Woods Hole Oceanographic Institution

Amy L. Kukulya

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»Under-ice Operatioins REMUS AUV
»Towed Hydrophone Array
»Remus 600
»REMUS 100
»AUV, Docking REMUS
»Autonomous Underwater Vehicle Operations Beneath Coastal Sea Ice
»White Shark Predation Observations from an AUV
»White Shark observations from an AUV

Jason D. Holmes, William M. Carey, James F. Lynch, Arthur E. Newhall and Amy Kukulya, An Autonomous Underwater Vehicle Towed Array for Ocean Acoustic Measurements and Inversions

A novel experimental method involving an autonomous

underwater vehicle (AUV) with a towed hydrophone

array has been developed to measure the single path interaction

from the surface, bottom and volume of the shallow water

waveguide. The system is designed to operate from the low

( 100 Hz) to the mid frequencies ( 10 kHz) with a directional

source. The effects of surface, volume, and bottom scattering on

the coherency of direct and direct-reflected signals are difficult to

measure and a mobile directional receiver provides an adaptive

capability. For example, the quantification of the role microbubble

layers near the surface and in surface ship wakes plays

on the coherency and scattering of sound could be measured with

this device. In addition, an AUV with a hydrophone array can

be easily and rapidly deployed and because of its mobility can

provide area wide characterization. However, AUV radiated noise

measurements indicated vehicle noise would limit the ability of

hull-mounted or interior hydrophone arrays and thus suggested

the use of a low noise towed array. The AUV discussed here

is the Remus1 vehicle, a tested as well as a readily-available

tow platform for a small low drag array. To demonstrate the

ability of Remus to act as a low noise tow vehicle, radiated

noise measurements were made on the vehicle at Dodge Pond2

acoustic test facility. The vehicle was rotated on a shaft at a depth

of 8 meters and calibrated noise levels measured at 13 meters

distance. At the maximum RPM of the AUV, the 1/3rd octave

noise level, when converted to source level by the calibrated

transmission factor, was 130 dB re 1µPa at 1m. This would

represent the radiated noise source level for a vehicle moving at

3 knots. A small-diameter (2.8 cm O.D.) fluid-filled hydrophone

array has been developed with 6 channels spaced evenly at 0.75

meters, each channel having a receiving sensitivity of -174 dB re

1µPa/V from 100 Hz to 10 kHz. The recording system consisted

of three commercial off-the-shelf (COTS) battery powered minidisc

recorders with a 20 kHz band pass, sampling frequency of

44 kHz and a 16 bit analog to digital converter providing storage

capability of 90 minutes of raw data. The prototype system was

deployed in a “proof-of-concept” test at the Dodge Pond test

facility. The vehicle was programmed to navigate along paths that

provided straight courses as well as several turns to determine the

operational characteristics of the system. Results on capabilities

of the vehicle with the towed system are presented including

vehicle and array noise, beamforming, and element localization.

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