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Related Experiment Videos

Computed narrow-band time-reversing array retrofocusing in a dynamic shallow ocean.

M R Dungan1, D R Dowling

  • 1Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor 48109-2121, USA.

The Journal of the Acoustical Society of America
|June 30, 2000
PubMed
Summary

Time-reversing arrays (TRA) can focus sound energy back to its source. TRA performance in shallow waters is affected by factors like frequency, depth, and environmental conditions, with dynamic conditions showing mixed results.

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Area of Science:

  • Acoustics
  • Oceanography
  • Signal Processing

Background:

  • Time-reversing arrays (TRA) possess the unique ability to retrofocus acoustic energy to its source location without prior environmental knowledge.
  • TRA performance can be compromised in challenging acoustic environments, including those with time-dependent variations, noise, or significant propagation losses.

Purpose of the Study:

  • To predict the retrofocusing performance of TRA in shallow-water sound channels.
  • To investigate the impact of various environmental and operational parameters on TRA capabilities.

Main Methods:

  • Monochromatic acoustic propagation simulations using the parabolic equation code, RAM.
  • Analysis of TRA performance under varying conditions, including source-array range, source depth, acoustic frequency, bottom absorption, internal wave strength, and round-trip time delay.

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Main Results:

  • Higher acoustic frequencies, deeper source depths, and lower bottom absorption enhance TRA performance and extend retrofocusing range in static channels.
  • In dynamic shallow-water channels with internal waves, retrofocus size slightly decreases, and sidelobes are suppressed compared to static channels.
  • These dynamic effects provide benefits for approximately 1-2 minutes at 500 Hz and 10 km range, after which internal waves cause significant amplitude decay.

Conclusions:

  • TRA performance is sensitive to environmental parameters in shallow-water acoustics.
  • Dynamic oceanographic conditions, specifically internal waves, can both degrade and, for short durations, improve TRA retrofocusing characteristics.
  • Optimizing TRA deployment requires careful consideration of acoustic frequency, source-array geometry, and environmental dynamics.