Surface-Generated Noise under Low Wind Speed at Kilohertz Frequencies

摘要

Some experimental observations of the ocean surface under low wind speed conditions, carried out with the high gain acoustic distribution array, ADA, indicate that bubbles may play an important role in the noise generating mechanism in this wind speed regime. One of the mechanisms discussed in the theory is that of bubble collapse in the surface turbulence layer as first proposed by Furduev (Atmos. Ocean. Phys. 2, 314 (1966)). Under typical ocean conditions, low wind speeds, and the available bubble population data, the calculated noise level agrees well with experimental results, both in magnitude and in the shape of the spectrum. The spectrum has a peak in the frequency range of 100 to 1000 Hz and an omega to the -2d power behavior at high frequencies. Several geophysical parameters could influence the noise generation. Local wind speed probably controls the population of bubbles, and swell-induced static pressure variations could play an important role in the critical turbulence pressure for bubble collapse. There seems to be further evidence that additional structure within the water, perhaps bubble density associated with different water masses, generates a patch type of distribution on the sea surface in the low wind speed situation. (Author)