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  回声定位是一些动物在难以使用视觉（夜间、黑暗的地方：洞穴或海底等）的情况下来远程定位物体的能力，尤其被齿鲸类的动物（海豚、剑吻鲸和抹香鲸）所使用。

  其原理与声纳相同：动物向周围环境发出短暂而强烈的声波，其中部分声波被障碍物反射后被动物接收。信号发射和接收的时间表示发射器和目标物体间的距离。反馈信号的波形和强度进一步显示出目标物体的形状和大小。最后，方位由两个互补的系统决定：

• 首先，发射的声波会聚焦为小角度的波束，这使得动物可以“扫描”它面向的空间。
• 其次，接收反馈波的声学传感器通常是高度不对称的，例如，人们认为海豚的骨骼（下颌骨、头骨）在回声定位中起重要作用。

  视频1. 宽吻海豚（Tursiops truncatus）的回声定位原理。[来源：弗兰克·马里奇（Franck Malige）和朱莉·帕特莉丝（Julie Patris）]

  与声学发射器相关的器官被称为“melon（瓜状体）”，它使得海豚的前额变得宽阔而隆起。

  齿鲸类的特征：对于大多数齿鲸类的动物来说，声波脉冲是由头前部的猴唇发出的。对于抹香鲸来说，其呼吸孔位于前部，猴唇发出的声波通过名为鲸蜡的脂肪器官向颅骨内部传递，然后被前额气囊反射，最后通过吻部的脂肪组织聚焦。由于这种声波放大过程极为复杂，每个传递阶段都会造成声波信号的损失，所以抹香鲸有着本物种独特的多重结构的声信号。

  视频2. 另一种齿鲸类动物抹香鲸（Physeter macrocephalus）的回声定位原理。[来源：弗兰克·马里奇（Franck Malige）和朱莉·帕特莉丝（Julie Patris）]

  被发射的声信号通常时间短、频率高。发射和接收之间的时间其实很短：声波在 15 / 1500 = 1/100 秒内往返15米。发射信号的时间必须比预估的往返时间要短，通常需要在几毫秒以内。齿鲸类动物发出的信号被称为“咔哒声”，因为它们的声学特性（时间短、频率高）。

  视频3. 抹香鲸（Physeter macrocephalus）发出的咔哒声。由CNRS DYNI团队在地中海的土伦附近录制。[来源：弗兰克·马里奇（Franck Malige）和朱莉·帕特莉丝（Julie Patris）]

  这些咔哒声的频率范围因物种而异。抹香鲸是一种生活在广阔空间中的巨大动物，人类可以听到它发出的5千赫兹的中频咔哒声（视频3）。而生活在淡水中的豚类另一个极端例子，它们生活在复杂、异质性显著的小型生境中（有树根等频繁出现的障碍物），它们可以发出频率极高的咔哒声（超过50千赫兹，大多数动物都无法听到），这可能使它们获得了高精度的定位能力（视频4）。

  视频4. 亚马逊河豚（Inia geoffrensis）发出的咔哒声。为了使人们能听到，视频将其声波频率缩小至原来的五分之一。由CNRS DYNI团队在秘鲁的伊基托斯附近录制。[来源：弗兰克·马里奇（Franck Malige）和朱莉·帕特莉丝（Julie Patris）]

Echolocation is a technique used by some animals to locate objects at a distance when the view is not or hardly practicable (at night, in dark areas such as caves or underwater). It is notably used by all toothed or odontocetes cetaceans (dolphins, beaked whales and sperm whales).

The physical principle is the same as that of sonar: a short and intense acoustic wave is emitted, part of which is reflected by the obstacle and is picked up in return by the animal. The time between transmission and reception of the signal gives information on the distance between the transmitter and the target. The shape and strength of the return signal gives further indication of the texture and size of the target. Finally, the direction is determined by two complementary devices:

• on the one hand, at emission, by focusing the wave, i.e. the emitted energy is concentrated in a beam of small angular dimension. This system allows the animal to essentially “scan” the space in front of it.
• on the other hand, on reception, by acoustic sensors whose geometry is strongly non-symmetrical. Thus, it is thought that the bones (of the jaw, of the skull) of dolphins play an important role in the detection of echoes.

Video 1. Animation describing the principle of echolocation of an odontocete, the bottlenose dolphin (Tursiops truncatus). [Source: Animation Franck Malige and Julie Patris]

The organ associated with the focusing of the acoustic emission is called the “melon”, which gives the wide rounded forehead characteristic of dolphins. For most toothed cetaceans, the impulse is emitted by the phonic lips at the back of the skull. For sperm whales on the other hand, the respiratory vent being located at the front of the head, the phonic lips emit towards the inside of the skull, through the fatty organ called spermaceti. The wave is then reflected on the air sac present at the back of the melon before being focused again through the fatty masses of the muzzle. Because of the losses at each stage of this complex amplification, sperm whale clicks have a multiple structure characteristic of the species.

Video 2. Animations describing the principle of echolocation in another odontocete, the sperm whale (Physeter macrocephalus). [Source: Animation Franck Malige and Julie Patris]

The emitted signals are generally short, and at high frequency. Indeed, the time between transmission and reception is short: a round-trip distance of 15 metres is covered by the sound wave in 15 / 1500 = 1/100th of a second. It is necessary to emit signals shorter than the estimated round trip time, generally shorter than a few milliseconds. The signals emitted by toothed cetaceans are called “clicks” because of their acoustic properties (short and wide frequency range).

Video 3. Clicks emitted by a sperm whale (Physeter macrocephalus). Sounds recorded by the CNRS DYNI team in the Mediterranean, near Toulon. [Source: Animation Franck Malige and Julie Patris]

We can see that the frequency ranges of these clicks vary greatly from one species to another. Sperm whales, immense inhabitants of the open spaces, emit medium frequency clicks, of the order of 5 kHz, audible to the human ear (Video 3). At the other extreme, river dolphins, which live in a complex environment, very diversified on a small scale (tree roots, frequent obstacles), emit very high frequency clicks (more than 50 kHz, inaudible by most other animals), probably allowing them a high precision (Video 4).

Video 4. Clicks emitted by an Amazonian pink dolphin (Inia geoffrensis). To be audible, the frequency of the sounds has been divided by 5. Sounds recorded by the CNRS DYNI team in Peru, near Iquitos. [Source: Animation Franck Malige and Julie Patris]