보름달 및 유령해파의 군체에 의한 음향 산란 특성

Abstract

Acoustic target strength (TS) information is essential parameter in the acoustic survey and target detection. Recently, the TS measurements have been conducted for the several gelatinous organisms, jellyfish. Although gelatinous organisms shape a large size patch in the ocean, the TS measurements were carried out for the single target with various bell sizes in many cases. Therefore, the TS information for multiple targets to be very closed each other is necessary. In the study, acoustic measurements of ex situ TS were made on living multiple jellyfish. The target species were Aurelia aurita and Cyanea nozakii, and carried 3-frequencies were 120, 200, and 420 kHz split-beam transducers. In order to arrange multiple targets, 9 A. aurita and 4 C. nozakii were used in the experiment. Totally, mean TS for both jellyfish has a trend to increase with an individual number and mean TS of the multiple A. aurita ranged from -72.7 to -57.9 dB and that of C. nozakii ranged from -61.9 and -49.3 dB. At the same arrangement of the multiple jellyfish, frequency dependency didn’t apparently appear in A. aurita, but it was apparently appeared in C. nozakii. As an additional case, mean TS of multiple C. nozakii together with symbiotic fish approximately -50 dB for all frequency. Considering C. nozakii ii lives together symbiotic fishes in the ocean, the result of the TS value suggests that the mean TS of multiple C. nozakii are very high because of symbiotic fish. The results can be applied to improve acoustic detection of the multiple jellyfish.