Coastal ocean wave retrieval from ASAR complex images
Fabrice Collard(1) , bertrand chapron(2) , fabrice ARDHUIN(3) , harald Johnsen(4) , and geir ENGEN(4)
135 rue Claude Chappe,
(2) IFREMER, Technopole Brest-Iroise, 29280 PLOUZANE, France
(3) SHOM, 13, rue du Châtelier, 29275 Brest, France
(4) NORUT, P.O. box 6434, Forskningsparken, 9294 Tromsø, Norway
Retrieval of surface wave parameters from SAR data has recently gained some robustness thanks to the analysis of the long time serie of ERS/ENVISAT SAR Wave Mode for wave spectrum inversion. These improvements in the understanding of sea echo in SAR signal have contributed to the ASAR level2 wave mode reprocessing and their extention to narrow and wide swath complex images over coastal waters is discussed.
Wave spectra derived from Synthetic Aperture Radar images acquired by ENVISAT's in narrow swath mode are compared to insitu measurements by 7 sensors, deployed in a field experiment carried out on the French coast of La Manche (English Channel). Under the low to moderate wind speed observed conditions, overall good agreement is found between insitu and SAR observations, over a wide range of wave heights and directions, including waves propagating in the radar azimuth direction, and incidence angles different from the standard wave mode products.
It is shown that the extraction of swell wave parameters from the new wide swath Single Look Complex images is possible and can bring some clear picture of wave refraction and diffraction in coastal area but also within Hurricanes with an illustration of the striking wide swath wave distribution generated by devastating Hurricane Katrina last September before making landfall in Louisiana.
All inversion algorithms to derive Wave Level2 products are developped in an operational point of view and do not require any external information.