In early descriptions, ocean noise was related to sea state (Knudsen et al. 1948). By this theory, noise
levels increase with increasing sea state by the same amount across the entire frequency band from 1 kHz
to 100 kHz. More recent work has suggested that noise is better correlated with wind speed than with sea
state or wave height. The correlation between noise and wind speed allows for more accurate prediction, as
sea states are more difficult to estimate than wind speeds. In the open ocean, the noise of breaking waves is
correlated with wind speed. Spilling and plunging breakers raise underwater sound levels by more than 20
dB across the band from 10 Hz to 10 kHz (Wilson et al. 1985). Precipitation is another factor that can
increase ambient noise levels by up to 35 dB across a broad band of frequencies from 100 Hz to more than
20 kHz (Nystuen and Farmer 1987). Ice cover alters the ocean noise field depending on its type and degree,
for instance, whether it is shore-fast pack ice, moving pack ice, or at the marginal ice zone (Milne 1967).
Shore-fast pack ice isolates the water column from the effects of wind, and results in a decrease in ambient
noise of 10-20 dB. Sounds from ice cracking, however, may increase noise levels by as much as 30 dB.
Ice cracking can generate broadband pulses up to 1 kHz lasting for a second or longer. Interaction of ocean
waves with the marginal ice zone may raise noise levels by 4-12 dB (Diachok and Winokur 1974).