Comparing Acoustic Measurements of Underwater Materials in Pressure Tanks Using a Calibration Panel

Researchers in the United Kingdom and the United States worked together to compare acoustic panel measurement methods and equipment using a calibration test panel. Underwater testing can be used to calibrate various transducers or to measure acoustic properties of materials, from which material properties can then be derived. The calibration panel used in this study consisted of a rubber material. Tests were initially conducted in the Acoustic Pressure Vessel (APV) at the National Physical Laboratory (NPL) in Teddington, UK and were subsequently performed in the Acoustic Pressure Tank Facility (APTF) at the Naval Undersea Warfare Center (NUWC) in Newport, Rhode Island, USA. The UK tank is a smaller-scale version of the US tank. However, the measurement approaches developed by the two groups of researchers differs. The UK utilized a parametric source with a baffle and a planar hydrophone array for reflection and transmission measurements. The US used a spherical source, a linear pseudo-array along with coherent subtraction for reflection, and a single hydrophone for transmission measurements. Early results indicated that the measurement methods showed significant discrepancies, but refurbishment of the US facility and subsequent re-testing of the panel delivered results that were in good agreement between the two groups.