2023_programme: Low frequency primary pressure calibration techniques at NPL

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  • Session: 18. Underwater acoustic calibration and standards
    Organiser(s): Stephen Robinson, Markus Linné and Victor Évora
  • Lecture: Low frequency primary pressure calibration techniques at NPL
    Paper ID: 1962
    Author(s): Malcher Freya, Barham Richard, Ford Benjamin, Robinson Stephen, Cheong Sei-Him, Ablitt Justin, Wang Lian
    Presenter: Malcher Freya
    Abstract: Low frequency Acoustics, Underwater Acoustics and Vibration (AUV) phenomena are used to detect major natural events such as tsunamis, earthquakes and volcanic activity. They are also used by the International Monitoring System to check compliance of the Comprehensive Nuclear-Test-Ban Treaty. Low frequency sound monitoring technologies are well established, but the reliability of the data obtained is limited because the lowest frequencies are not sufficiently covered by current measurement standards. In my presentation I will describe the work that NPL is doing as part of the Infra-AUV project to develop low frequency primary pressure calibration techniques for hydrophones.\nTwo techniques for primary pressure calibration are under development. The first is a laser pistonphone which used a piston to drive a small air-filled chamber containing the hydrophone under test. Optical interferometry is used to determine the motion of a piston and therefore the pressure generated in the chamber. The laser pistonphone can be used to calibrate hydrophones the frequency range from 0.5 Hz to 250 Hz. The second is the coupler reciprocity method in which hydrophones are calibrated in a small chamber of water using the same set of measurements as those required for free-field reciprocity calibration. The hydrostatic pressure in the coupler chamber can also be increased to simulate depth in the ocean. The coupler reciprocity method can be used to calibrate hydrophones the frequency range from 20 Hz to 2 kHz and hydrostatic pressures up to 7 MPa. These primary pressure calibration methods will support new measurement services at NPL and improve the traceability of sound measurement and monitoring applications at low frequencies.
  • Corresponding author: Ms Freya Malcher
    Affiliation: National Physical Laboratory
    Country: United Kingdom
    e-mail:

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