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Published on: September 3, 2021
Temporal coherence of mode arrivals
The Journal of the Acoustical Society of America
|December 3, 2008
Summary
Low-frequency (100 Hz) acoustic signals show high temporal coherence in shallow water, unaffected by internal waves. Higher frequencies (800 Hz) exhibit reduced coherence due to combined internal wave and bottom scattering.
Area of Science:
- Ocean Acoustics
- Acoustic Wave Propagation
- Underwater Sound Scattering
Background:
- Internal waves significantly impact acoustic signal coherence in shallow water environments.
- Understanding acoustic propagation variability is crucial for underwater acoustic applications.
Purpose of the Study:
- To compare temporal coherencies of 100 Hz and 800 Hz acoustic signals under varying internal wave conditions.
- To investigate the dominant scattering mechanisms affecting different acoustic frequencies in shallow channels.
Main Methods:
- Broadband acoustic signals (100 Hz and 800 Hz) were transmitted through identical shallow channels.
- Signal coherencies were analyzed during periods of low and high internal wave energy.
- The influence of internal wave and bottom scattering was assessed.
Main Results:
- 100 Hz signals maintained high temporal coherence (t(coh)>1 h) and distinct modes.
- 800 Hz signals showed a near continuum of modes with significantly shorter coherence times.
- Higher-order modes at 800 Hz were less coherent.
- Internal wave scattering dominated 100 Hz signals, while both internal wave and bottom scattering affected 800 Hz signals.
Conclusions:
- Acoustic signal coherence is frequency-dependent and influenced by scattering mechanisms.
- Internal wave scattering is a primary factor for lower frequencies, while higher frequencies are affected by both internal wave and bottom scattering.
- Results align with previous observations at intermediate frequencies and other sites.
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