Underwater Wireless Communications and Networks: Theory and Application: Part 2 [Guest Editorial]

The Earth is a water planet, two-thirds of which is covered by water. With the rapid developments in technology, underwater wireless communications and networks have become a fast growing field, with broad applications in commercial and military waterbased systems. The need for underwater wireless communications exists in applications such as remote control in the off-shore oil industry, pollution monitoring in environmental systems, collection of scientific data from ocean-bottom stations, disaster detection and early warning, national security and defense (intrusion detection and underwater surveillance), as well as new resource discovery. Thus, the research into new underwater wireless communication techniques has played the most important role in the exploration of oceans and other aquatic environments. In contrast to terrestrial wireless radio communications, the underwater channel poses serious technical challenges depending on the communications modalities (e.g., acoustic, optical, or RF/magnetic) employed. These include, but are not limited to, ambient channel noise, severe attenuation, propagation delay, multipath, frequency dispersion, bio-fouling, lack of access to precise time synchronization (GPS), and constrained bandwidth and power resources. These challenges also provide an opportunity for design of hybrid and adaptive transmission, such as the underwater acoustic and optical communications and networks, which have somewhat complementary properties, with potential for longer range and higher bandwidth networked communications in size- and power-constrained modems and mobile unmanned systems.