Very low frequency (VLF) wind-generated noise produced by turbulent pressure fluctuations in the atmosphere near the ocean surface

Measurements of ambient noise for very low frequencies (VLF) from 5 to 50 Hz indicate that wind-generated noise is a significant source of the total ambient noise field during high-wind/sea-state conditions. Determining dominant physical mechanism(s) for transfer of energy from the wind field into the underwater acoustic field is very important in modeling the wind-generated noise field at very low frequencies. Frequency dependence, wind speed dependence, directivity characteristics, and dependence on oceanographic parameters of the wind-generated noise source can be established only after the physical mechanism is understood. The objective of this paper is to extend the development of the theory of turbulent pressure fluctuations initiated by Isakovich and Kur’yanov. In their original paper, Isakovich and Kur’yanov established a very good basic theoretical approach to describe the energy transfer from the wind field into the underwater acoustic field as a result of turbulent pressure fluctuations in the atmosphere near the ocean surface. However, in developing their approach, they made errors in algebra, mistakes in integration, and unsubstantiated assumptions. In this paper, these mistakes are corrected and their theory is revised accordingly. In addition, the wave height spectra of Mitsuyasu and Honda is incorporated into the theory, since this is the accepted wave height spectra in the VLF acoustic region. (These wave height data were not available to Isakovich and Kur’yanov at the time of publication of their original theory.) The wind speed and frequency dependence of the resulting source spectrum level agrees well with data measured in the northeastern Pacific Ocean under low distant and local shipping noise conditions.