Abstract
Spectra of omnidirectional ambient sound have been collected since 1994 at 13 locations around the North Pacific. Data were acquired for 3 minutes every 6 minutes and spectra calculated from 0–500 Hz in 1 Hz bands. With a million spectra per site, this database allows investigation into the statistical character of low-frequency ambient sound at multiple scales. At the shortest scales, the spectral levels in the shipping bands have a fluctuation spectrum similar to a 1/f process, with decorrelation times less than 20 minutes. At intermediate scales, the seasonal baleen whale component becomes the most dominant and repeatable feature. At the longest scales (averaging over the entire record) the ambient levels (at the Pt. Sur site) seem to have increased by up to 10 dB since the 1960s. The distribution of the levels (in decibels) generally indicates a short tail for quieter levels but a long tail for loud events. The Pt. Sur data set has also been used to validate the new dynamic ambient noise model (DANM), which shows good agreement in one-third octave bands to within a couple of decibels for January 1998. These and further results will be discussed. [Work supported by ONR and SPAWAR.]
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