Attenuation of the modes of propagation in an homogeneous floating ice plate

Abstract

The characteristic equation for plane‐wave propagation in a homogeneous floating ice plate was solved numerically to determine the phase speeds and attenuations of the first‐ and second‐order modes. While discussion of the phase speeds of the first‐order modes constitutes a review, the discussion of the second‐order modes, along with the attenuation characteristics of the modes when ice absorption is introduced, gives new insight into which modes might be observed in Arctic pack ice. Only the flexural and longitudinal waves, which exist below a frequency‐ice thickness product of 300 Hz‐m, propagate with losses less than 0.1 dB/m in ice less than 3 m thick. This is important to the study of noise from nearby ice events. Results of using a nearby explosive charge to measure the ice longitudinal wave speed and attenuation are given. The ice loss in the 40‐Hz region was found to be approximately a factor of two higher than expected from current empirical absorption values. This may be important to understanding losses from ice interaction in long range propagation. [Work supported by ONR.]