Ranging bowhead whale calls in a shallow-water dispersive waveguide

Abstract

This paper presents 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. The first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel. The triangulation technique used here, while requiring no knowledge about the propagation environment, relies on a distributed array of directional autonomous seafloor acoustics recorders (DASARs) arranged in triangular grid with 7 km spacing. This study uses simulations and acoustic data collected in 2010 from coastal waters near Kaktovik, Alaska. At that time, a 12-element vertical array, spanning the bottom 63% of the water column, was deployed alongside a distributed array of seven DASARs. The estimated call location-to-array ranges determined from CMF and STR are compared with DASAR triangulation results for 19 whale calls. The vertical-array ranging results are generally within ±10% of the DASAR results with the STR results providing slightly better agreement. The results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here, whenever the call locations are beyond the distributed array boundaries.

Seasonal patterns in acoustic detections of marine mammals near Sachs Harbour, Northwest Territories

“…Bowhead whale vocalizations have been recorded up to 34 km (Bonnel et al 2014) and 40 km away (Abadi et al 2014) off the north coast of Alaska and as far as 130 km away in Greenland (Tervo et al 2012). Unlike bowhead whales, beluga whales have much shorter propagation distances due to their smaller body size and higher call frequency but can still be detected when 3 km away from a recorder (Simard et al 2010).…”

“…We also extracted daily sea ice concentrations at multiple scales centered over the location of the recorders, while masking out land areas, to capture ice dynamics at multiple scales around the recorder: 3 × 3 pixels (width = 18.75 km, area = 351.56 km 2 ), 5 × 5 pixels (width = 31.25 km, area = 976.56 km 2 ), and 17 × 17 pixels (width = 106.25 km, area = 11 289.06 km 2 ). We selected these scales to capture an expanding area around the recorders (first three scales) and to also capture >100 km around the recorders, which may represent the distances that bowhead whales that we record are calling from (Tervo et al 2012;Abadi et al 2014;Bonnel et al 2014). We also used the daily ice concentration data to measure the distance from our recorders to open water.…”

Nonlinear time-warping made simple: A step-by-step tutorial on underwater acoustic modal separation with a single hydrophone

“…Since then, with the advance of numerical signal processing and of TF analysis, the techniques have advanced further. Modal TF dispersion has notably been used for geoacoustic inversion (Potty et al, 2000;Potty et al, 2004;Rajan and Becker, 2010) and for ranging marine mammals (Abadi et al, 2014;Munger et al, 2011;Wiggins et al, 2004). However, these studies have been performed on sources at relatively distant ranges, so that modes were clearly time-separated on a conventional spectrogram.…”

Frequency-Difference Source Localization and Blind Deconvolution in Shallow Ocean Environments

“…Since early 2009 this project has focused on developing an acoustic-ray-based version of synthetic time reversal (STR), a fully-passive technique for recovering the original signal and the source-toarray-element impulse responses for a remote unknown sound source in an unknown underwater waveguide [1,2,3]. Along the way, a new method for beamforming (frequency difference beamforming) [4] and a new method for ranging marine mammal calls [5] were developed. The current specific objectives are to: a) assess the performance of STR using 4-by-4 planar hydrophone array recordings in a reverberant laboratory water tank, and b) assess and understand the performance of frequency-difference MFP using ocean propagation measurements made as part of the Kauai Acomms MURI 2011 (KAM11) Experiment.…”