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Automatic Dependent Surveillance-Broadcast (ADS-B) is a GNSS based surveillance technology for tracking aircraft. It is still under development and most likely will replace radar as main surveillance system.
ADS-B technology consists of two different services: ADS-B Out and ADS-B In. ADS-B Out periodically broadcasts information about aircraft, such as identification code, position, course, and velocity, through an onboard transmitter. ADS-B In is the reception by aircraft of traffic information, flight information, and weather information, as well as other ADS-B data such as direct communication from nearby aircraft. The system relies on two fundamental components: a satellite navigation system (GPS nowadays; in the future a GNSS system with more integrity is desirable) and a datalink (ADS-B unit). With all this information, two fundamental issues will be acquired: first, controllers will be able to position and separate aircraft with improved precision and timing (since the information is more accurate); second, pilots will increase their situational awareness.
The potential benefits of ADS-B are:
Improve situational awareness: Pilots in an ADS-B equipped cockpit will have the ability to see, on their in-cockpit flight display, other traffic operating in the airspace as well as access to clear and detailed weather information. They will also be able to receive pertinent updates ranging from temporary flight restrictions (TFR’s) to runway closings.
Improve visibility: aircraft will be benefited by air traffic controllers ability to more accurately and reliably monitor their position. Fully equipped aircraft using the airspace around them will be able to more easily identify and avoid conflict with ADS-B out equipped aircraft. ADS-B provides better surveillance in fringe areas of radar coverage.
Others such as: Reduce environmental impact (more efficient trajectories), increase safety (by increasing situational awareness and visibility as mentioned above), increase capacity and efficiency of the system (enhance visual approaches, closely spaced parallel approaches, reduced spacing on final approach, reduce aircraft separations, improve ATC services in non-radar airspace (such oceans, enabling free routes), etc.
Figure 11.18: ADS-B sketch. Author: User:AuburnADS-B / Wikimedia Commons / Public Domain.
Nowadays, most airliners are equipped with ADS-B. However, since the equipment is very expensive, most regional aircraft do not have it. Therefore, still ADS-B can not be used as primary surveillance system due to its low degree of implantation. Nevertheless, there is a road map both in Europe and the US to increasingly equip all aircraft with ADSB by 2020. Another issue is the low integrity of GPS as main satellite system. The implementation of the GNSS-2 will circumvent this problem.