어군의 3차원 음향 산란 특성 측정

Abstract

Although various echo-sounders have been used to quantify biomass in fisheries acoustics, the systems used are inherently limited by a narrow acoustic detection area. Recently, various sonar systems have been increasingly used in fisheries acoustics to study school structure and behavior, and for estimating abundance. The three-dimensional (3D) acoustic scattering by a fish school provides indispensable information for fisheries acoustics using sonar systems. We measured the 3D acoustic scattering from a live fish school using a fixed source and moving receiving system. To construct a fish school, 70 black porgy (Acanthopagrus schlegeli) with total lengths ranging from 9 to 14 cm were placed in a small cage underwater. As the source signal, a 200-kHz transducer was positioned such that the fish school was located on the beam axis. The echoes from the fish school were received with a hydrophone at each angle using hemisphere coordinates. On combining the corresponding scattering target strength functions of the fish school, the 3D scattering pattern has no changed with receiving angles. These results can contribute to converting the volume backscattering strength of a fish school to fish biomass by considering fish school direction in 3D coordinates.