secondary surveillance radar

Secondary surveillance radarSecondary Surveillance Radar, Stevens M.C. Artech House, is a radar system used in air traffic control, that unlike primary radar systems that measure the bearing and distance of targets using the detected reflections of radio signals, relies on targets equipped with a radar transponder, that reply to each interrogation signal by transmitting encoded data such as an identity code, the aircraft's altitude and further information depending on its chosen mode.