As Mac and Chanel completed their equipment check and SAC rates, it was just about time to make the dive. The final preparation was to use the boat's SONAR to determine what lies beneath the murky waters off the coast of Fernandina. SONAR is the acronym for SOund Navigation And Ranging. SONAR is a technique that uses sound propagation (usually underwater) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
Mac and Chanel are going to use active SONAR. Active SONAR creates a pulse sound, often called a "ping," and then listens for reflections or "echoes" of the pulse. The distance of the object can be calculated by measuring the time between when the signal is sent out and when the echo is received. For example, if four seconds elapse between the emission of the outgoing sound and the return of its echo, the sound has taken two seconds to travel to the object and two seconds to return.