Radio tracking

Radio tracking estimates the location or movement of a target using radio waves associated with it. In a basic beacon system, a radio transmitter travels with the target while a radio receiver and directional antenna provide observations from known positions. An audible received pulse can identify a transmitter and help determine its direction; it does not itself supply map coordinates.^[ref]

Radio direction finding can be combined across stations by radio triangulation. In a hypothetical horizontal Cartesian coordinate system, station $A=(0,0)$ finds a target along $y=x$, while station $B=(2,0)$ finds it along $y=2-x$, with distances in kilometres. The intersecting forward bearings give $(1,1)$. A single bearing instead leaves many possible positions along one direction. Nearly parallel bearings constrain the intersection poorly: a small angular error can then produce a large position error.

A field example is local bird tracking described by the Smithsonian Migratory Bird Center. Researchers use received signals to follow a tagged bird or combine directions from different observation points, allowing repeated observations without continuous visual contact. Receiver range, battery life and the placement of observing stations limit which movements are recorded. A missing signal therefore need not mean that the animal stopped moving or died; it may have moved beyond detection.^[ref]