(Color online) Experimental apparatus including a submerged biteplate, five receiver hydrophones (H1–H5) and a projector. H1 is located at the on-axis position, whereas the remaining hydrophones are positioned in 45° increments. H1–H4 are positioned at a 1 m radial distance from the dolphin’s blowhole. H5 is 3 m from the dolphin’s blowhole so the dolphin’s tail would not be impaled. All hydrophones are at the same depth as the dolphin’s blowhole.
Comparison between on-axis echolocation clicks (A) and burst-pulse signals (B). Both signals have similar waveforms (A2 and B2)
(Color online) Spectrograms of a burst-pulse sound from five different axial positions relative to the dolphin. Higher frequencies become attenuated at a greater rate at greater angles. The 10 kHz tone used to cue the animal to phonate can be observed in the first 100 ms.
Comparison between beam patters for echolocation clicks (A) and burst-pulse sounds (B). The center bold curve represents the average beam patterns (N = 156 and 91 for clicks and burst-pulse sounds respectively), whereas lighter curves represent the standard deviation. Cubic spline interpolation was used to generate smooth curves. The average on-axis SPL(p-p) were 181 and 195 dB for clicks and burst-pulse sounds, respectively. Wave forms and corresponding spectral densities for each angle are presented to the right of their corresponding beam patterns. Measurements were only taken from 0 to 180° (filled circles) and 225°–315° are mirror images (open circles).
(Color online) SPLs for double clicks at 45°. There was a weak linear relationship between the SPL of pulse 1 and pulse 2 (of each click) (R 2 = 0.21). Different symbols represents clicks from different click train.
(Color online) Spectrogram of an on-axis whistle with 10 visible harmonics. The constant frequency portion of the signal (identified by the box) was used to measure pressure spectral density levels for beam pattern calculations.
Pressure spectral density of a single whistle (same whistle as Fig. 5) from five different horizontal azimuths. Higher frequency harmonics become progressively attenuated at larger angles, whereas the lower frequencies are less attenuated.
Averaged whistle beam patterns. (A) Beam pattern for the fundamental frequency of the dolphin’s whistle. (B)–(D) Whistle beam patterns for harmonics h 2–h 4, respectively. Beam patterns were only calculated for the first four harmonics because higher order harmonics were not detectable at the larger off-axis locations. Bold beam patterns are the average of eight whistles. Light beam patterns represent standard deviations. The higher frequency harmonics become progressively more directional. Filled circles were measured locations and open circles are mirror images.
Directivity index as a function of frequency clearly showing the mixed directional properties of the dolphin’s whistles.
On-axis frequency (kHz) and SPL (re 1 μPa2/Hz) for the fundamental frequency (f 0) and harmonics (h 2–h 10).
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