|
|
|
| Registros recuperados: 211 | |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00376/48758/49151.pdf |
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00482/59394/62160.pdf |
| |
|
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00324/43542/43178.pdf |
| |
|
|
| 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 |
| |
|
|
| 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 |
| |
|
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-3001.pdf |
| |
|
|
| Kudryavtsev, Vladimir; Monzikova, Anna; Combot, Clement; Chapron, Bertrand; Reul, Nicolas; Quilfen, Yves. |
| Changes of sea surface temperature (SST) and height (SSH) derived from 20‐days passive microwave and altimeter measurements for three tropical cyclones (TCs), Jimena, Ignacio and Kilo, during the 2015 Pacific hurricane season, sampling different stages of intensification, wind speeds, radii, Coriolis parameter, translation velocities, and ocean stratification conditions, are reported and analyzed. As triggered along the path of moving TCs, very large interior ocean displacements can occur to leave prominent SSH anomalies in the TC wake. Resulting surface depressions can reach.3‐.5 m, depending upon size, translation speed, and ocean stratification conditions. These signatures can be quite persistent, i.e. more than few weeks, to possibly be intercepted... |
| Tipo: Text |
Palavras-chave: Tropical cyclones; Surface temperature anomalies; Surface height anomalies. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00491/60252/63653.pdf |
| |
|
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00295/40644/39603.pdf |
| |
|
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00091/20226/17877.pdf |
| |
|
| |
|
|
| 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 |
| |
|
|
| 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... |
| Tipo: Text |
|
| Ano: 1997 |
URL: http://archimer.ifremer.fr/doc/00336/44711/44902.pdf |
| |
| Registros recuperados: 211 | |
|
|
|
