Remote sensing of oceanic current features by synthetic aperture radar - achievements and perspectives

It is generally accepted that synthetic aperture radar (SAR) images can be quite useful for a better understanding of hydrodynamic processes in the ocean, because they provide valuable information on the location and spatial scales of oceanic features such as fronts, internal waves, and eddies. However, the retrieval of actual surface current fields from the shape and modulation depth of radar signatures is a much more challenging problem, since the imaging mechanism is a complex and nonlinear two-step mechanism which cannot be inverted easily. In this article we review the state-of-the-art in modeling radar signatures of current features, and we present the concept of an iterative scheme for inverting radar images into current fields, which will be implemented within the framework of the European project MARSAIS. We estimate the accuracy and spatial resolution of the proposed remote sensing system on the basis of findings from recent case studies and some dedicated simulations. According to the results of our analyses, it should be possible to retrieve spatial surface current variations an current gradients from a typical spaceborne C band SAR image with an accuracy on the order of 20% and a spatial resolution on the order of 50 m.