International comparisons of hydrophone calibrations

In the global markets which are increasingly dominating industrial trade, international comparison of hydrophone calibrations is the primary mechanism of ensuring harmonization of underwater acoustics measurement standards across national borders. This paper describes the results of several recent comparison exercises initiated in Europe and the USA. These include both informal comparisons of hydrophone calibrations of a bilateral nature and formal comparisons involving a number of countries organized under the auspices of regional or international metrology organizations. Completed projects which will be described include a Euromet/European Commission project involving a total of 12 participants from seven European countries and a comparison between the Russian Federation and China. In these cases, results will be given and the important conclusions summarized. Finally, a relatively new comparison project will be described which has been set up under the auspices of the Consultative Committee for Acoustics, Ultrasound and Vibration (CCAUV) of the Bureau International des Poids et Mesures (BIPM) in Paris. This key comparison has now been agreed to for the kilohertz frequency range 1–500 kHz and will involve the circulation of three hydrophones. Countries participating in the comparison include the UK, China, Germany, Russian Federation, and USA, with Canada expected to join soon.