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Pressure-particle velocity coherence

Pressure-particle velocity coherence Environmental effects on coherence of pressure–vertical particle velocity 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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Pressure-particle velocity coherence

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  1. Pressure-particle velocity coherence Environmental effects on coherence of pressure–vertical particle velocity 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. R/V Knorr 200 m 77 m 25 m 40 m 50 m WHOI Temp. Array MORAY R/V Knorr (200 m) VLA SSP from WHOI Temp. Array Radar overlay of ISW: Luo, et. al JASA EL 2008 Bottom model from: Choi, et. al JASA EL 2008 Experimental Overview: SW06 • Source suspended at 40 m depth (1 kHz, 4 ms pulses) • Pressure measurements on 2 short VLA (25 m and 50 m depth) • SSP and Bottom Model for PE Simulation

  3. d = 20 cm Instantaneous Intensity PE simulation Data: Finite Difference Approximation pressure horizontal velocity vertical velocity real-valued “measured” signals horizontal instantaneous intensity complex hilbert transform pair ^ : (hilbert transform) vertical instantaneous intensity vertical instantaneous intensity

  4. Complex Intensity active and reactive intensity envelopes Active Reactive PE simulation Data pressure magnitude squared gradients non-propagating energy phase gradients propagating energy flux

  5. SSP Dependent Focusing Focusing of rays due to refraction (creates pressure magnitude gradients beyond spherical spreading) Reactive intensity envelope indicates region of focused sound energy Active intensity envelope indicates arrival angle Scalar intensity, proportional to magnitude pressure squared, is steady PE simulation 4 min Data 25 m Nearby Pressure Maxima 50 m No focusing No focusing

  6. DP BP R SP Pressure-Particle Velocity Coherence 25 m depth - 20 pings (loss of coherence on DP) scalar intensity (log space) vertical intensity (25 m) R DP BP SP p-vz coherence (25 m) Absolute Value Real Part Imaginary Part

  7. Summary • Instantaneous complex intensity describes: • Active • direction of propagating energy • Reactive • focusing of energy: soundspeed profile • constructive/destructive interference • Pressure-vertical particle velocity coherence effected by waveguide focusing effects • Real part signifies direction of propagating intensity • Imaginary part indicates degree of focusing/interference

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