The word "sonar" is an abbreviation of which phrase?
And the answer: Sound Navigation and Ranging.
Using sound waves, sonar is a technique for detecting and locating underwater objects. First devised as a way of detecting icebergs, the use of sonar greatly increased during World War I, as submarine warfare increased.
If you've ever heard a whale call or dolphin chirp, you may be familiar with just how far sound waves can travel underwater. Instead of light or radar, sonar is used to navigate the ocean's depths via sound. Since submarines and other military vessels do not have windows, sonar acts as the eyes of the ship.
There are two primary types of sonar: active and passive. Passive sonar simply listens to the sounds of the water – any marine life or nearby ship will be heard in passive sonar. Active sonar, on the other hand, sends out pulses of sound in a targeted direction and listens for how long they take to return. In active sonar, all that's needed to compute distance is the speed of sound in water, and the consequent echo. The sonar sound waves "bounce" off of a target and relay the frequency back to its sender, giving the submarine a fairly accurate estimate.
A sonar ping can be as loud as 235 decibels. To the naked ear, this can be shatteringly loud, as human eardrums can only withstand around 160 decibels. In fact, at 194 decibels, sound waves become classified as shock waves in the air. Yet, water carries sound differently, and oftentimes sonar output is far too high-pitched for humans to hear. For this reason, submarine occupants do not usually sustain any injuries from sonar emissions.
Learn more about sonar below.