超音波の応用としての魚探機による魚群の生態に関する研究 : 魚体の超音波反応率に就て(日本航海学会第7回講演会)

Abstract

The measurement of ultrasonic reflection coefficient of fish body presents a serious problem to the use of fish-finder, the solution of which has not ever been published. We measured the reflection coefficient by a new method. Through this experiment, we bound that two values measured in field tests and in tank tests are almost equal. Therefore, the future investigation will be simplified. First, matchiag transformers and an attenuator are put between receiver and amplifier. Then, the acoustic pressure of reflected wave is obtainod from the value in decibel (db) shown on the attenuator when the image on the recording paper extinguishes. Second, the curves showing the relation between the acoustic pressure of direct wave and distance and that between the acoustic pressure of reflected wave and distance are obtained with a sender, and a small magnetosrtriction receiver, going up and down over a body to be measured. These two curves thus obtained are shown in Fig 1 ; the former, in the left side of the discontinuous line and the latter, in the rigt. The difference between the two curves at the dscontinuous line is the reflection loss of that body. We measured the reflection coefficient of living Gray rock cod, Horse mackel, Flatfish, Cuttlefish, and Carp. The results showed that the reflection is closely connected with form of fish body and is in proportion to difference of densities of sea water and fish body, and square of frequency. The reflectin of ultrasonic wave from a fish body, in a cap, is not effected by its air bladder alone, but its whole body. The reflection loss from the whole body is 10-15 db less than that from the air bladder. The same may be true with other fish. (1951)