COMPARISON OF SIR-B SAR WAVE IMAGE SPECTRA WITH WAVE MODEL PREDICTIONS - IMPLICATIONS ON THE SAR MODULATION TRANSFER-FUNCTION

During the Spaceborne Imaging Radar (SIR-B) mission in October 1984, t he on-board synthetic aperture radar (SAR) acquired data in the vicini ty of Hurricane Josephine. In this paper, ocean wave spectra computed from the SAR imagery are compared with Ocean Data Gathering Project (O DGP) model forecasts. Because the apparent propagation direction of th e dominant wave system rotated over 90-degrees along the pass, the dat a set affords a unique opportunity to observe the same wave system as imaged by different SAR imaging mechanisms. It is shown here that, for the SIR-B geometry, the wavenumbers and propagation directions extrac ted from the wave spectra are not strongly dependent upon the exact na ture of the SAR imaging mechanisms. However, the estimation of ocean s ignificant wave height (SWH) requires accurate knowledge of such mecha nisms. 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.