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. 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 24 cm thick. Intensive in situ measurements of the pancake ice in the MIZ 280 km W of the image location were made from FS Polarstern during a period covering the satellite imaging, and also yielded a mean ice thickness of 24 cm. We conclude that this technique gives 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 monitoring ice thickness in pancake icefields.