Localizing bioacoustic signals with long-baseline hydrophone arrays

Real-time localization and tracking of vocalizing marine mammals is a powerful tool to a) mitigate the risk of ship strikes and disturbance of the animals as well as b) to understand the impact of anthropogenic noise on habitat use of cetaceans. A long baseline hydrophone array has been installed in Squally Channel, a culturally, ecologically, and economically important marine environment in northern British Columbia, Canada. The array consists of four synchronized bottom-mounted hydrophones that permanently record and radio-transmit data to a land-based laboratory. Automated analysis tools have been developed to detect and localize transient bioacoustic signals from three or more hydrophones in real-time. They comprise the correlation of hydrophone signals, the construction of a replica surface using acoustic propagation models, and signal localization from a spatial likelihood surface. An overview of the localization method is presented. We assess spatial localization precision and discuss random and systematic sources of error stemming from the signal type and quality, bathymetry, sound speed profile, as well as the spatial distribution of hydrophones and acoustic sources. Simulation results are compared to field measurements. Based on our findings, challenges and opportunities associated with localization using long baseline arrays in coastal environments are discussed.