Underwater acoustics are used by UUVs (unmanned underwater vehicles), AUVs (autonomous underwater vehicles) and ROVs (remotely operated vehicles) for a variety of applications. RF and other electromagnetic waves do not propagate well in water, and so sound waves, which can be received and measured over useful distances underwater, are the most viable alternative.
Underwater communications are typically carried out using acoustic transducers, which convert electrical energy into sound waves, and hydrophones, which are the underwater equivalent of microphones. Such communications are used not only from vehicle to vehicle but also to collect data from networks of acoustic underwater sensors that can monitor a variety of parameters.
Hydrophones can also be used by UUVs to gather information about the underwater environment. This can include monitoring for noise pollution, detection of marine mammals, and searching for the signatures of specific vessels such as naval ships or submarines.
Underwater acoustics can also be used for subsea vehicle tracking and navigation. Acoustic underwater positioning systems use distance and direction measurements to achieve this, and are generally organised into three types – long-baseline (LBL), short-baseline (SBL) and ultra-short-baseline (USBL). LBL acoustic positioning systems utilise networks of seafloor acoustic transponders, whereas SBL and USBL make use of transducers that are usually mounted on surface vessels.
Sonar is used by UUVs and AUVs, as well as USVs (uncrewed surface vessels) for underwater mapping and bathymetry. Side scan sonar is typically deployed as a towfish that can be attached to a UUV, and covers large areas in great detail by measuring the intensity of the return signal. Multibeam echosounders emit multiple acoustic waves in a fan shape below the vessel, and use the measured time of reflection to make distance and depth measurements. Read more about sonar and echosounders for unmanned underwater vehicles.