Acoustic ray propagation in the waters off eastern Australia using ocean glider data

The waters off Eastern Australia are very dynamic. The most prominent feature is the East Australian Current (EAC), a strong western boundary current, and eddies it spins off. Along with the EAC and its eddies, upwelling of cold waters, and wind and tide-induced mixing generate an active thermal environment in the coastal waters on the continental shelf. Additionally, internal waves, fronts, and continental shelf waves shifting water masses back and forth across the continental shelf/slope break add further complexity to the oceanographic conditions. Propagation of acoustic rays depends on the temperature field and is affected by these processes which influence the temperature structure. Using temperature and salinity data collected by ocean gliders transiting the waters off Eastern Australia, the dependence of acoustic ray propagation was investigated for several source depths. The formation of surface ducts, sound channels, and convergence were identified and correlated with oceanographic conditions and features. The acoustic rays’ propagation depended both on these features and the sound source depth. Rays with high originating angles typically bounced back and forth between the surface and bottom; whereas rays from low originating angles were impacted more by the conditions. This is of key importance to navies for sonar operation.