Spectrogram (down-sampled to 8 kHz, window size 256 samples with 95% overlap, fft size 512 with a factor two spectra interpolation), oscillogram (below) and power spectrum (right, Welch power spectral density estimate with a window size of 256 samples) of a bowhead whale song (A) and a fin whale song note (B) (data from Simon et al. 2010

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Simon1" target="_blank">[<b>53</b>]</a><b>).</b> The distance to the bowhead whale making the song note is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone-0052072-g002" target="_blank">Figure 2</a>. The song consisted of repetitions of this single note. The frequency of the fundamental ranged from 104 Hz to 1356 Hz (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone-0052072-t001" target="_blank">Table 1</a>).</p

Fundamental frequency of songs and range of body weights (reference IWC) for singing baleen whale species together with the excess transmission loss from absorption (α) at 10 km, 100 km and 1000 km

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Kinsler1" target="_blank">[<b>45</b>]</a><b>.</b> A) The grey colour for bowhead whale and humpback whale mark the frequency range of harmonics. References for frequency of song: blue whale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Cummings1" target="_blank">[11]</a>; fin whale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Watkins1" target="_blank">[13]</a>; bowhead whale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Ljungblad1" target="_blank">[24]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Cummings3" target="_blank">[25]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Tervo1" target="_blank">[27]</a>; humpback whale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Payne2" target="_blank">[21]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Cerchio1" target="_blank">[22]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Au2" target="_blank">[60]</a>; and minke whale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052072#pone.0052072-Mellinger1" target="_blank">[68]</a>. Illustrations by Uko Gorter. B) Bowhead whale <i>Balaena mysticetus</i> showing its tail fluke before a dive in Disko Bay, West Greenland (Photo: C. Ilmoni, Qeqertarsuaq Bowhead Research Group).</p

Apparent source level (ASL), defined as dB re 1 µPa (rms) @ 1 m from the whale, for 35 song notes from each of the four recording stations during a song session presumably produced by one individual at 5333±295 m from the centre of the array.

<p>Apparent source level (ASL), defined as dB re 1 µPa (rms) @ 1 m from the whale, for 35 song notes from each of the four recording stations during a song session presumably produced by one individual at 5333±295 m from the centre of the array.</p

Ambient spectral noise level in Disko Bay at 25 m depth from March 6 and 9 2009.

<p>The solid line shows the mean ambient noise level (n = 720) and the dashed line shows the positive standard deviation for these values. The vertical dashed black line marks the centroid frequency of 444 Hz of bowhead whale song notes and the grey area indicates the 285 Hz root-mean-square (rms) bandwidth of these signals. The spectrum level of the masking noise is about 40 dB re 1 µPa²/Hz in the bandwidth of a bowhead whale song note.</p

Acoustic parameters of song notes.

<p>Localized = song notes fulfilling the criteria for source level estimation. Others = song notes with equally high quality, but were unable to be localized. (Dur, s) = duration, F_max (Hz) = maximum frequency, F_min(Hz) = minimum frequency, F_c (Hz) = centroid frequency, F_peak (Hz) = peak frequency, BW_rms (Hz) = rms bandwidth, R(m) = distance, TL(dB) = transmission loss, RL = received level (rms = root-mean-squared, pp = peak to peak, efd = energy flux density), ASL = apparent source level referenced to 1 m from the source (whale). Standard deviation is given in parentheses.</p

Acoustic localization using a four-channel hydrophone array at four stations separated by about 500 m.

<p>A) Cross correlation functions for three stations relative to station 1 (upper panel, an autocorrelation). The peak of each station (stations 2 to 4) indicates the time-of-arrival difference relative to station 1. B) 2D localization plot in a coordinate system (km) referenced to station 1. Each hyperbola indicates all source positions that would result in the time-of-arrival difference measured between station 1 and each of the three other stations. The cross indicates the most likely position of the source as calculated with the method of least squares.</p