Slicks, waves, and fronts observed in a sea coastal area by an X-band airborne synthetic aperture radar

This article reports observations made in a sea coastal zone by an airborne X-band SAR. This zone includes a basin connected to the sea and the vicinity of the Rhône river estuary. We present the experiment and the data processing procedures including, in particular, a method for removing speckle effects from image spectra of waves. Observations of slick patterns in the basin are reported and used to relate their spatial distribution to features of the circulation as predicted by modelling. Then, we present the wave phenomena observed at sea. Off-shore, the observations are found to be consistent with actual wind conditions. Differences in wave visibility between the images are discussed using the ocean wave SAR imaging theory. The significant wave height is calculated from the image presenting the best geometry for wave detection. Along the coast, the wave transformations observed are discussed on the basis of the results of a simple wave model initialized by the main wave parameters measured off-shore. The complicated refraction effects predicted by the model can only be partially detected on the radar images because of the geometry of the observations. Finally, a frontal event is detected and interpreted as the signature of the boundary of the river plume. The wave-current model of Skop and Leipold (1988) explains the brightness of the radar signature of the front. Among other results, the conclusion emphasizes the good adequation of airborne SAR systems for remote sensing of the coastal environment.