A study on calibration for commercial echosounder using the bottom backscattering strength from a fishing vessel near the South Shetland Islands in Antarctic

In this study, we calibrated a commercial echosounder (ES70) installed on a krill fishing vessel to use it in estimating biomass of Antarctic krill (Euphausia superba). The method of calibration was to analyze the difference between the bottom backscattering strength of the commercial echosounder (i.e. ES70) and the scientific echosounder (i.e. EK60) at some transects designated by CCAMLR. 38kHz and 120kHz were used for the calibration, and krill swarm signals, obtained from multi frequencies, was examined to verify the calibration result. The analysis result confirmed the possibility of calibration by bottom backscattering strength, since the proportion of krill swarm signals within 2 dB < S_{V120kHz‒38 kHz} < 12 dB (i.e. a common ΔMVBS range of 38kHz and 120kHz to be an indicative of Antarctic krill) over the total acoustic signals were 26.95% and 92.04%, respectively before and after the calibration.