Calibration of a Digital Hydrophone Line Array at Low Frequency

The challenges of comparison calibrations of hydrophones in linear arrays at low frequencies are inherent in the length of the array, number of hydrophones, difficulty in achieving free-field conditions, and lack of a suitable low-frequency projector. These challenges were addressed by the development of complementary methods to simultaneously measure the complex sensitivity in the acoustic data channels of hydrophone line arrays with digital telemetry systems. The voltage sensitivities and RC time constants of the array data channels were then estimated by nonlinear regression of calibration data to a simplified model of the acoustic data channel. The methods are demonstrated by the simultaneous calibration of 200 data channels of a digital hydrophone line array at 1/3 octave band center frequencies ranging from 1.2 to 400 Hz. The 95% confidence interval of the voltage sensitivity estimates was not more than 1 dB.