Acoustic communication is better than none

The transmission of electromagnetic energy through seawater is so heavily attenuated that it is necessary to turn to acoustic energy to transmit information over any appreciable range of ocean. In the sea, the absorption of acoustic energy is several orders of magnitude less than that of electromagnetic waves. Still, this absorption constitutes a limitation on the bandwidth of the communication link. In addition, the upper and lower boundaries of the ocean, and the multipaths caused by them, distort the communication path and further reduce the usable bandwidth.