Sonar

Sonar uses sound waves to detect, locate, or characterize objects underwater. It can operate by listening for sounds or by transmitting pulses and analyzing returning echoes.

Sound propagation underwater: The transmission of acoustic energy through water, shaped by temperature, pressure, salinity, and depth. Water’s changing sound speed bends sonar paths and affects range estimates.
Side-scan sonar: An imaging sonar that maps seabed features by recording echoes sent sideways from a moving platform. It produces detailed seafloor images for surveys and wreck searches.
Reginald Fessenden: A Canadian inventor whose underwater acoustic experiments included an early oscillator for signaling and echo detection. His 1914 device demonstrated an early form of active underwater echo ranging.
Radar: A system that detects objects by transmitting radio waves and analyzing their reflections. Radar also uses returned waves for ranging, but seawater strongly limits radio transmission.
Echo sounding: A method that measures depth by timing sound pulses sent toward the seabed and their returning echoes. It is the basic pulse-and-return measurement behind many sonar systems.
Multibeam echosounder: A sonar instrument that measures seafloor depth across many narrow beams in a swath beneath a vessel. Its swath measurements build high-resolution bathymetric maps.
Paul Langevin: A French physicist who developed piezoelectric ultrasonic systems for detecting submarines during World War I. His work helped establish practical active sonar using high-frequency sound.
Lidar: A remote-sensing method that measures distance using reflected laser light. It offers an optical counterpart to sonar, with different range and water-clarity limits.
Beamforming: A signal-processing method that combines signals from multiple sensors to emphasize sound arriving from selected directions. Sonar arrays use it to estimate target direction and narrow listening or transmission beams.
Forward-looking sonar: A sonar system that scans the water ahead of a vessel or underwater vehicle. It helps detect obstacles and terrain before a platform reaches them.

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