Note 1 to entry: A sonar can be used actively to transmit sound, passively to receive sound, or in a coordinated manner to transmit sound and to receive resulting echoes.

Note 2 to entry: Sonars are often qualified by type, referring especially to properties of directionality, that depend on their transducer(s) and/or are achieved by beamforming.

Note 3 to entry: The term "sonar" was coined as an acoustical counterpart to "radar". The term "sound navigation and ranging" was constructed later to match the chosen acronym [AIP Oral History Interviews, 1964].

Note 4 to entry: Note that the use in underwater acoustics of the words "transmit", "transmitter" and "transmission" to describe the process of sound radiation by a source is commonplace, but this deviates from the usage prescribed in IEV 702-02-05 where the words "emit", "emitter" and "emission" are preferred.