The acronym for sound fixing and ranging. The concept is based on finding the geographic location of sound that is created by an explosive or other impulsive event, such as a missile impact, by using the time of arrival of the signal at three or more receiving stations. This is known as hyperbolic fixing. This concept was used to locate aircraft that crashed at sea. Although other techniques have replaced this application, the term sofar channel has remained in use, referring to what is also known as the deep sound channel.