Correlation of deep ocean noise (0.4-30 Hz) with wind, and the Holu Spectrum-a worldwide constant

One year of ambient ocean noise data, 0.4 to 30 Hz, from the Wake Island hydrophone array in the northwestern Pacific are compared to surface wind speeds, 0–14 m/s (0–28 kn). Between 0.4 and 6 Hz, noise levels increase with wind speed at rates of up to 2 dB per m/s until a saturation is reached having a slope of about −23 dB/octave and a level of 75 dB relative to 1 μPa/√Hz at 4 Hz. This noise saturation, called the ‘‘Holu Spectrum,’’ likely corresponds to saturation of short-wavelength ocean wind waves. It is probably a worldwide constant. Between 4 and 30 Hz, noise also increases with wind speed at rates of up to 2 dB per m/s, but no saturation level is observed and the slope increases to about 4 dB/octave. This may be acoustic noise from whitecaps. On a hydrophone less than 3 km from Wake, noise between 0.5 and 10 Hz increases with wind speed at a rate up to 2 dB per m/s, but absolute noise levels are significantly higher than levels on the other hydrophones more distant from Wake, and no saturation is apparent. Surf breaking against the shore of the island is the probable source of this noise.