CNRS, ISTerre, University Grenoble Alpes, 38000, Grenoble, France.
iXblue, Sonar Division, 13600, La Ciotat, France.
Sci Rep. 2021 Sep 2;11(1):17541. doi: 10.1038/s41598-021-97062-4.
A dramatic slowing down of acoustic wave transport in dense fish shoals is observed in open-sea fish cages. By employing a multi-beam ultrasonic antenna, we observe the coherent backscattering phenomenon. We extract key parameters of wave transport such as the transport mean free path and the energy transport velocity of diffusive waves from diffusion theory fits to the experimental data. The energy transport velocity is found to be about 10 times smaller than the speed of sound in water, a value that is exceptionally low compared with most observations in acoustics. By studying different models of the fish body, we explain the basic mechanism responsible for the observed very slow transport of ultrasonic waves in dense fish shoals. Our results show that, while the fish swim bladder plays an important role in wave scattering, other organs have to be considered to explain ultra-low energy transport velocities.
在开阔海域的鱼笼中，观察到密集鱼群中的声波传输急剧减慢。通过采用多波束超声天线，我们观察到相干反向散射现象。我们从扩散理论拟合实验数据中提取了波传输的关键参数，例如输运平均自由程和扩散波的能量输运速度。发现能量输运速度比水中的声速小约 10 倍，与声学中大多数观察结果相比，这个值异常低。通过研究鱼体的不同模型，我们解释了导致密集鱼群中超声传播非常缓慢的基本机制。我们的结果表明，虽然鱼鳔在波散射中起着重要作用，但为了解释超低能量输运速度，还需要考虑其他器官。
