Service Hydrographique et Oceanographique de la Marine SHOM

Brest, France

Service Hydrographique et Oceanographique de la Marine SHOM

Brest, France
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Biscara L.,French National Center for Scientific Research | Hanquiez V.,French National Center for Scientific Research | Leynaud D.,French National Center for Scientific Research | Marieu V.,French National Center for Scientific Research | And 5 more authors.
Marine Geology | Year: 2012

Time serial bathymetric data acquired between 2004 and 2009 are used to evaluate the morphological evolution of the coastal area offshore Pointe Odden, located on the Mandji Island (Gabon). Data analysis highlights the alternation between fast sedimentation periods at shallow water depth related to intense longshore drift and catastrophic erosional events. Because of sediment overloading and slope oversteepening, small-scale instabilities are generated (successive slide scars, channel formation and growth by retrogressive erosion). However, when critical stability conditions are reached, large failures occur (2005 submarine slide). Geotechnical measurements and sedimentological analyses on the study area suggest that flow liquefaction would be the triggering mechanism of the 2005 event. Moreover, our analysis shows that the associated slide scar is rapidly filled by compensation and that failure morphology could disappear from the seafloor in about 15-20. years. © 2012 Elsevier B.V.

Schmeltz M.,University of Bordeaux 1 | Froidefond J.-M.,University of Bordeaux 1 | Jourdin F.,Service Hydrographique et Oceanographique de la Marine SHOM | Gege P.,German Aerospace Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We use a multiple regression analysis and a data bank of about 400 reflectance spectra to reconstruct hyperspectral reflectances between 400 and 900 nm with a 5 nm step using only the values known at the wavelengths of the MERIS sensor level 2 data. For in situ remote sensing reflectances measured during different oceanographic missions, the reconstruction is within 2 per cent almost over the entire spectrum. The main difference (to a maximum of 4 per cent) usually occurs at the inflexion point of the reflectance curve between 580 and 600 nm. Observed in-situ remote sensing reflectances or reconstructed spectra are inverted using a Water Colour Simulator bio-optical model (WASI) to obtain the inherent optical properties (IOP) of the water. The values derived by the model are compared with the measurements when available. To validate the reconstruction, we compare the results of the model inversion using the initial spectrum or the reconstructed one as input. Preliminary results show that the derived values from the inversion of the reconstructed spectrum are very close to the values generated from the inversion of the initial spectrum, especially in case 1 waters. This reconstruction technique is used to generate hyperspectral remote sensing reflectances from reflectance data calculated by the MERIS sensor. We use the reconstructed spectra as input to be inverted in the WASI model in order to quantify the substances' concentrations; in particular, the inversion is working well for the suspended particulate matter concentrations. © 2010 SPIE.

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.

Mulder T.,French National Center for Scientific Research | Hassan R.,French National Center for Scientific Research | Ducassou E.,French National Center for Scientific Research | Zaragosi S.,French National Center for Scientific Research | And 4 more authors.
Geo-Marine Letters | Year: 2013

Facies associations in cores collected in the deep part of the Gulf of Cadiz, which is under the influence of the lower branch of the Mediterranean Outflow Water, are investigated in terms of the classical contourite model using grain-size analyses and thin sections of indurated sediment. Cores include both low-energy (contourite drift) and high-energy (channel) environments. The thin sections and grain-size distributions show that clayey fine silts and sandy coarse silts are the most common facies associations in the studied contourite sequences, while coarse-grained, gravelly contourites are less common. Grain-size distributions are unimodal in the fine-grained and bi- or trimodal in the coarser-grained contourites. This change in grain-size composition is related both to the partial removal of the fine-grained fraction and to the replenishment of the coarser-grained one. In addition, most of the contacts between individual facies are sharp rather than transitional. This suggests that the contourite sequence is only in part related to changes in bottom current velocity and flow competency, but may also be related to the supply of a coarser terrigeneous particle stock, provided by either increased erosion of indurated mud along the flanks of confined contourite channels (mud clasts), or by increased sediment supply by rivers (quartz grains) and downslope mass transport on the continental shelf and upper slope. The classical contourite facies association may therefore not be solely controlled by current velocity, but may be the product of a variety of depositional histories. The classical contourite depositional sequence should therefore be interpreted with greater care and in the light of the regional sedimentological background. In addition, the wisdom of exclusively using mean or modal particle size for the interpretation of depositional contourite processes is questioned. Instead, it is proposed that the vertical evolution of grain-size populations in the facies successions forming contourite sequences be assessed. © 2013 Springer-Verlag Berlin Heidelberg.

PubMed | CIRAD - Agricultural Research for Development, French National Center for Scientific Research, Service Hydrographique et Oceanographique de la Marine SHOM and University Pierre and Marie Curie
Type: | Journal: Scientific data | Year: 2015

French Research vessels have been collecting thermo-salinometer (TSG) data since 1999 to contribute to the Global Ocean Surface Underway Data (GOSUD) programme. The instruments are regularly calibrated and continuously monitored. Water samples are taken on a daily basis by the crew and later analysed in the laboratory. We present here the delayed mode processing of the 2001-2013 dataset and an overview of the resulting quality. Salinity measurement error was a few hundredths of a unit or less on the practical salinity scale (PSS), due to careful calibration and instrument maintenance, complemented with a rigorous adjustment on water samples. In a global comparison, these data show excellent agreement with an ARGO-based salinity gridded product. The Sea Surface Salinity and Temperature from French REsearch SHips (SSST-FRESH) dataset is very valuable for the calibration and validation of the new satellite observations delivered by the Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions.

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.

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

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.

Cailleau S.,Mercator Ocean | Chanut J.,Mercator Ocean | Lellouche J.-M.,Mercator Ocean | Levier B.,Mercator Ocean | And 3 more authors.
Ocean Science | Year: 2012

The regional ocean operational system remains a key element in downscaling from large scale (global or basin scale) systems to coastal ones. It enables the transition between systems in which the resolution and the resolved physics are quite different. Indeed, coastal applications need a system to predict local high frequency events (inferior to the day) such as storm surges, while deep sea applications need a system to predict large scale lower frequency ocean features. In the framework of the ECOOP project, a regional system for the Iberia-Biscay-Ireland area has been upgraded from an existing V0 version to a V2. This paper focuses on the improvements from the V1 system, for which the physics are close to a large scale basin system, to the V2 for which the physics are more adapted to shelf and coastal issues. Strong developments such as higher regional physics resolution in the NEMO Ocean General Circulation Model for tides, non linear free surface and adapted vertical mixing schemes among others have been implemented in the V2 version. Thus, regional thermal fronts due to tidal mixing now appear in the latest version solution and are quite well positioned. Moreover, simulation of the stratification in shelf areas is also improved in the V2. © 2012 Author(s).

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