With the great increase in air traffic and planes flying all over the world, it has become increasingly necessary to monitor the exact position of all aircraft using airspace, so that accidents can be avoided, and aircraft can fly safely. The high speed of aircraft makes visual methods increasingly unreliable. Airspace is used by commercial, military and private planes all of which function independently and under different jurisdictions. This makes their control and ensuring their safety increasingly difficult.
Here is where ADS-B, a surveillance technology can help to make the task of monitoring that much easier. ADS-B is automatic dependent surveillance-broadcast, that is broadcast periodically and helps the movement of an aircraft carrying this system to be continually tracked. This data is available to other aircraft in the vicinity and to air traffic controllers. It does not need radar, which was the previously used surveillance system, that had severe distance and other limitations. The position of the aircraft and its location in terms of geographical position and altitude is constantly displayed on a screen. ADS-B uses a global positioning system or GPS to verify the position of an aircraft. This information is then broadcast at regular intervals. The broadcast will also identify the aircraft, with its unique call sign, and give details of its present velocity and altitude and any other data that is relevant for tracking its movement. The system is also linked to dedicated stations on the ground that then relays the information to air traffic controllers so that they know the position of the aircraft on a real-time basis so that they can guide them correctly in their flight, landing, and takeoff.
The ADS-B system is automatic and requires no input from the pilot of the aircraft or any other device or agency. The system is called dependent because it depends on all its data from the navigation or GPS system of the aircraft. The position of the aircraft, its velocity and altitude and other required data assist the surveillance of the aircraft at all times. All this information is constantly broadcast to ground stations and other aircraft, every half second on a universally common 1090MHz digital data link. These broadcasts will also have the flight number call sign that identifies the aircraft, along with its unique airframe code that each aircraft is given by the ICAO. Positions give the exact latitude and longitude of the position of the aircraft and well as its horizontal position. Barometric and Geometric altitudes are also part of the transmitted data. Other important data needed for ensuring safe distances between aircraft to help to avoid two aircraft being in close proximity is their rate of climb or descent, their ground speed, and track angle. There is also a provision in these systems for emergency broadcasts and special position identification.
Each ground station has a maximum range of 250 nautical miles or approx 290 miles as we generally know them. Ground stations are situated so that they overlap over each other, and on established flight paths so that the aircraft flying remain under constant surveillance.