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Registros recuperados: 7
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A C-Band Geophysical Model Function for Determining Coastal Wind Speed Using Synthetic Aperture Radar ArchiMer
Lu, Yiru; Zhang, Biao; Perrie, William; Mouche, Alexis; Li, Xiaofeng; Wang, He.
A new geophysical model function (GMF), called C_SARMOD2, has been developed to relate high-resolution C-band normalized radar cross section (NRCS), acquired in VV polarization over the ocean, to the 10-m height wind speed. A total of 3078 RADARSAT-2 and Sentinel-1A VV-polarized synthetic aperture radar (SAR) images, acquired under different wind speed conditions, were collocated with in situ buoy measurements. The paired dataset was used to derive transfer functions and coefficients of C_SARMOD2, and then to validate the wind speed retrievals. The comparison between SAR-retrieved wind speeds and buoy measurements show almost no bias and a root mean square error of 1.84 m/s. Two representative quad-and dual-polarization SAR images, acquired from coastal...
Tipo: Text Palavras-chave: Coastal wind speed; Geophysical model function (GMF); Synthetic aperture radar (SAR).
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00452/56390/60555.pdf
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An Ocean Wind Doppler Model Based on the Generalized Curvature Ocean Surface Scattering Model ArchiMer
Said, Faozi; Johnsen, Harald; Chapron, Bertrand; Engen, Geir.
A Doppler centroid D-C model based on the generalized curvature ocean surface scattering model (generalized curvature model or GCM) is presented. Two key features are included in this model: a skewness-related phase coefficient based on empirical skewness coefficients of sea-surface-slope probability density function (pdf) for wind speed less than 10 m/s and effects from wave breaking for wind speed greater than 10 m/s. Simulated D-c values are exclusively compared with the empirical geophysical Doppler model function named CDOP, for hh and vv polarizations, various wind conditions, and incidence angles. Good agreement is found overall between CDOP and simulated D-C values. The overall bias for simulated Dc-vv with and without skewness are 2.63 versus...
Tipo: Text Palavras-chave: Doppler measurements; Geophysical measurement techniques; Sea surface; Synthetic aperture radar (SAR).
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00283/39411/39116.pdf
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Estimation of Wind Direction in Tropical Cyclones Using C-Band Dual-Polarization Synthetic Aperture Radar ArchiMer
Fan, Shengren; Zhang, Biao; Mouche, Alexis; Perrie, William; Zhang, Jun A.; Zhang, Guosheng.
Under extreme weather conditions, the imprints of kilometer-scale marine atmospheric boundary layer roll vortices on the ocean surface are clearly visible in synthetic aperture radar (SAR) images of storms. Therefore, information about wind direction in storms can be obtained by analyzing SAR image features caused by boundary layer rolls. VH-polarized SAR imagery captures the structural features of storms well and shows prominent image gradients along the radial directions of the storm. The signal-to-noise ratios of VH-polarized images are small in low wind speed areas, but they are large in the same regions of VV-polarized images. Also, the capability of retrieving the atmospheric rolls orientation in VV-polarization is found to be sensitive to incidence...
Tipo: Text Palavras-chave: Synthetic aperture radar; Radar polarimetry; Wind speed; Atmospheric modeling; Spaceborne radar; Radar measurements; Synthetic aperture radar (SAR); Tropical cyclone (TC); Wind direction.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00609/72143/70953.pdf
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Fuzzy Logic Applied to Track Generation Areas of Swell Systems Observed by SAR ArchiMer
De Farias, Eduardo G. G.; Lorenzzetti, Joao A.; Bentamy, Abderrahim; Chapron, Bertrand; Romain, Husson.
Recently, with the availability of a great number of synthetic aperture radar (SAR) wave mode spectra, it has been possible to derive a set of great circle lines of swell propagation whose intersection points indicate the position of the storm generating the observed swell field. However, due to the inherent limitations of SAR spectra, the locus of convergence of great circle of swell propagation can be sometimes diffuse or contain multiple convergence regions. In this letter, we adapted the fuzzy cluster logic method to identify the regions of convergence of SAR wave field rays. The analysis of the results of the fuzzy algorithm clearly indicates the ability of this statistical method to identify the cluster center region of swell fields observed in SAR...
Tipo: Text Palavras-chave: Swell wave fields and fuzzy logic; Synthetic aperture radar (SAR).
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00109/21992/20637.pdf
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GF-3 SAR Ocean Wind Retrieval: The First View and Preliminary Assessment ArchiMer
Wang, He; Yang, Jingsong; Mouche, Alexis; Shao, Weizeng; Zhu, Jianhua; Ren, Lin; Xie, Chunhua.
Gaofen-3 (GF-3) is the first Chinese civil C-band synthetic aperture radar (SAR) launched on 10 August 2016 by the China Academy of Space Technology (CAST), which operates in 12 imaging modes with a fine spatial resolution up to 1 m. As one of the primary users, the State Oceanic Administration (SOA) operationally processes GF-3 SAR Level-1 products into ocean surface wind vector and plans to officially release the near real-time SAR wind products in the near future. In this paper, the methodology of wind retrieval at C-band SAR is introduced and the first results of GF-3 SAR-derived winds are presented. In particular, the case of the coastal katabatic wind off the west coast of the U.S. captured by GF-3 is discussed. The preliminary accuracy assessment of...
Tipo: Text Palavras-chave: GF-3; Synthetic aperture radar (SAR); Ocean surface wind; Validation.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00396/50731/51435.pdf
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On the Use of Doppler Shift for Sea Surface Wind Retrieval From SAR ArchiMer
Mouche, Alexis; Collard, Fabrice; Chapron, Bertrand; Dagestad, Knut-frode; Guitton, Gilles; Johannessen, Johnny A.; Kerbaol, Vincent; Hansen, Morten Wergeland.
The synthetic aperture radar (SAR) Doppler centroid has been used to estimate the scatter line-of-sight radar velocity. In weak to moderate ocean surface current environment, the SAR Doppler centroid is dominated by the directionality and strength of wave-induced ocean surface displacements. In this paper, we show how this sea state signature can be used to improve surface wind retrieval from SAR. Doppler shifts of C-band radar return signals from the ocean are thoroughly investigated by colocating wind measurements from the ASCAT scatterometer with Doppler centroid anomalies retrieved from Envisat ASAR. An empirical geophysical model function (CDOP) is derived, predicting Doppler shifts at both VV and HH polarization as function of wind speed, radar...
Tipo: Text Palavras-chave: Doppler; Surface wind; Synthetic aperture radar (SAR).
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00088/19896/17554.pdf
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Validation of Sea Surface Wind From Sentinel-1A/B SAR Data in the Coastal Regions of the Korean Peninsula ArchiMer
Jang, Jae-cheol; Park, Kyung-ae; Mouche, Alexis; Chapron, Bertrand; Lee, Ji-hyun.
In this study, using in situ measurements at 17 buoy stations off the Korean Peninsula, C-band model (CMOD) functions for Sentinel-1A/B IW mode synthetic aperture radar (SAR) data were validated. In total, 395 Sentinel-1A/B IW mode dual-vertical polarized images were used for collocation with in situ measurements from May 1, 2015, to September 30, 2017, and 807 matchup points were obtained. Prior to the validation, preprocessing such as speckle noise reduction and ship and land masking was completed. The in situ wind speeds were converted to a 10-m neutral wind considering atmospheric stability. High-resolution wind speeds were estimated by using the CMOD functions such as CMOD4, CMOD_IFR2, CMOD5, CMOD5.N, and CMOD5.Na. The root-mean-square errors of...
Tipo: Text Palavras-chave: C-band model (CMOD) functions; Synthetic aperture radar (SAR); Sentinel-1A/B; Wind speed; Wind speed error.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00512/62395/66792.pdf
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