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From your friends
at ATCMonitor.com. © 2006 - Reproduction without
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Thousands of passengers board airplanes every
day and travel from one destination to another. With so much congestion in the skies, one may wonder how air traffic control manages all of this traffic.
One of the ways this traffic management is handled is through the use of
radar.
 RAdio Detection And Ranging (RADAR) is a method of detection used by
Air Traffic Control (ATC) to detect and identify aircraft. In fact,
radar systems (such as ASR1 shown to the left) have been in use since the early 1930's when the first aircraft was detected at a U.S. Naval Station.
This early radar method was known as continuous wave radar, because the signal from the radar equipment was one continuous signal projected onto the target, which would only provide ATC with the knowledge that there was a target, but no information about the aircraft type, or its position, speed or altitude.
Today the military still utilizes continuous wave radar methods for
applications such as air to air missiles. The Federal Aviation Administration (FAA) is moving forward with its modernization of Air Traffic Control surveillance systems.
In the United States, the air traffic system has radar coverage of over 90% of the airspace and often with multiple radar systems.
The FAA has been working on the progressive modernization of Air Traffic surveillance systems since 1981 and although it began as a 10 year, $12 billion program, it has evolved into more than a $44 billion program through fiscal year 2005.
The involvement of the FAA in its modernization of ATC equipment has permitted ATC to utilize a variety of
radar methods and systems to detect aircraft over the years. These systems are
comprised of airport surface detection
radar, terminal area radar, and long range radar. For instance, the Airfield Surface Detection Equipment (ASDE) provides radar surveillance of aircraft and airport surface vehicles at high activity
airports (Atlanta's ASDE is shown on top of the Atlanta tower in the
picture to the right). Radar monitoring of airport surface operations is required to aid in the orderly movement of aircraft and ground vehicles on the airport surface, especially during periods of low visibility such as rain, fog, and night operations.
The latest version of this surface detection radar is the ASDE-3. The Federal Aviation Administration (FAA) developed these radars to replace the aging and less reliable ASDE-2 radars.
While ASDE-3 provides a video display for controllers to assist them in preventing potential runway collisions, controllers are not able to watch the display at all times. As a result, the FAA is developing an Airport Movement Area Safety System
(AMASS) to provide automated auditory and visual warnings to alert controllers of potential runway collisions.
Terminal Radar Approach Control (TRACON) area radar sensor systems are utilized in the terminal area, which is typically within 50 nautical miles of the
airport.
These systems are comprised of two major components; Secondary Surveillance Radar (SSR) and Primary Surveillance Radar (PSR). These two methods of detecting aircraft are utilized with one
rotating radar antenna which are installed at airports and remote FAA facilities across the United States. The Primary Surveillance Radar (PSR) portion of the antenna is known as non-cooperative radar because it doesn't collect any unique data about its targets. On the other hand, Secondary Surveillance Radar (SSR), utilizes cooperative equipment (a radio receiver/transmitter or transponder) located onboard aircraft to replace the conventional radar's passive reflected return signal with an active reply signal from the aircraft. This allows ATC to collect unique data about the target being tracked.
In fact, the transponder that is located inside the aircraft listens for the Secondary Surveillance Radar (SSR) signal and sends out
a 4 digit transponder code which is assigned by ATC. This allows the SSR antenna to receive information such as aircraft type, and changes in altitude.
Both of these forms of radar are used for en-route and approach/departure
control. The latest version of this equipment is called ASR-11.
Some of the earlier systems, which were called ASR-7 and ASR-8, have been in service for 20 or 30 years.
These older versions are analog systems and work in conjunction with a radar computer system called Automated Radar Terminal System
(ARTS).
The ARTS system used older monochrome displays and limited ATC to a certain level of technology.
The newer ASR-11 version is considered a Digital Air Surveillance Radar (DASR).
Secondary Surveillance Radar
(SSR) is identified by the ladder shaped component on the top of
the radar. It provides ATC with unique information about the
aircraft type and altitude. Primary Surveillance Radar
(PSR) is identified by the larger half-circle shaped component on
the bottom of the radar . It provides ATC with calculation
of speed and position of the aircraft.
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The DASR system detects an aircrafts position and weather conditions in the vicinity of civilian airfields.
In fact, it can detect up to 6 layers of intensity when it comes to bad weather.
The components of this new digital system are comprised of the new STARS system, which stands for Standard Terminal Automation Replacement System.
STARS and ASR-11 are both manufactured by Raytheon
Corporation. Since the STARS system was designed as a digital system, older analog systems have to be retrofitted with digital component upgrades in order to interface with this new component.
But it's worth it. The STARS 20-by-20 inch full-color display shows aircraft positions and other flight information to the controller.
The display has been specially developed for air traffic control and is exceptionally readable when viewed at close range by controllers.
The displays provide information more clearly and in particular it displays details about local weather and will allow controllers to track as many as 1,350 aircraft at a time in a 60-mile radius around the airport.
One other type of frequently used radar sensor is Air Route Surveillance Radar (ARSR).
These systems are frequently used by Air Route Traffic Control Centers (ARTCC) and are considered long range radar systems.
There are 21 ARTCC's around the United States that will use this type of radar technology.
The latest version of this system is called ARSR-4 and can track targets as far out as 300 nautical miles.
The FAA has acquired 44 of the ARSR-4 radar systems and is in the process of strategically placing 42 of them along the perimeter of the U.S. Borders to monitor traffic from Alaska to Cuba.
The other two systems will be utilized for field training and support for Air Traffic Controllers in Oklahoma City, Oklahoma.
Since the 1960s, the FAA has been the leader in using computers manufactured
by companies such as IBM, Raytheon,
and Sensis to help air traffic controller's
monitor and direct aircraft. As new technologies have become available, the FAA has progressively
worked to integrate newer generations of computers to those already in service, and therefore retiring the most obsolete equipment.
However, some of the equipment still in use is more than 20 years old and is becoming increasingly difficult to maintain.
In addition, some of the computers in service today use as many as five different kinds of older computers and three displays for a controller to complete their job role.
This older equipment is having difficulty handling the increase in traffic projected for coming years.
But with the invention of systems like STARS and ASR-11, the FAA is on course to integrating all these displays and computers into one unique system.
This suggests that air traffic systems of the future will bring an enhanced margin of safety, and increase the efficiency of the air traffic control system.
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