每日一词：声纳（Sonar）

声纳是一种船舶利用声波来导航和探测其他船只，或绘制海底地图的技术。“被动”声纳仪器倾听其他船只或潜艇发出的声音，而 "主动 "声纳系统发射声波并倾听回声。

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声纳的英文是 "声音导航和测距 "的缩写。早期的声呐在第一次世界大战期间迅速发展，用于探测敌人的潜艇。主动声纳产生一个声音脉冲，通常被称为“ping”，然后倾听脉冲的反射，反射的到达时间表明了与障碍物的距离。传出的ping是单频音或频率变化的chirps，它允许从回声中提取更多的信息。由于多普勒效应，ping和回声之间的频率差异可以测量目标的速度。

渔船使用声纳来确定鱼群的位置，而一些动物，包括蝙蝠和海豚，使用类似的自然回声定位来导航或定位伴侣、捕食者和猎物。

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Sonar is a technique that ships use to navigate and detect other vessels, or to map the ocean floor, using sound waves. Passive sonar instruments listen out for the sounds made by other ships or submarines, while active sonar systems emit sound waves and listen for the echoes.

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Sonar stands for sound navigation and ranging, and the first instruments developed rapidly during the First World War for the detection of enemy submarines. Active sonar creates a pulse of sound, often called a ping, and then listens for reflections of the pulse, the arrival time of the reflections indicating the distance of an obstacle. Outgoing pings are single-frequency tones or changing-frequency chirps, which allow more information to be extracted from the echo. Differences in frequency between pings and echoes can allow measurement of a targets speed, thanks to the Doppler effect.

Fishing boats use sonar to pinpoint fish shoals, while some animals, including bats and dolphins, use similar natural echolocation to navigate or locate mates, predators, and prey.

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