ore 654 applications of ocean acoustics lecture 6b ocean noise
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ORE 654 Applications of Ocean Acoustics Lecture 6b Ocean Noise. Bruce Howe Ocean and Resources Engineering School of Ocean and Earth Science and Technology University of Hawai’i at Manoa Fall Semester 2011. Noise. Noise spectra NL = 10 log(/I ref ) dB re 1 μPa 2 /Hz Classic - PowerPoint PPT PresentationTRANSCRIPT
ORE 654Applications of Ocean Acoustics
Lecture 6bOcean Noise
Bruce HoweOcean and Resources Engineering
School of Ocean and Earth Science and TechnologyUniversity of Hawai’i at Manoa
Fall Semester 2011
04/21/23 1ORE 654 L5
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Noise• Noise spectra• NL = 10 log(<Inoise>/Iref)
dB re 1 μPa2/Hz
• Classic“Urick” curves
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Ship noise
• Radiated sound
04/21/23 ORE 654 L1 4Gerald D’Spain
Low frequency noise - wind
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Station ALOHA, 20 months
Bioacoustic sound
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D’Spain
Offshore a military training base
Measuring wind and rain
04/21/23 ORE 654 L1 8Nystuen
Wind
Rain
Rain
Nystuen
Large whales – using SOSUS
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Andrew, Howe, and Mercer
Annual average
All – 6 yrs
Bowhead and beluga whale and walrus sounds
• Spectrogram of under ice
• northernBering Sea in May 2007
04/21/23 ORE 654 L1 10
159th Meeting of the Acoustical Society of America Spring 2010:
Baltimore
Comparison Wenz vs APL vs Ross Ross: Mechanics of Underwater Noise (1976)Ross: Mechanics of Underwater Noise (1976)
& Acoustics Bulletin (1993) & Acoustics Bulletin (1993)
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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NLS1 = 17 - 30(log f)
NLS2 = 40 + 20(D - 0.5) + 26(log f) - 60(log(f + 0.03)
NLS3 = 50 + 7.5 w1/2 + 20(log f) - 40(log(f + 0.4)
NLS4 = -15 + 20(log f)
NLSAll = 10 log(10NLS1 /10 +10NLS2 /10 +10NLS3 /10 +10NLS4 /10 )NL = NLS + 10 log BW
Noise• Noise spectra• NL = 10 log(<Inoise>/Iref)
dB re 1 μPa2/Hz
• Bandwidth Δf• BW = 10 log Δf
• Total noise level NLtotal = NL + BW
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SNR BudgetAcoustic Signal-to-Noise Ratio (SNR) Calculation
Enter values in yellow boxes
Valueunits ValueUnits
Acoustic source level 262W 195.0dB re 1 microPascal at 1 mRange - spherical spreading 10000m -80.0dBAbsorption for center frequency 10000Hz -10.8dB
Scattering loss (3 dB/bounce) 0bounces 0.0dBTotal received signal 104.2dB
Noise level 10000Hz 52.0dB/HzNoise in rms bandwidth 1000Hz 30.0dB Total Noise 82.0dB
Received SNR 22.2dB
Coherent processing time 0.1sProcessing gain 20.0dB
SNR - 1 receiver 42.2dB
SNR - n receivers 1 42.2dB
Travel time precision 0.024351ms
Sound speed precision 0.005479m/sTemperature precision 0.001370KRange precision 0.036526mN digits 100digitsTime per digit 1msCycles per digit 10cycles
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SNR =SL−TL−αR−(NL + BW)+ PG
Rms precision of peak locations
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β f = 2π ( f − f0 )2 ϒ( f )⎢⎣ ⎥⎦2df
0
∞
∫⎡
⎣⎢
⎤
⎦⎥
1/2
rms bandwidth
β t = 2π (t − t0 )2 γ (t)⎢⎣ ⎥⎦2dt
0
∞
∫⎡
⎣⎢
⎤
⎦⎥
1/2
rms time duration
βφ = 2π (x − x0 )2 In (x)dx0
∞
∫⎡
⎣⎢
⎤
⎦⎥
1/2
rms antenna length, x in λ
SNRa ≡2E
Namplitude SNR
σ t =1
β f; σ ν =
1
β t; σ φ =
1
βφhalf peak widths - time, Doppler, angle
σ t ' ==σ tSNRa
; σ ν ' ==σ νSNRa
; σ φ ' ==σ φSNRa
peak precisions
σ t ' =1
f0SNRaif high SNR, can use phase/carrier frequency