Periodic fluctuations in the vertical directionality of surface-generated noise have been observed during multiple deep-water drifting platform deployments in the New England Seamount, Southern California Bight, and Hawaiian Ridge regions. Ambient sound in the 500–20 000 Hz band was recorded using co-located hydrophone arrays and an acoustic vector sensor. Consistent 15- to 20-min oscillations in the apparent vertical angle and intensity of surface noise were detected at depths between 100 and 800 m, suggesting that upper-ocean processes modulate surface-noise generation and/or its propagation. To investigate these potential physical drivers, we analyze environmental data, including from a high-resolution thermistor string and upward-looking echosounder, collected during earlier deployments in a subset of the study regions, along with new experiments conducted in the Southern California Bight. Acoustic observations are compared with numerical simulations of surface noise generation and propagation in stratified, range-dependent environments. The results provide new insight into how temporal variability in near-surface structure, such as bubble plume distribution or internal wave sound speed fluctuations, can influence the angular dependence of ambient noise. Work sponsored by ONR TFO.
Laferriere et al. (Wed,) studied this question.