Multibeam Sonar.
Sonar stands for ( SOund Navigation and Ranging ) which is a technique that will use sound to communicate or detect objects on or way under the surface a=of the water. Usually in this case you would be going in the water in a submarine to navigate these things. There are two different types of technology that share the same name "sonar" which is, Passive Sonar=the essential listening for the sound being made by vessels and then you have Active Sonar= the pulses of sounds and listening for any echoes that may occur. Sonar however is used for the measurement of the echo characteristics of certain targets in the water. The term sonar can also be used for the equipment that is used to receive and generate sound.