Which type of waves used in SONAR?

Sound Navigation and Ranging is the full name of SONAR. SONAR is a device that is used to detect objects and calculate their distance from them. It works on the premise of sound waves being reflected.

A SONAR operates on the basis of sound wave reflection. We know that when a sound wave hits or falls on an obstruction, it reflects back at the same speed. 

Ultrasound waves are used in SONAR. It is made up of a transmitter that delivers or emits ultrasonic waves in the direction of the obstruction.

The waves reflect off the surface of the barrier and are picked up by a receiver in the SONAR.

Hence, In SONAR, we use ultrasonic waves.