A broadband target strength measurement method for weakly scattering animals using a 50-ms-long linear frequency modulated signal in a small tank

We built a new pulse-echo system using a small tank (1 × 1 × 1 m) for measuring the broadband target strength of weakly scattering animals such as krill and shrimp. The system transmits a linear frequency modulated signal with a frequency sweep of 20–220 kHz. To increase the signal-to-noise ratio (S...

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Bibliographic Details
Published in:	Fisheries science Vol. 87; no. 5; pp. 627 - 638
Main Authors:	Saygili, Burak, Tsuyuki, Soma, Liu, Jing, Yamamoto, Natsuki, Kobayashi, Kenichi, Amakasu, Kazuo
Format:	Journal Article
Language:	English
Published:	Tokyo Springer Japan 01-09-2021 Springer Nature B.V
Subjects:	Acoustic scattering Acoustics Animals Biomedical and Life Sciences Broadband Coefficients Compression Correlation coefficient Correlation coefficients Cylinders Echoes Fish & Wildlife Biology & Management Fisheries Food Science Frequency ranges Freshwater & Marine Ecology Krill Life Sciences Marine crustaceans Measurement Measurement methods Original Article Pulse compression Scattering Signal processing Signal to noise ratio Sound Spectra Spheres Target strength Theoretical acoustic scattering models Target strength spectra Signal-to-noise ratio Pulse compression processing Sakura shrimp Distorted-wave Born approximation Sound-speed contrast
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Summary:	We built a new pulse-echo system using a small tank (1 × 1 × 1 m) for measuring the broadband target strength of weakly scattering animals such as krill and shrimp. The system transmits a linear frequency modulated signal with a frequency sweep of 20–220 kHz. To increase the signal-to-noise ratio (SNR), a very long (50 ms) signal is used, and pulse compression processing is applied to received echoes. To determine the accuracy and effectiveness of the system and method, the obtained measurements were compared with predictions by theoretical acoustic scattering models. According to the verification experiment for a sphere and cylinders, the mean absolute errors were < 0.30 dB and the correlation coefficients r were > 0.97 in the frequency range above 20-dB SNR (40–210 kHz for the cylinders). Our measurement system was thus very accurate. We then performed the experiment for a commercially important shrimp, sakura shrimp Lucensosergia lucens . The measured spectra of three samples (35–38 mm) were in good agreement with the predicted spectra using an assumed sound-speed contrast. The r values were > 0.88 in the frequency range above 20-dB SNR (approximately 110–190 kHz). The effectiveness of our new method for weakly scattering animals was confirmed.
ISSN:	0919-9268 1444-2906
DOI:	10.1007/s12562-021-01532-7