Sonar, the Submarine and the Arctic Ocean

During the past 14 years, the development of special sonars has made the exploration of the entire Arctic Ocean possible by submarine during either winter or summer. Sonar is required to detect ice that extends down to cruising depth. Information regarding the distribution and thickness of the ice canopy is required in order to choose an area in which the submarine can surface. Sonar must then guide the surfacing through the ice sheet. What little information is available on acoustic properties of sea ice indicates that, in the 15- to 50-kc region, sea ice acts primarily as a volume scatterer of sound in contrast to a diffuse reflector. Upward refraction is the dominant, stable sound transmission condition in the Arctic Ocean and enhances the importance of the acoustic properties of sea ice in determining long-range sound transmission. The acoustic properties of sea ice probably change greatly with temperature and history of growth.