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Analysis of Dual-Frequency Ocean Backscatter Measurements at Ku- and Ka-Bands Using Near-Nadir Incidence GPM Radar Data ArchiMer
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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Analytical Techniques for the Doppler Signature of Sea Surfaces in the Microwave Regime-I: Linear Surfaces ArchiMer
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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Analytical Techniques for the Doppler Signature of Sea Surfaces in the Microwave Regime-II: Nonlinear Surfaces ArchiMer
Nouguier, Frederic; Guerin, Charles-antoine; Soriano, Gabriel.
This paper extends the results of a previous work by combining hydrodynamic and electromagnetic analytical models for the simulation of the ocean Doppler spectrum at microwave frequencies. We consider weakly nonlinear sea surfaces after the choppy wave model and incorporate them in classical and unified scattering models, namely, the Kirchhoff and weighted curvature approximations. We show that statistical expressions can be obtained for the Doppler spectrum in a way similar to the case of linear surfaces. As expected, the nonlinear nature of the sea surface dramatically impacts the Doppler spectrum at moderate to large incidence angles, with a shift of the central frequency and a broadening of the spectrum. Monte Carlo comparisons are performed with the...
Tipo: Text Palavras-chave: Doppler spectrum; Microwave; Nonlinear gravity waves; Remote sensing; Rough surfaces; Scattering; Sea surface.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00054/16555/14380.pdf
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"Choppy wave" model for nonlinear gravity waves ArchiMer
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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Eddy-Current Modeling of a Continous Conductivity Profile Resulting From a Diffusion Process ArchiMer
Lambert, Marc; Nouguier, Frederic; Zorgati, Riadh.
This paper deals with the modelization of eddy-current measurements over combustion turbine blade coatings affected by depletion of aluminum. First, we model the response of an eddy-current coil over a layered metallic structure with a top over-aluminized coating by extending the analytical Uzal-Rose's model for one hyperbolic tangent conductivity profile to a conductivity profile using two hyperbolic tangents for taking inward and outward depletion of aluminum inside the coating into account. Results obtained with this model are similar to those obtained with a numerical multilayer model but with a reduced computing time.
Tipo: Text Palavras-chave: Coils; Eddy current testing; Electrical conductivity measurement; Inverse problems; Probes.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00043/15424/12976.pdf
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Intense deformation field at oceanic front inferred from directional sea surface roughness observations ArchiMer
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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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
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Onto a Skewness Approach to the Generalized Curvature Ocean Surface Scattering Model ArchiMer
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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Scattering From Nonlinear Gravity Waves: The "Choppy Wave" Model ArchiMer
Nouguier, Frederic; Guerin, Charles-antoine; Chapron, Bertrand.
To progress in the understanding of the impact of nonlinear wave profiles in scattering from sea surfaces, a nonlinear model for infinite-depth gravity waves is considered. This model, termed as the "Choppy Wave" Model (CWM), is based on horizontal deformation of a linear reference random surface. It is numerically efficient and enjoys explicit second-order statistics for height and slope, which makes it well adapted to a large family of scattering models. We incorporate the CWM into a Kirchhoff or small-slope approximation and derive statistical expressions for the corresponding incoherent cross section. We insist on the importance of "undressing" the wavenumber spectrum to generate a nonlinear surface with a prescribed spectrum. Interestingly, the...
Tipo: Text Palavras-chave: Nonlinear gravity waves; Remote sensing; Rough surfaces; Scattering; Sea clutter; Undressed spectrum.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00018/12974/10175.pdf
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Second-order Lagrangian description of tri-dimensional gravity wave interactions ArchiMer
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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SKIM, a Candidate Satellite Mission Exploring Global Ocean Currents and Waves ArchiMer
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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Sun glint Imagery of Landsat 8 for ocean surface waves ArchiMer
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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Sunglint images of current gradients at high resolution: Critical angle and directional observing strategy ArchiMer
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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Surface roughness changes by fine scale current gradients: Properties at multiple azimuth view angles ArchiMer
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
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00358/46878/46759.pdf
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The GO4 Model in Near-Nadir Microwave Scattering From the Sea Surface ArchiMer
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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