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Temporal Fluctuations and Coherencies of Broadband Signals Observed - - PowerPoint PPT Presentation

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Temporal Fluctuations and Coherencies of Broadband Signals Observed during SW06 Jennifer Wylie Harry DeFerrari University of Miami jwylie@rsmas.miami.edu Outline Experimental Setup Internal Wave Field Potential Energy Temporal

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Temporal Fluctuations and Coherencies of Broadband Signals Observed during SW06

Jennifer Wylie Harry DeFerrari University of Miami jwylie@rsmas.miami.edu

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Outline

  • Experimental Setup
  • Internal Wave Field Potential Energy
  • Temporal Coherence
  • Single Mode, Broadband
  • Data and Models
  • 100 Hz Summary
  • 200 Hz, 800 Hz, 1600 Hz
  • Determination of Modes
  • Summary
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Experimental Setup

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Internal Wave Field Potential Energy

PE = (r /2)h

2N 2

η = T

' /dT /dz

The potential energy of the internal wave field can be estimated by (Gill, 1982): with: On the NJ shelf the Buoyancy Frequency is relatively stable, so the potential energy can be estimated from η 2

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Internal Wave Field Potential Energy

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Temporal Coherence

Temporal coherence is the statistical measure of the change

  • f a waveform in time

COH t,t ( ) = ( p(t)* p(t + t ) )

2 Dt,DT

p(t)2

Dt,DT p(t + t )2 Dt,DT

Types of Coherence:

  • Deterministic: slow changes in coherence, typically recoverable

with phase tracking

  • Multipath: Deterministic but typically unrecoverable
  • Stochastic: Randomized by internal waves, bottom scattering, or a

combination of both

  • Single Mode vs. Multimode
  • Broadband coherence: coherence of the entire pulse

response

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Data and Models

100 Hz Summary

  • 100 Hz coherency is effected by Internal Wave activity
  • Bottom scattering negligible, behaves as if there was a smooth bototm

Low IW Activity High IW Activity

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100 Hz

Shark VLA Data and Model

Cb=1595 m/s One to One mode correspondance

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SLIDE 9

200 Hz

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200Hz

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SLIDE 11

200 Hz

Low IW Activity High IW Activity

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800 Hz

Low IW Activity High IW Activity

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800 Hz

2D PE Model @ 100m depth

C_b=1605 m/s 1st mode – direct path

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1600 Hz

Low IW Activity High IW Activity

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Summary

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Summary

  • 100 Hz
  • Coherency affected by internal wave activity
  • Bottom scattering negligible, behaves like smooth bottom
  • 200 Hz & 800 Hz
  • Bottom scattering becomes important
  • Direct path still affected by internal wave activity
  • Higher modes affected greater by bottom scattering
  • 1600 Hz
  • Bottom Scattering plays the dominate role
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SLIDE 17

References

Gill, A. E., 1982: Atmosphere-Ocean Dynamics. Academic Press, London, United Kingdom, 661 pp Oceanus, Vol. 45, NO. 3, July 2007