On the Use of Doppler Shift for Sea Surface Wind Retrieval From SAR

Type Publication
Date 2012-07
Language English
Copyright 2012 IEEE
Author(s) Mouche Alexis1, Collard Fabrice1, Chapron Bertrand2, Dagestad Knut-Frode3, Guitton Gilles2, Johannessen Johnny A.3, Kerbaol Vincent1, Hansen Morten Wergeland3
Affiliation(s) 1 : CLS, Direct Radar Applicat, F-29280 Plouzane, France.
2 : IFREMER, CERSAT, F-29280 Plouzane, France.
3 : Nansen Environm & Remote Sensing Ctr, N-5006 Bergen, Norway.
Source Ieee Transactions On Geoscience And Remote Sensing (0196-2892) (Ieee-inst Electrical Electronics Engineers Inc), 2012-07 , Vol. 50 , N. 7 , P. 2901-2909
DOI 10.1109/TGRS.2011.2174998
WOS© Times Cited 71
Keyword(s) Doppler, surface wind, synthetic aperture radar (SAR)
Abstract 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 incidence angle, and wind direction with respect to radar look direction. This function is used into a Bayesian inversion scheme in combination with wind from a priori forecast model and the normalized radar cross section (NRCS). The benefit of Doppler for SAR wind retrieval is shown in complex meteorological situations such as atmospheric fronts or low pressure systems. Using in situ information, validation reveals that this method helps to improve the wind direction retrieval. Uncertainty of the calibration of Doppler shift from Envisat ASAR hampers the inversion scheme in cases where NRCS and model wind are accurate and in close agreement. The method is however very promising with respect of future SAR missions, in particular Sentinel-1, where the Doppler centroid anomaly will be more robustly retrieved.
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Mouche Alexis, Collard Fabrice, Chapron Bertrand, Dagestad Knut-Frode, Guitton Gilles, Johannessen Johnny A., Kerbaol Vincent, Hansen Morten Wergeland (2012). On the Use of Doppler Shift for Sea Surface Wind Retrieval From SAR. Ieee Transactions On Geoscience And Remote Sensing, 50(7), 2901-2909. Publisher's official version : http://doi.org/10.1109/TGRS.2011.2174998 , Open Access version : http://archimer.ifremer.fr/doc/00088/19896/