Spectra of wind, wave, and ship‐generated noise at very low frequencies

Abstract

Measurements of ambient noise at very low frequencies in deep ocean environments are reviewed in light of three proposed noise‐generating mechanisms. Unpublished measurements by McGrath and Lawson, coupled with data reported by Perrone, reveal noise levels increasing with velocity to approximately the 3.5 power, and a small dependence of spectrum level on frequency in the vicinity of 10 Hz. These results are in accord with the predictions of the turbulent wind model proposed by Isakovich and Kuryanov. In the frequency range of 0.1–2 Hz, previously reported measurements of noise levels by Latham and others reveal a peak in the spectrum at about 0.3 Hz and lend credence to the Longuet‐Higgins hypothesis that nonlinear interaction of water surface waves produce sound at twice the dominant surface wave frequency. In the vicinity of 1 Hz these data are characterized by spectra which fall off rapidly with frequency in quantitative agreement with recent predictions by Hughes. Above 1.5 Hz harmonic shaft and blade rate lines of ships may dominate noise levels at low sea states and in close proximity to traffic lanes.