PRINCIPLES OF SWELL MEASUREMENT BY SAR WITH APPLICATION TO ERS-1 OBSERVATIONS OFF THE MAURITANIAN COAST

This paper addresses the imaging of swell waves by Synthetic Aperture Radar (SAR). We give the principles for the determination of swell par ameters from image data. Wave height determination is based on a simpl e method derived from the quasi-linear version of the wave imaging mod el of Hasselmann and Hasselmann. The influence of wind waves on wave h eight determination is discussed. Results on coastal swell events obse rved by ERS-1 off the Bane d'Arguin (Mauritania) are presented. These results are compared, generally favourably, with estimates from the wa ve prediction model of Meteofrance and from a model of swell propagati on in finite depth water. However, in intermediate to shallow water, S AR wave length estimates were found to be greater than the theoretical values obtained without currents. The results are discussed in terms of swell-current interaction phenomena. A general conclusion of the st udy is that satellite SAR can be considered as a quasi-operational ins trument for swell monitoring at low to moderate wind speeds. Also, we point out that SAR imagery can henceforth be envisaged for physical st udies on swell propagation in the coastal zone.