The source properties and radiation patterns of animal vocalisations define, along with propagation and noise conditions, the active space in which these vocalisations can be detected by conspecifics, predators, prey, and by passive acoustic monitoring (PAM). This study reports the 4π (360° horizontal and vertical) beam profile of a free-swimming, trained harbour porpoise measured using a 27-element hydrophone array. The forward echolocation beam is highly directional, as predicted by a piston model, and is consistent with previous measurements. However, at off-axis angles greater than ±30°, the beam attenuates more rapidly than the piston model and no side lobes are present. A diffuse back beam is also present with levels about −30 dB relative to the source level. In PAM, up to 50% of detections can be from portions of the beam profile with distorted click spectra, although this drops substantially for higher detection thresholds. Simulations of the probability of acoustically detecting a harbour porpoise show that a traditional piston model can underestimate the probability of detection compared to the actual three-dimensional radiation pattern documented here. This highlights the importance of empirical 4π measurements of beam profiles of toothed whales, both to improve understanding of toothed whale biology and to inform PAM.

中文翻译：

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港口海豚喀哒声的高分辨率三维束辐射方向图，对无源声波监测具有重要意义。

动物声音的源特性和辐射模式，以及传播和噪声条件，定义了可以通过同种动物，捕食者，猎物和被动声学监测（PAM）检测到这些声音的活动空间。这项研究报告了使用27元素水听器阵列测得的自由游泳，训练有素的海豚的4π（水平和垂直360°）波束轮廓。如活塞模型所预测的，前向回波定位光束是高度定向的，并且与先前的测量结果一致。但是，离轴角度大于±30°时，光束的衰减比活塞模型更快，并且不存在旁瓣。相对于源电平，还存在约30 dB的扩散后束。在PAM中 高达50％的检测可能来自光束轮廓中具有扭曲的喀嗒光谱的部分，尽管对于较高的检测阈值而言，这一点会大大降低。声学检测港口海豚的概率的仿真表明，与此处记录的实际三维辐射方向图相比，传统的活塞模型可以低估检测的概率。这突出了对齿鲸的波束轮廓进行经验性的4π测量的重要性，这对于增进对齿鲸生物学的了解并为PAM提供依据。声学检测港口海豚的概率的仿真表明，与此处记录的实际三维辐射方向图相比，传统的活塞模型可以低估检测的概率。这突出了对齿鲸的波束轮廓进行经验性的4π测量的重要性，这对于增进对齿鲸生物学的了解并为PAM提供依据。声学检测港口海豚的概率的仿真表明，与此处记录的实际三维辐射方向图相比，传统的活塞模型可以低估检测的概率。这突出了对齿鲸的波束轮廓进行经验性的4π测量的重要性，这对于增进对齿鲸生物学的了解并为PAM提供依据。