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Pastol Y.,Service Hydrographique et Oceanographique de la Marine
Journal of Coastal Research | Year: 2011

Starting in 2005, the French Naval Hydrographic and Oceanographic Office (Service Hydrographique et Océanographique de la Marine [SHOM]) and the French National Geographic Institute (Institut Géographique National [IGN]) began conducting a series of coastal surveys using airborne light detection and ranging (LIDAR) bathymetry (ALB) and topographic LIDAR technologies. This paper describes SHOM's experience using ALB in very shallow coastal waters and under challenging hydrographic survey conditions. The performance of ALB in comparison to multibeam echosounder (MBES) and topographic LIDAR surveys is discussed. Further, a procedure is described for integrating ALB data sets from SHOM with topographic data sets from IGN. Recommendations on conducting future survey operations are provided in this paper based on the experience gained and lessons learned. Based on these experiences, SHOM and IGN have begun a national survey project on mapping the coastal areas (sea and land) of France. © 2011 Coastal Education and Research Foundation.

Filipot J.-F.,Service Hydrographique et Oceanographique de la Marine | Ardhuin F.,French Research Institute for Exploitation of the Sea
Journal of Geophysical Research: Oceans | Year: 2012

A new wave-breaking dissipation parameterization designed for phase-averaged spectral wave models is presented. It combines wave breaking basic physical quantities, namely, the breaking probability and the dissipation rate per unit area. The energy lost by waves is first explicitly calculated in physical space before being distributed over the relevant spectral components. The transition from deep to shallow water is made possible by using a dissipation rate per unit area of breaking waves that varies with the wave height, wavelength and water depth. This parameterization is implemented in the WAVEWATCH III modeling framework, which is applied to a wide range of conditions and scales, from the global ocean to the beach scale. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Model errors are comparable to those of other specialized deep or shallow water parameterizations. This work shows that it is possible to have a seamless parameterization from the deep ocean to the surf zone. © 2012 by the American Geophysical Union.

Leckler F.,Service Hydrographique et Oceanographique de la Marine | Ardhuin F.,CNRS Physics Laboratory | Peureux C.,CNRS Physics Laboratory | Benetazzo A.,CNR Marine Science Institute | And 2 more authors.
Journal of Physical Oceanography | Year: 2015

The energy level and its directional distribution are key observations for understanding the energy balance in the wind-wave spectrum between wind-wave generation, nonlinear interactions, and dissipation. Here, properties of gravity waves are investigated from a fixed platform in the Black Sea, equipped with a stereo video system that resolves waves with frequency f up to 1.4Hz and wavelengths from 0.6 to 11m. One representative record is analyzed, corresponding to young wind waves with a peak frequency fp = 0.33Hz and a wind speed of 13ms21. These measurements allow for a separation of the linear waves from the bound second-order harmonics. These harmonics are negligible for frequencies f up to 3 times fp but account formost of the energy at higher frequencies. The full spectrum is well described by a combination of linear components and the second-order spectrum. In the range 2fp to 4fp, the full frequency spectrum decays like f-5, which means a steeper decay of the linear spectrum. The directional spectrum exhibits a very pronounced bimodal distribution, with two peaks on either side of the wind direction, separated by 150° at 4fp. This large separation is associated with a significant amount of energy traveling in opposite directions and thus sources of underwater acoustic and seismic noise. The magnitude of these sources can be quantified by the overlap integral I( f ), which is found to increase sharply from less than 0.01 at f= 2fp to 0.11 at f = 4fp and possibly up to 0.2 at f = 5fp, close to the 0.5π value proposed in previous studies. © 2015 American Meteorological Society.

Rossi V.,CNRS Geophysical Research and Oceanographic Laboratory | Morel Y.,Service Hydrographique et Oceanographique de la Marine | Garcon V.,CNRS Geophysical Research and Oceanographic Laboratory
Ocean Modelling | Year: 2010

In this paper, the authors study the influence of the wind on the dynamics of the continental shelf and margin, in particular the formation of a secondary upwelling (or downwelling) front along the shelf break. Observations during the MOUTON2007 campaign at sea along the Portuguese coast in summer 2007 reveal the presence of several upwelling fronts, one being located near the shelf break. All upwellings are characterized by deep cold waters close to or reaching the surface and with high chlorophyll concentrations. Simplified numerical models are built in order to study a possible physical mechanism behind this observation. First, a simple shallow water model with three distinct layers is used to study the formation of secondary upwelling fronts. We show that the physical mechanism behind this process is associated with onshore transport of high potential vorticity anomalies of the shelf for upwelling favorable conditions. Sensitivity studies to bottom friction, shelf width, continental slope steepness, shelf "length" are analysed in terms of potential vorticity dynamics. In particular bottom friction is analyzed in detail and we find that, even though bottom friction limits the barotropic velocity field, it enhances the cross-shore circulation, so that no steady state is possible when stratification is taken into account. Bottom friction accelerates the onshore advection of high potential vorticity, but also drastically reduces its amplitude because of diabatic effects. The net effect of bottom friction is to reduce the secondary upwelling development. Based on similar mechanisms, previous results are then extended to downwelling favorable conditions. Finally a more realistic configuration, with bottom topography, wind forcing and stratification set up from observations, is then developed and the results confronted to the observations. Simulations overestimate the velocity amplitude but exhibit good agreement in terms of density ranges brought over the shelf and general isopycnal patterns. The application and extension of the results to more general oceanic regions is discussed and we conclude on the influence of such process on the dynamics of wind driven circulation over a shelf. © 2009 Elsevier Ltd. All rights reserved.

Le Henaff M.,University of Miami | Kourafalou V.H.,University of Miami | Morel Y.,Service Hydrographique et Oceanographique de la Marine | Morel Y.,CNRS Geophysical Research and Oceanographic Laboratory | Srinivasan A.,University of Miami
Journal of Geophysical Research: Oceans | Year: 2012

The dynamics associated with the Loop Current (LC) variability in the Gulf of Mexico (GoM) are studied using a 5-year, free-running numerical simulation with the Hybrid Coordinate Ocean Model (HYCOM). The dynamics of major GoM circulation features are represented: the extension of the LC and the associated anticyclonic, warm core Loop Current Eddies (LCEs) and cyclonic Loop Current Frontal Eddies (LCFEs). The study focuses on the dynamics of the LCFEs and their role during the LCEs shedding, which dramatically affects the GoM circulation. We analyze several characteristics of the LC frontal dynamics. Modeled LCFEs have a coherent vertical structure, which extends to the deep layers of the GoM. They may split in two separate upper and lower layer eddies. Deep and surface remnants from different frontal eddies are able to align to form new, coherent structures. LCFEs intensify along the extended LC northern edge when flowing over the deep northern GoM shelf slope that forms the Mississippi Fan, through a "promontory effect" in which the incoming cyclone aggregates positive potential vorticity anomalies in lower layers, leading to the intensification of the whole vortex structure. LCFEs may also expand further along the LC path by horizontal vortex merging, when they are blocked between the LC and the northeast corner of the continental shelf in the GoM. The intensification and merging due to topographic effects explain the enlarged frontal eddies observed on the eastern side of the Loop Current. These larger eddies further migrate along the LC front and may play a role in the shedding sequence. Copyright © 2012 by the American Geophysical Union.

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