Direction finding

"Direction finding (DF) refers to the establishment of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication. By combining the direction information from two or more suitably spaced receivers, the source of a transmission may be located in space via triangulation. This is called a cross-cut or fix."[1]

The Coast Guard LORAN station on Nikumaroro is an example of a sophisticated navigation system based, in part, on DF principles.