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2D ocean waves spectra from space: a challenge for validation and synergetic use ArchiMer
Mouche, Alexis; He, W.; Husson, R.; Guitton, Gilles; Chapron, Bertrand; Li, Huimin.
Sentinel-1 A now routinely acquires data over the ocean since 2014. Data are processed by ESA through the Payload Data Ground Segment up to Level-2 for Copernicus users. Level-2 products consist of geo-located geophysical parameters related to wind, waves and ocean current. In particular, Sentinel-1A wave measurements provide 2D ocean swell spectra (2D wave energy distribution as a function of wavelength and direction) as well as integrated parameters such as significant wave height, dominant wavelength and direction for each partition. In 2016, Sentinel-1 B will be launched by ESA and GF-3 by CNSA. Then in 2018, CFOSAT (China France Oceanography Satellite project), a joint mission from the Chinese and French Space Agencies, will be launched. They will...
Tipo: Text Palavras-chave: Ocean remote sensing; Synthetics aperture radar; Ocean wave-spectrometer; 2D ocean wave spectrum; Level-4.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00364/47469/47488.pdf
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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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A labelled ocean SAR imagery dataset of ten geophysical phenomena from Sentinel‐1 wave mode ArchiMer
Wang, Chen; Mouche, Alexis; Tandeo, Pierre; Stopa, Justin; Longépé, Nicolas; Erhard, Guillaume; Foster, Ralph C.; Vandemark, Douglas; Chapron, Bertrand.
The Sentinel‐1 mission is part of the European Copernicus program aiming at providing observations for Land, Marine and Atmosphere Monitoring, Emergency Management, Security and Climate Change. It is a constellation of two (Sentinel‐1 A and B) Synthetic Aperture Radar (SAR) satellites. The SAR wave mode (WV) routinely collects high‐resolution SAR images of the ocean surface during day and night and through clouds. In this study, a subset of more than 37,000 SAR images is labelled corresponding to ten geophysical phenomena, including both oceanic and meteorologic features. These images cover the entire open ocean and are manually selected from Sentinel‐1A WV acquisitions in 2016. For each image, only one prevalent geophysical phenomenon with its prescribed...
Tipo: Text Palavras-chave: Manual labelling; Ocean surface phenomena; Sentinel-1 wave mode; Synthetic aperture radar.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00512/62406/66659.pdf
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A model of sea-foam thickness distribution for passive microwave remote sensing applications ArchiMer
Reul, Nicolas; Chapron, Bertrand.
[1] Foam formations at the sea surface significantly contribute to microwave brightness temperature signatures over the ocean for moderate to high wind speeds. The thickness of foam layers generated by breaking waves follows a specific distribution due to unsteadiness of breaking and the large range of wave scales involved in the phenomenon. Although the effect of a distributed thickness-parameter on the foam-induced microwave brightness temperature may be comparable to or larger than the fractional whitecap coverage, it is not yet included in brightness models. To fill this gap, we develop a dynamical model for the conditional fraction of sea-surface covered by whitecaps with given thickness, as a function of wind speed. It is an integrated function of...
Tipo: Text Palavras-chave: Sea foam; Breaking waves; Thickness; Fractional coverage; Microwave brightness temperature.
Ano: 2003 URL: http://archimer.ifremer.fr/doc/00000/10693/9320.pdf
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A new generation of Tropical Cyclone Size measurements from space ArchiMer
Reul, Nicolas; Chapron, Bertrand; Zabolotskikh, E.; Donlon, C.; Mouche, Alexis; Tenerelli, Joseph; Collard, F.; Piolle, Jean-francois; Fore, A.; Yueh, S.; Cotton, J.; Francis, P.; Quilfen, Yves; Kudryavtsev, V..
Combined microwave brightness temperature measurements from recent L- and dual C-band satellite radiometers provide new estimates of surface wind speed structure in Tropical Cyclones which enhances temporal sampling capability for gale (34-knots), damaging (50-knots) and destructive (64-knots) wind radii. Wind radii estimates in Tropical Cyclones (TC) are crucial to help determine the TC wind structure for the production of effective warnings and to constrain initial conditions for a number of applications. In that context, we report on the capabilities of a new generation of satellite microwave radiometers operating at L-band frequency (~1.4 GHz) and dual C-band (~6.9 and 7.3 GHz). These radiometers provide wide swath (> 1000 km) coverage at a spatial...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00376/48758/49151.pdf
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A new ocean SAR cross-spectral parameter: definition and directional property using the global Sentinel-1 measurements ArchiMer
Li, Huimin; Chapron, Bertrand; Mouche, Alexis; Stopa, Justin.
Space‐borne synthetic aperture radar (SAR) measurements have already been proven to be invaluable in detecting and quantifying properties of ocean swell systems. With the improved spatial resolution, Sentinel‐1 wave mode measurements can further be extended towards shorter scale waves, i.e. within the surface wave equilibrium range. In this study, a new parameter is derived from filtering SAR image cross‐spectra around range‐traveling intermediate wind waves (wavelengths 15‐20 m). This parameter captures both the radar cross section variability and its time evolution. Given the dependence of intermediate waves on local wind field, this parameter is statistically documented to confirm its sensitivity to both wind speed and wind direction. Comparable to...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00482/59394/62160.pdf
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A note on the direct injection of turbulence by breaking waves ArchiMer
Rascle, Nicolas; Chapron, Bertrand; Ardhuin, Fabrice; Soloviev, Alexander.
We investigate the turbulence induced by wave-breaking at the ocean surface. Two recent models use a mechanism of direct depth injection of turbulent kinetic energy (TKE) by breaking waves. Those models aim to reproduce the near-surface mean and turbulent properties, in particular the TKE dissipation rates. Of critical importance are the injection depth of each breaking wave and the size distribution of those breaking waves. The models by Sullivan et al. (2007) and by Kudryavtsev et al. (2008) have very different parameterizations, and those differences are reviewed here and compared to available observations. Using realistic parameterizations in these models leads to TKE injections too shallow to compare to observations, in particular for developed seas....
Tipo: Text Palavras-chave: Surface waves; Wave breaking; Wave-induced turbulence; Vertical mixing; Mixed layer; Ekman currents.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00155/26581/25476.pdf
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A revised L-band radio-brightness sensitivity to extreme winds under tropical cyclones: The 5 year SMOS-Storm database ArchiMer
Reul, Nicolas; Chapron, Bertrand; Zabolotskikh, E.; Donlon, C.; Quilfen, Yves; Guimbard, Sebastien; Piolle, Jean-francois.
Five years of SMOS L-band brightness temperature data intercepting a large number of tropical cyclones (TCs) are analyzed. The storm-induced half-power radio-brightness contrast (ΔI) is defined as the difference between the brightness observed at a specific wind force and that for a smooth water surface with the same physical parameters. ΔI can be related to surface wind speed and has been estimated for ~ 300 TCs that intercept with SMOS measurements. ΔI, expressed in a common storm-centric coordinate system, shows that mean brightness contrast monotonically increases with increased storm intensity ranging from ~ 5 K for strong storms to ~ 24 K for the most intense Category 5 TCs. A remarkable feature of the 2D mean ΔI fields and their variability is that...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00324/43542/43178.pdf
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A satellite altimeter model for ocean slick detection - art. no. C04004 ArchiMer
Tournadre, Jean; Chapron, Bertrand; Reul, Nicolas; Vandemark, D.
[1] About 5% of Ku-band altimeter ocean data are degraded by the occurrence of high radar return cross sections (sigma(0)), usually called sigma(0) blooms. During blooms, which occur during no or low wind conditions, the mean altimeter waveform can significantly depart from the expected shape. In about 60% of the cases the waveforms are distorted to such an extent that either the range tracker loses lock or the off-nadir angle estimate becomes unrealistic. The analysis of high data rate altimeter waveforms during bloom events reveals the presence of V-shaped patterns similar to the ones observed during rain events. These patterns trace small-scale (i.e., smaller than the altimeter footprint) changes in surface backscatter. Such variations of surface...
Tipo: Text Palavras-chave: Slick; Sigma blooms; Altimeter waveforms.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1353.pdf
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A semiempirical model of the normalized radar cross section of the sea surface, 2. Radar modulation transfer function ArchiMer
Kudryavtsev, V; Hauser, D; Caudal, G; Chapron, Bertrand.
normalized radar cross section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations. In particular, even if they may provide consistent results for vertical transmit and receive (VV) polarization, they fail in horizontal transmit and receive (HH) polarization. In addition, there are still important discrepancies between model and observations of the radar modulation transfer function (MTF), which relates the modulations of the NRCS to the long waves. In this context, we have developed a physical model that takes into account not only the Bragg mechanism but also the non-Bragg scattering associated with radio wave scattering from breaking waves. The same model was built to explain both the...
Tipo: Text Palavras-chave: Radar cross section; Ocean surface; Surface gravity waves; Wave breaking; Modulation transfer function; Non Bragg scattering.
Ano: 2003 URL: http://archimer.ifremer.fr/doc/00000/10183/9581.pdf
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A semiempirical model of the normalized radar cross-section of the sea surface - 1. Background model ArchiMer
Kudryavtsev, V; Hauser, D; Caudal, G; Chapron, Bertrand.
Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross-section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations and wind wave conditions. We have developed a physical model that takes into account, not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking. A single model was built to explain on the same physical basis both the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization. The NRCS is assumed to be the sum of a Bragg part (two-scale model) and of a non-Bragg part. The description of the sea surface is based on the short wind...
Tipo: Text Palavras-chave: Ocean surface waves; Radar cross section; Short wind waves; Wave breaking; Bragg scattering; Non Bragg scattering.
Ano: 2003 URL: https://archimer.ifremer.fr/doc/00000/10182/9580.pdf
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A simplified asymptotic theory for ocean surface electromagnetic wave scattering ArchiMer
Mouche, Alexis; Chapron, Bertrand; Reul, Nicolas.
The normalized radar cross-section ( NRCS) expression of the Local Curvature Approximation (LCA-1) is derived to first order. The polarization sensitivity of this model is compared to the Kirchhoff Approximation ( KA), Two-Scale Model (TSM), Small Slope Approximation (SSA-1) and Small Perturbation Method (SPM-1) to first order in the backscattering configuration. Analytical comparisons and numerical simulations show that LCA-1 and TSM could be rewritten with the same formulation and that their polarization sensitivities are comparable. Comparisons with experimental data acquired in C- and Ku-band reveal that the polarization sensitivities of these models are not adequate. However, the NRCS azimuth modulation predicted by LCA-1 is found to be dependent on...
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-3001.pdf
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A simplified wave enhancement criterion for moving extreme events ArchiMer
Kudryavtsev, Vladimir; Golubkin, Pavel; Chapron, Bertrand.
An analytical model is derived to efficiently describe the wave energy distribution along the main transects of a moving extreme weather event. The model essentially builds on a generalization of the self-similar wave growth model and the assumption of a strongly dominant single spectral mode in a given quadrant of the storm. The criterion to anticipate wave enhancement with the generation of trapped abnormal waves defined as inline image, with inline image, inline image, and inline image, radial distance, average sustained wind speed, and translation velocity, respectively. Constants inline image and inline image follow the fetch-law definitions. If forced during a sufficient time scale interval, also defined from this generalized self-similar wave growth...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00295/40644/39603.pdf
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A time-frequency application with the Stokes-Woodward technique ArchiMer
Elfouhaily, Tanos; Guignard, S; Branger, H; Thompson, D; Chapron, Bertrand; Vandemark, D.
In a recent paper, we have generalized Woodward's theorem and applied it to the case of random signals jointly modulated in amplitude and frequency. This generalization yields a new spectral technique to estimate the amount of energy due to mode coupling without calling for higher order statistics. Two power spectra are detected; the first is related to the independent modes, and the second contains extra energy caused by mode coupling. This detection is now extended from frequency to time-frequency domain. A comparison between a wavelet transform and our time-frequency technique shows good agreement along with new insight into the time occurrence of the nonlinearities or mode coupling. An application to water surface waves is given in this letter as an...
Tipo: Text Palavras-chave: Wind waves; Wave wave interaction; Vertical asymmetry; Time frequency distributions; Nonlinear hydrodynamic processes; Mode coupling; Instantaneous frequency; Instantaneous amplitude; Horizontal asymmetry; AM FM; Amplitude modulation frequency modulation.
Ano: 2003 URL: https://archimer.ifremer.fr/doc/2003/publication-744.pdf
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A unified directional spectrum for long and short wind-driven waves ArchiMer
Elfouhaily, Tanos; Chapron, Bertrand; Katsaros, Kristina; Vandemark, D.
Review of several recent ocean surface wave models finds that while comprehensive in many regards, these spectral models do not satisfy certain additional, but fundamental, criteria. We propose that these criteria include the ability to properly describe diverse fetch conditions and to provide agreement with in situ observations of Cox and Munk [1954] and Jahne and Riemer [1990] and Hara et al. [1994] data in the high-wavenumber regime. Moreover, we find numerous analytically undesirable aspects such as discontinuities across wavenumber limits, nonphysical tuning or adjustment parameters, and noncentrosymmetric directional spreading functions. This paper describes a two-dimensional wavenumber spectrum valid over all wavenumbers and analytically amenable to...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00091/20226/17877.pdf
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Altimeter dual-frequency observations of surface winds, waves, and rain rate in tropical cyclone Isabel - art. no. C01004, ArchiMer
Quilfen, Yves; Tournadre, Jean; Chapron, Bertrand.
[1] Extreme weather events such as tropical cyclones are difficult to observe with conventional means. Satellite-based observations provide essential measurements of key parameters governing tropical cyclones. They are critical for short-term forecasting. Radiometers onboard the Defense Meteorological Satellite Program satellite series, WindSat and Tropical Rainfall Measuring Mission satellites, scatterometers onboard the ERS, ADEOS, and QuikScat satellites offer unprecedented synoptic observations of surface wind and atmospheric liquid water content, revealing the storm structures with good accuracy. However, satellite estimates do not provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors...
Tipo: Text Palavras-chave: Mesearement limitations; Dual frequency altimeter; High resolution measurement; Tropical cyclone.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1033.pdf
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Altimeter estimation of sea surface wind stress for light to moderate winds ArchiMer
Vandemark, Douglas; Edson, James B; Chapron, Bertrand.
Aircraft altimeter and in situ measurements are used to examine relationships between altimeter backscatter and the magnitude of near-surface wind and friction velocities. Comparison of altimeter radar cross section with wind speed is made through the modified Chelton-Wentz algorithm. Improved agreement is found after correcting 10-m winds for both surface current and atmospheric stability. An altimeter friction velocity algorithm is derived based on the wind speed model and an open-ocean drag coefficient. Close agreement between altimeter- and in situ-derived friction velocities is found. For this dataset, quality of the altimeter inversion to surface friction velocity is comparable to that for adjusted winds and clearly better than the inversion to true...
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Ano: 1997 URL: http://archimer.ifremer.fr/doc/00336/44711/44902.pdf
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Altimeter sea state bias: A new look at global range error estimates ArchiMer
Chapron, Bertrand; Vandemark, D; Elfouhaily, T; Thompson, Dr; Gaspar, P; Labroue, S.
A nonparametric SSB model, derived using the TOPEX altimeter, is analyzed to show a new decomposition of the form SSB = bH(s) + f(sigma (o)), where b is 0.03 and the function of radar cross section (sigma (o)) is an absolute second-order range correction residing outside the conventional nondimensional SSB model. Expected variability in the dominant bH(s) term and its ties to the long wave orbital velocity and shorter-scale slope variances are discussed using a physic ally-motivated restatement of recent EM bias theory. The geometry of steep near-breaking waves, neglected within current theory, is invoked as one plausible explanation for the observed H-s-independent SSB component.
Tipo: Text
Ano: 2001 URL: https://archimer.ifremer.fr/doc/00000/10275/10691.pdf
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An Ocean Wind Doppler Model Based on the Generalized Curvature Ocean Surface Scattering Model ArchiMer
Said, Faozi; Johnsen, Harald; Chapron, Bertrand; Engen, Geir.
A Doppler centroid D-C model based on the generalized curvature ocean surface scattering model (generalized curvature model or GCM) is presented. Two key features are included in this model: a skewness-related phase coefficient based on empirical skewness coefficients of sea-surface-slope probability density function (pdf) for wind speed less than 10 m/s and effects from wave breaking for wind speed greater than 10 m/s. Simulated D-c values are exclusively compared with the empirical geophysical Doppler model function named CDOP, for hh and vv polarizations, various wind conditions, and incidence angles. Good agreement is found overall between CDOP and simulated D-C values. The overall bias for simulated Dc-vv with and without skewness are 2.63 versus...
Tipo: Text Palavras-chave: Doppler measurements; Geophysical measurement techniques; Sea surface; Synthetic aperture radar (SAR).
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00283/39411/39116.pdf
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An Updated Geophysical Model for AMSR-E and SSMIS Brightness Temperature Simulations over Oceans ArchiMer
Zabolotskikh, Elizaveta; Mitnik, Leonid; Chapron, Bertrand.
In this study, we considered the geophysical model for microwave brightness temperature (BT) simulation for the Atmosphere-Ocean System under non-precipitating conditions. The model is presented as a combination of atmospheric absorption and ocean emission models. We validated this model for two satellite instruments-for Advanced Microwave Sounding Radiometer-Earth Observing System (AMSR-E) onboard Aqua satellite and for Special Sensor Microwave Imager/Sounder (SSMIS) onboard F16 satellite of Defense Meteorological Satellite Program (DMSP) series. We compared simulated BT values with satellite BT measurements for different combinations of various water vapor and oxygen absorption models and wind induced ocean emission models. A dataset of clear sky...
Tipo: Text Palavras-chave: Calibration; Geophysical model; Numerical simulation; SSMIS; AMSR-E; Satellite passive microwave.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00190/30101/28628.pdf
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