Last Updated: 02/11/2013*
Automatic Dependent Surveillance-Broadcast, known as ADS-B, differs from traditional radar in two significant ways. First, unlike radar it does not transmit but is a passive, receive-only system. Second, unlike radar it does not calculate the position of the aircraft but is entirely reliant upon the GPS position as reported by the aircraft.
ADS-B data is transmitted repeatedly by an aircraft equipped with a suitable transponder. Unlike secondary radar, in which the transponder responds only when stimulated by an interrogation, an ADS-B capable transponder transmits (or squitters) continuously. These transmissions contain the aircraft’s identity, its position and height, and other avionic data. This data is received by an ADS-B ground station, which decodes the data and then sends it to the air traffic control centre, or tower, for display and use by air traffic controllers. Apart from a change of target icon, the data displayed to controllers looks the same as data from a traditional radar system.
A traditional radar system is quite large, and it requires a lot of power and supporting infrastructure. By contrast, an ADS-B ground station is considerably smaller, can be placed more or less anywhere—as long as it has a clear sky view for the much smaller antenna—and uses much less power. This means that an ADS-B system can be located in places unsuitable for radar, such as in desert regions where solar energy can be used to power the ground station and its associated data communications transmission equipment e.g. VSAT. Most importantly, it is much cheaper to buy than a radar system, can be deployed quickly and, because it has no moving parts, requires far less maintenance support.
ADS-B data will allow aircraft to fly more efficient routes — saving time and fuel and reducing pollution — and allow airports to handle more aircraft with greater safety.
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