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| Registros recuperados: 17 | |
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| Nouguier, Frederic; Mouche, Alexis; Rascle, Nicolas; Chapron, Bertrand; Vandemark, Douglas. |
| Global colocalized ocean surface measurements using the Global Precipitation Measurement near-nadir dual-frequency Ku- and Ka-band microwave measurements are analyzed and compared. Focusing on the Ka and Ku cross-sections fall-off with incidence angles, the contemporaneous measurements enable to more precisely document differing ocean scattering characteristics for both microwave frequencies. Sensitivity with wind speed and significant wave height is further reported using global comparisons with numerical estimates. As demonstrated, the bifrequency capability can provide direct means to efficiently separate short-scale wave contributions, between mean squared slope and curvature characteristics, and to further gain valuable insights concerning near-nadir... |
| Tipo: Text |
Palavras-chave: Microwave; Radar cross section; Scattering; Spaceborne radar. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00352/46334/47128.pdf |
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| Nouguier, Frederic; Guerin, Charles-antoine; Soriano, Gabriel. |
| This paper is the first in a series of two papers on the use of combined improved hydrodynamic and electromagnetic analytical models for the simulation of the ocean Doppler spectrum at microwave frequencies. Under a linear assumption for the sea surface, we derive statistical expression for the main Doppler characteristics according to asymptotic scattering models. We consider classical models such as the Kirchhoff approximation and the two-scale model, as well as the more recent weighted curvature approximation (WCA). We recover two salient features of Doppler signature in the microwave regime. First, the Doppler characteristics are very sensitive to polarization, with higher mean Doppler shift in horizontal polarization. This is correctly rendered by the... |
| Tipo: Text |
Palavras-chave: Doppler spectrum; Gravity waves; Microwave; Remote sensing; Rough surfaces; Scattering; Sea surface. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00054/16524/14379.pdf |
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| Nouguier, Frederic; Guerin, Charles-antoine; Chapron, Bertrand. |
| We investigate the statistical properties of a three-dimensional simple and versatile model for weakly nonlinear gravity waves in infinite depth, referred to as the "choppy wave model" (CWM). This model is analytically tractable, numerically efficient, and robust to the inclusion of high frequencies. It is based on horizontal rather than vertical local displacement of a linear surface and is a priori not restricted to large wavelengths. Under the assumption of space and time stationarity, we establish the complete first- and second-order statistical properties of surface random elevations and slopes for long-crested as well as fully two-dimensional surfaces, and we provide some characteristics of the surface variation rate and frequency spectrum. We... |
| Tipo: Text |
Palavras-chave: Sea surface statistics; Nonlinear gravity waves. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6832.pdf |
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| Rascle, Nicolas; Molemaker, Jeroen; Marie, Louis; Nouguier, Frederic; Chapron, Bertrand; Lund, Bjorn; Mouche, Alexis. |
| Fine scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the LASER (LAgrangian Submesoscale ExpeRiment) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature and sea surface roughness. A new observational method is applied, using sun glitter reflections during multiple airplane passes to reconstruct the multi-angle roughness anomaly. This multi-angle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and... |
| Tipo: Text |
Palavras-chave: Sea surface roughness; Surface current; Remote sensing; Sun glitter; High resolution; Oceanic fronts. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00386/49767/50301.pdf |
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| 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 |
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| Ano: 2018 |
URL: http://archimer.ifremer.fr/doc/00442/55318/56843.pdf |
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| Marié, Louis; Collard, Fabrice; Nouguier, Frederic; Pineau-guillou, Lucia; Hauser, Danièle; Boy, François; Méric, Stéphane; Sutherland, Peter; Peureux, Charles; Monnier, Goulven; Chapron, Bertrand; Martin, Adrien; Dubois, Pierre; Donlon, Craig; Casal, Tania; Ardhuin, Fabrice. |
| Surface currents are poorly known over most of the world's oceans. Satellite-borne Doppler wave and current scatterometers (DWaCSs) are among the proposed techniques to fill this observation gap. The Sea surface KInematics Multiscale (SKIM) proposal is the first satellite concept built on a DWaCS design at near-nadir angles and was demonstrated to be technically feasible as part of the European Space Agency Earth Explorer program. This article describes preliminary results from a field experiment performed in November 2018 off the French Atlantic coast, with sea states representative of the open ocean and a well-known tide-dominated current regime, as part of the detailed design and feasibility studies for SKIM. This experiment comprised airborne... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00658/77056/78354.pdf |
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| Rascle, Nicolas; Chapron, Bertrand; Molemaker, Jeroen; Nouguier, Frederic; Ocampo‐torres, Francisco J.; Osuna Cañedo, J. Pedro; Marié, Louis; Lund, Björn; Horstmann, Jochen. |
| Sea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10~km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite Synthetic Aperture Radar, satellite and airborne multi‐angle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple... |
| Tipo: Text |
Palavras-chave: Sea surface roughness; Submesoscale current; Fine-scale current; Synthetic aperture radar (SAR); Sunglint Sun glitter; Ocean front. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00636/74788/75035.pdf |
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| Said, Faozi; Johnsen, Harald; Nouguier, Frederic; Chapron, Bertrand; Engen, Geir. |
| The generalized curvature ocean surface scattering model [general curvature model (GCM)] is extended and revisited. Two key steps are addressed in this paper, namely, a necessary sea surface spectrum undressing procedure and the inclusion of a skewness phase-related component. Normalized radar cross-section (NRCS) simulations are generated at C-band for various wind conditions, polarizations, and incidence angles. Results are compared with CMOD5.n. Although the sea surface spectrum undressing procedure is a necessary step, the overall NRCS dynamic is notably affected only in low wind conditions (<= 5 m/s). The inclusion of the skewness phase-related component makes the most impact to the NRCS dynamic where the upwind/downwind asymmetry is clearly... |
| Tipo: Text |
Palavras-chave: Geophysical measurements; Radar cross section; Remote sensing; Sea surface; Surface waves. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00409/52013/52725.pdf |
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| Nouguier, Frederic; Chapron, Bertrand; Guerin, Charles-antoine. |
| We revisit and supplement the description of gravity waves based on perturbation expansions in Lagrangian coordinates. A general analytical framework is developed to derive a second-order Lagrangian solution to the motion of arbitrary surface gravity wave fields in a compact and vectorial form. The result is shown to be consistent with the classical second-order Eulerian expansion by Longuet-Higgins (J. Fluid Mech., vol. 17, 1963, pp. 459-480) and is used to improve the original derivation by Pierson (1961 Models of random seas based on the Lagrangian equations of motion. Tech. Rep. New York University) for long-crested waves. As demonstrated, the Lagrangian perturbation expansion captures nonlinearities to a higher degree than does the corresponding... |
| Tipo: Text |
Palavras-chave: Surface gravity waves; Waves/free-surface flows. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00274/38476/37042.pdf |
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| Ardhuin, Fabrice; Brandt, Peter; Gaultier, Lucile; Donlon, Craig; Battaglia, Alessandro; Boy, François; Casal, Tania; Chapron, Bertrand; Collard, Fabrice; Cravatte, Sophie; Delouis, Jean Marc; De Witte, Erik; Dibarboure, Gerald; Engen, Geir; Johnsen, Harald; Lique, Camille; Lopez-dekker, Paco; Maes, Christophe; Martin, Adrien; Marié, Louis; Menemenlis, Dimitris; Nouguier, Frederic; Peureux, Charles; Rampal, Pierre; Ressler, Gerhard; Rio, Marie-helene; Rommen, Bjorn; Shutler, Jamie D.; Suess, Martin; Tsamados, Michel; Ubelmann, Clement; Van Sebille, Erik; Van Den Oever, Martin; Stammer, Detlef. |
| The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the poorly known patterns of divergence and their impact on the ocean heat budget, and monitoring of the emerging Arctic up to 82.5°N. SKIM will also make unprecedented direct measurements of strong currents, from boundary currents to the Antarctic circumpolar current, and their interaction with ocean waves with expected impacts on air-sea fluxes and extreme waves. For the first time, SKIM will directly measure the ocean surface current vector from space. The main instrument on SKIM is a Ka-band conically scanning, multi-beam Doppler radar altimeter/wave scatterometer that includes a... |
| Tipo: Text |
Palavras-chave: Ocean current; Tropics; Arctic; Doppler; Altimetry; Sea state; Remote sensing; Ocean waves. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00498/60964/64372.pdf |
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| Misra, Ankita; Chapron, Bertrand; Nouguier, Frederic; Ramakrishnan, Balaji; Yurovskaya, Maria. |
| Local changes in specular reflections of visible sunlight on the ocean surfaces can be captured effectively by satellite sensors operating in the visible range of the electromagnetic spectrum. This causes the sun-glint imagery to closely resemble the oceanic images obtained using Synthetic Aperture Radar (SAR) further allowing the identification of the various fine scale structures and patterns of the ocean. Moreover, at relevant spatial resolutions, cloud-free conditions as well as optimum relative positions of the sensor, sun and the wave front it is possible to image ocean waves, wave transformations and refraction patterns using Satellite Sun-glint imagery (SSGI). In the present study, Landsat OLI imagery captured along the coast of Brest, France is... |
| Tipo: Text |
Palavras-chave: Sun-glint Imagery; Wave transformation; Landsat 8 OLI; Fast Fourier Transform(FFT); Cross-spectral analysis. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00476/58787/61791.pdf |
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| Rascle, Nicolas; Nouguier, Frederic; Chapron, Bertrand; Ocampo-torres, Francisco J.. |
| High-resolution satellite images of the ocean surface in and around the sunglint often provide unique observations of sub-mesoscale upper ocean surface processes. Local anomalies of wind, waves, currents or surfactants appear on the images as local anomalies of brightness. A quantitative interpretation of those brightness anomalies must relate them to slope properties of the wave field, which are to the lowest order described by the mean square slope (mss). The prevailing paradigm for such interpretation is that of the critical zenith angle. It states that, for sub-critical zenith view angle, brightness and mss anomalies have opposite signs, and this defines the so-called inversion region. This prevailing paradigm implicitly builds on the assumption that... |
| Tipo: Text |
Palavras-chave: Sea surface roughness; Surface current gradients; Submesoscale turbulence; Wave-current interaction; Surfactants; Sun glint imagery; SAR images; Multi-angle radiometers; Surface slope distribution; Mean square slope. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00448/55964/57498.pdf |
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| Rascle, Nicolas; Nouguier, Frederic; Chapron, Bertrand; Mouche, Alexis; Ponte, Aurelien. |
| At times, high resolution images of sea surface roughness can provide stunning details of submesoscale upper ocean dynamics. As interpreted, transformations of short scale wind waves by horizontal current gradients are responsible for those spectacular observations. Those observations could prove particularly useful to validate numerical ocean models which reach increasingly high resolutions. Focusing on surface roughness at optical wavelengths, two steps have recently been performed in that direction. First, it was shown by Rascle et al. (2014, Journal of Physical Oceanography) that surface roughness variations not only trace surface current divergence but also other characteristics of the current gradient tensor, mainly the strain in the wind direction.... |
| Tipo: Text |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00358/46878/46759.pdf |
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| Boisot, Olivier; Nouguier, Frederic; Chapron, Bertrand; Guerin, Charles-antoine. |
| We introduce a practical and accurate model, referred to as "GO4," to describe near-nadir microwave scattering from the sea surface, and at the same time, we address the issue of the filtered mean square slope (mss) conventionally used in the geometrical optics model. GO4 is a simple correction of this last model, taking into account the diffraction correction induced by the rough surface through what we call an effective mean square curvature (msc). We evaluate the effective msc as a function of the surface wavenumber spectrum and the radar frequency and show that GO4 reaches the same accuracy as the physical optics model in a wide range of incidence and frequency bands with the sole knowledge of the mss and msc parameters. The key point is that the mss... |
| Tipo: Text |
Palavras-chave: Curvature; Geometrical optics; Near-nadir; Ocean radar sensing; Slope. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00277/38789/37537.pdf |
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| Registros recuperados: 17 | |
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