Underwater acoustic metrology related activities at the USRD are multi-faceted in the protocols, depth and capabilities related to acoustic reference services.
Formalized protocols established in ANSI/ASA S1.20 (Procedures for Calibration of Underwater Electroacoustic Transducers) and, to a degree, those established in IEC 60565 (Underwater acoustics - Hydrophones - Calibration in the frequency range 0,01 Hz to 1 MHz ) form the foundation of the standardized procedures utilized in the underwater acoustic calibration work performed by USRD. These are, respectively, nationally and internationally recognized standards. USRD has had and continues to have key involvement in the content and structure of the ANSI/ASA S1.20 standard.
Primary calibrations of acoustic receive sensitivity for underwater hydrophones are accomplished via the use of the reciprocity calibration technique. This technique utilizes the measurement of electronic parameters coupled with an intimate knowledge of the controlled acoustic environment under which the measurements are undertaken. The reciprocity technique is performed at USRD within acoustical free-field test environments and within small pressure vessels (designated as Reciprocity Couplers) for applicable low frequency measurements.
Round Robin Units
USRD participates in internal and external tests of devices designated as Round Robin units. These Round Robin units are comprised of a representative set of hydrophones covering the significant frequency range over which measurements are typically conducted in the underwater acoustics arena. The Round Robins allow comparisons of measurements to be made on the same physical unit at multiple test locations. The data gathered from these measurements is used as part of an overall quality assurance process. Significant external test events of this nature have involved USRD’s past and continuing participation in the CIPM (International Committee for Weights and Measures) Key Comparison for the Calibration of hydrophones in the frequency range from 1 kHz to 500 kHz. CIPM meets in accordance with the BIPM (International Bureau of Weights and Measures). The involvement with the CIPM highlights USRD’s presence with an international community emphasizing the promotion of world-wide uniformity in units of measurement and their traceability to the International Systems of Units (SI). USRD is the United States recognized NIST-deferred to activity for underwater acoustic calibrations.
For questions or assistance in obtaining acoustic metrology services, please contact the Acoustic Metrology Group at: