2019_programme: LOW FREQUENCY HYDROPHONE CALIBRATION WITH A LASER INTERFEROMETER

• Session: 02. Underwater acoustic calibration, testing, facilities and standards
  Organiser(s): Robinson Stephen, Humphrey Victor, Linné Markus, Évora Victor
• Lecture: LOW FREQUENCY HYDROPHONE CALIBRATION WITH A LASER INTERFEROMETER [invited]
  Paper ID: 930
  Author(s): Ward Jacob, Robinson Stephen
  Presenter: Ward Jake
  Presentation type: oral
  Abstract: This paper describes experimental work that aims to provide a new method for primary pressure calibration of hydrophones in the frequency range from 20 Hz to 250 Hz. A measurement setup with a laser interferometer has been used to realise the acoustic pascal in an enclosed chamber. An optically flat piston is driven harmonically in a chamber containing both a fluid and a hydrophone to be tested. The absolute displacement of the piston is determined by fringe counting on a Michaelson interferometer. The thermodynamic properties of the fluid are used to calculate the absolute acoustic pressure that the hydrophone is exposed to from the volume change in the chamber. An advantage of such primary calibration is its traceability to primary standards of length via the wavelength of laser light. Some provisional hydrophone calibration results are shown and a discussion provided on potential sources of uncertainty. This method offers a possible primary standard for the low frequency range where regulation mandates the monitoring of absolute noise levels in the ocean, and where many sound sources of concern emit the most of their energy.
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• Corresponding author: Dr Ward Jacob
  Affiliation: National Physical Laboratory UK
  Country: United Kingdom
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