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Automatic Dependent Surveillance – Broadcast

ADS-B is a cooperative surveillance technique for air traffic control and related applications being developed as part of global CNS/ATM plan. The successful implementation of this new technology has resulted in many ground systems providing advanced platforms suitable for ATM systems based on the used of data-link and satellite technology.

Automatic dependent surveillance-broadcast (ADS-B) is a cooperative surveillance technique for air traffic control and related applications being developed as part of global CNS/ATM plan. The successful implementation of this new technology has resulted in many ground systems providing advanced platforms suitable for Air Traffic Management (ATM) systems based on the used of data-link and satellite technology. The main objective for air navigation service providers by implementing these new systems is to increase safety and efficiency to the aviation industry in a cost-effective manner.

As opposed to radar, which works by bouncing radio waves from fixed terrestrial antennas off of airborne targets and then interpreting the reflected signals, ADS-B uses conventional Global Navigation Satellite System (GNSS) technology and a relatively simple broadcast communications link as its fundamental components. In addition, ADS-B accuracy does not seriously degrade with range, atmospheric conditions, or target altitude and update intervals do not depend on the rotational speed or reliability of mechanical antennas.

A typical ADS-B application uses an ordinary GNSS (GPS, Galileo, etc) receiver to derive an aircraft’s precise position from the GNSS constellation, then combines that position with any number of other information, such as speed, heading, altitude and flight number. This information is then simultaneously broadcast to other ADS-B capable aircraft and to ADS-B ground, or satellite communications transceivers which then relay the aircraft’s position and additional information to Air Traffic Control centers in real time. ADS-B data is broadcasted every half-second on a 1090MHz, digital data link.

Automatic – Requires no pilot input or external interrogation.

Dependant – Depends on accurate position and velocity data from the aircraft’s navigation system (eg. GPS).

Surveillance – Provides aircraft position, altitude, velocity, and other surveillance data to facilities that require the information.

Broadcast – Information is continually broadcasted for monitoring by appropriately equipped ground stations or aircraft.

ADS-B is relatively inexpensive technology, which costs a fraction for the equivalent radar coverage. The footprint and power requirements for ADS-B are miniscule compared to radar, allowing an ADS-B ground station to be installed in even the most remote areas.

The ability of a ground station to receive a signal depends on altitude, distance from the site and obstructing terrain. The maximum range of each ground station can exceed 250 nautical miles. In airspace immediately surrounding each ground station, surveillance coverage extends to near the surface.

Australia is the first country with full, nationwide ADS-B coverage having installed 28 ground stations by the end of 2009. Their ongoing ADS-B program will see a total of 43 ground stations bringing coverage over the entire continent from 30,000 feet to much lower levels. While there is already substantial coverage at lower levels, this will extend to near the surface when all planned ground stations are installed.

In December 2009, ADS-B coverage in the Gulf of Mexico was implemented where helicopter pilots are now able talk to air traffic controllers in Houston, who see them on virtual radar, as they fly to increasingly distant platforms in the Gulf.

In the Caribbean, Guyana’s ADS-B surveillance system implementation program is on the way with scheduled completion by the end of 2012.

Worldwide ADS-B Coverage

Relationship to ADS-A/ADS-C

The other commonly recognized types of ADS for aircraft applications are ADS-Addressed (ADS-A) and ADS-Contract (ADS-C), which are essentially the same.

ADS-B differs from ADS-A in that ADS-A is based on a negotiated one-to-one peer relationship between an aircraft providing ADS information and a ground facility requiring receipt of ADS messages. For example, ADS-A reports are employed in the Future Air Navigation System (FANS) using the Aircraft Communication Addressing and Reporting System (ACARS) as the communication protocol. During flight over areas without radar coverage (e.g. oceanic and polar), reports are periodically sent by an aircraft to the controlling air traffic center.

The transmission delay caused by protocol, satellites, etc., is significant enough that significant aircraft separations are required. The cost of using the satellite channel leads to less frequent updates. Another drawback is that no other aircraft can benefit from the transmitted information.

Relationship to other broadcast services

The ADS-B link can be used to provide other broadcast services, such as TIS-B and FIS-B. Another potential aircraft-based broadcast capability is to transmit aircraft measurements of meteorological data.

Traffic information services-broadcast (TIS-B)

TIS-B supplements ADS-B air-to-air services to provide complete situational awareness in the cockpit of all traffic known to the ATC system. TIS-B is an important service for an ADS-B link in airspace where not all aircraft are transmitting ADS-B information. The ground TIS-B station transmits surveillance target information on the ADS-B data link for unequipped targets or targets transmitting only on another ADS-B link.

Flight information services-broadcast (FIS-B)

FIS-B provides weather text, weather graphics, NOTAMs, ATIS, and similar information. FIS-B is inherently different from ADS-B in that it requires sources of data external to the aircraft or broadcasting unit, and has different performance requirements such as periodicity of broadcast.

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About Wayne Farley

Wayne Farley

I am Wayne, an aviation safety evangelist who once made my living working in the control tower. Engage me while I share my thoughts, experience, and news from the aviation world. After writing "13 Characteristics of an air traffic controller" in 2010, it went viral and established me as an unofficial ambassador for ATC.


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