Gliders for passive acoustic monitoring of the oceanic environment

Abstract

Ocean gliders are quiet, buoyancy-driven, long-endurance, profiling autonomous platforms. Gliders therefore possess unique advantages as platforms for Passive Acoustic Monitoring (PAM) of the marine environment. In this paper, we review available glider platforms and passive acoustic monitoring systems, and explore current and potential uses of passive acoustic monitoring-equipped gliders for the study of physical oceanography, biology, ecology and for regulatory purposes. We evaluate limiting factors for passive acoustic monitoring glider surveys, such as platform-generated and flow noise, weight, size and energy constraints, profiling ability and slow movement. Based on data from 34 passive acoustic monitoring glider missions, it was found that <13% of the time spent at sea was unsuitable for passive acoustic monitoring measurements, either because of surface communications or glider manoeuvre, leaving the remainder available for subsequent analysis. To facilitate the broader use of passive acoustic monitoring gliders, we document best practices and include workarounds for the typical challenges of a passive acoustic monitoring glider mission. Three research priorities are also identified to improve future passive acoustic monitoring glider observations: 1) Technological developments to improve sensor integration and preserve glider endurance; 2) improved sampling methods and statistical analysis techniques to perform population density estimation from passive acoustic monitoring glider observations; and 3) calibration of the passive acoustic monitoring glider to record absolute noise levels, for anthropogenic noise monitoring. It is hoped this methodological review will assist glider users to broaden the observational capability of their instruments, and help researchers in related fields to deploy passive acoustic monitoring gliders in their studies.

A wave glider for passive acoustic monitoring of cetaceans in the Mediterranean Sea

“…Within this type of platforms, there are two main categories based on their buoyancy and locomotion system: ocean gliders and wave gliders. In the Mediterranean Sea, ocean gliders have been shown to be effective in detecting the presence of cetaceans and to be able to characterize their habitats [13]. Preliminary results presented in this study showed that also wave gliders can provide essential information about cetaceans in the Mediterranean Sea, especially in remote and offshore areas.…”

“…More recently, autonomous observation systems (AOS) have been used for passive acoustic monitoring [5]. In particular, gliders can stay at sea for several months and are equipped with sensors to measure both environmental parameters and ambient noise [12][13][14]. Within this type of platforms, there are two main categories based on their buoyancy and locomotion system: ocean gliders and wave gliders.…”

Advanced Technologies for Cetacean Monitoring: A One-Health and Multidisciplinary Approach for Ocean Effective Surveillance

“…The above studies [39][40][41][42][43][44][46][47][48], including our present study, highlight promising perspectives for cetacean population monitoring and reasonable price/energy cost acoustic transects [6,49]. However, precautions must be taken when trying to estimate population densities with a surface autonomous vehicle [38,50,51] as the usual assumption, that the animal's speed is slow compared with the vessel's speed, is violated. As such, this can introduce overestimation bias [52].…”

The present and future contribution of ships to the underwater soundscape

“…underwater Wi-Fi) (Figure 5, Duarte et al, 2021;Thomsen et al, 2021). In the future autonomous vehicles will replace ships in many ocean monitoring applications, which may contribute to reduce ambient noise because autonomous vehicles can operate substantially quieter than manned ships (Griffiths et al, 2001;Cauchy et al, 2023). In general, predictions should be taken as rough estimates because models cannot accurately quantify economic growths and they cannot predict adverse economic events such as wars, pandemics and economic crises.…”