The radar and ADS systems monitor the progress of aircraft in flight.

Navigation and Surveillance: Description

The action of identifying and tracking an aircraft throughout its flight for keeping the air traffic safety is known as the surveillance system. Currently, this tracking is carried out using radar (primary and secondary).

The radar technique is based on principles discovered in the late 19th century and developed for aerial applications during the Second World War.

Primary radar uses the reflection of electromagnetic waves to determine the distance and direction of aircraft relative to the radar station. The distance is calculated by measuring the time elapsed between the signal leaving the radar station and returning.

Civil aviation principally uses secondary surveillance radar, through a transponder onboard the aircraft: when the radar station interrogates the aircraft, the transponder replies enabling the ground station to determine the position, altitude and identification of the aircraft (co-operative vigilance).

These surveillance systems have geographical and operational limitations and, since the 1980s, the International Civil Aviation Organisation has been searching for more efficient methods of aircraft surveillance, which has resulted in new systems such as S-Mode radar, the evolution of secondary surveillance radar and ADS (Automatic Dependant Surveillance).


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