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Testut L.,French National Center for Space Studies | Miguez B.M.,University of La Rochelle | Miguez B.M.,French National Center for Scientific Research | Wppelmann G.,University of La Rochelle | And 4 more authors.
Journal of Geophysical Research: Oceans | Year: 2010

A data archeology exercise was carried out on sea level observations recorded during the transit of Venus across the Sun observed in 1874 from Saint Paul Island (3841S, 7731 E) in the southern Indian Ocean. Historical (1874) and recent (1994-2009) sea level observations were assembled into a consistent time series. A thorough check of the data and its precise geodetic connection to the same datum was only possible thanks to the recent installation of new technologies (GPS buoy and radar water level sensor) and leveling campaigns. The estimated rate of relative sea level change, spanning the last 135 years at Saint Paul Island, was not significantly different from zero (-0.1 0.3 mm yr-1), a value which could be reconciled with estimates of global average sea level rise for the 20th century assuming the DORIS vertical velocity estimate at Amsterdam Island (100 km distant) could be applied to correct for the land motion at the tide gauge. Considering the scarcity of long-term sea level data in the Southern Hemisphere, the exercise provides an invaluable additional observational constraint for further investigations of the spatial variability of sea level change, once vertical land rates can be determined. Copyright 2010 by the American Geophysical Union. Source

Mazieres A.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Gillet H.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Castelle B.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Mulder T.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | And 3 more authors.
Marine Geology | Year: 2014

In this study, the Capbreton canyon head, just off the coast, is investigated using high-resolution multibeam bathymetry datasets, sediment samples and numerical modeling. The HR bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon. The analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore. Hydrodynamic modeling (a coupled wave-flow model) shows that for high-energy waves, the rotational nature of surf-zone circulation reverses and wave-induced currents have the potential to transport large quantities of nearshore sands toward the canyon head. All these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift. Over the 15. years of observation (1998-2013), time-lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking. In terms of hazards, despite this strong activity, the position of the canyon head and the profile of its longitudinal slope remained stable and appear as a comforting factor. However, the activity of unusual lateral erosions needs to be monitored. © 2014 Elsevier B.V. Source

Abdallah H.,IRSTEA | Baghdadi N.,IRSTEA | Bailly J.-S.,Agro ParisTech | Pastol Y.,SHOM | Fabre F.,Airbus
IEEE Geoscience and Remote Sensing Letters | Year: 2012

A simulator (Wa-LiD) was developed to simulate the reflection of LiDAR waveforms from water across visible wavelengths. The specific features of the simulator include 1) a geometrical representation of the water surface properties; 2) the use of laws of radiative transfer in water adjusted for wavelength and the water's physical properties; and 3) modeling of detection noise and signal level due to solar radiation. A set of simulated waveforms was compared with observed LiDAR waveforms acquired by the HawkEye airborne and Geoscience Laser Altimeter System (GLAS) satellite systems in the near infrared or green wavelengths and across inland or coastal waters. Signal-to-noise ratio (SNR) distributions for the water surface and bottom waveform peaks are compared with simulated and observed waveforms. For both systems (GLAS and HawkEye), Wa-LiD simulated SNR conform to the observed SNR distributions. Moreover, Wa-LiD showed a good ability to reproduce observed waveforms according to some realistic water parameters fitting. © 2012 IEEE. Source

The French Hydrographic Service, the heir of which the SHOM is, participated in the hydrography of the coasts of Africa during the French presence on this continent. The result of these surveys was a detailed cartography which, apart from a few exceptions, little evolved between the independence of the concerned countries and the end of the 1990s. If some countries have set up of a national hydrographic service able to produce nautical charts, only South Africa has reached a regular distribution of its production. In 2002, the Convention on the Safety Of Life At Sea (SOLAS), administered by the International Maritime Organization, was amended to clarify the obligations of the signatory States regarding the production and the distribution of the nautical information in their national waters. This is the reason that led the SHOM to revise its management policy of African water cartography. On the one hand it was decided to conduct new hydrographic surveys and, on the other hand, to conclude administrative arrangements from State to State. These arrangements allow the official recognition of the work achieved by France. Meanwhile updating the hydrographic knowledge in the region, the SHOM also welcomes trainees in hydrography and cartography in its school in Brest. These trainings participate in supporting the creation of local structures which will take over from the SHOM in the future for the dissemination of the nautical information. Thus, the SHOM wants to give a significant boost for a longlasting maintenance of the African coast cartography. Source

Franzetti M.,CNRS Oceanic Domains Laboratory | Le Roy P.,CNRS Oceanic Domains Laboratory | Delacourt C.,CNRS Oceanic Domains Laboratory | Garlan T.,SHOM | And 3 more authors.
Marine Geology | Year: 2013

The aim of this paper is to improve the knowledge of spatio-temporal variability of very large to giant dunes in deep tide dominated environment. Their growth mechanisms and dynamic evolution still remain in debate and constitute a significant scientific challenge in regard to difficulties to achieve accurate measures of migrations. This motivated the realisation of three recent swath bathymetry surveys across the wide dune field of the Banc du Four located offshore the western Brittany. The Banc du Four field is composed of more than 500 large dunes exhibiting a great diversity of morphologies ranging from 2D to 3D shapes and reaching the largest sizes of such sedimentary structure ever described (wavelength over 1000m and height over 30m). The analysis of the entire ensemble of dune parameters offers the opportunity to discuss the relative influence of forcings and the validity of the equations predicting the bedform geometry in shallow waters. Our results show a good height-spacing power law correlation but do not strike the usual statistical regression observed in previous studies. The steeper positive slope of the equation and the outstanding values of the height parameter reveal the complexity of local hydrodynamic regime, interacting with bed load transport and sediment supply. No clear relationship has been observed between asymmetry and size parameters. Water depth cannot be considered as a major factor controlling the size of dunes. Otherwise, the vertical sedimentary variation suggests the action of storm waves on dune crests and the horizontal migration rates of dunes in the eastern field of the Banc du Four were found to range from 3 to 20m·yr-1. Such velocities were only mentioned before by Van Landeghem et al. (2012) on deep continental shelves (>70m deep) and attest of the still present morphodynamical equilibrium of the large dunes. Furthermore, as was previously found for similar dunes in the Irish Sea, no power-law relationship between dune migration rates and dune size can be deduced. Similarly, no strong correlation is established between migration rates and the degree of asymmetry. Nevertheless, the dune asymmetry can be used to predict the migration direction. As for dimension parameters, the evolution asymmetry depends on the study area and migration rates. More precisely, when the crest lines of dunes form straight lines and their migration rates remain below 8-10m·yr-1, the degree of dune asymmetry increases with the migration rate. This trend is reversed for the dunes with higher migration velocities and crests which are sinuous. These results relativize the migratory predictions based on punctual geometrical observations. © 2013 Elsevier B.V. Source

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