Measuring the target strength spectra of fish using dolphin-like short broadband sonar signals
Frequency characteristics of (a) transmit and (b) receive transducers and (c) the product of both sensitivities. (d) Amplitude spectra of tone burst, (e) bottlenose dolphin sound, and (f) finless porpoise sound.
Original waveforms of the sonar sounds used: (a) tone burst wave, (b) bottlenose dolphin, and (c) finless porpoise. Incident waveforms obtained by setting the transducers face to face: (d) tone burst wave, (e) bottlenose dolphin, and (f) finless porpoise.
System for the measurement of the fish target strength (TS) spectra in a tank.
Setup for the measurement of the TS spectra of tethered fish swimming in the sea.
The form function of tungsten carbide (TC) (left) and copper (right) spheres measured using (a) a tone burst wave, (b) a finless porpoise-like sound, and (c) a bottlenose dolphin-like sound. Also shown is the amplitude spectrum of the incident wave (upper), the reflected wave (middle), and the measured (lower, thin line) and theoretical (lower, bold line) form functions. The dotted and dot-dashed lines show the and bandwidths of the incident waves, respectively. The rms errors, , between the measurements and the theory are shown in the form function panel.
Measured TS spectra of horse mackerel (H-1 to H-10), sea bream (S-1 to S-5), and chub mackerel (C-1 to C-5).
Normalized TS at 70 and 100 kHz for three species of fish. The dotted line at shows the normalized average TS.
Variations in echo waveforms (left) and TS spectra (right) of a sea bream obtained by changing the tilt angle from (top) to (bottom). For comparison, grid lines are shown. The TS values at 100 kHz shown by solid lines were sampled for Fig. 9.
Comparison of the dependence of TS on the tilt angle for sea bream of similar sizes at 100 kHz. The white markers are data obtained from Miyanohana et al.;4 black circles denote the TS for a 28.5 cm sea bream from Fig. 8.
Echogram showing two TC spheres and a chicken grunt fish with fork length of 14.5 cm. The dotted lines at pings 100 and 110 (1 s in time) indicate the detailed analysis region shown in Fig. 11(b).
The TS spectra of a chicken grunt fish. The directivities of the transducers were compensated for by TC sphere echoes. The -axis shows the ping number, the -axis shows the frequency, and the gray scale indicates the TS value. The variations in TS spectra at pings 101–110 indicated by the dotted lines in Fig. 10 are expanded and shown in (b).
(a) Echogram of a school of fish obtained at sea using the finless porpoise-like sound and (b) the spectra of a single echo amplitude.
Standard deviation of the TS spectra for different individuals and tilt angles. The standard deviation for the tilt angle was calculated in steps from to .
Maximum, average, and normalized target strengths (TSs) for three fish at 70 and 100 kHz.
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