皮刀魚對超音波之單體反射特性研究

Studies on the Acoustic Scattering Characteristics of Individual Moonfish

李國添(Kuo-Tien Lee) ； 吳滿全(Mann-Chen Wu) ； 李明安(Ming-Anne Lee)

《臺灣水產學會刊》 13卷2期 (1986/12) Pp. 1-11

https://doi.org/10.29822/JFST.198612.0001

摘要

為了嘗試能否直接從魚探記錄辨識皮刀魚及究明其標的物反射強度以做為定量參數。本研究選取尾叉長3.9至22.4公分之皮刀魚，在音響水槽實驗室內，用懸垂法懸掛測試魚體，並以側傾、俯仰、橫搖等三平面旋轉之，模擬200 KHz之超音脈波入射魚體不同方位時之反射特性。其結果如次：
(l)超音脈波入射皮刀魚體兩側扁部位時，其反射強度較背腹部或頭尾部高20 dB以上，在Roll plane下，經測定其反射強度之頻度分佈呈Rayleigh分佈，此一高度方向性之特性，加上其側扁體形易受海潮流影響之結果，使其在魚探記錄紙上呈現濃淡相間之羣聚型縱型記錄跡。
(2)超音脈波入射在任一同方位之大小不同皮刀魚時，其反射強度與皮刀魚之尾叉長及體重等成正比關係，故200 KHz之超音脈波探測皮刀魚時並無共振現象，用超音波定量計測是可行的。唯皮刀魚之體形側扁，成羣之方向性不明，故羣體之定量反射特性有待進一步之究明。

並列摘要

For the purposes of identification and abundance estimation, the acoustic scattering properties of 3.9-cm to 22.4-cm moonfish sampled in the coastal waters of Western Taiwan were measured. Target specimens were suspended and rotated to accept the ultrasonic pulses with frequency of 200 KHz from various aspect angles, and the backscattering strengths from each aspect angle were measured and analyzed. The results are summarized as following:
1) Polar plots show that the moonfish was omnidirectional in its sound scattering characteristics. The echo level of the dorsal-ventral side (or head-tail aspect) was at least 20 dB below the lateral-flat side aspect echo level. When the target was rotated with roll plane, the distribution of the target strength followed the Rayleigh distribution. This acoustic property of a moonfish patch is characterized by an alternating heavy and light echogram.
2) The target strength at any aspect angles was dependent on fork length and body weight of moonfish. Hence the mechanical resonances of the moonfish could be negligible. It is possible to estimate the abundance by acoustic methods.