Measurement of directivity pattern of target strength of Japanese horse mackerel by split-beam echo sounder

The target strength (TS) of Japanese horse mackerel was measured by using s plit-beam echo sounder. The target was kept at the position of dorsal direc tion incidence and moved across to the beam. Characteristics of TS directiv ity pattern and measuring precision of position angle by split-beam method were estimated. As a result, TS pattern in pitch plane shows drastic variation. Beside that , the fluctuations of position angle were increased. I took notice the cohe rent scattering of fish body structures, also examined the difference of ph ase in carrier wave. And we discussed the relationship between fish body st ructures and interference.