Wave dispersion by frazil-pancake ice from SAR imagery

On the basis of a theory of wave propagation from open sea in frazil-pancake ice developed in Wadhams (1986), a project was carried out, during 1994-96 under the EU Environment Programme, to map ice thickness from SAR imagery in the Odden Ice Tongue, Greenland Sea. Ground truth data (ice thickness and composition, wind stress and local wave spectrum, etc.) were available from a field experiment carried out in the Odden during April 1993. Twenty six high-resolution SAR images for the same period and covering the same area were acquired and processed. A first, “simple”, procedure was developed to perform spectral analysis in order to obtain the change of wavelength and angle of refraction of the dominant wave entering the ice field. Ice thickness values derived from the theory were larger than those measured during the field experiment. The inversion scheme presented by Hasselmann et al. (1996) was then utilized to retrieve the ocean spectrum from the SAR spectrum. This was done for three scenes (April 3 and 10, 1993) for which wave spectra from buoy data were available. Variations of wavelength and propagation direction of the dominant wave systems are analyzed before and after they enter ice zones in order to: (i) evaluate the optimal conditions occurring for spectral changes detection with the ERS SAR system; and (ii) gain more insight into applicability limits of the inversion algorithm when applied to sea-ice scenes