Abstract: Underwater sensor network consists of number of various sensors and autonomous underwater vehicles deployed underwater to coordinate, interact and share information among themselves to carry out sensing and monitoring functions. Underwater sensor networks have wide range of applications like pollution monitoring, disaster preventions, assisted navigation, under sea explorations, advance military capabilities, mine reconnaissance etc. underwater sensor networks pose great challenge to our existing technologies used in terrestrial sensor network, because underwater environment differs from terrestrial radio environment both in terms of energy costs and channel propagation phenomena. In underwater sensor network, acoustic wireless communication is used in place of radio frequency and optical signal. Some of the issues in which underwater sensor network differ from terrestrial are limited bandwidth, battery power, failure of sensor nodes due to fouling and corrosion. Thus, design of routing protocols for underwater sensor networks pose many challenges due to intrinsic properties of underwater environment.

Keywords: underwater sensor networks, routing, depth based protocols, energy efficiency, acoustic communication.