1,720,984 research outputs found
Experiment and results of the italian activity in the field of ocean microwave backscattering
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An automatic procedure to retrieve the windfields from SAR Images
Full text linkThis paper describes an automatic procedure to download and process SAR images in the coastal areas, in order to get the wind field. The images processed are the Envisat ASARWide Swath. The methodology to retrieve b the wind fields is based on the 2-D Continuous Wavelet Transform, developed in Zecchetto and De Biasio [2002] and applied in Zecchetto and De Biasio [2008]. About three images per day are processed since May 2008. Co-location of the SAR derived winds with those provided by QuikSCAT and Metop will permit to validate the methodology over a large variety of atmospheric regimes. Once validation will be accomplished, the procedure described in this paper will be used to derive the wind fields for coastal meteorology applications
A comparison between modelled and observed atmospheric fields over the Adriatic and Tyrrhenian Seas
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Wind stress structure in the unstable marine surface layer detected by SAR
No full textThe wind stress in the marine surface layer under unstable conditions and low wind speed has been studied using a Synthetic Aperture Radar (SAR) image of the sea surface and time series of the horizontal and vertical wind velocities and of the wind stress recorded on board the C.N.R. research platform, in the northern Adriatic Sea, during a SAR overflight. A conditional sampling technique has been used on the wind stress time series and on the SAR image to detect downward (sweep) and upward (ejection) bursts of the momentum flux, as well as the two-dimensional structure of the radar backscatter. From the ensemble average of both the wind stress and the backscatter structures, it has been possible to estimate the mean duration of the upward (≈11 s) and the downward (≈15 s) wind stress bursts and the mean size of the bright patches of the SAR image (≈120 m). The front of the mean backscatter structure, associated with the downward wind stress bursts, has been related to the time length of the mean sweep stress structure to get, after accounting for a threshold of the wind stress for the generation of the sea surface wavelets, the translation velocity Ut of the mean wind stress of sweep, very close to the mean wind speed. The vertical coherence of the wind stress structures has permitted to refer the translation velocity to a level very close to the sea surface, but above the viscous sublayer. The variability of Ut with height has been studied through comparison with the mean wind speed at different heights z calculated by a boundary-layer model. Accounting for the results reported in the literature, there is an indication that Ut is constant with height in the range 0.5 m ≤ z ≤ 15 m. The two-dimensional pattern of the wind stress structures has been derived from the SAR image. The structures appear elongated crosswind, as with microfronts, with an average cross- to down-wind ratio of ≈ 4. The area covered by the downward wind stress structures represents 13% of the total area
The spatial structure of the downward momentum flux on sea derived from a SAR image
No full textThe spatial structure of the atmospheric surface layer over the sea has been investigated through a radar image taken by an airborne Synthetic Aperture Radar (SAR) at C-band (5.3 GHz) and wind stress data recorded on board of the C.N.R. research platform located in the northern Adriatic Sea. The SAR image shows quasi-ordered structures of radar backscatter hundreds of meters long, while the wind stress time series are characterized by the well known intermittent bursts of tenth of seconds. A conditional sampling technique has been applied both to the wind stress time series and the SAR image, to get the mean structure of the downward momentum flux and the one and two dimensional shape of the structures of the image. It has been shown that a part of the backscatter structures represents the imprint of the downward wind stress. They appear like microfronts, 50 m wide in the up-downwind direction, elongated in the crosswind direction. The crosswind size is in average four times larger than the up-downwind one. The downward wind stress structures cover the 13% of the total area
Use of synoptic real data for relating the sea surface roughness to the backscattering signal fractal dimension
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