How does sound travel long distances? The SOFAR Channel

A sound channel exists in the ocean that allows low-frequency sound to travel great distances. This channel is called the SOund Fixing And Ranging , or SOFAR, channel.

Image os sound channel axis
Sound channel axis. On the left, sound speed profile from mid-latitudes. On the right is shown only the paths sound travels from a source at 1000m depth to a receiver at 1000m depth that is 210km away from the source. The color intensity represents the speed of sound. Adapted from Figure 1.1 of Munk et al., 1995.

The following sections include information on how the sound channel was discovered and used over the years, how the sound channel is formed, how sound travels in it, and how the sound channel varies in different parts of the ocean.