Wide_area_multilateration
Wide area multilateration (WAM) is a cooperative aircraft surveillance technology based on the same time difference of arrival principle that is used on an airport surface. WAM is a technique where several ground receiving stations listen to signals transmitted from an aircraft; then the aircraft's location is mathematically calculated -- typically in two dimensions, with the aircraft providing its altitude.[1] Aircraft position, altitude and other data are ultimately transmitted, through an Air Traffic Control automation system, to screens viewed by air traffic controllers for separation of aircraft.[2] It can and has been interfaced to terminal or en-route automation systems.