ORE 654 Applications of Ocean Acoustics Lecture 6b Ocean Noise

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ORE 654Applications of Ocean AcousticsLecture
6bOcean Noise

• Bruce Howe
• Ocean and Resources Engineering
• School of Ocean and Earth Science and Technology
• University of Hawaii at Manoa
• Fall Semester 2011

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(No Transcript)
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Noise

• Noise spectra
• NL 10 log(ltInoisegt/Iref) dB re 1 µPa2/Hz
• Classic
• Urick curves

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Ship noise

• Radiated sound

Gerald DSpain
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Low frequency noise - wind
Station ALOHA, 20 months
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Bioacoustic sound
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Offshore a military training base
DSpain
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Measuring wind and rain
Nystuen
Nystuen
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Large whales using SOSUS
All 6 yrs
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Bowhead and beluga whale and walrus sounds

• Spectrogram of under ice
• northernBering Sea in May 2007

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Comparison Wenz vs APL vs Ross
Ross Mechanics of Underwater Noise (1976)
Acoustics Bulletin (1993)
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Simplified noise spectra

• Low frequency flow turbulence/seismics/wave-wave
• Shipping
• Wind/waves

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Simplified noise spectra - terms

• Turbulence/microseisms
• Shipping
• Wind/waves
• Thermal

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Noise

• Noise spectra
• NL 10 log(ltInoisegt/Iref) dB re 1 µPa2/Hz
• Bandwidth ?f
• BW 10 log ?f
• Total noise level NLtotal NL BW

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SNR Budget
Acoustic Signal-to-Noise Ratio (SNR) Calculation Acoustic Signal-to-Noise Ratio (SNR) Calculation Acoustic Signal-to-Noise Ratio (SNR) Calculation

Enter values in yellow boxes

Value units Value Units
Acoustic source level 262 W 195.0 dB re 1 microPascal at 1 m
Range - spherical spreading 10000 m -80.0 dB
Absorption for center frequency 10000 Hz -10.8 dB
Scattering loss (3 dB/bounce) 0 bounces 0.0 dB
Total received signal 104.2 dB

Noise level 10000 Hz 52.0 dB/Hz
Noise in rms bandwidth 1000 Hz 30.0 dB
Total Noise 82.0 dB

Received SNR 22.2 dB

Coherent processing time 0.1 s
Processing gain 20.0 dB

SNR - 1 receiver 42.2 dB

SNR - n receivers 1 42.2 dB

Travel time precision 0.024351 ms

Sound speed precision 0.005479 m/s
Temperature precision 0.001370 K
Range precision 0.036526 m
N digits 100 digits
Time per digit 1 ms
Cycles per digit 10 cycles
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Rms precision of peak locations