Journal Article

Volume backscattering spectra measurements of Antarctic krill using a broadband echosounder

Matsukura, Ryuichi, Matsuura, Tomohiko, Imaizumi, Tomohito, Amakasu, Kazuo, Yamamoto, Natsuki, Murase, Hiroto, Abe, Koki

2023

Overview

For the acoustic inference of lengths and orientation angles of Antarctic krill (krill), reliable theoretical acoustic scattering models and parameters are necessary. To measure the volume backscattering (SV) spectra, and to clarify if the spectral shapes of target strength (TS) predicted by the stochastic distorted-wave Born approximation-based deformed cylinder model (SDWBA-DCM) are in agreement with those of the measured SV, we conducted simultaneous sampling with a broadband echosounder and a rectangular midwater trawl targeting 9 aggregations in the eastern Indian sector of the Antarctic in the 2018/19 austral summer. The SV spectra were measured at 50–85 kHz and 95–255 kHz. Using the SDWBA-DCM and the length frequency distribution obtained from the trawl samples, the length-averaged TS spectra were predicted. Both spectra were normalized by SV and TS values at 120 kHz, respectively, and the relative frequency responses were compared. The spectral shapes were in reasonable agreement in the case of the aggregations dominated by krill smaller than 35 mm. On the other hand, in the case of the krill larger than 35 mm, the spectral shapes were not in agreement. The possible causes of the discrepancy included the orientation angle distribution and the shape of krill.

• Publisher: Springer Nature B.V
• Subject: Acoustic scattering / Approximation / Backscatter / Backscattering / Born approximation / Broadband / Echo sounding / Echosounders / Ecological aggregations / Euphausiacea / Frequency distribution / Krill / Length-frequency distribution / Marine crustaceans / Midwater trawls / Plankton / Spectra / Target strength