The ocean sciences are beginning a new phase in which scientists will enter the ocean environment and adaptively observe the earth-ocean system using ocean observatories that provide power and communication to access and manipulate real-time sensor networks. Instruments will be plugged into the infrastructure, and hence areal sensor coverage will require the costly and time-consuming lay of numerous cables around a site of scientific interest. This limitation could be reduced with the development of "wireless" technologies suitable for operation underwater. Wireless bi-directional data links would enable remote operation of autonomous deep vehicles over the Internet. This would allow high cost, high capability sensors to be concentrated on a few mobile platforms capable of operating over an extended region in an adaptive manner. The ocean is essentially opaque to electromagnetic radiation except over the visible light range, and hence "wireless" underwater communication requires the development of optical modem technology. High data rates (1-10 Mbit/s or more) are achievable in the blue part of the spectrum over ranges of order 100 meters, and more under good conditions. The PIs propose to design, fabricate, test, and validate a bi-directional optical modem intended to link a mobile deep submergence vehicle to a fixed node which is in turn connected to an ocean observatory by fiber optic cable. Multiple nodes per cable will be supported, enabling the coverage of relatively wide areas. With further development, the optical modem technology will be able to simultaneously support many sensors per node, resulting in an underwater network analogous to a cellular telephone system. Fundamental research includes work on optical propagation in random media, low-power optical signal generation, plus acquisition and detection over a wide field of view. In addition, devising an optical communications system explicitly for operation on a mobile vehicle poses novel technological challenges. Finally, underwater optical communications technology to link mobile platforms to ocean observatories would be scientifically enabling in a wide range of disciplines, including biological, chemical, physical, and geological oceanography.
