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Monday, July 8 • 15:50 - 16:10
A PARAMETRIC STUDY OF THE ENVIRONMENT AND THE ARRAY CONFIGURATION FOR UNDERWATER NOISE MEASUREMENT FROM SHIPS IN SHALLOW WATER

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In 2016, a standard describing the experimental procedure to measure the underwater sound from ships has been published (ISO17208-1). A second part has been written to correct the measured data from the reflection on the sea surface, effect known as the Lloyd's mirror effect (not published yet). For these procedures, deep waters are required, i.e. a minimum depth of 150 m or 1.5 times the overall ship length. In some maritime areas, this requirement can be difficult to fulfill and the measurements can only be done in shallow waters. It is well known that in a shallow water environment, it is difficult to assess the level of a sound source, because of the multiple reflections on the bottom and on the sea surface. The aim of this study is to understand which parameters influence the sound measured by a hydrophone array in such a configuration, assuming the source level is known. The sound level measured by the hydrophone array is simulated using open source underwater propagation models for propagation distances up to a few hundred meters. The influence of different parameters is successively investigated: source depth, water depth, source range, number of hydrophones, sea bottom properties, speed of sound profile. At low frequencies, the radiation of the source is similar to a dipole because of the Lloyd's mirror effect. At high frequencies, the third-octave bands level tends to a constant number with respect to frequency, which depends on the ratio of water depth to distance to source, and to the sea floor properties. Observations of the results show also that the gap between these two frequency domains is at a fixed value of the acoustic wavenumber multiplied by the source depth. Based on the simulations, empirical formulas are proposed to correct the effect of the shallow water environment.

Moderators
avatar for VENUGOPALAN PALLAYIL

VENUGOPALAN PALLAYIL

DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →

Authors

Monday July 8, 2019 15:50 - 16:10 EDT
Westmount 5
  T12 Underwater & marit. noise, RS01 Underwater sound