This paper describes the design and implementation of a low frequency hydrophone calibration system, using a vibrating water column. The hydrophone to be calibrated is immersed in the water column and the position of the transducer is kept constant while a hydrodynamic pressure field is generated in the water column by means of a shaker (similar to what is described in IEC 60565). F. Schloss et al. used a vibrating water column for hydrophone calibration in the frequency range from 10 Hz to 700 Hz. 1 An interlaboratory comparison calibration was carried out by the Russian Metrological Institute of Technical Physics and Radio Engineering (VNIIFTRI) and Hangzhou Applied Acoustics Research Institute (HAARI) in the frequency range from 250 Hz to 1 kHz. 2 The dimensions of the test vessel are important for deciding the frequency range of operation. Simulations were carried out for the selection of vessel material and dimension. To overcome limitations in the frequency range caused by resonance in the water column, the principle of operation was modified from absolute calibration to calibration by comparison. By using a single cylindrical vessel, the frequency range is extended to cover frequencies from less than 100 Hz to 1 kHz. The calibrated reference hydrophone type Bruel & Kjaer (B&K) 8104 is used in this calibration. Some results obtained from the use of the calibration system are also presented in this paper.

Accurate determination of sensitivity and directivity is important for any underwater acoustic transducer. In this work, an automatic measuring platform was designed and implemented for characterizing underwater acoustic transducers. The overall hardware setup includes a PXI (PCI Extensions for Instrumentation)-based data acquisition system, computer-based controller module, motion controller module, and LabVIEW-based automatic calibration program. The system performs a sequence of operations automatically and achieves synchronous control of transmission and acquisition of real-time acoustic signals as well as processing, recording, and report generation. This measurement platform can be utilized for characterizing any type of acoustic transducer for its receiving sensitivity, transmitting response, and directivity measurement as per IEC60565 standard. The measurement results for RESON TC4034 and RESON TC 2080 transducers are presented and the results show that the system is able to carry out accurate calibration and characterization of any underwater acoustic transducer. Sources of uncertainty for calibration are also presented with the confidence level of approximately 95%.