Calibration of an underwater sound source at very low frequency

Abstract

Describes an experiment carried out to calibrate a very low frequency sound source in deep water using a method similar to that described by Carey et al. (1987). In the experiment, a cw sound signal was recorded as the uncalibrated source was towed past a vertical line array out to ranges of about 3 km. At these close ranges the sound field is dominated by the Lloyd's mirror interference pattern which arises as a result of the interaction between the direct and surface-reflected sound paths. The calibration procedure is based on a comparison of the measured sound field with numerical calculations of the Lloyd's mirror interference field. The experimental track for the towed source was determined using GPS navigation records, and the source-receiver range was checked using the beamforming capability of the array. The signals recorded on a single hydrophone were processed to determine the received sound level versus range, and these data were corrected for the transmission loss using a full-wave numerical model for the sound field. The corrected sound levels provided a measure of the source level of the uncalibrated source. Calibration results are presented for three phones when the source was transmitting at a frequency of 10 Hz with an output voltage of 30 volts.<>