What is an acoustic shadow?

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Chapter Atmospheric Phenomena

An acoustic shadow is kind of like a mirage, only involving sound instead of light. Differences in temperatures at varying atmospheric layers causes sound waves to refract or bend; also wind shears and the absorption of sound on soft surfaces can contribute to the effect. The result can be that sounds coming from a particular source might not be heard by someone standing fairly close by, while other people located farther away, but in a direction where sounds are being refracted, can hear the sound.

A famous example the consequences of acoustic shadow is often cited from the U.S. Civil War. During the 1862 Battle of Seven Pines in Richmond, Virginia, Confederate General Joseph Johnston told his commanders that, upon hearing gunfire from soldiers being led under Major General D.H. Hill, he would order Brigadier General W.H.C. Whiting to send in an attack on the Union’s flank. However, because of acoustic shadow, Johnston was unable to hear the battle noise and the flank attack was not sent in when it was needed. The Confederates subsequently lost the battle.


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