TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors

ACQUISITION PROGRAM: Unmanned Undersea Vehicles (UUV) Program Office, PMS 403; ACAT IV

OBJECTIVE: develop and demonstrate the ability to perform one-way 1m or better accuracy acoustic ranging using acoustic modems integrated with miniature atomic clocks that are small, low power and have low enough drift to support the specified ranging accuracy for weeks between re-synchronization.

DESCRIPTION: Ranging between systems underwater is typically accomplished through a series of communications and range is estimated using the round trip travel time from one system to the other; i.e. vessel 1 sends an interrogation and vessel 2 replies, vessel 1 determines the range by the total elapsed time divided by 2. If the two vessels have clocks, then ranging could be accomplished by sending a time stamp and the recipient can determine range by comparing the received time stamp with its own clock time. However, off-the-shelf clock technology is either too large, consumes too much power or has too high a drift for application on a UUV. New chip-based atomic clock technologies have demonstrated very low power (NIST clock is 75mW), very small size (4mm on a side) and very low drift (100 nsec/year). Clock synchronization on the order of 100 microsec between vessels is needed to achieve 1m range resolution. Acoustic signals robust against multi-path will be required. The acoustic modems used in this project must be compatible with existing/emerging navy UUV modems. A method will need to be developed to allow accurate synchronization between two systems while underwater using acoustic communications.

PHASE I: Propose design, specifications and development cost for an integrated chip-scale atomic clock and acoustic modem. Propose approach to underwater clock synchronization between two or more systems. Estimate of achievable ranging accuracy and underwater synchronization accuracy.

PHASE II: Develop and deliver (4) prototype integrated atomic clock and acoustic modem systems.
Demonstrate ability to achieve 1m or better ranging using 1 way acoustic communications.
Demonstrate ability to clock synchronization between systems underwater to 100 microsec or better.
Integrate and demonstrate the new modems with a Navy program of record UUVs.

PHASE III: Transition of the developed modem will be accomplished through planned product improvements to Navy UUVs and other systems utilizing acoustic modems.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This technology will be applicable to commercial underwater systems including UUVs and digital transponder systems that are being used by the offshore oil and construction industries.

REFERENCES:
1) http://tf.nist.gov/ofm/smallclock (NIST atomic clock on a chip)
2) http://www.eurekalert.org/pub_releases/2003-09/oonr-oon090203.php (Kernco atomic clock funded by ONR and AFRL)
3) http://www.kernco.com/pdfs/ULAC_Press_Release.pdf

KEYWORDS: acoustic modems; atomic clock; time

TPOC: Brian Bourgeois
Phone: (228)688-5321
Fax: (228)688-4853
Email: [email protected]
2nd TPOC: Tom Swean
Phone: (703)696-4025
Fax: (703)696-2710
Email: [email protected]

** TOPIC AUTHOR (TPOC) **

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