Seagulls and SAR: atmospheric convection effects in SAR images over the ocean

Interpretation of features in synthetic aperture radar (SAR) ocean images has most often dealt with oceanic phenomena. The authors focus on atmospheric boundary layer processes that express themselves in SAR images via spatial variations in the surface wind field that drives small scale ocean ripple waves (<1 m wavelength) and hence SAR image intensity. Since the 1930s, observations (from seagull soaring to satellite images) have revealed geometric patterns in the air flow related to convection in an unstable atmospheric boundary layer. Woodcock (1948) noted that patterned sea gull soaring and cloud layers occurred where the boundary layer was thermally unstable, whereas uniform cloud layers corresponded to a stable boundary layer. When wind shear was low, polygonal cloud patterns prevailed; but when wind shear was high, the clouds were formed into horizontal columns, referred to as cloud streets. The authors along with others (Alpers and Brummer, 1994; Sikora, et al., 1995 and P. Moreau, 1995) argue that the geometrical `puff´ patterns in SAR images are the surface counterpart to the cloud patterns and result from convective air flows in an unstable marine atmospheric boundary layer. Further, it is thought that these patterns contain information on the convective processes and bulk wind flow going on and that this information can be extracted by pattern analysis on the SAR images