Sylvain Ouillon

Bio: Sylvain Ouillon is an academic researcher from University of Toulouse. The author has contributed to research in topics: Sediment & Coral reef. The author has an hindex of 33, co-authored 82 publications receiving 2611 citations. Previous affiliations of Sylvain Ouillon include Institut de recherche pour le développement & University of Bordeaux.

Three-dimensional computation of flow around groyne

Abstract: The three-dimensional (3D) numerical simulation of a steady, shallow turbulent flow around a groyne in a rectangular channel is presented. A method used to track a moving surface boundary and to follow its evolution, using a one-phase 3D Reynolds solver with rigid grids, by means of a transient fraction of fluid or “porosity” field is applied. Some results are compared with experimental data, such as the isolines of water depths and the mean velocity field. A comparison of the reattachment length prediction using the free-surface model and the rigid-lid assumption is given. Other results concerning the pressure field, turbulence, or shear stress distribution are presented and analyzed.

Coupling satellite data with in situ measurements and numerical modeling to study fine suspended-sediment transport: a study for the lagoon of New Caledonia

Abstract: This paper investigates the potential of re- motely sensed data to map turbidity in a coral reef la- goon and to calibrate a numerical model of fine suspended-sediment transport. Simultaneous measure- ments of turbidity depth-profile and above-water spec- tral reflectance integrated according Landsat 7 ETM+ band 2 spectral sensitivity provide a linear regression relationship for the southwest lagoon of New Caledonia (r 2 =0.95, n=40). This relationship is applied to an empirically atmospherically corrected Landsat ETM+ image of the lagoon acquired on October 23, 2002. A comparison between Landsat estimates of turbidity and concurrent measurements at 14 stations indicates that the mean standard error in the satellite-estimated tur- bidity is 17.5%. The numerical model introduced in Douillet et al. (2001) is used to simulate the transport of fine suspended sediments in the lagoon in October 2002. A calibration of the erosion rate coefficient required by the model is proposed using in situ turbidity profiles and the remotely sensed turbidity field. In situ data are used to tune locally the erosion rate coefficient, while satellite data are used to determine its spatial zonation. We discuss necessary improvements in coupled studies of fine-sediment transport in coastal zones, namely rela- tionships between turbidity and sediment concentration, integration of wave influence in the model, and correc- tion of bottom reflection in satellite data processing.

A numerical model for fine suspended sediment transport in the southwest lagoon of New Caledonia

Abstract: A hydrodynamic-transport coupled model is used to understand the transport of fine suspended sediments in the southwest lagoon of New Caledonia The hydrodynamic model is briefly presented and the circulation due to the tide and to averaged trade wind forcings is analyzed The transport model for fine suspended sediment is described Parameters involved in this model (settling velocity, critical shear stresses, erosion rate coefficient, Schmidt number) are discussed and a calibration procedure is proposed Using the resultant parameters, the erosion and deposition areas predicted by the sediment-transport model are in very good agreement with the distribution of the percentage of mud at the seabed The sensitivity of the model to the different sedimentary parameters is studied, and the influences of the tide and wind on deposition and erosion are discussed The influence of the wind is dominant in seabed exchange processes in shallow areas and produces large erosion rates where the water depth is less than 20 m The tide controls the particulate transport, vertical mixing, and deposition rates in the areas where the influence of the wind is weak

Statistical Methods For Environmental Pollution Monitoring

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Atmospheric correction of SeaWiFS imagery for turbid coastal and inland waters

Abstract: The standard SeaWiFS atmospheric correction algorithm, designed for open ocean water, has been extended for use over turbid coastal and inland waters. Failure of the standard algorithm over turbid waters can be attributed to invalid assumptions of zero water-leaving radiance for the near-infrared bands at 765 and 865 nm. In the present study these assumptions are replaced by the assumptions of spatial homogeneity of the 765:865-nm ratios for aerosol reflectance and for water-leaving reflectance. These two ratios are imposed as calibration parameters after inspection of the Rayleigh-corrected reflectance scatterplot. The performance of the new algorithm is demonstrated for imagery of Belgian coastal waters and yields physically realistic water-leaving radiance spectra. A preliminary comparison with in situ radiance spectra for the Dutch Lake Markermeer shows significant improvement over the standard atmospheric correction algorithm. An analysis is made of the sensitivity of results to the choice of calibration parameters, and perspectives for application of the method to other sensors are briefly discussed. © 2000 Optical Society of America OCIS codes: 010.1290, 010.4450, 120.0280.

A Decade of Satellite Ocean Color Observations

Abstract: After the successful Coastal Zone Color Scanner (CZCS, 1978-1986), demonstration that quantitative estimations of geophysical variables such as chlorophyll a and diffuse attenuation coefficient could be derived from top of the atmosphere radiances, a number of international missions with ocean color capabilities were launched beginning in the late 1990s. Most notable were those with global data acquisition capabilities, i.e., the Ocean Color and Temperature Sensor (OCTS 1996-1997), the Sea-viewing Wide Field-of-view Sensor (SeaWiFS, United States, 1997-present), two Moderate Resolution Imaging Spectroradiometers, (MODIS, United States, Terra/2000-present and Aqua/2002-present), the Global Imager (GLI, Japan, 2002-2003), and the Medium Resolution Imaging Spectrometer (MERIS, European Space Agency, 2002-present). These missions have provided data of exceptional quality and continuity, allowing for scientific inquiries into a wide variety of marine research topics not possible with the CZCS. This review focuses on the scientific advances made over the past decade using these data sets.