Abstract
By using the 50 kHz fish finder the measurements were carried out at an indoor 50 ton-water tank. Some nylon balls (diameter 15.8mm) were used instead of fish. The horizontal and vertical settings of these balls were made at random by a personal computer. A transducer of the fish finder received the reflected waves, and a hydrophone received the transmitted waves. These signals were analyzed by means of the signal analyzer.
The results obtained were as follows:(1) The relationship between the density and the transmitted voltage is more reliable than that between the density and the reflected voltage.(2) When each distance of the respecive ball from the transducer changes within a pulse length, the transmitted voltage is far more stable than the reflected voltage in all the measured densities.
The applicability of the transmitted voltage in determining the density of the fish school is suggested by these two items, (1), (2).
