Experiment location in the western Woodlark Basin in Eastern Papua New Guinea. Ocean-bottom sensors (white triangles) were deployed in 2.0–3.2 km ocean depth.
(a) Fourteen minutes from hydrophones at GEO, ABE, SAL stations showing consistency of blue whale vocalizations in the time domain. This segment is typical of the entire 3-h period with no gaps that might correspond to rest or feeding. Signals always arrive first at the GEO location, indicating the source is to the northwest of the array. (b) Spectrogram of the GEO signal in (a) calculated using a 16 s Hanning window with 78% overlap. (c) Acoustic vocalization recorded at the GEO location during minute 8 of the study period showing the initial A blue whale call arriving at approximately 20 s followed by intermediate B1 unit arriving near 38 s, and the final B2 unit arriving at 60 s. (d) Spectrogram of signal in (c) using a 4 s Hanning window with 88% overlap. The A call is downswept from 23 to 19 Hz, while the B1 and B2 calls are both tonal with fundamentals at 19 Hz and harmonics at 23 Hz. The B2 call also has an apparent harmonic at 26 Hz. These characteristics are present throughout the study.
Individual vocalization recorded at by the vertical component of each seismometer (black curves) and attached hydrophones (gray curves). Note arrival times between different types of instruments are nearly the same for all units in the phrase. Relative amplitudes are not preserved across instrument type with hydrophones showing more amplitude variation than the seismometers, especially in the intermediate B1 and late B2 units. The hydrophone at the SAL location did not operate during the study period.
Localization results for (a) latitude, (b) longitude, and (c) range from the GEO location using an isospeed water column model (filled dots with error bars) and a Munk deep ocean profile (open diamonds with gray error boxes). Error bars for each vocalization are obtained by calculating standard deviation of points on the calculation grid with probability greater than 0.1 using Eq. (1). (d) Source level estimates obtained by averaging root mean square received level over four hydrophones then adding corresponding theoretical transmission loss from isospeed water column parabolic equation computations.
Localization results from isospeed ocean model in relation to instrument array (gray triangles) and local bathymetry. Location estimates for particular times are labeled and indicated with filled dots. The animal appears to be moving northward and to the west along the edge of the Woodlark Basin, following a shelf that separates the shallow waters of the Trobriand platform (see Fig. 1) from the deep waters (∼3.8 km) of the basin. The shaded region represents the extent of the uncertainty intervals from Fig. 4.
Bottom properties used for both types of parabolic equation simulations not including a basement absorbing layer. For all parameters, transitions to different values are linear from the value of the previous layer.
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