Sea surface as seen at L-band microwaves: modeling and applications

In the microwave domain, the development of interaction models has proved itself necessary for the understanding of the interaction between the electromagnetic wave and the sea surface and for the efficient retrieval of surface parameters from spaceborne measurements, such as in altimetry and wind scatterometry. New potential applications of microwaves over oceans involve frequencies such as L-band (around 1.5 GHz), both for active (such as the use of reflected GNSS signals for scatterometry and altimetry) and passive (extraction of ocean salinity from radiometric products) measurements. Classical models, mostly developed for higher frequencies and for close-to-nadir geometry's, may show limitations when applied to these new configurations. Another important issue is the sea surface description, which may need to be somehow refined to enable a complete picture of the interaction mechanisms at these wavelengths. L-band measurements of the sea surface (concurrent to local measurements of the sea state) are still quite scarce and this makes difficult the validation of modeling tools. It is however possible to use a well controlled full-wave approach, such as the moment method, as a reference to evaluate the assets and drawbacks of simpler asymptotic models (Physical Optics, two-scale model, etc .). The objective of this exercise is to exhibit a parameterization of the simpler models efficient enough to ensure an adequate restitution of the main scattering/emission mechanisms. Studies are conducted for different sea conditions. The wave-surface interaction mechanisms expected to drive the signal are studied for different configurations of observation. Then, the preliminary consequences in terms of interaction model accuracy at these wavelengths are pointed out.