Backscatter and Doppler signals of surface current in SAR images. A step towards inverse modelling
Johnny Johannessen(1) , Vladimir Kudryavtsev(2) , Bertrand Chapron(3) , Fabrice Collard(4) , Dmitry Akimov(2) , and Knut-Frode Dagestad(1)
Nansen Environmental and Remote Sensing Center,
N-5006 Bergen, Norway,
(2) NIERSC, 14th Line Street 7A, 199034 St. Petersburg, Russian Federation
(3) IFREMER, BP 70, 29280 Plouzane, France
(4) BOOST Technology, 135, rue Calude Chappe, 29280 Plouzane, France
Recently two new independent methods for quantitative studies of SAR imaging of current features were presented in the July 2005 issue of Journal of Geophysical Research-Ocean. They are the Doppler shift approach and the radar imaging modelling (RIM) approach.
It is thus timely to develop a DopRim model combining these two approaches for quantitative studies of SAR imaging of current features. This new model is supplemented with a independent wind-wave SAR retrieval tool. Forward simulations of SAR images using this DopRim model are being conducted for three test areas, including the Gulf Stream, Iroise Sea at the entrance to the English Channel, and the Norwegian Coastal current. The 3D current fields are taken from numerical ocean models, while the wind and dominant wave field are retrieved from the independent SAR tool. These products serve as the input for the forward DopRim module. Extensive testing and validation of this method is currently ongoing. Preliminary results show that surface current velocities and estimation of current deformation such as zones of divergence and convergence, current shear and vorticity can be derived in consistence with the SAR backscatter anomalies, near surface wind and wave fields, and the measured Doppler shifts. The inverse module, when fully tested and validated, is therefore expected to significantly advance the use of SAR images in quantitative studies of mesoscale features such as fronts, eddies and filaments. In the longer term it may thus open up for routine application of SAR image data in operational oceanography.