Ocean sound measurements collected from underwater gliders with marginal effects of flow noise.

The Global Ocean Observing System recently designated ocean sound an essential ocean variable to support passive acoustic observation of the ocean. Underwater gliders have the demonstrated ability to fill gaps within usual ocean monitoring networks and are increasingly used for passive acoustic monitoring studies focusing on acoustic detection and identification of soniferous species. Comprehensive understanding of glider-generated noise and flow noise and characterization of their potential impact on acoustic measurements are critical to further development of glider-borne applications to ocean sound measurements. This study investigates flow noise, generated by glider motion through water, and its potential contribution to noise levels measured from underwater gliders, particularly at low frequencies. From glider-borne acoustic recordings collected in the Ross Sea, free from low-frequency shipping noise contribution, this study provides a comprehensive characterization of flow noise at speed through water representative of underwater glider operations (15-63 cm s-1). It quantifies the effects of flow noise on measurements at frequencies ranging from 3 to 100 Hz. Finally, this study demonstrates the possibility to collect unaffected measurements above 20 Hz from an underwater glider and discuss solutions to reduce flow noise or mitigate its effects.