UACE2017 Proceedings: Discrete Time Techniques for Digital Hydrophone Calibration

Session:
Underwater acoustic calibration, testing, facilities and standards
Paper:
Discrete Time Techniques for Digital Hydrophone Calibration
Author(s):
Jay Abel
Abstract:
A digital hydrophone is an acoustic acquisition system comprised of a sensing element, amplifier, acquisition subsystem and means for communicating a digital representation of the received signal. The entire system is integrated into a single waterproof enclosure which becomes part of the acoustic environment. Since the operator does not have access to the analogue hydrophone output, calibration signal amplitudes must be determined from the digital output alone. The requirements for calibrating analogue hydrophones still apply, however additional challenges to be overcome include: Synchronization of the digital output signal to the projector and reference hydrophone waveforms; accurate determination of test tone amplitudes from data sampled at rates close to the Nyquist-Shannon limit; low-frequency amplitude errors caused by improper signal gating, and accommodating the waterproof enclosure, which in some cases may be too large for a standard test tank, and which may affect acoustic compliance. Sources of amplitude error as high as 1 dB at low frequencies and up to 6 dB for certain higher frequencies are identified. Specific recommendations are given to address the challenges identified
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