Modeling Very Low Frequency Wind-Generated Ocean Noise

Friday, January 24, 2024, 4:00 p.m. Central Time

Dr. Christopher A. Stockinger
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu/

Historically, shipping is assumed to dominate ambient underwater acoustic Noise Levels (NL) from 10 to 100 Hz, however, the data acquired from the north hydrophone triplet of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) station at Crozet Island provides unique wind noise observations with minimal shipping interference. First, NL was correlated to local wind speed through a frequency dependent power relation, and second, the distant wind contributions were modeled through a source density and propagation model. For the source density model, wind-related noise was modeled as a layer of monopole sources located at a quarter-wavelength below the surface to replicate a dipole radiation pattern. The total acoustic intensity received by the array and the modeled wind-related source intensity were both related to wind speed through a power relationship where the two share the same frequency dependent exponent, n. The model parameters were computed empirically from the acoustic and wind speed data. The source layer model accurately predicts the NL within a standard deviation of 3 dB. An important observation is that the exponent n increases as frequency decreases and reaches a value around 7 at 10 Hz, which is much larger than often measured at higher frequencies.