Status report on the remote sensing of current features by spaceborne synthetic aperture radar

Spatial variations in ocean surface currents can become visible in synthetic aperture radar (SAR) images via hydrodynamic modulation of the surface roughness. The interpretation of such SAR signatures is a challenging problem, since the imaging mechanism is quite complex and nonlinear and cannot be inverted easily. Furthermore, the distinction between SAR signatures of current features and other phenomena can be difficult. However, SAR is the only existing technique for the observation of current variations on spatial scales of tens of meters from satellites. There is a vital demand for such information, particularly in coastal regions. A variety of algorithms have been developed for the retrieval of information on current features from SAR images for different purposes. We give an overview of the state of the art, existing and potential applications, and future perspectives and requirements.