Long-term analysis of ocean noise floor in the northeast Pacific Ocean
Date:
Abstract:
Characterizing the ocean noise floor is important for tracking long-term acoustic changes and creating environmental regulations to mitigate the effects of human activities on the ocean soundscape. Underwater noise levels have been measured at two sites in the northeast Pacific off the coast of Oregon between 2015 and 2019. The acoustic data were recorded continuously at a sample rate of 64 kHz at 81 m depth and 581 m depth at the continental shelf and slope, respectively. Sequential one-minute power spectral density estimates are computed and used to calculate spectral probability density functions (SPDFs) for every month of the measurement period. The ocean noise floor is then defined as the 5th percentile of the SPDF. Multi-year data are used to compute time series of the ocean noise floor at various frequencies, which are then examined for long-term trends and seasonal patterns. The frequency dependence of the noise floor is analyzed and the results are compared between two measurement sites. Environmental data from surface buoys and Conductivity, Temperature, Depth (CTD) instruments collocated with the hydrophones are used to study how the ocean noise floor changes with wind, temperature, and sound speed. [Work supported by ONR.]