THE ACOUSTIC FUNCTIONS OF THE MELON OF THE CHINESE RIVER DOLPHIN(Lipotes vexillifer)

In this paper,the acoustic functions of the melon of the Chinese river dolphin(Lipotes vexillifer)are studied.Based on the comparison between the directivity patterns of the whole head and the skull,it is suggested that the melon plays an important role in beamforming.At the frequencuy of 40 kHz,the—3 dB beamwidth of the emitted vertical beam of the whole head is approximately 21.6°,withthe major axis elevated 10°above the ristrum plane;the—3 dB beamwidth of the horizontal beam ofthe whole head is approximately 20°,with the major axis deviated 12°rightward from the body axis.The vertical and horizontal—3dB beamwidths of the whole head are 9.4°and 13°,narrower than thoseof the skull respectively,and the directions of the major axes are different for both cases.It canbe seen that the melon narrows the width of the main beam and greatly reduces the side lobes of thebeam formed by the skull.The distribution of the sound velocity in the melon tissue is measured andthe distribution pattern is drawn.Fr     

白(既鱼)豚(Lipotes vexillifer)的声信号及声行为

本文记录了白暨豚(Lipotes vexillifer)水下声信号,并对信号进行了分析,分析表明,白暨豚声信号可分为两大类:短持续期信号(脉冲列或单脉冲)和长持续期信号(啸叫声)。文中给出了这些信号的时间波形和它们的频谱,讨论了信号的特点,进行了白暨豚声行为实验。实验表明,以长度为300毫秒左右的正弦脉冲作为呼叫信号,在一定的频率范围内,一声呼叫,白暨豚即发出二三声啸叫声作为回答,反应最灵敏的频率范围是4-7千赫,在此范围内,应答率达到100％,向水中回放录制的白暨豚本身的声信号,可使白暨豚游向发射换能器。而对其它信号,如噪声、音乐则无此反应。     

白鱀豚[Lipotes vexillifer]额隆的声功能

额隆是海豚声呐系统的重要部件。我们以白鱀豚为材料,对额隆的声功能进行了研究。通过整体头和头骨声指向性的对比,揭示了额隆的波束形成作用。在40kHz时整体头垂直波束—3dB束宽为21.6°,主轴相对于吻平面有10°仰角;水平波束—3dB束宽为20°,主轴相对体轴右旋12°。束宽分别比头骨骨骼的测试结果窄9.4°和13°,主轴的指向亦产生变化。额隆把头骨初步形成的波束主瓣变窄,并对旁瓣有较大的抑制。测试了额隆组织的声速分布,给出了声速分布图。在额隆的右后下方有一低速核,离此核愈远,声速愈大。核的左面等速线密度小声速梯度小;而右面等速线密度大,声速梯度大。接近表皮时声速已接近水中的声速,表明额隆的声阻抗匹配作用。按斯奈尔定律,用几何法做出额隆垂直和水平面的声线图,解释了额隆的波束形成作用。还以胆鼻海豚和江豚为材料进行了类似工作,得到大体一致的结果。