Comparison of SIR-B SAR wave image spectra with wave model predictions: implications on the SAR modulation transfer function

Abstract

During the Spaceborne Imaging Radar (SIR-B) mission in October 1984, the onboard synthetic aperture radar (SAR) acquired data in the vicinity of Hurricane Josephine. Ocean wave spectra computed from the SAR imagery are compared with Ocean Data Gathering Project (ODGP) model forecasts. Because the apparent propagation direction of the dominant wave system rotated over 90 degrees along the pass, the data set affords a unique opportunity to observe the same wave system as imaged by different SAR mechanisms. It is shown that, for the SIR-B geometry, the wave numbers and propagation directions extracted from the wave spectra are not strongly dependent on the exact nature of the SAR imaging mechanism. However,the estimation of ocean significant wave height (SWH) requires accurate knowledge of such mechanisms. The spatial variation of SWH as estimated from SAR-derived wave spectra and ODGP model spectra compare most favorably when the phase of the hydrodynamic portion of the SAR modulation transfer function is approximately 90 degrees past the long wave crest. >