Wave propagation in frazil/pancake, pancake, and fragmented ice covers

• Laboratory study of frazil, pancake, and fragmented ice covers
• Wave number and attenuation are obtained for each type of ice covers.
• Inverse method is used to estimate the viscoelastic parameters of each ice cover type.

As waves propagate under ice covers, their length and amplitude, as well as the directional distribution of energy may change. These changes depend on the wave frequency and properties of the ice cover. There are several theories for these phenomena, but very limited data to validate these theories. In 2008 a laboratory study at the Hamburgische Schiffbau-Versuchsanstalt GmbH (HSVA) the wave dispersion, including both wavelength change and wave attenuation, was measured for a grease/pancake ice field. The results were compared to those from a grease ice field formed in a smaller wave tank at the University of Washington. It was shown that wave propagation under a grease ice cover followed that of a viscous layer model, but under a pancake ice field it did not. A more extensive experiment was conducted again in 2013 at HSVA to further investigate the wave dispersion. The results reported here are from that experiment with three different types of ice covers: frazil/pancake ice, pancake ice, and fragmented ice floes. The wave number and attenuation are obtained for several monochromatic waves over a range of frequencies. Using an optimization procedure to inversely determine the model parameters, we estimate the equivalent viscoelastic properties of these ice covers. We show that different ice covers require different parameterization to reflect the observed dispersion, hence a possibility of a direct relation between ice morphology and its equivalent mechanical parameters.