An integrated, underwater optical /acoustic communications system

Abstract

Communication underwater is severely limited when compared to communications in air because water is essentially opaque to electromagnetic radiation except in the visible band. Even in the visible band, light penetrates only a few hundred meters in the clearest waters and much less in waters made turbid by suspended sediment or high concentrations of marine life. Consequently, acoustic techniques have been developed for underwater communication systems and now represent a relatively mature and robust technology. Acoustic systems are capable of long range communication, but offer limited data rates and significant latency (due to the speed of sound in water). We are developing an optical communication system that complements and integrates with existing acoustic systems resulting in an underwater communications capability offering high data rates and low latency when within optical range combined with long range and robustness of acoustics when outside of optical range. Amongst a wide array of applications, this combination of capabilities will make it possible to operate self-powered ROVs from support vessels or platforms without requiring a physical connection to the ROV. Such a capability will help simplify operations and potentially reduce costs through the use of less capable surface vessels. New deployment strategies may offer game-changing opportunities within all areas of undersea activities. For example, rapid event response will be enhanced and repair and maintenance of the emerging ocean observatory infrastructure will become more cost effective. Such through-water communications will likewise enable exchange of large data files from fixed sensors using AUVs (or ROVs) as data mules, shuttling real-time video from untethered vehicles for inspection, identification, and other related operations. Interconnectivity for dense arrays of underwater sensors without the need for expensive and difficult to install undersea cables is also possible. An unmanned battery operated vehicle, dedicated to a subsea node, that can be wirelessly operated though a combination of acoustic and optical communications, will be an important asset for both scientific exploration and commercial applications. We have demonstrated robust multi-point, low power omnidirectional optical communications over ranges of 100 meters at data rates up to 10 mega bits per second using a few tens of Watts of battery power with small, inexpensive transmitters and receivers. During the next few years, we will be exploring applications of this new technology directly in support of ongoing science and engineering programs. High-speed underwater optical communication is an enabling technology that has many potential applications in a range of environments from the deep sea to coastal waters. This development effort will enhance infrastructure for scientific research and commercial use by providing technology to efficiently communicate between surface vessels, underwater vehicles and seafloor infrastructure.