Using nonlinear time warping to estimate North Pacific right whale calling depths and propagation environment in the Bering Sea

• Published in: The Journal of the Acoustical Society of America 2017-10, Vol.142 (4), p.2711-2712
• Main Authors: Thode, Aaron, Bonnel, Julien, Thieury, Margaux, Fagan, Aileen, Verlinden, Christopher M., Wright, Dana, Crance, Jessica, Berchok, Catherine L.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5014894

Calling depth distributions and ranges are estimated for two types of calls produced by critically endangered eastern North Pacific right whales (NPRW) in the Bering Sea, using passive acoustic data collected with bottom-mounted single-hydrophone recorders in 50–90 m water depths. Nonlinear time resampling of 12 NPRW “upcalls” and 20 broadband “gunshots” typically isolated 3 to 4 individual mode arrivals below 200 Hz. Matched-mode processing (MMP) methods were used to remove the unknown source phase and amplitude structure, but incoherently averaging MMP ambiguity surfaces across frequency yielded many local minima when inverting for sediment properties. Instead, the ambiguity surfaces were plotted as a function of range and frequency, which revealed the type and degree of environmental mismatch present in initial waveguide models. This qualitative approach revealed the existence of large sound speed gradients in the sediment, along with downward-refracting sound speed profiles during the summer months. Gunshot sounds were generally produced at a few meters depth, while upcall depths clustered between 10 and 25 m, consistent with previously published bioacoustic tagging results from North Atlantic right whales.