Theoretical modeling of reflection loss from ridged sea ice

Abstract

A theoretical model of underwater acoustic reflection loss from ridged sea ice has been developed using the method of Twersky [J. Acoust. Soc. Am. 29, 209–255 (1957)]. Ridges are represented by a distribution of randomly spaced elliptical half-cylinders. An approximate solution for reflectivity as a function of grazing angle and ridge depth, width, and number per unit distance has been obtained for the case where the average ridge spacing, the average ridge depth, and the average plate thickness are large compared to wavelength. Using this frequency-independent equation, reflection loss was computed over the measurable range of ridge characteristics for comparison with the results of coincident measurements of reflection loss and ridge parameters. Good agreement between the theoretical computations and experimental measurements demonstrates the applicability of this theory to model under-ice reflection loss. Some of the limitations of this model, and the problems involved in experimental determinations of sea ice ridge characteristics and acoustic reflection loss are discussed. Theoretical modeling of under-ice reflection loss for the case where wavelengths are large compared to average ridge depth and the average plate thickness is also considered.