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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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slide1

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

slide2

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
slide3

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

slide4

Complex Intensity

active and reactive intensity envelopes

Active

Reactive

PE simulation

Data

pressure magnitude squared gradients

non-propagating energy

phase gradients

propagating energy flux

slide5

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

slide6

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

summary
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