SONAR stands for Sound Navigation And Ranging. It works by emitting sound pulses and listening for the echoes that return after bouncing off objects or the seabed. For most applications, SONAR uses ultrasonic waves, which are sound waves with frequencies higher than the upper audible limit of human hearing (typically above 20 kHz). Ultrasonic waves offer better directionality and resolution than audible sound waves, making them suitable for detecting underwater objects, mapping the sea floor, and communication.