VARIABILITY OF LOW-FREQUENCY AMBIENT SEA NOISE

In March 1976, measurements were made of the ambient sea noise in the South Fiji Basin to the northeast of New Zealand. As part of the analysis, the standard deviation of the noise in each 1/3 octave band between 10–500 Hz was computed. The effect of receiver depth, wind speed, and frequency was examined. There is not a marked dependence of standard deviation on receiver depth. When no shipping was present, the standard deviation was less than 2.5 dB at all frequencies and decreased to under 0.1 dB above 100 Hz. When shipping dominated, the standard deviation was much higher below 100 Hz, being 5.5-7 dB at 10 Hz but decreasing to less than 2 dB above 200 Hz. This behavior is explained by a model in which a single ship dominates. A comparison with the results from other ocean areas indicates three regimes for ship dominated noise: (1) single-ship dominated areas where the standard deviation decreases with frequency; (2) distant multiple-ship dominated areas where the standard deviation increases with frequency; and (3) local multiple-ship dominated areas where the standard deviation is almost independent of frequency. © 1979, American Association of Physics Teachers. All rights reserved.