Validation of Multi-frequency Acoustic Measurement Method of Zooplankton by using Dummy Scatterers

The calibration and validation are very important for quantitative underwater acoustic systems including the multi-frequency system, because their observation results are directly related to evaluation of marine resources. The standard sphere calibration method is widely used to calibrate the quantitative echo sounder for fisheries resource surveys by reasons of simple process and high precision of the method. We derived an optimum size of standard sphere and confirmed the practicability and precision of the standard sphere calibration method for our high-and multi-frequency system, TAPS-6 (Tracer Acoustic Profiling System, BAE Systems). Although the Multi-frequency inversion (MFI) method has been validated by physical and mathematical theories, few attempts to validate the method have so far been made through actual scatterer measurement. Dummy scatterers such as metal spheres has been used to validate methods or results of acoustic measurements. We designed a school or cluster of dummy scatterers of zooplankton with small tungsten carbide spheres, and measured their SV values by TAPS-6. By comparing the result of the inversion with their real composition, we could validate and examined the features of MFI method.