Directional Acoustic Transponder

"The U.S. Navy requires the development of an AUV-based, AUV localization system which will inform multiple vehicles of their range and bearing from a central controller. There are existing systems which do this now, but they are limited in range, use veryunsophisticated signaling techniques which generally preclude clandestine operations, or use by multiple units. Furthermore, they may require synchronized clocks between the controller and the vehicle, are very expensive, and are not necessarily suitablefor use on an AUV platform. Benthos, with a long history of military and commercial development of underwater acoustic communications (acomms), proposes to enhance our existing technology to provide the required capability. Virtually all AUVs eithercurrently use or will require acomms. Our proposal will use a COTS modem, installed on the vehicle without modification, to communicate with a central controller aboard a separate AUV, itself built around a standard modem. The controller will receive aranging inquiry from the vehicle (a standard technique), will evaluate bearing from that signal using either a modified ultra-short baseline technique, or a novel, physically small beamformer, and will return the ranging signal along with the computedbearing. Because the system is modem-based, it may also provide conventional telemetry functions. The system will use a modified version of the multi-access signaling scheme developed join