Obtaining a Reverberant Tank’s Transfer Function and Its Application to the Calibration of Acoustic Transducers and Recorders

Abstract

This article describes a method for the experimental determination of the reverberant field transfer function of an acoustic test tank in the frequency domain. Once obtained, the transfer function enables the calibration of transducers and marine recorders in a reverberant field. The method relies on a room acoustics framework for mathematically separating the direct and reverberant fields in a point inside the tank, but employs a transducer-centric model that dispenses with extensive characterization of the tank itself. A calibration experiment in the 1–24 kHz band of an omnidirectional SX147 transducer is conducted in the reverberant field, resulting in mean absolute errors of 0.78 and 1.00 dB, respectively for the receive and transmit voltage responses, relative to the free-field calibration. The expanded uncertainty (coverage factor of 2) in the calibration arising from the spatial averaging of the transfer function ranges from 4.63% to 8.57% . The model is extended to include a transfer function that models the effect of an acoustic recorder’s body on the field near the hydrophone, presenting a feasible method for obtaining the sensitivity of the recorder. An experiment shows that the free-field sensitivity of the standalone hydrophone can be recovered after compensating the measurements for the tank’s and recorder’s transfer functions with absolute errors smaller than 0.92 dB. The expanded uncertainty due to spatial averaging of 20 measurements in determining the recorder’s transfer function ranges from 6.31% to 13.23% .