Sabiia Seb
PortuguêsEspañolEnglish
Embrapa
        Busca avançada

Botão Atualizar


Botão Atualizar

Ordenar por: RelevânciaAutorTítuloAnoImprime registros no formato resumido
Registros recuperados: 28
Primeira ... 12 ... Última
Imagem não selecionada

Imprime registro no formato completo
Direct measurements of ocean surface velocity from space: Interpretation and validation - art. no. C07008 ArchiMer
Chapron, Bertrand; Collard, Fabrice; Ardhuin, Fabrice.
[1] The median Doppler shift of radar echoes is analyzed in measurements by ENVISAT's Advanced Synthetic Aperture Radar (ASAR) over the ocean. This Doppler centroid differs from a predicted signal based on the predicted motion of the satellite and Earth. This anomaly, converted to a surface Doppler velocity U-D, appears to be of geophysical origin. Two wide-swath images over the Gulf Stream around Cape Hatteras suggest that U-D contains high-resolution information on surface currents, while on a global scale, UD is found to vary with the wind speed in the range direction. A simple quantitative forward model is proposed, based on a practical two-scale decomposition of the surface geometry and kinematics. The model represents the effect of the wind through...
Tipo: Text Palavras-chave: Wind data Wind speed boundary layer Ocean atmosphere system Satellite sensing ESA satellite; ENVISAT Wind fields Sea surface roughness Inversions Radar echoes Tidal currents Gulf Stream Synthetic aperture radar Wind direction Surface currents Radar wind measurements.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-1704.pdf
Imagem não selecionada

Imprime registro no formato completo
Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A ArchiMer
Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin.
Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1A wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity toward the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this...
Tipo: Text Palavras-chave: Ocean waves; SAR; Sea ice.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00256/36718/35332.pdf
Imagem não selecionada

Imprime registro no formato completo
Estimating wave orbital velocity through the azimuth cutoff from space-borne satellites ArchiMer
Stopa, Justin; Ardhuin, Fabrice; Chapron, Bertrand; Collard, Fabrice.
It has been long accepted that ocean wave conditions recorded from synthetic aperture radar (SAR) aboard satellites resolve large scale swells. SARs make use of its displacement to achieve fine resolution; however the random surface motions can reduce its nominal azimuthal resolution. Accordingly, the SAR spectral azimuth response mirrors the probability distribution of the radial velocity component of the scatters. This effect, quantified in a measure called the azimuth cutoff, is estimated by defining a scale based on the fitting of a Gaussian function to the radar cross section azimuth spectrum. The independent measure provides additional sea state information related to the root mean square surface orbital wave velocity. We use data recorded from the...
Tipo: Text
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00310/42170/41471.pdf
Imagem não selecionada

Imprime registro no formato completo
Extraction of coastal ocean wave fields from SAR images ArchiMer
Collard, Fabrice; Ardhuin, Fabrice; Chapron, Bertrand.
Wave spectra derived from synthetic aperture radar (SAR) images acquired by ENVISATs are compared to in situ measurements by seven sensors, deployed in a field experiment carried out on the French coast of La Manche (English Channel). The wave spectra inversion scheme is adapted for shallow water from the European Space Agency (ESA)'s operational processing techniques used for level 2 ocean wave products. Under the low to moderate wind speed observed conditions, overall good agreement is found between in situ and SAR observations over a wide range of wave heights and directions, including waves propagating in the radar azimuth direction and incidence angles different from the standard imagette products.
Tipo: Text Palavras-chave: Synthetic aperture radar; Ocean waves.
Ano: 2005 URL: http://archimer.ifremer.fr/doc/2005/publication-1109.pdf
Imagem não selecionada

Imprime registro no formato completo
Imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data ArchiMer
Kudryavtsev, Vladimir; Myasoedov, Alexander; Chapron, Bertrand; Johannessen, Johnny A.; Collard, Fabrice.
A synergetic approach for quantitative analysis of high-resolution ocean synthetic aperture radar (SAR) and imaging spectrometer data, including the infrared (IR) channels, is suggested. This approach first clearly demonstrates that sea surface roughness anomalies derived from Sun glitter imagery compare very well to SAR roughness anomalies. As further revealed using these fine-resolution (similar to 1 km) observations, the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature (SST) field. To quantitatively interpret SAR and optical (in visible and IR ranges) images, equations are derived to relate the "surface roughness" signatures to the upper ocean flow characteristics. As developed, a direct link...
Tipo: Text
Ano: 2012 URL: https://archimer.ifremer.fr/doc/00079/18999/16570.pdf
Imagem não selecionada

Imprime registro no formato completo
Joint sun-glitter and radar imagery of surface slicks ArchiMer
Kudryavtsev, Vladimir; Myasoedov, Alexander; Chapron, Bertrand; Johannessen, Johnny A.; Collard, Fabrice.
A method is proposed to retrieve and interpret fine spatial variations of the sea surface roughness in sun glitter imagery. Observed sun glitter brightness anomalies are converted using a transfer function determined from the smoothed shape of sun glitter brightness. The method is applied to MODIS and MERIS sun glitter imagery of natural oil seeps and the catastrophic Deepwater Horizon oil spill in the Gulf of Mexico. The short-scale roughness variations in the presence of mineral oils slicks are consistently extracted and compared to variations associated with the biogenic slicks. In doing so, the wind speed dependency on the roughness anomalies is also considered. A comparison to normalized radar cross section (NRCS) anomalies taken from the...
Tipo: Text Palavras-chave: Sun-glitter; Mean square slope; Surface slicks; Oil spills; SAR imaging model; SAR and optical synergy.
Ano: 2012 URL: https://archimer.ifremer.fr/doc/00083/19439/17217.pdf
Imagem não selecionada

Imprime registro no formato completo
Mapping the Agulhas Current from space: An assessment of ASAR surface current velocities ArchiMer
Rouault, M. J.; Mouche, Alexis; Collard, Fabrice; Johannessen, J. A.; Chapron, Bertrand.
Over 2 years of surface current information collected in the Agulhas Current region and derived from the Doppler centroid anomalies of Envisat's advanced synthetic aperture radar (ASAR) are examined. The sources of errors and potential use of ASAR surface current velocities for oceanographic research are assessed. ASAR surface current velocities are compared to surface drifter data and merged altimetry observations. Maps of sea surface temperature are used to establish the ASAR's capacity to capture the synoptic circulation. Discrepancies between observed and predicted ASAR velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 degrees. Occasionally observed wind-induced outliers cause a bias in the...
Tipo: Text
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00016/12712/9639.pdf
Imagem não selecionada

Imprime registro no formato completo
Measuring currents, ice drift, and waves from space: the Sea surface KInematics Multiscale monitoring (SKIM) concept ArchiMer
Ardhuin, Fabrice; Aksenov, Yevgueny; Benetazzo, Alvise; Bertino, Laurent; Brandt, Peter; Caubet, Eric; Chapron, Bertrand; Collard, Fabrice; Cravatte, Sophie; Delouis, Jean Marc; Dias, Frederic; Dibarboure, Gerald; Gaultier, Lucile; Johannessen, Johnny; Korosov, Anton; Manucharyan, Georgy; Menemenlis, Dimitris; Menendez, Melisa; Monnier, Goulven; Mouche, Alexis; Nouguier, Frederic; Nurser, George; Rampal, Pierre; Reniers, Ad; Rodriguez, Ernesto; Stopa, Justin; Tison, Celine; Ubelmann, Clement; Van Sebille, Erik; Xie, Jiping.
We propose a satellite mission that uses a near-nadir Ka-band Doppler radar to measure surface currents, ice drift and ocean waves at spatial scales of 40 km and more, with snapshots at least every day for latitudes 75 to 82 degrees, and every few days for other latitudes. The use of incidence angles of 6 and 12 degrees allows for measurement of the directional wave spectrum, which yields accurate corrections of the wave-induced bias in the current measurements. The instrument's design, an algorithm for current vector retrieval and the expected mission performance are presented here. The instrument proposed can reveal features of tropical ocean and marginal ice zone (MIZ) dynamics that are inaccessible to other measurement systems, and providing global...
Tipo: Text
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00442/55318/56843.pdf
Imagem não selecionada

Imprime registro no formato completo
Measuring ocean waves in sea ice using SAR imagery: A quasi-deterministic approach evaluated with Sentinel-1 and in situ data ArchiMer
Ardhuin, Fabrice; Stopa, Justin; Chapron, Bertrand; Collard, Fabrice; Smith, Madison; Thomson, Jim; Doble, Martin; Blomquist, Byron; Persson, Ola; Collins, Clarence O., Iii; Wadhams, Peter.
Measurements of wave heights in marginal ice zones are limited to very few in situ data. Here we revisit the linear and quasilinear theories of Synthetic Aperture Radar imaging of waves in the particular case of waves in sea ice. Instead of only working with spectra, we have developed an iterative nonlinear algorithm to estimate phase-resolved deterministic maps of wave-induced orbital velocities, from which elevation spectra can be derived. Application of this algorithm to Sentinel 1A wave mode images in the Southern Ocean shows that it produces reasonable results for swells in all directions except when they propagate at a few degrees off the range direction. The estimate of wave parameters is expected to work best when the shortest wave components,...
Tipo: Text Palavras-chave: SAR; Sentinel-1A; Ocean waves; Sea ice.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00361/47214/47451.pdf
Imagem não selecionada

Imprime registro no formato completo
Monitoring and analysis of ocean swell fields from space: New methods for routine observations ArchiMer
Collard, Fabrice; Ardhuin, Fabrice; Chapron, Bertrand.
Satellite synthetic aperture radar (SAR) observations can provide a global view of ocean swell fields when using a specific "wave mode" sampling. A methodology is presented to routinely derive integral properties of the longer-wavelength ( swell) portion of the wave spectrum from SAR level 2 products and both monitor and predict their evolution across ocean basins. SAR-derived estimates of swell height and energy-weighted peak period and direction are validated against buoy observations, and the peak directions are used to project the peak periods in one dimension along the corresponding great circle route, both forward and back in time, using the peak period group velocity. The resulting real-time data set of great circle-projected peak periods produces...
Tipo: Text
Ano: 2009 URL: http://archimer.ifremer.fr/doc/00000/11101/7417.pdf
Imagem não selecionada

Imprime registro no formato completo
Monitoring the surface inflow of Atlantic Water to the Norwegian Sea using Envisat ASAR ArchiMer
Hansen, M. W.; Johannessen, J. A.; Dagestad, K. F.; Collard, Fabrice; Chapron, Bertrand.
Sea surface range Doppler velocities from nearly 1200 Envisat Advanced Synthetic Aperture Radar (ASAR) acquisitions between 2007 and 2011, covering the Norwegian Sea, the North Sea, and the Skagerrak Sea, have been examined. After systematic corrections, the inflow of Atlantic Water to the Norwegian Sea, via the two branches of the Norwegian Atlantic Current, is investigated. Distinct expressions of the eastern branch, the Norwegian Atlantic Slope Current, are revealed with a speed of 20-40 cm/s and a clear manifestation of topographic steering along the 500 m isobath. The western branch, the Norwegian Atlantic Front Current, is also depicted but with lower surface velocities. Moreover, parts of the Norwegian Coastal Current are also detected with...
Tipo: Text
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00056/16771/14216.pdf
Imagem não selecionada

Imprime registro no formato completo
Neural Network Based Kalman Filters for the Spatio-Temporal Interpolation of Satellite-Derived Sea Surface Temperature ArchiMer
Ouala, Said; Fablet, Ronan; Herzet, Cedric; Chapron, Bertrand; Pascual, Ananda; Collard, Fabrice; Gaultier, Lucile.
The forecasting and reconstruction of oceanic dynamics is a crucial challenge. While model driven strategies are still the state-of-the-art approaches in the reconstruction of spatio-temporal dynamics. The ever increasing availability of data collections in oceanography raised the relevance of data-driven approaches as computationally efficient representations of spatio-temporal fields reconstruction. This tools proved to outperform classical state-of-the-art interpolation techniques such as optimal interpolation and DINEOF in the retrievement of fine scale structures while still been computationally efficient comparing to model based data assimilation schemes. However, coupling this data-driven priors to classical filtering schemes limits their potential...
Tipo: Text Palavras-chave: Data assimilation; Dynamical model; Kalman filter; Neural networks; Data-driven models; Interpolation.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00481/59286/61979.pdf
Imagem não selecionada

Imprime registro no formato completo
Observation and parameterization of small icebergs: Drifting breakwaters in the southern ocean ArchiMer
Ardhuin, Fabrice; Tournadre, Jean; Queffeulou, Pierre; Ardhuin, Fanny; Collard, Fabrice.
The variability of small-size iceberg distributions is revealed from a novel analysis of satellite altimeter data. A strong annual cycle is modulated by pulse-like events confined to single ocean basins, with dense iceberg populations in the South Atlantic in 2004-2005, and in the South Pacific in 2008. Anomalies in sea surface temperatures of the order of 1 degrees C may be related to the iceberg distribution. Icebergs also appear very strongly associated with anomalies in the heights of ocean waves. A preliminary parameterization of wave blocking by icebergs significantly reduces wave model errors in the region south of 45 degrees South, and has a perceptible influence on all the west coasts of the Southern hemisphere. (C) 2011 Elsevier Ltd. All rights...
Tipo: Text
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00044/15535/13317.pdf
Imagem não selecionada

Imprime registro no formato completo
Observation of swell dissipation across oceans ArchiMer
Ardhuin, Fabrice; Chapron, Bertrand; Collard, Fabrice.
Global observations of ocean swell, from satellite Synthetic Aperture Radar data, are used to estimate the dissipation of swell energy for a number of storms. Swells can be very persistent with energy e-folding scales exceeding 20,000 km. For increasing swell steepness this scale shrinks systematically, down to 2800 km for the steepest observed swells, revealing a significant loss of swell energy. This value corresponds to a normalized energy decay in time beta = 4.2 x 10(-6) s(-1). Many processes may be responsible for this dissipation. The increase of dissipation rate in dissipation with swell steepness is interpreted as a laminar to turbulent transition of the boundary layer, with a threshold Reynolds number of the order of 100,000. These observations...
Tipo: Text
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6452.pdf
Imagem não selecionada

Imprime registro no formato completo
Observing Sea States ArchiMer
Ardhuin, Fabrice; Stopa, Justin; Chapron, Bertrand; Collard, Fabrice; Husson, Romain; Jensen, Robert E.; Johannessen, Johnny; Mouche, Alexis; Passaro, Marcello; Quartly, Graham D.; Swail, Val; Young, Ian.
Sea state information is needed for many applications, ranging from safety at sea and on the coast, for which real time data are essential, to planning and design needs for infrastructure that require long time series. The definition of the wave climate and its possible evolution requires high resolution data, and knowledge on possible drift in the observing system. Sea state is also an important climate variable that enters in air-sea fluxes parameterizations. Finally, sea state patterns can reveal the intensity of storms and associated climate patterns at large scales, and the intensity of currents at small scales. A synthesis of user requirements leads to requests for spatial resolution at kilometer scales, and estimations of trends of a few centimeters...
Tipo: Text Palavras-chave: Sea state; Waves; Altimeter; SAR; Swell; Remote sensing; Buoy; Microseisms.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00489/60090/63432.pdf
Imagem não selecionada

Imprime registro no formato completo
Ocean doppler anomaly and ocean surface current from Sentinel 1 tops mode ArchiMer
Johnsen, Harald; Nilsen, Vegard; Engen, Geir; Mouche, Alexis; Collard, Fabrice.
Processing and analysis of Doppler information from Sentinel 1A Interferometric Wide (IW) and Extra Wide (EW) modes are performed for assessing the capabilities of mapping ocean surface current field. Data from Agulhas (South-Africa) and Norwegian Coast are used in combination with numerical models, higher-order satellite products, and Lagrangian drifters. Results show strong Doppler signal and dynamics from coastal areas caused by a mixture of surface current and wind/wave induced drifts at a spatial resolution of around 2 km2 in IW mode and 4km2 in EW mode. Doppler values of up to 70 Hz are observed, corresponding to a surface drift velocity of 3.5 m/s. The Sentinel 1 retrieved surface current component is in reasonable agreement with the circulation...
Tipo: Text Palavras-chave: Doppler effect; Sea surface; Sea measurements; Ocean temperature; Surface treatment; Antennas.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00356/46713/46589.pdf
Imagem não selecionada

Imprime registro no formato completo
Ocean remote sensing data integration - examples and outlook ArchiMer
Chapron, Bertrand; Bingham, A; Collard, Fabrice; Donlon, Craig; Johannessen, Johnny A.; Piolle, Jean-francois; Reul, Nicolas.
Satellite remote sensing has emerged as an essential and necessary observing system to acquire global information about the state of the ocean. Complemented with in situ observing networks, the ultimate goals are to be able to make accurate estimates of selected key sets of geophysical variables, with the intention of either making operational predictions across time and spatial boundaries, or advancing fundamental knowledge through development of empirical relationships and theoretical models. For satellite oceanography, improvements are then constantly being sought in our understandings of the geophysical processes, the sensor physics, the electromagnetic and microwave properties and interactions at the complex air-sea interface. Challenges appear as...
Tipo: Text
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00029/14046/11241.pdf
Imagem não selecionada

Imprime registro no formato completo
On Dual Co-Polarized SAR Measurements of the Ocean Surface ArchiMer
Kudryavtsev, Vladimir N.; Chapron, Bertrand; Myasoedov, Alexander G.; Collard, Fabrice; Johannessen, Johnny A..
An effective methodology using satellite high-resolution polarized information to interpret and quantitatively assess various surface ocean phenomena is suggested. Using a sample RADARSAT-2 quad-polarization ocean synthetic aperture radar (SAR) scene, the dual co-polarization (VV and HH) radar data are combined into polarization difference, polarization ratio, and nonpolarized components. As demonstrated, these field quantities provide means to distinguish Bragg scattering mechanism and radar returns from breaking waves. As shown, quantitative characteristics of the surface manifestation of ocean currents, slicks, and wind field features in these dual co-polarization properties are very different and may be effectively used in the development of new SAR...
Tipo: Text Palavras-chave: Radar cross sections; Radar signal analysis; Synthetic aperture radar (SAR) imaging.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00149/26042/24890.pdf
Imagem não selecionada

Imprime registro no formato completo
On the Use of Doppler Shift for Sea Surface Wind Retrieval From SAR ArchiMer
Mouche, Alexis; Collard, Fabrice; Chapron, Bertrand; Dagestad, Knut-frode; Guitton, Gilles; Johannessen, Johnny A.; Kerbaol, Vincent; Hansen, Morten Wergeland.
The synthetic aperture radar (SAR) Doppler centroid has been used to estimate the scatter line-of-sight radar velocity. In weak to moderate ocean surface current environment, the SAR Doppler centroid is dominated by the directionality and strength of wave-induced ocean surface displacements. In this paper, we show how this sea state signature can be used to improve surface wind retrieval from SAR. Doppler shifts of C-band radar return signals from the ocean are thoroughly investigated by colocating wind measurements from the ASCAT scatterometer with Doppler centroid anomalies retrieved from Envisat ASAR. An empirical geophysical model function (CDOP) is derived, predicting Doppler shifts at both VV and HH polarization as function of wind speed, radar...
Tipo: Text Palavras-chave: Doppler; Surface wind; Synthetic aperture radar (SAR).
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00088/19896/17554.pdf
Imagem não selecionada

Imprime registro no formato completo
Phenomenal sea states and swell from a North Atlantic Storm in February 2011: a comprehensive analysis ArchiMer
Hanafin, Jennifer; Quilfen, Yves; Ardhuin, Fabrice; Sienkiewicz, Joseph; Queffeulou, Pierre; Obrebski, Mathias; Chapron, Bertrand; Reul, Nicolas; Collard, Fabrice; Corman, David; De Azevedo, Eduardo B.; Vandemark, Doug; Stutzmann, Eleonore.
Tipo: Text
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00094/20538/18197.pdf
Registros recuperados: 28
Primeira ... 12 ... Última
 

Empresa Brasileira de Pesquisa Agropecuária - Embrapa
Todos os direitos reservados, conforme Lei n° 9.610
Política de Privacidade
Área restrita

Embrapa
Parque Estação Biológica - PqEB s/n°
Brasília, DF - Brasil - CEP 70770-901
Fone: (61) 3448-4433 - Fax: (61) 3448-4890 / 3448-4891 SAC: https://www.embrapa.br/fale-conosco

Valid HTML 4.01 Transitional