Underwater Acoustic Channel

The underwater acoustic channel is the propagation environment that shapes any sound signal in the sea, governed by the depth- and range-varying sound-speed profile. Refraction along that profile creates shadow zones, surface and bottom ducts, convergence zones, and the deep SOFAR channel, while multipath from surface and seabed reflections spreads arrivals in time and Doppler from motion and waves spreads them in frequency. Absorption rises sharply with frequency, capping practical bandwidth, so the channel is range-, frequency-, and time-varying at once. These constraints set the limits on sonar detection, acoustic tomography, and underwater acoustic communication.