Automatic Dependent Surveillance Broadcast

Hello Visitors who watch this blog continuosly they know we have already posted about GPS and how it is used in various fields. Now here is an new place where you can wonder how GPS helps them.

Satellite navigation and positioning took a step closer to ruling the skies

Automatic Dependent Surveillance Broadcast (ADS-B) “the backbone of the Next Generation System” — and GPS in turn supplies the data backbone for ADS-B.

In pilot phase testing for several years AT USA, ADS-B relies on GPS as the major source of data for both airliner cockpit and traffic control tower, replacing radar.

ADS-B will provide real-time cockpit displays of traffic information, both on the ground and in the air, giving pilots and controllers a better sense of what’s going on around them at any given time.

After implementing ADS - B System the accident rate has decreased to 49%

Part of the reason for this may be the increased position accuracy provided by GPS. “The ADS-B system presents an advantage over secondary radar,” . “The horizontal position accuracy does not depend on the distance of the aircraft with regard to the ground station. With radar, the farther an aircraft is from the antenna, the less accurate its computed position is.

“In the ADS-B system, the position is known with an accuracy of about 25 meters for an airborne GPS receiver and about 5 meters for a DGPS one” . “With a secondary radar, the azimuth accuracy is inferior to 0.08 degrees and the distance accuracy is inferior to 70 meters.”

How ADS-B Works. Aircraft transponders receive GPS signals and determine the aircraft’s precise location. The system converts that position into a unique digital code and combines it with other data from the aircraft’s flight monitoring system, such as the type of aircraft, its speed, its flight number, and whether it is turning, climbing, or descending. An integrity indicator derived from the GPS horizontal protection limit (HPL) is also proposed in the European version of ADS-B under testing by Eurocontrol.

The aircraft’s transponder automatically broadcasts code containing all of the data once per second. Appropriately equipped aircraft and ADS-B ground stations up to 200 miles away will receive the broadcasts. The ground stations add radar-based targets for non-ADS-B-equipped aircraft and rebroadcast the data to all equipped aircraft, in a function called Traffic Information Service-Broadcast (TIS-B). Ground stations also broadcast aircraft information from the national weather service and flight information, such as temporary flight restrictions, in the Flight Information Service-Broadcast (FIS-B).

Pilots will see the data in their cockpit traffic display screens, and air traffic controllers will see the information on displays they are already using, so little additional training would be needed for them to accept this.