind-current correlations. Although originally designed to monitor the structure behavior and to supply wave climate to marine pilots, the system has developed different time applications. For example, sediment dredge bottom discharge has
P. Gaufrès (*) and B. Andres Centre d'Etudes Techniques Maritimes et Fluviales (CETMEF), Boulevard du Président Kennedy, 13097, Aix-en-Provence cedex 02, France e-mail:
[email protected] F. Dufois Institut de Radioprotection et de Sûreté Nucléaire (IRSN) DEI/SESURE/LERCM – Base IFREMER CT, 330 83507 La Seyne-sur-Mer, cedex, France
been optimized in the Gulf of Fos and frequency analysis of sea level has been compared to coastal tide gauge data for the historical Rhône flood in December 2003.
1 Introduction The origin of the instrumentation of two BFIs in the Gulf of Fos came from different needs from two partners. On the one hand, the CETMEF (French Institute for Maritime and Inland Waterways) wanted to improve in situ knowledge of BFI’s structural behavior. However, Port Authority of Marseilles, owner of a wavemeter (Datawell type) in the Gulf of Fos, often stormed by ships, wanted to secure this. In 2001, the Port Authority of Marseilles, CETMEF, and Maritime Service of Bouches-du-Rhône (SM13) agreed to build a metocean observatory on two BFIs (Fig. 1) located in the Golf of Fos (France).
2 Instrumentation Description The current profiler is an Awac type from Nortek. It uses Doppler technology, based on a phase difference calculation between the emitted and received frequencies. Phase difference is linked to particle speed in the water (plankton, sediments, etc.). Those particles are driven by the current and permit its measurement. The instrument also measures sea level (pressure sensors), sea temperature, and eventually wave parameters. The Awac is clamped on supporting arms perpendicular to the beacon’s main pipe (Fig. 2). The arms were calculated so as to install ADCP 3.5 m away from the main pipe so that Awac beams
H.-J. Ceccaldi et al. (eds.), Global Change: Mankind-Marine Environment Interactions, Proceedings of the 13th French–Japanese Oceanography Symposium, DOI 10.1007/978-90-481-8630-3_43, © Springer Science+Business Media B.V. 2011
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are not disturbed by BFI structures. Depths are 15.5 m for the Fos no. 2 ADCP and 14.5 m for the Balancelle one along the Rhône deltaic margin. The ultrasonic anemometer is a Vaisala WS425 type. It was fixed on a metal bar on the BFI nacelle, 7.0 m above average sea level.
3 Operational Use and Research For the Marseilles Port Authority navigation needs, data are displayed on control screens of the Integrated Regulation Center (CRI) located in Port-de-Bouc and can be communicated to approaching ships. Data are treated by CETMEF for applied research: structural behavior, marine hydraulics, statistic analysis, metocean parameters, treatment, etc. Correlations were produced among wave height, wave direction, wind intensity, wave height, wind direction, and current direction. The surface current and wind are well correlated, especially the mistral and SW storm winds (135° and 315°) (see Fig. 3); shear current on the subsurface may be observed during some episodes (Fig. 4). Fig. 1 BFI in its environment (left) and structure (right)
4 Conclusions
Fig. 2 ADCP on the perpendicular arm during an inspection
Years of real-time data experience provided by profiler technology fixed on BFIs shows the interest in coupling marine observations to AtoN buoys: direct energy supply (solar or wind), localization, safety of equipment, etc. However, we advise keeping the instrument in its original configuration, including magnetic North, independently positioned on sea bottom on a tripod and connected to a buoy by a short umbilical wire to avoid trawling. Many prospects are foreseen with spatial altimetry or coastal oceanic modeling for integrating those observations as boundary conditions. Current projects with actual and future MESURHO instrumentation are projected in order to study flow structure in the Rhône river mouth, hydrosedimentary
Oceanographic Real-Time Measurement on Buoyancy Beacon Feedback in the Rhône Delta and Gulf of Fos Fruce France
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processes off the coast of the Gracieuse They, or North Occidental Mediterranean Sea meso-scale dynamics of vortexes identified in the 3D Symphonie model.
Acknowledgments G. Cunty, H. Barreda (CETMEF), C. Roblin (SM13), B. Vion (CETE Méditerranée), J. Moisan, and F. Denivet (Port Authority of Marseilles).