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Registros recuperados: 6
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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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Copolarized and Cross‐Polarized SAR Measurements for High‐Resolution Description of Major Hurricane Wind Structures: Application to Irma Category 5 Hurricane ArchiMer
Mouche, Alexis; Chapron, Bertrand; Knaff, John; Zhao, Yili; Zhang, Biao; Combot, Clement.
C‐Band high resolution radar (SAR) is the only space‐borne instrument able to probe at very high resolution and over all ocean basins the sea surface under extreme weather conditions. When co‐analyzed with Stepped Frequency Microwave Radiometer (SFMR) wind estimates, the radar backscatter signals acquired in major Hurricanes from Sentinel‐1 and Radarsat‐2 SAR, reveal high sensitivity in the cross‐polarized channel for wind speeds up to 75 m/s. The combination of the two co‐ and cross‐ polarized channels can then be used to derive high resolution surface wind estimates. The retrieval methods and impacts of intense rainfall are discussed in the context of a Hurricane Irma (2017) case study. On September 7, 2017, Sentinel‐1 measurements intercepted Hurricane...
Tipo: Text Palavras-chave: SAR; Copolarization and cross-polarization; High resolution; Category 5 Hurricane; Hurricane Irma.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00497/60898/64236.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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Ku-Band Sea Surface Radar Backscatter at Low Incidence Angles under Extreme Wind Conditions ArchiMer
Li, Xiuzhong; Zhang, Biao; Mouche, Alexis; He, Yijun; Perrie, William.
This paper reports Ku-band normalized radar cross section (NRCS) at low incidence angles ranging from 0° to 18° and in the wind speed range from 6 to 70 m/s. The precipitation radar onboard the tropical rainfall measuring mission and Jason-1 and 2 have provided 152 hurricanes observations between 2008 and 2013 that were collocated with stepped-frequency microwave radiometer measurements. It is found that the NRCS decreases with increasing incidence angle. The decrease is more dramatic in the 40–70 m/s range of wind speeds than in the 6–20 m/s range, indicating that the NRCS is very sensitive to low incidence angles under extreme wind conditions and insensitive to the extreme wind speed. Consequently, the sea surface appears relatively “smooth” to Ku-band...
Tipo: Text Palavras-chave: NRCS; Extreme wind conditions; Low incidence angles.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00385/49659/50197.pdf
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On C-Band Quad-Polarized Synthetic Aperture Radar Properties of Ocean Surface Currents ArchiMer
Fan, Shengren; Kudryavtsev, Vladimir; Zhang, Biao; Perrie, William; Chapron, Bertrand; Mouche, Alexis.
We present new results for ocean surface current signatures in dual co- and cross-polarized synthetic aperture radar (SAR) images. C-band RADARSAT-2 quad-polarized SAR ocean scenes are decomposed into resonant Bragg scattering from regular (non-breaking) surface waves and scattering from breaking waves. Surface current signatures in dual co- and cross-polarized SAR images are confirmed to be governed by the modulations due to wave breaking. Due to their small relaxation scale, short Bragg waves are almost insensitive to surface currents. Remarkably, the contrast in sensitivity of the non-polarized contribution to dual co-polarized signals is found to largely exceed, by a factor of about 3, the contrast in sensitivity of the corresponding cross-polarized...
Tipo: Text Palavras-chave: Quad-polarized SAR; Ocean surface current; Polarization decomposition; Bragg scattering; Breaking waves.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00588/70030/67948.pdf
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Rain footprints on C-band synthetic aperture radar images of the ocean - Revisited ArchiMer
Alpers, Werner; Zhang, Biao; Mouche, Alexis; Zeng, Kan; Chan, Pak Wai.
It is well known that rain leaves footprints on the sea surface that sometimes become visible on synthetic aperture radar (SAR) images. Rain cells can easily be detected on SAR images at all radar frequencies when they are associated with a downdraft pattern. But rain cells are not always associated with downdraft and rain can also occur in other forms, as stratified rain, rain bands, and squall lines. It turns out that radar signatures of rain at C-band are much more complex than at L- or X-band radar and that it is particularly difficult to identify unambiguously rain events on C-band SAR images acquired over the ocean. This is because C-band lies in the transition region where raindrops impinging onto the sea surface can increase (usually) or decrease...
Tipo: Text Palavras-chave: Rain over the ocean; Synthetic aperture radar; Sea surface winds; C-band radar backscattering; Ring waves.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00355/46574/46446.pdf
Registros recuperados: 6
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