Calibration of an underwater sound source at very low frequency

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