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 2021-09, Vol.87 (5), p.627-638
Main Authors: Saygili, Burak, Tsuyuki, Soma, Liu, Jing, Yamamoto, Natsuki, Kobayashi, Kenichi, Amakasu, Kazuo
Format: Article
Language:English
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
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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  0.97 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