TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors

ACQUISITION PROGRAM: PEO-IWS via PLUS via UPS

OBJECTIVE: Support the development of mounting systems that could be faired into the hull of a UUV and provide isolation from hull vibrations without significantly reducing the sensitivity to waterborne signals.

DESCRIPTION: Vector sensors have been shown to operate very effectively in free field applications and are showing promise in the area of towed array configurations. The four channel (combination three axis accelerometers and hydrophone) sensors allow narrower beams to be generated with a smaller number of sensors over a smaller foot print than can be obtained from simple hydrophones; however, they have been shown to be sensitive to vibrations when rigidly mounted to moving platforms. The effort would support the development of mounting systems that could be faired into the hull of an ASW support UUV and provide isolation from hull vibrations without significantly reducing the sensitivity to waterborne signals.

Discovery of an ideal solution to this problem is unlikely. Current thinking points to using a towed array of sensors attached to the UUV to maximize the isolation of the sensors from the vehicle. Other the other extreme, a tight coupling of the sensor to the vehicle would make the vehicle itself a part of the sensor, possibly enhancing the response at some frequencies, but likely introducing vibrational resonances at others. Ad hoc solutions include foam isolation and bungee cord setups.

For submarine applications, vector sensor towed arrays are already in development. Should a suitable solution to the mounting problem be developed, their use in hull arrays could be developed as well.

In addition to underwater applications there is the potential for using vector sensors to improve systems that acoustically detect shock wave and muzzle blast form gunfire to pinpoint the location of snipers. These HMMWV applications clearly require some sort semi-rigid mounting system.

PHASE I: Identify, analyze and recommend a preliminary design for the candidate mounting system.

PHASE II: Develop and demonstrate the mounting system identified in Phase I.

PHASE III: Installation, testing, and data acquisition from a number of vector sensors mounted/faired into the hull of a UUV.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The smaller footprint for acoustic sensors that could be realized by using vector sensor arrays has potential benefit to the both land based and off-shore oil and gas exploration and production industries. Acoustic well logging and cross-well seismic surveys can often resolve dynamic reservoir production processes much better than conventional surface seismic efforts, but sensor size down hole is always a consideration. Ref 5. describes a 10-level hydrophone system used for a cross-well survey with an analysis bandwidth from 200 to 2000 Hz. The Wilcoxon TV-001 vector sensor which has operational bandwidth from 5Hz�7kHz, would provide much finer spatial resolution across a much greater bandwidth in a similar configuration. The small footprint of this sensor is suitable for down hole applications, but may have to be mounted in some sort of fairing in order to safely move it in and out of the well hole. The ocean seismology sector of the industry is also interested in these sensors for Marine Mammal monitoring, mainly for the left-right ambiguity resolution.

REFERENCES:
1. G. L. D'Spain, W. S. Hodgkiss, and G. L. Edmonds, "The simultaneous measurement of infrasonic acoustic particle velocity and acoustic pressure in the ocean by freely drifting Swallow floats," IEEE J. Ocean. Eng. 16, 195-207 (1991).
2. Nehorai, A., and Paldi, E., 1994, "Acoustic Vector-Sensor Array Processing," IEEE Trans. on Signal Proc., Vol. 42, No. 9, 2481-2491.
3. Gabrielson, Gardner, D. L., and Garrett, S. L., 1995, A simple neutrally buoyant sensor for direct measurement of particle velocity and intensity in water, J. Acoust. Soc. of Am., Vol. 97, pp. 2227-2237
4. Cray, B. A., and Nuttall, A. H., 2001, "Directivity factors for linear arrays of velocity sensors," J. Acoust. Soc. Of Am., Vol. 110, pp. 324-331
5. Jorge O. Parra, Chris L. Hackert, Michael Bennett, and Hughbert A. Collier,
"High-Resolution Acoustic And Seismic Investigation of Carbonate Rock Properties," Paper presented at Society of Petroleum and Well Log Analyst (SPWLA), International Symposium, June 22-25, 2003, Galveston, Texas

KEYWORDS: AUV; UUV; Vector Sensor; acoustic velocity sensor; mounting; vibration isolation

TPOC: Robert Headrick
Phone: (703)696-4135
Fax:
Email: [email protected]
2nd TPOC: Ellen Livingston
Phone: (703)696-4203
Fax: (703)696-8423
Email: [email protected]

** TOPIC AUTHOR (TPOC) **

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