Abstract
Air-dropped sonobuoys have been used to record sounds near bowhead whales since 1979. They have not been observed to react to sonobuoys dropped 0.5–1 km from them during numerous studies conducted during the summer; however, on a few occasions they have reacted to sonobuoys air dropped near them during their spring and fall migrations. The sound from an AN/SSQ-57A sonobuoy impact was recorded at distance 800 m in water 90 m deep in the western Beaufort Sea. Hydrophone depths were 3 and 18 m. Analysis of the impact signature and sound transmission paths revealed two reflected paths: one with a single bottom reflection and the second with two bottom reflections. A third arrival, occurring later and very weak, was also noted. The presence of a strong, low-frequency sound source nearby led us to high-pass filter the signal at 1 kHz. Analysis of the received signal amplitude, corrected for spreading loss, revealed a peak source pressure level of 211 dB re: 1 μPa/m. The positive acoustic impulse at a distance of 1 m, assuming no positive pulse spreading and scaling the pressure for spherical spreading, is estimated to be 5.55 Pa/s. The overall sound duration of the single bottom bounce arrival was 0.9 ms. [Work supported by MMS.]
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