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Spatial orientation of different frequencies within the echolocation beam of a Tursiops truncatus and Pseudorca crassidens
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10.1121/1.4730900
/content/asa/journal/jasa/132/2/10.1121/1.4730900
http://aip.metastore.ingenta.com/content/asa/journal/jasa/132/2/10.1121/1.4730900
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Schematic of the experimental setup for the Pseudorca’s target discrimination tasks. In this illustration the array is shown edge on in this representation and is aligned so that the central hydrophone is directly between the whale and the target. The dotted lines represent the echolocation beam.

Image of FIG. 2.
FIG. 2.

Schematics showing (A) the five arm array and (B) the seven arm array designs for recording frequency content from within the echolocation beam. The black diamonds represent the hydrophone elements and the dark black lines represent the PVC supports. The corresponding XY coordinates (in meters) for each element are shown in the tables to the right.

Image of FIG. 3.
FIG. 3.

(Color online) Schematic of the analysis process used to generate intensity contour maps of individual frequencies from within the echolocation beam using the array data. (A) Each click was recorded in its entirety by all 16 hydrophones of the array simultaneously. An amplitude spectrum was generated from the signal recorded by each element. Each spectrum was analyzed to find the intensity at a single frequency of interest. This intensity was assigned to the XY coordinate position from the corresponding hydrophone as shown in Fig. 2 generating a spatial intensity map. Custom written software programs used this spatial intensity map to create contour lines at three levels of intensity. Contours at 99% of the maximum intensity were chosen to show the spatial location of the highest intensity portion of the beam and are represented by the inner circle on the five arm array configuration. The diameter of the 99% contour also gave an indication of how focused that particular click was. The 3 dB contour (71% of the maximum recorded intensity) is shown by the middle circle and the 6 dB contour (50% of the maximum recorded intensity) is shown by the outer circle. (B) The three contour levels are shown on an XY coordinate map illustrating real data generated by the whale during a target discrimination task for 30 kHz. Data from six different clicks are represented here and have been overlaid upon one another to show the amount of variation that occurred between these six clicks.

Image of FIG. 4.
FIG. 4.

(Color online) Analysis of two different click trains generated by the Pseudorca during echolocation target discrimination tasks. Click Train 1, which consisted of 21 clicks, is represented at three different frequencies (A) 30 kHz, (B) 50 kHz, and (C) 100 kHz. The echolocation beam at 30 kHz was tightly focused at the central hydrophone of the array and consequentially at the target itself. The beam was radially symmetric with the 71% and 50% contours fitting within one another. At 50 kHz the echolocation beam was less focused and was more erratically directed, sometimes away from the target. At 100 kHz the beam became more disorganized. This same trend is demonstrated for Click Train 2 which consisted of 19 clicks and is shown in (D), (E), and (F). (G) This graph shows the normalized amplitude spectra of 250 clicks made during target discrimination tasks of a previous study (Ibsen et al., 2011). They were collected by a single hydrophone located on-axis between the Pseudorca and the target. It was observed at the time that there was a consistent region of frequency content from 0–42 kHz that was generated from click to click with simultaneous variability in frequency content above 42 kHz. The region of consistency is represented by the intensity contour plots at 30 kHz in (A) and (D) and demonstrated a high degree of focus. At 50 kHz there was a decrease in the focus of the beam and a corresponding increase in frequency content variability. At 100 kHz the high degree of viability in frequency content was represented by a significant loss of beam focus and directional control. (H) Here the amplitude spectra of the same 250 clicks shown in (G) are displayed without any normalization so their individual intensity levels are all relative.

Image of FIG. 5.
FIG. 5.

(Color online) Analysis of two different click trains generated by the Tursiops during free swimming recording sessions. Click Train 1, which consisted of 31 clicks, is represented at three different frequencies (A) 30 kHz, (B) 50 kHz, and (C) 100 kHz. The echolocation beam at 30 kHz was focused at the central hydrophone of the array. The beam was radially symmetrical with the 71% and 50% contours fitting within one another. These contours show that the beam was less focused than that of the Pseudorca, but the Tursiops was in a free swimming situation with no real consistent target positioned behind the array. At 50 kHz the echolocation beam was less focused and was more erratically directed, sometimes away from the target. At 100 kHz the beam became more disorganized. This same trend is demonstrated for Click Train 2 which consisted of 16 clicks and is shown in (D), (E), and (F). (G) This graph shows the normalized amplitude spectra of 250 clicks made during target discrimination tasks of a previous study (Ibsen et al., 2010). They were collected by a single hydrophone located on-axis between the dolphin and the target. Just like for the Pseudorca, it was observed that there was a consistent region of frequency content from 0–42 kHz that was generated consistently from click to click with simultaneous variability in frequency content above 42 kHz. The region of consistency represented by the intensity contour plots at 30 kHz in (A) and (D) demonstrated a higher degree of focus than at 50 kHz where there was a corresponding increase in frequency content variability. At 100 kHz the high degree of viability in frequency content was represented by a significant loss of beam focus and directional control. (H) Here the amplitude spectra of the same 250 clicks shown in (G) are displayed without any normalization so their individual intensity levels are all relative.

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/content/asa/journal/jasa/132/2/10.1121/1.4730900
2012-08-08
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spatial orientation of different frequencies within the echolocation beam of a Tursiops truncatus and Pseudorca crassidens
http://aip.metastore.ingenta.com/content/asa/journal/jasa/132/2/10.1121/1.4730900
10.1121/1.4730900
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