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Ambient and Ship-Induced Low-Frequency Noise in Shallow Water

  • Bernd Schmalfeldt
  • Dieter Rauch
Part of the NATO Conference Series book series (NATOCS, volume 5)

Abstract

This paper describes some features of extremely low-frequency hydroacoustic and seismic noise (1 to 10 Hz) in coastal waters. The data have been collected by a single tri-axial ocean-bottom seismometer equipped with an additional hydrophone. The following aspects are considered.
  1. a.

    modification of the background power-spectra by ship noise.

     
  2. b.

    coherence and phase spectra between the seismic components.

     
  3. c.

    direction-finding based on the azimuthal power-distribution.

     

The hydroacoustic and seismic power-spectra are very similar in general shape. However, for some significant lines the output of the horizontal geophones indicates a higher signal-to-noise ratio. The horizontally polarized energy may be used to determine the direction to the source once the propagation mechanism has been identified by means of all seismic sensors. It has been proved that ship-induced infrasonic noise is propagating in form of seismic interface waves with their characteristic elliptical particle motion.

Keywords

Ambient Noise Seismic Noise Phase Spectrum Seismic Sensor Power Pattern 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    D. Rauch, Experimental and theoretical studies of seismic interface waves in coastal waters, (This volume).Google Scholar
  2. 2.
    H. H. Essen, Model computations for low-velocity surface waves on marine sediments, (This volume).Google Scholar
  3. 3.
    F. Schirmer, Experimental determination of properties of the Scholte wave in the bottom of the North Sea, (This volume).Google Scholar
  4. 4.
    G. C. Carter, C. H. Knapp and A. H. Nuttall, Estimation of the magnitude-squared coherence function via overlapped fast Fourier transform processing, IEEE Trans. Audio Electro-acoustics AU-21: 337–344 (1973).CrossRefGoogle Scholar
  5. 5.
    H. Berckhemer, The concept of wide band seismometry, in: “Proceedings of XIIe Assemblée Générale de la Commission Séismologique Européenne, Luxembourg, 21–29 Sep, 1970”, pp. 214–220.Google Scholar

Copyright information

© Plenum Press, New York 1980

Authors and Affiliations

  • Bernd Schmalfeldt
    • 1
  • Dieter Rauch
    • 1
  1. 1.SACLANT ASW Research CentreLa SpeziaItaly

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