Statistical analysis and modeling of underwater wind noise at the northeast pacific continental margin

Approximately 11 400 h of acoustic recordings from two sites off the Oregon coast have been evaluated to characterize and model the frequency and wind dependence of wind noise in the northeast Pacific continental margin. Acoustic data are provided by two bottom-mounted broadband hydrophones (64 kHz sampling frequency) deployed at depths of 81 and 581 m at the continental shelf and slope, respectively. To describe the spectral level versus frequency relation, separate linear models for the 0.2-3 kHz and 3-25 kHz frequency range are fitted to the data. While spectral slopes for the 0.2-3 kHz range generally decrease with increasing wind speed, slopes remain constant (shallow location) or increase with increasing wind speed (deep location) above 3 kHz. The latter is in strong contrast to results from previous studies. The relation between spectral level and wind speed is described by a piecewise linear model where spectral levels are approximately constant below a critical wind speed v_c and increase linearly with logarithmic wind speed above v_c. It is shown that the critical wind speed and the slopes of the piecewise linear model strongly depend on the acoustic frequency.