Sonar and Sonic depth finder

Sonar noun - A measuring instrument that sends out an acoustic pulse in water and measures distances in terms of the time for the echo of the pulse to return.

Sonic depth finder and sonar are semantically related. In some cases you can use "Sonic depth finder" instead a noun "Sonar".

Sonic depth finder noun - Depth finder for determining depth of water or a submerged object by means of ultrasound waves.

Sonar and sonic depth finder are semantically related. You can use "Sonar" instead a noun phrase "Sonic depth finder".