Quantification of Marine Acoustic Environments

The soundscape is an acoustic environment made up of all sounds arriving at a receiver. A methodology for the analysis of soundscapes was developed in an attempt to facilitate efficient and accurate soundscape comparisons across time and space. The methodology included generating and combining results from a collection of traditional soundscape metrics, statistical measures, and acoustic indices that were selected to quantify several salient properties of marine soundscapes: amplitude, impulsiveness, periodicity, and uniformity. The metrics were calculated using approximately 30 hours using semi-continuous passive acoustic data gathered in seven unique acoustic environments. The calculated values for each candidate metric were compared to a priori soundscape descriptions and cross-examined statistically to determine which combination of metrics most effectively captured the characteristics of the representative soundscapes. The selected measures of were SPLrms and SPLpk for amplitude, kurtosis for impulsiveness, an autocorrelation-based metric for periodicity, and the dissimilarity index for uniformity. The metrics were combined to develop a proposed soundscape code, which enables rapid multidimensional and direct comparisons of salient soundscape properties across time and space. The proposed soundscape code was applied to a series of soundscapes that were recorded at several deep ocean environments along the US outer continental shelf (OCS) and the Great Barrier Reef. The soundscape code clearly distinguished between the deep OCS soundscapes and the shallow Great Barrier Reef soundscape in terms of amplitude, impulsiveness, and periodicity. Nuanced differences in deep OCS soundscape codes in terms of periodicity, impulsiveness, and the frequency of dominant signals suggest a connection between the respective soundscapes and bottom type or habitat. The combination of metrics that make up the soundscape code provided a first assessment to establish baseline acoustic properties for the deep ocean OCS sites. This initial soundscape characterization will aid in directing further analyses and guiding subsequent assessments used in understanding soundscape dynamics