Effects of Sea Ice Ridge Characteristics on Under-Ice Reflection Loss

A set of coincident measurements of low-frequency under-ice transmission loss and sea-ice ridge characteristics were made in the Arctic Ocean using airborne acoustic and environmental remote sensing techniques. The resulting measured transmission loss data were compared to theoretical computations of long-range transmission loss which include a parametric surface reflection loss factor to account for absorption/scattering losses at the ice-water interface. Preliminary analysis of data and theory indicates that under-ice reflection losses at frequencies below 500 Hz may be quantitively related to the ridge frequency (number per kilometer) and the rms ridge depth. Using the results of this analysis and a recently compiled atlas of the temporal and spatial variability of sea-ice ridge frequency in the Arctic Ocean, estimates of low-frequency reflection loss were computed over the measurable range of ridge frequencies. Comparisons of predicted reflection loss with measurements by previous investigators show good agreement, thereby demonstrating the feasibility of making meaningful predictions of reflection loss from ice roughness data anywhere in the Arctic Ocean.