Pressure-particle velocity coherence Environmental effects on coherence of pressure–vertical...
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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
Transcript of Pressure-particle velocity coherence Environmental effects on coherence of pressure–vertical...
Pressure-particle velocity coherence
Environmental effects on coherence of pressure–vertical particle velocity
David Dall’Osto and Peter H. Dahl
Applied Physics LaboratoryUniversity of Washington
Pacific Rim Underwater Acoustics Conference 20115-7 October 2011Jeju Island, Korea
Radar overlay of ISW: Luo, et. al JASA EL 2008
WHOI Temp. Array
MORAY R/V Knorr (200 m) VLA
Bottom model from: Choi, et. al JASA EL 2008
SSP from WHOI Temp. Array
200 m
40 m
25 m
50 m
R/V Knorr
77 m
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
)}(Re{)}(Re{)( tvtptS
Data: Finite Difference Approximation
dtd
tptptv
tptptp
t
M
M
z
0
21
0
21
)()(1)(
2
)()()(
)(ˆ)()(
)(ˆ)()(
tvitvtv
tpitptp
zz MMz
MM
real-valued “measured” signals
complex hilbert transform pair
d = 20 cm
Instantaneous Intensity
PE simulation
: (hilbert transform)
vertical instantaneous intensity
horizontal instantaneous intensity
pressure horizontal velocity vertical velocity
vertical instantaneous intensity
^
)()()( *21 tvtptIc
Complex Intensity
active and reactive intensity envelopes
)()()( tQitItIc
)(Re)( tItI c
Active
)(Im)( tItQ c
Reactive
pressure magnitude squared gradientsnon-propagating energy
phase gradientspropagating energy flux
PE simulation
Data
)(tI z )(tQz
4 min
No focusing
SSP Dependent Focusing
Nearby Pressure Maxima
25 m
50 m
)(tI z )(tQz )(tI p
Focusing of rays due to refraction (creates pressure magnitude gradients beyond spherical spreading)
Active intensity envelope indicates arrival angle
Reactive intensity envelope indicates region of focused sound energy
PE simulation
Data
Scalar intensity, proportional to magnitude pressure squared, is steady
No focusing
)(tI p )(tQz )(tQz)(tI p
25 m depth - 20 pings (loss of coherence on DP)
nzzn
nz
pvtvtvtptp
tvtpt
z
)()()()(
)()(
**
*
Pressure-Particle Velocity Coherence
DP
SP
BP R
vertical intensity (25 m)
p-vz coherence (25 m)
Real Part Imaginary Part
Absolute Value
scalar intensity (log space)
DPSP
BP R
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
