Radio waves are actively used for wireless communications in the air, such as cell phones, TV broadcasting, and wireless LAN. Undersea, on the other hand, where radio waves are severely attenuated, acoustic communication technology, which uses sound waves to transmit information, is used for observation. By exchanging information with observation equipment deployed in the ocean via radio waves, it is possible to perform observations beyond the limitations of the method of extending wire ropes and cables from ships. Figure 12 shows some examples of acoustic communication.
Acoustic signals are used for data communication with observation equipment such as ocean observational equipment moored in the sea or ocean-bottom seismometer installed on the seafloor, and for exchanging command signals when the equipment is recovered (Figure 12-a). Acoustic communication technology is also used to remotely control devices that operate underwater away from the mother ship, such as autonomous unmanned submersibles, and to monitor their measurements and video data without leaving the ship (Figure 12-b). The fishing gear shape measuring device also measures the state of the net during towing (depth, water temperature, slope, state of net opening, towing speed, etc.) with underwater sensors attached to the trawl net, allowing real-time monitoring of the ever-changing state of the net on board the ship. (Figure 12-c).
