Underwater soundscape description from cyclostationarity point of view.

The description of underwater soundscape is central to the understanding of the marine environment, both from the standpoint of the fauna and anthropic activities and its interactions with the atmosphere. Some of these sources produce signals whose patterns are periodically repeated over time (i.e., ship propellers in motion, odontocetes clicks, snapping shrimp, noise emanating from surface waves, etc.). As ocean noise is a combination of various sources sometimes sharing the same frequency band, it is necessary to develop efficient algorithms to process the increasingly voluminous data acquired. To this end, the theory of cyclostationarity is adopted as an effective tool for exposing hidden periodicities in low signal to noise ratio. This theory, widely used to analyze mechanical systems or communications, is extended and applied on underwater soundscapes. The method is demonstrated using data recorded in the Celtic Sea at the French coast of Brittany with practical experiments using field measurements obtained from recording stations.

Impulsive noise pollution in the Northeast Atlantic: Reported activity during 2015-2017.

Underwater noise pollution from impulsive sources (e.g. explosions, seismic airguns, percussive pile driving) can affect marine fauna through mortality, physical injury, auditory damage, physiological stress, acoustic masking, and behavioural responses. Given the potential for large-scale impact on marine ecosystems, some countries are now monitoring impulsive noise activity, coordinated internationally through Regional Seas Conventions. Here, we assess impulsive noise activity in the Northeast Atlantic reported during 2015-2017 to the first international impulsive noise register (INR), established in 2016 under the OSPAR Convention. Seismic airgun surveys were the dominant noise source (67%-83% of annual activity) and declined by 38% during 2015-2017. Reported pile driving activity increased 46%. Explosions and sonar/acoustic deterrent devices both had overall increases in reported activity. Some increases were attributable to more comprehensive reporting in later years. We discuss utilising the INR for risk assessment, target setting, and forward planning, and the implementation of similar systems in other regions.

Noise robust bird call localisation using the generalised cross-correlation with phase transform in the wavelet domain.

Bird localisation using passive acoustic methods is a non-intrusive solution for taking a census of bird species. Through the recordings from a microphone array, the generalised cross-correlation with phase transform (GCC-PHAT) has been adopted widely in the estimation of the direction-of-arrival (DOA) of audio signals especially speech in indoor environments, as it performs very well in a reverberant environment. However, the performance is degraded when the signal to noise ratio is low. This study investigates the performance of DOA estimation when the GCC-PHAT is applied in the wavelet domain. Three configurations are considered in this study and the performance of these configurations is assessed by numerical simulation under ideal setup and practical experiments using audio signals recorded in a typical native forest in New Zealand. The results suggest the configuration which applies GCC-PHAT and denoising in the wavelet domain and estimates DOA from the reconstructed cross-correlation can give more accurate estimation compared to the conventional GCC-PHAT.