Measurement of fish school volume by multi-beam sonar. Directional resolution and estimation error

Multibeam sonar is very useful for estimating fish abundance because of its wide detection area. In this study, we propose a method for measuring acoustical volume for different modes of a multibeam sonar. We also tried to measure the shape and volume of a model fish school in a tank using an ultrasound scanner and then measured the shape and volume of an actual fish school in the field using semicircular scanning sonar. However, the measured shape was distorted, and an error was contained in the estimated volume of the fish school. Therefore, we used a computer simulation to consider the error in the measurement volume using a spherical scattering object under various beam widths and distances. The characteristics of the error are presented and the possibility of reducing the error was confirmed.