Bowhead Whale Call Localization

The bowhead whale (Balaena mysticetus) is one such species, generating a large variety of calls, including impulsive and frequency-modulated (FM) sweeps, during its spring and fall migrations between the Bering and Beaufort Seas in Alaska.

Figure 1: Bowhead whale.

This research compares the performance of three methods for estimating the range of broadband (50-500 Hz) bowhead whale calls in a nominally 55 m deep waveguide: conventional mode filtering (CMF), synthetic time reversal (STR) , and triangulation. This study uses simulations and acoustic data collected in 2010 from coastal waters near Kaktovik, Alaska. At the time a 12-element vertical array, spanning the bottom 60% of the water column, was deployed alongside a distributed array of 7 Directional Autonomous Seafloor Acoustics Recorders (DASARs).

Figure 2: DASAR locations deployed in Beaufort Sea in 2010. Triangles are DASAR locations, and the diamond is the vertical array location.

A total of 19 bowhead whale calls were analyzed with frequencies in the range 50-500 Hz, which – at the low frequency end – is close to the cut-off frequencies of all propagating modes of the ocean sound channel. Table I lists each call's bandwidth, SNR, and ranges from CMF, STR, and triangulation (plus estimated uncertainties).

Table 1: Comparison between the performance of the CMF, STR and DASAR techniques using experimental data from the Arctic.

This table shows that the vertical-array ranging results are generally within ±10% of the DASAR results, with the STR results providing slightly better agreement with the DASAR results. The results also indicate that a single vertical array can range calls over larger ranges and with greater precision than a standard distributed array, whenever the call locations are beyond the distributed array boundaries.

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