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Pouvreau N.,Service Hydrographique et Oceanographique de la Marine SHOM
Annales Hydrographiques | Year: 2011

The Blue Book "A national strategy for the sea and oceans" (CIMER, 2009) announced by the "Président de la Ré publique" in July 2009 was adopted at the inter-ministerial committee of the sea, by the "Premier ministre" in December 2009. This document mentions the establishment of a network of national referents in charge of coordinating the collection of knowledge by public bodies and their provisions of putting it the disposal. In this context, a statement of the "Premier ministre" concerning the observation of sea level and the management and dissemination of the resulting data was signed by the "Secrétaire général de la mer (SGMer)" in April 2010. This statement appoints the "Service hydrographique et océanographique de la marine (SHOM)" as the national reference for the in situ sea level observation. This function consists to coordinate the efforts of national services performing data acquisition from sea level, in a context where access to such data is to respond to national and international issues, such as programs on the Global Sea Level Observing System (GLOSS) or the emergence of operational systems for the prevention of risks in relation to coastal flooding or tsunami. This responsibility leads among others to get involved in collecting and classifying all water level datas as well as disseminating them through a single portal: REFMAR (for tidal observation reference networks) since December, 2010 hosted at http://refmar.shom.fr.

Quidu I.,ENSTA Bretagne | Jaulin L.,ENSTA Bretagne | Bertholom A.,Directorate General of Armaments | Dupas Y.,Service Hydrographique et Oceanographique de la Marine SHOM
IEEE Journal of Oceanic Engineering | Year: 2012

This paper presents a new approach to the problem of tracking objects in sequences of forward-looking sonar images. Unlike previous work, navigational data are taken as inputs to the state model of the Kalman filter used for tracking fixed obstacles. This model allows a robust prediction of their apparent motion in relation to the position of the sonar. A complete framework is presented where detection and data association issues are also discussed. An assessment of the proposed method has been carried out on real data from two different systems. Moreover, whereas the state model was first derived for a ground obstacle, a modified state model is proposed to estimate the altitude of the obstacle in relation to the sonar position using a number of successive pings. © 2012 IEEE.

Casagrande G.,Directorate General of Armaments | Stephan Y.,Service Hydrographique et Oceanographique de la Marine SHOM | Warn Varnas A.C.,U.S. Navy | Folegot T.,Quiet Oceans
IEEE Journal of Oceanic Engineering | Year: 2011

This paper presents a novel approach to synthesize realistic environment for ocean-acoustic parametric studies. In its current form, this methodology applies to internal waves and tides. Empirical orthogonal function (EOF) decomposition is applied to a temporal series of temperature profiles. It can be observed that the first two time-dependent expansion coefficients are dynamically linked. When they are plotted one versus another in a scatter diagram, the cloud of points consists of a crescent shape that can easily be represented by a polynomial fit. If the first two expansion coefficients capture enough variability in the temperature profiles, the EOF modes plus the polynomial can be used to reconstruct temperature profiles independently from the set of data. This realistic synthesized environment can then be input to acoustic propagation models. This approach is applied to the case of the Messina Strait in which internal waves are known to be intensive. From a short-term series of temperature profiles collected on a thermistor string, range-dependent profiles along and across the strait are reconstructed. The acoustical impact study is conducted with the range-dependent acoustic model (RAM) parabolic equation (PE) model. The methodology presented in this paper is simple to run and requires a very affordable set of data. It could be used as an efficient alternative to ocean and acoustic model coupling for process studies or for regional studies especially in poorly known areas or highly variable areas, where it is difficult to obtain good sound-speed profile prediction from ocean models. © 2011 IEEE.

Mulder T.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Zaragosi S.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Garlan T.,Service Hydrographique et Oceanographique de la Marine SHOM | Mavel J.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | And 4 more authors.
Marine Geology | Year: 2012

Present sedimentation in three canyons of the Bay of Biscay (Audierne, Blackmud and Capbreton) is studied by the combined analysis of cores and current meter data collected over a 7. month period. At the current meter mooring locations, interface cores were collected to characterize the recent sedimentation processes. In the two canyons located in the Northern part of the Bay of Biscay (Audierne and Blackmud), there is no evidence of recent sedimentary deposits. Canyons are by-passing or erosive areas. In the southern part of the Bay of Biscay (Capbreton), recent turbidite are deposited. In the three canyons, current meters recorded energetic currents with velocities showing alternating upslope and downslope motions, and a period corresponding to the semi-diurnal component M2. These currents are supposed to be related to deep internal tides. The high speed of the current (1. m/s) in Audierne and Blackmud is consistent with the lack of preservation of recent sediments on the canyon floors. In Capbreton Canyon, the magnitude of currents is less and recent turbidites are preserved. In addition to periodical current motion, small magnitude gravity event corresponding to a low-concentration turbulent surge or a high-concentration nepheloid layer initiated during a storm was recorded during the mooring period. These results suggest that deep-sea canyons in the Bay of Biscay have behaviour at present varying between by passing or erosion areas and sediment trapping. These examples suggest that sediments are moved up and down by low-energy, tide-initiated hydrodynamic events during most of the time. During higher magnitude, short-duration gravity events, the sediments are transferred down canyon towards the deep sea. © 2011 Elsevier B.V.

Biscara L.,French National Center for Scientific Research | Mulder T.,French National Center for Scientific Research | Hanquiez V.,French National Center for Scientific Research | Marieu V.,French National Center for Scientific Research | And 3 more authors.
Marine Geology | Year: 2013

Comparison of bathymetric data on short time scales (1959-2008) is used to provide new insights into the modern sedimentary dynamics of the Cap Lopez Canyon (Gabon, West Africa). The canyon head evolution is characterized by a north-eastward lateral migration of ~ 180 m between 1959 and 2008. The evolution of the coastline position over the same period highlights the strong relationship between the probable increase of the longshore transport, related to the smoothing of the coast and the morphological evolution of the canyon head. Lateral migration of the thalweg from the inner bend to the outer bend is estimated between 77 and 190. m (or between 1.6 and 3.8. m/year), leading to an increase of the sinuosity (from 1-1.5 in 1959 to 1.3-3.6 in 2008). The migration of the thalweg is associated with strong erosion on the outer bends (up to 60. m) and sediment deposition on the inner bends (up to 25. m). Both the absence of overbank deposits and the developing point-bar morphology may reflect that equilibrium flows are the most frequent flows encountered in the Cap Lopez Canyon. Although erosion of the outer bends is the result of slope failures and steady erosional processes, our study suggests that erosion related to the transit of sediment gravity flows would be the predominant process. © 2013 Elsevier B.V.

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