An historical perspective on four Canadian initiatives in underwater acoustics will be presented: Towed Variable Depth Sonar (TVDS); the Chapman-Harris model for reverberation; seabed-interaction in shallow water; and Arctic acoustics. The poor performance of hull-mounted sonars in Canadian waters during WWII prompted TVDS development in 1947. The resulting prototype (CAST/1X) was tested against a UK developmental system in 1958. Subsequently, the UK purchased the Canadian system and the US "re-packaged" their sonars according to the Canadian design. An understanding of the effects of back-scattering from the sea surface and bottom was required to model sonar system performance. Experiments began circa 1960 leading to a new model for sea surface back-scattering, and revealing the ocean volume as an additional factor. The conditions governing propagation and noise in shallow waters remained mysterious in the 1970s, until the significant role of the seabed emerged through theoretical developments (e.g., loss due to shear waves) and experiments conducted over a variety of seabed types. Political, sovereignty and energy issues prompted Canada to investigate under-ice acoustics in the Arctic beginning circa 1958. The efforts ultimately resulted in the ability to undertake under-ice acoustic and geophysical surveys using long endurance Autonomous Underwater Vehicles (AUVs).

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