> The word "sonar" is an abbreviation of which phrase?And the answer: Sound Navigation and Ranging. Photo credit: public domain.Using sound waves, sonar is a technique fordetecting and locating underwater objects. First devised as a way of detectingicebergs, the use of sonar greatly increased during World War I, as submarinewarfare increased.If you've ever heard a whale call or dolphin chirp, you may be familiar withjust how far sound waves can travel underwater. Instead of light or radar, sonaris used to navigate the ocean's depths via sound. Since submarines and othermilitary 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 simplylistens to the sounds of the water – any marine life or nearby ship will beheard in passive sonar. Active sonar, on the other hand, sends out pulses ofsound in a targeted direction and listens for how long they take to return. Inactive sonar, all that's needed to compute distance is the speed of sound inwater, and the consequent echo. The sonar sound waves "bounce" off of a targetand relay the frequency back to its sender, giving the submarine a fairlyaccurate estimate. A sonar ping can be as loud as 235 decibels. To the naked ear, this can beshatteringly loud, as human eardrums can only withstand around 160 decibels. Infact, at 194 decibels, sound waves become classified as shock waves in the air.Yet, water carries sound differently, and oftentimes sonar output is far toohigh-pitched for humans to hear. For this reason, submarine occupants do notusually[https://www.intechopen.com/books/sonar-systems/the-effect-of-sonar-on-human-hearing] sustain any injuries from sonar emissions. Learn more about sonar below.