Site dependence of low-frequency Arctic ambient noise and signal attenuation

Our understanding of two significant, ice-related, low-frequency (below 1 kHz) underwater acoustic phenomena, characteristic of both Arctic and sub-Arctic environments, is briefly reviewed. Measurements suggest that ocean wave-generated noise at the periphery of the ice-covered Arctic Ocean is generally exceptionally high when the fetch is large, and can have very long range effects, when propagated signals are not subject to significant surface scattering and volume absorption losses. Surface scattering due to sea-ice ridges, which may be modeled as randomly distributed elliptical half-cylinders, dominates under-ice propagation at frequencies above about 20 Hz. Ray theoretical calculations incorporating this model are consistent with observed site-dependent transmission loss differences over a limited frequency range (40–1000 Hz). Results of new lower frequency wave theoretical calculations, which incorporate this model and a suitable geoacoustic structure of the ocean bottom, will be presented and compared with data. Initial concepts for extension of this work to three dimensions (including randomly oriented ridges) to enable more refined predictions of scattering/transmission losses and, in particular, spatial coherence losses will be outlined.