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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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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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Combined wind vector and sea state impact on ocean nadir-viewing Ku- and C-band radar cross-sections ArchiMer
Tran, Ngan; Chapron, Bertrand.
The authors report the first results in studying the polarization anisotropy of the microwave backscatter from nadir observations provided by Jason-1 altimeter in both Ku- and C-band. A small but clear wind direction signal for wind speeds above 6 m/s is revealed. These azimuthal variations of radar cross-section increase with increasing wind speed up to 14 m/s. The signatures then level off at higher winds. These results extend, for the first time, recent theoretical improved scattering approximation, and point some similarities between scattering and emission mechanisms at nadir. The observed directional effect can thus be interpreted as a signature of the curvature anisotropy of wind-generated short-scale waves. Sensitivities to both wind speed and sea...
Tipo: Text Palavras-chave: Altimeter; Radar cross section; Polarization; Wind direction; Sea state.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/00004/11557/8150.pdf
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Effect of long waves on Ku-band ocean radar backscatter at low incidence angles using TRMM and altimeter data ArchiMer
Tran, Ngan; Chapron, Bertrand; Vandemark, D.
This letter uses a large ocean satellite data set to document relationships between Ku-band radar backscatter (sigma-0) of the sea surface, near-surface wind speed (U), and ocean wave height (SWH). The observations come from satellite crossovers of the Tropical Rainfall Mapping Mission (TRMM) Precipitation Radar (PR) and two satellite altimeters, namely: 1) Jason-1 and 2) ENVISAT. At these nodes, we obtain TRMM clear-air normalized radar cross-section data along with coincident altimeter-derived significant wave height. Wind speed estimates come from the European Centre for Medium-Range Weather Forecast. TRMM PR is the first satellite to measure low incidence Ku-band ocean backscatter at a continuum of incidence angles from 0 degrees to 18 degrees. This...
Tipo: Text Palavras-chave: Space borne radar; Scattering; Radar cross section; Altimetry.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-3299.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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Radar scattering of the ocean surface and sea-roughness properties: A combined analysis from dual-polarizations airborne radar observations and models in C band ArchiMer
Mouche, Alexis; Hauser, D; Kudryavtsev, V.
[1] An analysis of radar observations in C band combined with models is proposed to study some of the ocean surface properties and their relation with the sea surface backscatter. The electromagnetic part of the models is of different kinds: composite Bragg model with or without including effect of wave breaking zones on the normalized radar cross-section (NRCS), geometrical optics approximation and small-slope approximation model. The surface description is based on the wave spectrum proposed by Kudryavtsev et al. (2003), but tests with the spectrum of Elfouhaily et al. (1997) are also discussed to assess our conclusions. The originality is to use not only the NRCS in HH and VV polarizations, but also their difference in linear units. First, we show that...
Tipo: Text Palavras-chave: Wave breaking; Sea surface anisotropy; Radar cross section.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1877.pdf
Registros recuperados: 7
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