鳀鱼(Engraulis japonicus)目标强度的模型法研究

Modeling study on the target strength of anchovy(Engraulis japonicus)

采用声散射理论和目标强度近似模型评估法对黄海鲤鱼（Engraulis japonicus）的声散射特征和目标强度进行了数值计算与评估研究。散射模型由鱼鳔模型和鱼体模型两个部分构成，其中鱼鳔采用充满气体的椭球体模型，鳔除外的鱼体采用充满液体的椭球体模型。理论数值计算所需参数取自全长12．6cm的鲤鱼个体，其鱼鳔尺寸利用X光照片测得。平均目标强度利用模型算得的不同角度下的声散射强度与鲲鱼倾角分布函数的卷积计算，其中倾角（度）的分布函数设为N（-3．9，12．8^2）。结果显示，鲲鱼对声波的散射具有明显指向性；在38kHz和120kHz工作频率下，鲲鱼的最大背向目标强度分别为-41．2dB和-39．5dB，有效平均目标强度分别为-48．0dB和-51．5dB，与实测结果吻合较好。另外还对鲲鱼的反向散射指向性特征、目标强度的频率特征以及鱼鳔对鲲鱼整体目标强度的贡献等进行了分析与讨论。以上研究表明，模型法作为现场测定研究方法的重要补充和认知鱼类声学散射特性的有效途径，可在我国鱼类目标强度的研究中发挥重要作用。

The scattering property and target strength of the anchovy in the Yellow Sea are studied numerically based on sound scattering theory and model approximation techniques. The scattering model is composed of swimbladder model and fish body model. The swimbladder is modeled by gas-filled prolate spheroid, and the fish body, exclusive of swimbladder, by liquid-filled prolate spheroid. Model parameters used for numerical calculations are based on an anchovy individual with a total length of 12.6cm, the dimension of its swimbladder being extracted from soft x-ray images. The effective mean target strength is estimated from the sound scattering intensities at different angles obtained from model calculation and the tilt-angle distribution of anchovy using convolution tech- nique, its tilt-angle （degree） distribution is assumed to be N （-3.9, 12.8^2）. The result shows that anchovy is a highly directive scatterer. At 38 and 120kHz, the maximum dorsal-aspect target strengths of the anchovy are -41.2dB and -39.5dB, respectively; and the effective mean target strengths are estimated to be -48.0dB and -51.5dB, respectively, which agree reasonably well with those obtained from in situ measurements. In addition, the backscattering directivity, frequency dependent characteristics of the target strength and the contribution of swimbladder to the composite target strength of anchovy are analyzed and discussed. The results indicate that modeling study can play an important role in fish target strength study in China both as an important supple- mentary technique to direct measurement methods and as an effective approach to the better understanding of sound scattering property of fish.