Seasat SAR observations of ocean waves

Abstract

Seasat demonstrated the potential of spaceborne synthetic aperture radar (SAR) for the study and routine monitoring of ocean waves on global scales, but it also raised questions about how these waves were imaged. Here we describe comparisons of wave spectra extracted from Seasat SAR data with simultaneous buoy measurements as tests of wave-imaging theory. Because of the large range-to-velocity ratio (128 seconds) of the Seasat SAR, its images are expected to be particularly sensitive to motions of the sea surface. These motions give rise to the imaging mechanism known as velocity bunching and a smearing of the image in azimuth. However, we do not obtain good agreement between the buoy and SAR-derived spectra when these effects are expected to be important. Similar results are obtained with data from the second Shuttle Imaging Radar SI R-B. The Seasat and SIR-B results combined allow us to assess both our overall understanding of how ocean waves are imaged by spaceborne SAR and the deficiencies in procedures to recover wave spectra from such data. The implications of these results for the plans to observe ocean waves with the SAR on the European Remote Sensing Satellite ERS-1 are discussed.