Spectral, spatial, and temporal characteristics of underwater ambient noise in the Beaufort Sea in 1994 and 2016

Abstract

Climate induced changes in the Arctic Ocean have severely impacted underwater acoustic communication and navigation; understanding underwater noise characteristics is critical to improving the performance of these operations. Ambient noise from the Beaufort Sea recorded in experiments more than 20 years apart (SIMI94 and ICEX16) are compared to determine differences that may be attributed to the region's rapidly changing environment. Both datasets are collected at spring time under packed ice conditions with 32 element vertical line arrays. Spectral comparison shows noise within 20–300 Hz band is 30–40 dB louder in 1994 than 2016, suggesting the ice cover during SIMI94 was more acoustically active. Beamforming results show ambient noise vertical directionality is focused near the horizontal during SIMI94 but more spread in elevation during ICEX16, with a robust noise notch at the horizontal. Numerical modeling demonstrates that this difference may be attributed to ambient noise during ICEX16 being dominated by surface noise sources at discrete ranges rather than the historical assumption of a continuous and uniform distribution of sources. Temporal statistics of transient ice events show more transient activity during SIMI94 and appear to support the new proposed surface source distribution for ICEX16. [Work supported by ONR and DARPA STO.]