Frequently used units 11. An array of hydrophones could be used to roughly locate the source of the charge thereby allowing rescue of downed pilots far out to sea. At low and middle latitudes, the deep sound channel axis is between 600-1200 m below the sea surface. It is deepest in the subtropics and comes to the surface in high latitudes, where the sound propagates in the surface layer. To simplify, think of the water column as a layer cake with different densities of water piled on top of each other.
Sound waves refract as they cross between layers of water with different densities.
The refraction of sound waves from higher velocities above and below the sound channel axis bend the sound back towards the axis. Sound energy is refracted towards the axis of the sound channel away from the surface and the bottom of the ocean. An example of ray paths for a source in the sound channel is shown below. Note that in this idealized situation, the sound waves do not interact with either the surface or the bottom. This is a simplified example of propagation in the sound channel.