Analysis of the temporal structure of fish echoes using the dolphin broadband sonar signal
System response and dolphin sound. (a) Frequency characteristics of both the transmit and receive transducers. (b) Original waveforms of the dolphin sonar sounds. (c) Amplitude spectra of the dolphin sound. (d) Waveform of incident signal, obtained by setting the transducers dace to face.
Diagram of measuring system. (a) Measurement of echo from dorsal aspect of fish. (b) Rotation of dorsal tilt angle. (c) Measurement of echo from tethered live fish.
Echo-analysis method. (a) Echo waveform (dotted curve) and envelope pattern (solid curve). (b) Low-passed pattern (solid curve) and envelope pattern (broken curve).
Echo waveforms and envelope patterns. Echoes were measured from the dorsal aspect. Envelope patterns were computed by the cross-correlation function between the incident waveform and echo waveform and the Hilbert transform.
Envelope patterns and low-passed patterns. Low-passed patterns were computed by convolving the envelope patterns with the Hanning window.
Characteristics of echo temporal structure. (a) Duration with width of low-passed pattern. (b) Numbers of envelope-pattern highlights. (c) Maximum values of envelope pattern. The normalized maximum amplitude is shown.
Echo waveforms and envelope patterns at different tilt angles.
Characteristics of echo temporal structure measured from anesthetized fish at different tilt angles. (a) Duration. (b) Numbers of envelope-pattern highlights. (c) Maximum values of the envelope pattern and the TS at . The normalized maximum amplitude at each tilt angle is shown.
Output of moving fish, chicken grunt. (a) Highlight structures plot. Amplitude of each highlight represented by circle radius. (b) Duration plot. This repetition period is .
Duration versus threshold value. The durations were calculated using values of 0.1–0.9 times the maximum of the low-passed pattern at each echo. The average duration for each threshold and species was calculated by averaging these values.
Fork length, body height, duration, and maximum value for fish species.
Fork length, body height, and duration for three fish.
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