Wave dispersion by Antartic pancake ice from SAR images: a method for measuring ice thickness

A synthetic aperture radar (SAR) image of the advancing winter marginal ice zone (MIZ) in the Antarctic, composed of frazil-pancake ice, has been analysed in a new way in order to test the predictions of a recently developed theory of wave dispersion in pancake ice which treats the ice as a viscous layer (Keller, 1998). In the image, obtained in April 2000, the structure of the wave spectrum in the MIZ and its change from the open-water spectrum are consistent with a pancake layer thickness of 0.2-0.3 m. Intensive in situ measurements of the pancake ice in the MIZ some 280 km W of the image location were made from FS Polarstern during a period covering the satellite imaging, and yielded a mean ice thickness of 0.24 m. We conclude that this technique is giving realistic results for ice thickness, whereas earlier work based on a different dispersion theory (mass loading) tended to over-estimate thickness. After further validation, it is therefore possible that the SAR wave technique can become an accepted method for remotely sensing ice thickness in pancake icefields.