Abstract:
In an effort to quantify the long-term statistics of ambient sound in an ocean basin, data are being collected on 13 SOSUS receivers in the North Pacific. The present data set is over a year long and consists of power spectra from single hydrophones computed every 5 min from 5 to 500 Hz in 1-Hz bands. The clearest feature in many of the spectrograms is a strong seasonal cycle in the 15- to 20-Hz band with peak-to-peak amplitudes up to 25 dB. This is attributed to the presence and the migration of blue and fin whales. Probability statistics as a function of frequency show that the 10% probablity sound level is typically 3--5 dB above the median level, and the 1% level is 10 dB higher. The records have been broken into three frequency bands for further analysis: 17 Hz (whales), 30--100 Hz (shipping), and 200--400 Hz (wind-generated sound). Only for the first band is there significant correlation between arrays. There is no correlation between the high-frequency band and ECMWF estimated wind speed at a receiver location. There is no obvious seasonal cycle in the 200- to 400-Hz band. [Work supported by ONR.]