Time-Synchronized Underwater Ranging

Traditionally, determining the distance between cooperative systems underwater is accomplished through an exchange of communications. Range is estimated from the round trip travel time from one system to the other; vessel 1 sends an interrogation signal and vessel 2 replies. Vessel 1 can then determine the range from the total elapsed time divided by 2. If stable clocks are available on the two vessels, then ranging can be accomplished by comparing the time difference between the transmitted time stamp from the first vessel and the time of reception as recorded by the second vessel. Legacy clocks, however, are too large, consume too much power and exhibit drift rates which are unacceptable for UUV applications. Kernco Coherent Population Trapping (CPT) atomic clocks, recently developed under ONR sponsorship, combine low-power operation with very high stability performance into subsystems ideally suited for long-duration underwater missions. Kernco proposes to integrate a customized version of its CPT clock family with an acoustic modem supplied by its subcontractor, Teledyne Benthos, Falmouth, MA. With Benthos support, Kernco will also develop algorithms and methodologies supporting one-way and two-way ranging, remote clock synchronization, and message time stamping.