The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water

Harry A Deferrari, Jennifer Wylie

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The loss of temporal coherence after long range propagation in shallow water is often studied as a consequence of sound speed variability from internal waves. Here we add the complication of small amplitude and very long wavelength random fluctuations of bottom bathymetry. It is shown that the same range dependent sound speed fluctuations result in markedly different coherence times depending on acoustic wavelength and mode number - a first order effect. A range dependent PE code (MMPE) is used to predict temporal coherence for individual surface reflected-bottom-reflected (SRBR) mode arrivals. Here a mode coherence calculation is developed and compared for varying RMS bathymetry. Temporal coherence is inferred from mode coherence. We find first order and/or low frequency modes are insensitive to the bottom but when the (sine of the mode angle approaches 1/10 of an acoustic wavelength) the modes structure in amplitude and phase is randomized and the signal decorrelate rapidly in time from just the slightest temporal variations in sound speed. It doesn't take much; just 1 m in 200m of range will randomize all but the first mode at mid frequencies (.5 to 1 kHz). Predictions are in close agreement with SW06 mode coherence measurements.

Original languageEnglish (US)
Title of host publicationProceedings of Meetings on Acoustics
Volume19
DOIs
StatePublished - 2013
Event21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America - Montreal, QC, Canada
Duration: Jun 2 2013Jun 7 2013

Other

Other21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America
CountryCanada
CityMontreal, QC
Period6/2/136/7/13

Fingerprint

bathymeters
shallow water
acoustics
wavelengths
internal waves
arrivals
low frequencies
propagation

ASJC Scopus subject areas

  • Acoustics and Ultrasonics

Cite this

Deferrari, H. A., & Wylie, J. (2013). The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water. In Proceedings of Meetings on Acoustics (Vol. 19). [070026] https://doi.org/10.1121/1.4800485

The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water. / Deferrari, Harry A; Wylie, Jennifer.

Proceedings of Meetings on Acoustics. Vol. 19 2013. 070026.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Deferrari, HA & Wylie, J 2013, The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water. in Proceedings of Meetings on Acoustics. vol. 19, 070026, 21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America, Montreal, QC, Canada, 6/2/13. https://doi.org/10.1121/1.4800485
Deferrari HA, Wylie J. The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water. In Proceedings of Meetings on Acoustics. Vol. 19. 2013. 070026 https://doi.org/10.1121/1.4800485
Deferrari, Harry A ; Wylie, Jennifer. / The effect of random fluctuations in bottom bathymetry on acoustic coherence in shallow water. Proceedings of Meetings on Acoustics. Vol. 19 2013.
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