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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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| Bringer, Alexandra; Chapron, Bertrand; Mouche, Alexis; Guerin, Charles-antoine. |
| Existing models for the short-wave spectrum of the sea surface are not consistent with microwave satellite data when multi-bands and multi-incidence data sets are considered. We devise a simple parametric model for the short-wave omnidirectional spectrum of the sea surface on the basis of a three-band (C, Ku, and Ka) and multi-incidence (low, moderate, and large) data set and an improved analytical scattering model, namely the non-Gaussian Weighted Curvature Approximation. This spectrum is also constrained by several optical measurements which provide a priori conditions on the total and filtered mean-square slopes. It is compared with classical models such as Elfouhaily and Kudryavtsev unified curvature spectra. Significant differences are observed at... |
| Tipo: Text |
Palavras-chave: Microwave ocean remote sensing; Omnidirectional spectrum. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00174/28562/28378.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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| 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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| Guerin, Charles-antoine; Soriano, Gabriel; Chapron, Bertrand. |
| A family of unified models in scattering from rough surfaces is based on local corrections of the tangent plane approximation through higher-order derivatives of the surface. We revisit these methods in a common framework when the correction is limited to the curvature, that is essentially the second-order derivative. The resulting expression is formally identical to the weighted curvature approximation, with several admissible kernels, however. For sea surfaces under the Gaussian assumption, we show that the weighted curvature approximation reduces to a universal and simple expression for the off-specular normalized radar cross-section ( NRCS), regardless of the chosen kernel. The formula involves merely the sum of the NRCS in the classical Kirchhoff... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00018/12967/10148.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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