2025 Volume 29 Issue 2 Pages 57-62
In underwater environments where electro-magnetic waves and light cannot travel far, sound waves have long been used for exploration and communication. This lecture introduces the recent developments of active and passive acoustic technologies. The lecture will also explore future technological prospects. In active technologies, a major turning point has been the application of multi-channel and wide-band methods. For example, multibeam sonar equips multiple receiving elements for the beam forming to separate reflected sounds from various directions as well as the echo delay time for the seabed topography, fish school shapes, subsurface exploration for mining using air guns, and even underwater visual-like imaging using acoustic lenses. Additionally, wide-band technologies provide various type of target information in addition to the location and time. Passive technology development has been largely driven by the detection of submarines. After the Cold War, underwater acoustic technologies were made available for civilian use. Not only marine mammals like whales and dolphins, but also sound-producing species such as fish and crustaceans, are now being monitored using passive technologies. These techniques are currently used globally for environmental assessments of the oceans. In these years, Underwater Domain Awareness is strongly demanded for the sustainable use of ocean. For active technologies, precise mapping and wide-band communication in long range is needed. For passive technologies, identifying the sources is a big issue. Annotated reference data of phonating targets is needed. The rising underwater noise levels from various human activities have become an international concern due to their impact on marine life.
