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Acoustic intensity properties in an ocean waveguide

Acoustic intensity properties in an ocean waveguide Measurement and simulation of waveguide intensity structures David Dall ’ Osto and Peter H. Dahl Applied Physics Laboratory University of Washington. Pacific Rim Underwater Acoustics Conference 2011 5-7 October 2011 Jeju Island, Korea.

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Acoustic intensity properties in an ocean waveguide

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  1. Acoustic intensity properties in an ocean waveguide Measurement and simulation of waveguide intensity structures David Dall’Ostoand Peter H. Dahl Applied Physics Laboratory University of Washington Pacific Rim Underwater Acoustics Conference 2011 5-7 October 2011 Jeju Island, Korea

  2. TAVEX Experiment R/V Sunjin NRL VLA Range : 190 ~ 920 m 16 channels seperation : 3m fs : 20.47 kHz Bulb source Depth: ~35 m Weight Battery & Data Acquisition frames Acoustic release Weight (1 ton) ρb = 1650 kg/m3 cb = 1600 m/s 12 bulb implosions (~40 m depth) measured on a VLA A1 pressure signal (190 m)

  3. Acoustic Intensity Requires collocated measurement of both pressure and particle velocity Finite Difference Approximation Scalar Intensity (conservation of momentum) Instantaneous Intensity pressure at midpoint Complex Intensity particle velocity along array complex signal from real signal Active Intensity Envelope Hilbert Transform measured signal 90° out of phase Reactive Intensity Envelope

  4. Complex Intensity: 190 m 27.5 m Active Intensity Envelope Reactive Intensity Envelope 27.5 m DATA SIMULATION

  5. Intensity structures: frequency domain B = 300 Hz fc = 210 Hz Normalized Quantity: pressure-intensity index • Crests (pressure/intensity maxima) • Dislocations (pressure/intensity nulls) scalar intensity: f = 210 Hz (pekeris) null crest

  6. DATA (190 m) PE SIMULATION Frequency/Range Structure waveguide invariant Waveguide invariant observed in broadband measurements

  7. DATA Experimental Visualization NB 210 Hz PE simulation Broadband every 50 m

  8. Summary • Complex Vertical Intensity: • Active: direction of energy propagation • Reactive: energy focusing/interference • Intensity structures: pressure-intensity index • crests: |pI|<1 and |pQ|<1 • nulls/dislocations: |pI|>1 and |pQ|>1 • The waveguide invariant: • map frequency to range • contours depict the modal structure of waveguide

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