Effects of Transducer Motion on Quantifying Single Fish Echoes

Abstract

Quantitative echo sounders are widely used to survey fisheries stocks. If the transducer of the sounder moves with ship motion, the directivity factors in transmitting a pulse and in receiving the echo differ causing errors in the individual fish observation such as the target strength measurement The errors are analyzed theoretically for general and special cases. Calculated results show that the error is significant, if the beam width is smaller than 10° and if the target depth is deeper than 100 m. Since recent quantitative echo sounders, such as the spilt-beam sounder, use sharp beams, a stabilization of transducer is necessary. © 1991, The Japanese Society of Fisheries Science. All rights reserved.