Soutenance de thèse : Global observations of ocean surface winds and waves using spaceborne synthetic aperture radar measurements

Vendredi 07.06.2019
Horaires :
De 14:00 à 16:00

Adresse :

IUEM : Institut Universitaire Européen de la Mer
Amphi D

Spaceborne synthetic aperture radar (SAR) has been demonstrated invaluable in observing the global ocean winds and waves. SAR images  acquired by multiple sensors are employed, including Sentinel-1 (S-1), Envisat/ASAR, Gaofen-3 and Radarsat-2. This thesis reviews the  commonly used SAR parameters (NRCS and azimuth cutoff) in the first part. A series of calibration steps are required to obtain a proper  NRCS and assessment of NRCS is carried out for S-1 wave mode (WV). It turns out that WV is poorly calibrated and is thus re-calibrated to  obtain accurate NRCS. Azimuth cutoff is demonstrated to be complementary to NRCS and can account for the sea state impact on the wind  retrieval. Based on the available fully polarimetric SAR products, azimuth cutoff is found to vary greatly with polarizations. The present SAR  mapping transformation is sufficient to interpret the co-polarized azimuth cutoff, while not for the cross-polarzation.

With the limitations of SAR imaging in mind, a new parameter is proposed and defined based on the SAR image cross-spectra, termed as  MACS. The imaginary part of MACS is found to be a signed quantity relative to the wind direction. Given this dependence, an independent  wind retrieval algorithm is expected to benefit. The magnitude of MACS is able to aid for estimate of modulation function of SAR mapping. In  addition, MACS also gives promising results regarding the global wave studies. The global signatures of MACS at various wavelengths are  well representative of the winds distributions, spatially and seasonally. MACS of long waves shows greater values over the storm tracks while  the shorter waves are mostly within the trader winds. These results are expected to help evaluate the model outputs and complement further  studies of the global wave spectral climate. Data continuity in the coming 10 years shall extend the study towards longer duration.

Publié le 06.06.2019