Near Real-Time Underwater Passive Acoustic Monitoring of Natural and Anthropogenic Sounds

Abstract

Passive acoustic monitoring takes advantage of the relative opacity of the ocean to sound. Traditionally, long-term monitoring has employed archival instruments from which data are accessed only when the recording instrument is retrieved. Recent advances in low-power instrumentation and computational speed allow passive acoustic data to be collected, processed and relayed to shore in near real time from fixed and mobile platforms deployed at the sea floor, in the water column or on the ocean’s surface. Measurements of ambient noise provide insight into natural sound sources, such as rainfall, earthquakes or marine animals, as well as anthropogenic sound sources, such as shipping or resource extraction. Near real-time passive acoustic measurements allow scientists and agencies to monitor shipping, observe underwater seismicity and detect the presence of critically endangered large whales. The development and use of real-time passive acoustic monitoring systems will grow in coming decades to help better manage increasing industrialization of the oceans. This chapter reviews the capabilities of real-time passive acoustic monitoring to address civilian scientific needs. The currently available suite of instrumentation and platforms used for passive acoustic monitoring are discussed along with the wide variety of measurements that can be made with this technology. Finally, examples of how real-time passive acoustic monitoring has improved our understanding of the ocean are presented.