Marine soundscape monitoring from underwater autonomous vehicles—Passive acoustic monitoring gliders

Ocean gliders are buoyancy-driven autonomous underwater platforms, able to collect oceanographic measurements along vertical profiles during multi-months missions, covering thousands of kilometers. They glide quietly through the water column without propulsion noise and are therefore extremely suitable for Passive Acoustic Monitoring (PAM) of the marine environment. From PAM glider data in the Mediterranean Sea and the Southern Ocean, we illustrate the current and potential uses of PAM gliders for the study of physical oceanography, biology, ecology and for regulatory purposes. We evaluate limiting factors for PAM glider survey, such as platform-generated and flow noise, instrument size and power constraints, profiling ability and movement of the platform. We provide recommendations and good practices for typical PAM glider surveys and present future developments identified by the PAM glider community to further develop the readiness level and societal impact of PAM glider observation: (1) Calibration of the PAM glider to collect absolute sound levels; (2) adapted sampling methods and statistical analysis techniques to perform population density estimation; and (3) Integration of PAM glider observation to existing monitoring programs.