Measurements and Theoretical Model Simulation of Target Strength of Pacific Chub Mackerel for Use in a Quantitative Sonar

Abstract

The horizontal target strength (TS) of fish is necessary to estimate the abundance of fish near the sea surface using a quantitative omnidirectional sonar. In this study, we measured the TS of Pacific chub mackerel by varying the yaw, pitch, and sonar tilt angles. We also estimated the theoretical TS using the prolate spheroidal model (PSM) to understand the horizontal TS of fish. The results revealed that the theoretical TS was very close to the measured TS for variation with respect to angle, indicating that PSM is a suitable model for Pacific chub mackerel. The measurements and theoretical prediction revealed that yaw angle distribution was the most important parameter for horizontal TS of Pacific chub mackerel. The influence of pitch angle and sonar tilt angle on horizontal TS was slight. Therefore, it is necessary to make the yaw angle distribution uniform to estimate average TS accurately during sonar surveys.