National Physical Laboratory

Calibration and characterisation of sonar transducers and systems


Wraysbury Open-Water Facility

The facility is based on the reservoir at Wraysbury, near Staines, Middlesex, and consists of a calibration raft located on a 1000 x 2000 metre fresh water reservoir.

Features include:

  • Average water depth of over 20 m
  • Frequency range from below 250 Hz to 350 kHz
  • Full range of acoustic parameters that characterise the performance of acoustic transducers or complete sonar systems
  • Three separate, fully instrumented measurement stations
  • Cranes and handling equipment capable of deploying large sonar arrays up to 1.5 tonne
  • Two launches for deploying targets or towing transducers such as side scans
  • Accreditation to ISO 17025 by UKAS for transducer sensitivity and electrical impedance in the frequency range 250 Hz to 350 kHz

The facility is the main provider of sonar calibration services to the UK Ministry of Defence (no charge for use when quoting a valid UK MOD contract).

The facility is also available for use by non MOD customers on a commercial basis.

With the Wraysbury open-water acoustic calibration and test facility, NPL offers:

  • Commercially independent service
  • Direct access to internationally validated standards at NPL, a world-recognised National Metrology Institute with a proven track record in international measurement comparisons
  • International recognition of calibration and test certificates

Wraysbury test rig


NPL provides a unique a range of facilities and measurement services to meet the individual measurement needs of the customer.

Calibration Services

NPL currently provides the following underwater acoustics calibration services, some of which are accredited to ISO17025 by the United Kingdom Accreditation Service (UKAS):

  • Calibration of underwater acoustic transducers and hydrophones in the frequency range 250 Hz to 350 kHz at the Wraysbury open-water facility. Measurements of sensitivity and electrical impedance are accredited to ISO 17025 via UKAS.
  • Directional response measurement of hydrophones and transducers in the frequency range 250 Hz to 350 kHz over 360 degrees of rotation in both the horizontal and vertical plane.
  • Full system characterisation for sonars including transmit and receive sensitivity, electrical impedance, directional response, etc.


Our experienced team of scientific staff offer a flexible cost-effective approach to test work with a choice of service arrangements:

  • Fixed price - Calibration and tests undertaken by NPL staff on customer devices to a schedule agreed with the customer, with results presented in a report.
  • Day rates - Calibration and tests undertaken by NPL staff in collaboration with customer staff on customer devices to a schedule agreed with the customer.
  • Facility hire rates - Hire of facility by customer including NPL staff trained to use the facility. The Wraysbury open-water facility has calibrated reference transducers/hydrophones and instrumentation available to measure the full range of acoustic parameters that characterise the performance of underwater acoustic devices and systems. The site has the capability to deploy large devices up to 1.5 tonne and a motor launch with GPS available for remote deployment/towing.

Other options may also be considered.

Download Underwater Open-Water Facility flyer Adobe pdf file
Download Characterisation of Underwater Acoustic Transducers flyer Adobe pdf file

Customer Services tel: +44 20 8943 8631

Last Updated: 18 Apr 2011
Created: 6 Jun 2007


Please note that the information will not be divulged to third parties, or used without your permission