Submarines and other ships can be tracked by listening to the underwater sound that ships produce under water (passively) and by listening to echoes of transmitted sounds that reflect against a submarine (active). The technique used is called “SOUND Navigation And Ranging” or sonar in analogy with “Radar” for Radio Detection And Ranging. Sonar only works much slower than radar because the speed of sound under water is only 1,500 m/s. By comparison, the speed of radio waves is 300,000 km/s.
The underwater loudspeaker, also a microphone, with which the sounds are transmitted underwater and with which sound and the echoes are captured under water are called “transducer”.
The Meetgebouw started with underwater acoustics research in 1938. Since that time there have been many developments:
- Pre-war research (1938 – 1940)
- The period 1946 – 1957: transducers, active and passive sonars, and measurement facilities
- The period 1957 – 1980: Doppler, towed arrays
- Low-Frequency Active Towed Array Sonar (1990’s)
- SOCRATES (2001+)