Designing practical on-site calibration protocols for acoustic systems: key elements and pitfalls

Although acoustic systems are increasingly being used for environmental and noise surveys of marine energy devices, there are currently no standard protocols for the on-site full bandwidth calibration of these systems. Reports often include little or no information on the methods of calibration used before, during or after surveys. Without proper calibration, the sound levels may be far from accurate, leading to skewed reporting and inaccurate conclusions. Hydrophone calibrations from internationally recognised standardisation centres, such as NPL, allow providers to reference their systems to international standards. Marine renewable energy devices, however, are often deployed in remote areas and it is not always practical or cost-effective to send every acoustic system to be independently tested before every deployment. On-site referencing of multiple units to a single standardised system can help improve calibration traceability. Although this may at first appear relatively simple, the production of an accurate, full-spectrum calibration, particularly in real-world test sites, is surprisingly difficult.