Sonar

Sonar (Sound Navigation And Ranging) detects and locates underwater objects using sound, the ocean’s only long-range remote-sensing medium. Active sonar emits a pulse and times the echo against a sound speed near 1500 m/s; passive sonar only listens for radiated noise. Performance is set by the sonar equation, which balances source level, transmission loss, target strength, reverberation, and ambient noise against a detection threshold. Applications span echo sounding and multibeam bathymetry, fish finding, mine hunting, submarine detection, and navigation. Frequency trades range against resolution: kilohertz systems reach far, hundreds of kilohertz image fine detail at short range.