What is a SOFAR?
How does SOFAR work? Think of the ocean as consisting of various zones, or layers — sort of like oil and vinegar salad dressing before it’s shaken up—except that ocean layers occur due to differences in salinity (salt content) and temperature variations. Saltier water, and colder water, lie beneath less salty, warmer water.
Because of SOFAR, sound emitted at a certain depth bounces between these various layers and can travel for hundreds of miles. This up-and-down bending of low-frequency soundwaves allows soundwaves to travel great distances without the signal losing significant energy. By placing hydrophones at the axis of the sound channel, researchers can record sounds such as whale calls, earthquakes, and manmade noise occurring vast distances from the hydrophones. In some instances, low-frequency sounds can be heard across entire ocean basins!