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Registros recuperados: 19
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A dual-frequency approach for retrieving sea surface wind speed from TOPEX altimetry ArchiMer
Chen, G; Chapron, Bertrand; Ezraty, Robert; Vandemark, D.
More than a dozen of wind speed (U) algorithms have been proposed during the past 2 decades, as a result of a continuing effort to improve altimeter wind measurement. The progress in terms of accuracy, however, is seen to be rather slow. The reported root mean square (RMS) error of prevailing algorithms varies mostly between 1.6 and 2.0 m/s for the dominant wind regime. As far as the TOPEX altimeter is concerned, three measured quantities, namely, the radar cross sections from Ku and C band (sigma(Ku) and sigma(C)), as well as the significant wave height (H-s), have been used in previous algorithm developments, resulting in a variety of single-, dual-, and three-parameter model functions. On the basis of the finding of a banded dependency of the...
Tipo: Text Palavras-chave: Sea surface wind speed; Retrieval; TOPEX; Altimeter; Dual frequency.
Ano: 2002 URL: https://archimer.ifremer.fr/doc/00000/10224/9579.pdf
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ASCAT/MetOp scatterometer data : first results for sea ice study ArchiMer
Ardhuin, Fanny; Ezraty, Robert; Croize-fillon, Denis.
Backscatter values from scatterometers are commonly used to estimate wind field over oceans, their ability to monitor sea ice coverage, age and drift has been also demonstrated. Here, ASCAT backscatter coefficient has been processed for sea ice geophysical interpretation in order to increase the long time series of ice parameters already available. It has been shown that incidence- adjustment is mandatory for geophysical meaning, the backscatter maps enable the discrimination between multi year ice and first year ice, these maps can also be used as a basic product for sea ice drift estimation. (Copyright : European Space Agency ISBN 978-92-9221-239-1 ISSN 1609-042X)
Tipo: Text Palavras-chave: Sea ice; Wind; Scatterometer; ASCAT; MetOp; Glaces de mer; Vent; Diffusiomètre; ASCAT; MetOp.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/acte-6970.pdf
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Comment se forme un pancake aux pôles ? ou l'importance d'observer la banquise... ArchiMer
Ardhuin, Fanny; Ezraty, Robert; Croize-fillon, Denis.
Sea water freezes at a temperature of -1,8°C, creating scattered pieces of ice similar to pancakes. When agglomerating, these pieces end up forming a compact surface... the ice floe!
Tipo: Text
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/acte-6365.pdf
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Defining a Sea Ice Flag for Envisat Altimetry Mission ArchiMer
Tran, N; Ardhuin, Fanny; Ezraty, Robert; Feng, H; Femenias, P.
This letter presents the development of a sea ice flag algorithm for the Envisat altimetry mission to detect sea ice corrupted sea surface height data within quality control processing. The algorithm takes advantage of having both passive and active microwave sensors on the same platform with coregistered measurements. Its performances have been evaluated based on collocations between the along-track Envisat data with reference maps built from combination of daily grids of sea ice concentration from SSM/I sensors and backscatter cross section from SeaWinds scatterometer on QuikSCAT satellite.
Tipo: Text Palavras-chave: Sea ice; Remote sensing; Microwave measurements; Altimetry.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-5289.pdf
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Enhanced Arctic Sea Ice Drift Estimation Merging Radiometer and Scatterometer Data ArchiMer
Ardhuin, Fanny; Ezraty, Robert.
Satellites enable daily and global coverage of the polar oceans and provide a unique monitoring capability of sea ice dynamics. Sea ice drift maps can be estimated in Arctic from several satellite sensors, particularly from scatterometers and radiometers. This study presents the benefits of combining single drift fields at the same resolution into a "merged" field, built at three-and six-day lags during winters with a 62.5-km resolution. It is shown that combining these drift fields not only increases the reliability of the displacement estimation and the number of estimated vectors to almost a full ice covered area but also expands the time period over which these estimations are reliable from freeze until the melt onset. The autumn-winter-spring sea ice...
Tipo: Text Palavras-chave: Arctic; Advanced Scatterometer (ASCAT); Drift; Merging; Scatterometry; Sea ice.
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00088/19895/17729.pdf
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Etude statistique de la houle littorale proche du déferlement ArchiMer
Cavanie, Alain; Ezraty, Robert.
The analysis of two sets of wave measurements close to shore verifies that as long as wave amplitudes are small with respect to mean depth a Rayleigh distribution remains satisfactory for wave heights. When mean depth is inferior to three times the significant wave heights, the statistical distribution of wave heights is best fit by Weibull's law whose exponent is an increasing function of relative wave height. All three parameters of Weibull's law can be rapidly estimated from Hr, Hr1/3 and Hr1/1O. [NOT CONTROLLED OCR]
Tipo: Text Palavras-chave: Histoire Ifremer.
Ano: 1976 URL: http://archimer.ifremer.fr/doc/1976/publication-5078.pdf
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Evaluation de la mesure de la direction des vagues à partir des données d'une bouée instrumentée ArchiMer
Ezraty, Robert; Cavanie, Alain.
The pitch and roll buoy developped at CNEXO-COB to measure directional spectra of waves (following the method employed by Cartwright, Longuet-Higgins and Smith) uses recently manufactured sensors for pitch, roll, heave and direction which give it a large autonomy. This article presents an evaluation of the validity of measurements obtained with this instrument during the Marsen expriment in the North Sea. To do this, we have sought to determine the errors arising at different stages of the acquisition and analysis of data : sensor calibrations, influence of numerical analysis (filtering) and Doppler effects due to tidal currents. The redundancy in the simultaneous measurements of the vertical displacements and the two components of slope of the sea...
Tipo: Text
Ano: 1981 URL: http://archimer.ifremer.fr/doc/1981/publication-5324.pdf
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Evolution of the passive and active microwave signatures of a large sea ice feature during its 2 1/2-year drift through the Arctic Ocean ArchiMer
Gohin, Francis; Cavanie, Alain; Ezraty, Robert.
Although estimation of the total ice concentration from special sensor microwave imagers (SSM/I) has proven to be successful, none of the various algorithms developed to discriminate new and older ice provide satisfying results. While the strong contrast between the emissivity of sea ice and that of open water can be utilized to provide reliable estimators of the total ice concentration, passive microwave characteristics of second-year and multiyear ice may locally evolve in different ways, even during the cold season. Scatterometers, as the active microwave instrument in wind mode (AMI-wind) on board the European Remote Sensing Satellites (ERS), provide backscatter data which have a higher sensitivity to the surface topography of ice and a better...
Tipo: Text
Ano: 1998 URL: http://archimer.ifremer.fr/doc/00447/55848/58406.pdf
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La mer vue du ciel, la glace de mer est cartographiée en continu ArchiMer
Ardhuin, Fanny; Ezraty, Robert.
Under the responsibility of French scientists, the Damocles program aims to evaluate the impact of the climate change on the Arctic ice floe. Some Bretons are involved: a team from the Ifremer Brest has been continuously mapping sea ice drift since 1992.
Tipo: Text
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-6369.pdf
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Les glaces de mer. Ca bouge ! ArchiMer
Ardhuin, Fanny; Ezraty, Robert.
Monitored by satellites and observed by the Ifremer's scientists, sea ices are under high supervision. Since 1992, the Ifremer is the only institute in the world to conduct a continuous mapping of sea ice drift.
Tipo: Text
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-6363.pdf
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Les glaces de mer : ça bouge ! ArchiMer
Ardhuin, Fanny; Ezraty, Robert; Croize Fillon, Denis.
Tipo: Text
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/acte-6342.pdf
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L'IFREMER met en cartes les glaces polaires ArchiMer
Ardhuin, Fanny; Ezraty, Robert.
The fourth International Polar Year (API) was officially launched at the Palais de la Découverte in Paris in the beginning of March. This international research effort will spread over two years. The polar specialists hope for an acceleration of the current programs, especially those dealing with the impact of climate warming on polar regions. Paul Tréguer, member of the French PAPI sponsoring committee, summarizes the different issues. And two Ifremer scientists explain how they've been observing, since 1992, the shrinking of the sea ice cover in the North Pole
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-6367.pdf
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Marine Wind Variability: Illustration and Comments ArchiMer
Ezraty, Robert.
Sea-state modelers introduce a mean wind vector at each grid point of their models that varies only once every time step. Real winds often fluctuate at much shorter space and time scales. Some examples of these fluctuating wind fields are given, along with possible implications for modeling.
Tipo: Text
Ano: 1990 URL: http://archimer.ifremer.fr/doc/00178/28919/37856.pdf
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Non-tidal aliasing in seasonal sea-level variability and annual Rossby waves as observed by satellite altimetry ArchiMer
Chen, Ge; Ezraty, Robert.
It is becoming well known that aliasing associated with ocean tides could be a major source of systematic error in altimeter sea-level measurements. due to asynoptic sampling and imperfect tide modelling. However, it has been shown that signals of non-tidal origin may also contribute significantly to the observed aliasing. In this paper, numerical simulations are performed to demonstrate the full aliasing potential associated with altimeter observations of seasonal sealevel variability and annual Rossby waves. Our results indicate that ignorance of non-tidal aliasing may lead to the possibility of underestimating the total aliasing and misinterpreting or overlooking existing geophysical phenomena. Therefore, it is argued that an entice aliasing picture...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00335/44650/57343.pdf
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Relation statistique entre hauteur et période des vagues de tempête ArchiMer
Arhan, Michel; Cavanie, Alain; Ezraty, Robert.
A theoretical model of composed probability density of wave height and period is based on the results of Cartwright and Longuet-Higgins on the maximums of a Gaussian random function of order two of narrow spectrum. The concordance with experiment is satisfactory, even for wide spectrums, in the case of recordings of storms in the North Sea.
Tipo: Text Palavras-chave: Histoire Ifremer.
Ano: 1976 URL: http://archimer.ifremer.fr/doc/1976/publication-5190.pdf
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Saisie et analyse de données des courants particulaires et pressions au voisinage du fond dans la houle littorale proche du déferlement ArchiMer
Arhan, M.; Ezraty, Robert.
In fact, coastal swell near to the breaker zone is feared by engineers when evaluating the stresses exerted on coastal civil engineering structures. This fear is mainly caused by the phenomenon's complex nature; a nature which can only be partially represented by the current theoretical models. Experimentally speaking, the observation techniques we have enable the quantitative study of coastal swell near to the breaker zone, as well as the characterization of some of its properties and the testing of some theoretical models which are valid off shore and could be adapted to the coast. This study demonstrates the strong non-linearity of free surface movements. It also details the conditions of utilization of the Airy and long wave theories in the evaluation...
Tipo: Text Palavras-chave: Histoire Ifremer.
Ano: 1975 URL: http://archimer.ifremer.fr/doc/1975/publication-4986.pdf
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Southern elephant seals from Kerguelen Islands confronted by Antarctic Sea ice. Changes in movements and in diving behaviour ArchiMer
Bailleul, Frédéric; Charrassin, Jean-benoit; Ezraty, Robert; Ardhuin, Fanny; Mcmahon, Clive R.; Field, Iain C.; Guinet, Christophe.
The behaviour of southern elephant seals from Kerguelen Island (4950′S, 7030′E) was investigated in relation to the oceanographic regions of the Southern Ocean. The oceanographic and the seal behaviour data, including location and diving activity, were collected using a new generation of satellite-relayed devices measuring and transmitting pressure, temperature, and salinity along with locations. Dive duration, maximum diving depth, time spent at the bottom of the dives, and shape of dive profiles were compared between male and female seals, and were related to the oceanographic characteristics of areas prospected by the seals. Most animals travelled to the Antarctic shelf. However, during winter, adult females travelled away from the...
Tipo: Text Palavras-chave: Mirounga leonina; Diving Behaviour; Pelagic environment; Benthic environment; Temperature profiles; Marine ecology.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-2500.pdf
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Statistical relations between successive wave heights ArchiMer
Arhan, Michel; Ezraty, Robert.
This paper presents a theoretical and experimental study of the correlation between successive waves. The theoretical model developed here, uses as starting point Rice's results on the autocorrelation function of the envelope of a narrow band random gaussian signal. Recent developments by Hasselmann et al. on wave spectra and Cavanie et al. on wave heights and periods statistics used as input in Rice's model, lead to a theoretical joint probability for successive wave heights. This model is compared to experimental results computed from 169 North Sea storm wave recordings corresponding to more than 26 000 individual waves. [NOT CONTROLLED OCR]
Tipo: Text
Ano: 1978 URL: http://archimer.ifremer.fr/doc/1978/publication-5222.pdf
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Validation of Arctic sea ice drift with IABP buoys ArchiMer
Ardhuin, Fanny; Ezraty, Robert.
Satellites enable daily and global coverage of the polar oceans, providing an unique monitoring capability of sea ice dynamics over Arctic and Antarctic. Available geophysical parameters include ice concentration, extent, type and sea ice drift. Backscatter map from SeaWinds/QuikSCAT and brightness temperature maps from Special Sensor Microwave Imager (SSM/I) are available at a pixel resolution of 12,5 km from which ice drift can be estimated for each sensor. Since 1999, IFREMER makes available a "Merged" sea ice drift data set based on the combination of these drifts at 3 and 6-day lags at the grid resolution of 62,5 km. It has been demonstrated that combining these drifts increases the number of valid vectors. In this paper, the validation of this...
Tipo: Text Palavras-chave: Arctic; Buoys; Drift; Sea ice; AMSR E; Radiometer; Scatterometer; Arctique; Bouées; Dérive; Glaces de mer; AMSR E; Radiomètre; Diffusiomètre.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/acte-1292.pdf
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