SYNTHETIC-APERTURE RADAR OBSERVATIONS OF INTERACTION OF OCEAN SWELL AND SEMIDI ISLANDS IN THE GULF OF ALASKA

Synthetic aperture radar (SAR) images of the ocean surface can show ev idence of the sheltering effects of barriers, such as islands, on the incoming long ocean waves. In the presence of high background noise in SAR images, these effects are not always observed by visual inspectio n. As shown in this paper, they can be determined most effectively in the spectral domain. From the ERS-1 SAR data of 17 October 1991, we no ticed that two separate swell components almost perpendicular to each other were incident on the Semidi Islands in the Gulf of Alaska. By sp ectral analysis, the shadow zone associated with each wave component c an be identified. The distribution of an equivalent diffraction coeffi cient has been estimated at the lee of the Chowiet Island which has a sharp tip. It has been compared to that obtained from the Sommerfeld s olution of diffraction for a semi-infinite barrier. The SAR data shows a similar diffraction pattern to the model solution but has a slower fall-off into the geometric shadow zone.