Source level and vocalizing depth estimation of two blue whale subspecies in the western Indian Ocean from single sensor observations

Abstract

The source level (SL) and vocalizing source depth (SD) of individuals from two blue whale (BW) subspecies, an Antarctic blue whale (Balaenoptera musculus intermedia; ABW) and a Madagascar pygmy blue whale (Balaenoptera musculus brevicauda; MPBW) are estimated from a single bottom-mounted hydrophone in the western Indian Ocean. Stereotyped units (male) are automatically detected and the range is estimated from the time delay between the direct and lowest-order multiply-reflected acoustic paths (multipath-ranging). Allowing for geometric spreading and the Lloyd's mirror effect (range-, depth-, and frequency-dependent) SL and SD are estimated by minimizing the SL variance over a series of units from the same individual over time (and hence also range). The average estimated SL of 188.5 ± 2.1 dB re 1μPa measured between [25–30] Hz for the ABW and 176.8 ± 1.8 dB re. 1μPa measured between [22–27] Hz for the MPBW agree with values published for other geographical areas. Units were vocalized at estimated depths of 25.0 ± 3.7 and 32.7 ± 5.7 m for the ABW Unit A and C and, ≃20 m for the MPBW. The measurements show that these BW calls series are stereotyped in frequency, amplitude, and depth.

Seasonal Trends and Diel Patterns of Downsweep and SEP Calls in Chilean Blue Whales

“…Blue whales produce sounds with frequencies among the lowest (16-100 Hz) and loudest (176.8-188.5 dB re 1uPa) in the ocean, capable of propagating over extremely long distances [23,24]. Blue whales in different geographic areas produce different song patterns, consisting of repeated sequences of 'phrases' made up of recurring pulsed sounds or 'units' [25], which are thought to function as a reproductive display [25][26][27].…”

Eavesdropping at the Speed of Light: Distributed Acoustic Sensing of Baleen Whales in the Arctic

“…Note that the slope of the downsweep hyperbolas tends towards sound speed away from the apex. The received strain amplitude decay is not constant along the fiber which can be interpreted as (1) DAS directivity & local variations in the coupling between the fiber and seafloor (Matsumoto et al, 2021;Taweesintananon et al, 2021), (2) Coherent interferences in the wavefield due to a nearsurface source (Lloyd's mirror effect) (Carey, 2009;Bouffaut et al, 2021), (3) Upward refracting trends in arctic waters sound propagation, with potential shadow zones and complex fjord and coastal 3D propagation (Jensen et al, 2011). Instrumental vertical and horizontal noise lines appear on the t-x plot.…”

“…DAS receivers at the positions R{x,r=0,z} and whale position is at S {x = x w , r = r w , z = z w } where x is the position along the FO cable, r the cross-line range from the FO cable, z the depth and the subscript w stands for the whale. A grid of potential whale positions along the FO cable x n and ranges r m is established for the optimization problem, assuming a fixed calling depth z w = 30 m (Lewis et al, 2018;Bouffaut et al, 2021). The source position is estimated by finding the theoretical TDOA that matches best the observed TDOA between all receivers an arbitrary chosen reference receiver position R 0 {x 0 ,r=0,z 0 } such as…”

“…Following the method in Pereira et al (2020); Bouffaut et al (2021), a side analysis provides an estimate of the source depth from frequency notches associated with the interferences patterns, using a 100 s window on the time-compensated signals to include the waterborne direct arrival and the sea-surface reflection (Figure 6).…”

Eavesdropping at the speed of light: distributed acoustic sensing of baleen whales in the Arctic

“…4) is performed on a short (110 ms) portion of the time-delay-compensated signal, chosen to include the waterborne direct arrival and the sea-surface reflection. The source depth is estimated from the frequency notches associated with the interferences patterns [10,42] and information on the time of arrival of the sea-surface reflected wave given by the delay in the source signature autocorrelation.…”