Roberta Aguirre
Airport surveillance radar (ASR) is a system used at airports to detect and display the position of aircraft in the terminal area. The primary radar consists of a large rotating parabolic antenna dish that sweeps a vertical fan-shaped beam of microwaves around the airspace surrounding the airport. The position of the aircraft is detected with the help of microwaves reflected back to the antenna from the surface of the aircraft. Air traffic controllers monitor the positions of the aircraft on screens and direct traffic by communicating with pilots via radio to maintain a safe and orderly flow of traffic and prevent mid-air collisions.
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What You'll Learn
Air Traffic Controllers
The ASR system consists of primary and secondary surveillance radars. The primary radar, with its large rotating parabolic antenna dish, sends out microwaves in a vertical fan-shaped beam, scanning the airspace every 5 seconds. When these microwaves strike an aircraft, they are reflected back to the dish, allowing the radar to calculate the distance and bearing to the aircraft. This information is then displayed on a radar screen, providing controllers with a precise location of the aircraft.
The secondary surveillance radar enhances the system by interrogating aircraft transponders. Transponders respond by transmitting a radio signal containing vital information such as the aircraft's identification, altitude, and emergency status. This data is displayed alongside the primary radar information, enabling air traffic controllers to make informed decisions and provide crucial instructions to pilots via radio communication.
To ensure accuracy and reliability, radar systems undergo strict government oversight and adhere to recommendations from organizations like the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA) in the United States. The design of airport surveillance radars prioritizes redundancy and low failure probability to maintain consistent performance.
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Primary Surveillance Radar
The primary surveillance radar (PSR) is a crucial component of airport surveillance systems, providing accurate information about aircraft locations. It typically consists of a large rotating parabolic antenna dish, often mounted on a tower, that sweeps a vertical fan-shaped beam of microwaves around the airspace. This beam is transmitted at a frequency of 2.7-2.9 GHz in the S band, with a peak power of up to 25 kW. The radar's main function is to determine an aircraft's location, bearing, and range.
The primary radar's dish rotates constantly, scanning the entire airspace every 5 seconds. When the microwave beam encounters an object, some of the energy is reflected back to the dish as an "echo". By measuring the time between the transmitted pulse and the returning echo, the radar calculates the distance and direction of the object. This information is then displayed on a radar screen, providing air traffic controllers with crucial data to direct traffic and maintain a safe distance between aircraft.
One limitation of primary radar is that it cannot distinguish between different types of objects, such as aircraft, drones, or birds, and it does not provide altitude information. This led to the development of secondary surveillance radar (SSR), which interrogates aircraft transponders to obtain additional data such as identification, altitude, and emergency status.
The current generation of airport surveillance radar, known as ASR-9, integrates both primary and secondary radar capabilities. It can detect weather conditions and aircraft simultaneously, displaying them on the same screen. ASR-9 has advanced clutter elimination capabilities and is theoretically capable of tracking up to 700 aircraft at once.
Additionally, the Federal Aviation Administration (FAA) in the US has introduced the ASDE-X/ASSC system, which includes a Primary Radar System. This system provides high-resolution, short-range surveillance information about aircraft and vehicles on or near the airport's runways and taxiways, enhancing safety and efficiency during airport operations. It also supports air-to-air and air-to-ground surveillance in areas where traditional radar is ineffective due to terrain or cost constraints.
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Secondary Surveillance Radar
SSR is based on military Identification Friend or Foe (IFF) technology, which was originally developed during World War II. Both SSR and IFF are compatible, allowing military aircraft to operate in civil airspace. SSR provides detailed information, such as aircraft altitude, and enables the direct exchange of data between aircraft for collision avoidance.
SSR operates in the range of 1030 to 1090 MHz. It is a rotating flat antenna, often mounted on top of the primary radar dish, transmitting a narrow vertical fan-shaped microwave beam. When interrogated by this signal, the aircraft's transponder beacon transmits a coded identifying microwave signal back to the secondary radar antenna. This coded signal includes a four-digit "transponder code" that identifies the aircraft, as well as the aircraft's pressure altitude from the pilot's altimeter. This information is displayed on the radar screen for the air traffic controller.
The transponder code is assigned to the aircraft by the air traffic controller before takeoff. Controllers use the term "squawk" when assigning a transponder code, for example, "Squawk 7421". Transponders can respond with different "modes" determined by the interrogation pulse from the radar. Modes 1 to 5 are for military use, while Modes A, B, C, and D, and Mode S are for civilian use. Only Mode C transponders report altitude, and busy airports often require all aircraft in their airspace to have a Mode C transponder to maintain strict altitude spacing requirements.
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Airport Radar Technology
Airport surveillance radar (ASR) is a critical technology for maintaining safe and efficient aircraft operations in the vicinity of airports. It is a mid-range primary radar system that detects and displays the presence and position of aircraft, vehicles, and other objects within the terminal area, typically within a 60-mile (96 km) radius and up to an elevation of 25,000 feet. ASR plays a vital role in ensuring the safe and orderly flow of air traffic, preventing mid-air collisions, and assisting pilots during landing and take-off.
The primary radar in an ASR system consists of a large rotating parabolic antenna dish that transmits and receives electromagnetic waves, specifically microwaves, in the form of a vertical fan-shaped beam. This beam scans the surrounding airspace, and when it strikes an object, the microwaves are reflected back as echoes, allowing the radar to calculate the distance, bearing, and range to the object. The primary radar can also provide data on rainfall intensity, enhancing situational awareness for air traffic controllers and pilots.
The secondary surveillance radar in an ASR system consists of a second rotating antenna, often mounted on the primary antenna. This secondary radar interrogates the transponders of aircraft, which respond with a radio signal containing crucial information such as identification, barometric altitude, and emergency status codes. This information is displayed on radar screens, aiding air traffic controllers in verifying aircraft locations and rapidly identifying aircraft in distress.
The current generation of airport surveillance radar is the ASR-9, developed by Westinghouse Electric Corporation. The ASR-9 is capable of detecting both weather conditions and aircraft with the same beam, providing an advanced ability to eliminate ground and weather clutter while tracking targets. It operates in the S-band frequency range, ensuring compatibility with highly directional antennas and improved performance in heavy rain regions.
To further enhance surveillance capabilities, technologies such as ADS-B (Automatic Dependent Surveillance-Broadcast) and ASDE-X/ASSC (Airport Surface Detection Equipment-Model X/Airport Surveillance and Surface Movement Control) are being integrated into airport radar systems. ADS-B provides improved air-to-air and air-air-ground surveillance, especially in areas where traditional radar coverage is limited. On the other hand, ASDE-X/ASSC is a multi-sensor surface surveillance system that offers high-resolution, short-range surveillance information about aircraft and vehicles on or near the airport's runways and taxiways, ensuring safe and efficient surface operations.
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Radar Range and Limitations
Surveillance radars are divided into two categories: Airport Surveillance Radar (ASR) and Air Route Surveillance Radar (ARSR). ASR provides short-range coverage in the airport's general vicinity, while ARSR is a long-range radar system that displays aircraft locations over large areas.
Airport Surveillance Radar (ASR) is a radar system used at airports to detect and display aircraft in the terminal area and the airspace around airports. At large airports, ASR controls traffic within a radius of 60 miles (96 km) of the airport, below an elevation of 25,000 feet. ASR has a range resolution of 1/64 nautical miles and an azimuth resolution of 1 ACP (azimuth change pulse). The radar antenna covers an elevation of 40° from the horizon, with two feedhorns creating two stacked vertical lobes 4° apart. The lower lobe detects distant targets near the horizon, while the upper lobe detects closer, higher-elevation aircraft with less ground clutter.
The primary radar consists of a large rotating parabolic antenna dish that sweeps a vertical fan-shaped beam of microwaves around the airport's airspace. It detects aircraft position and range by receiving microwaves reflected from the aircraft's surface. The secondary surveillance radar has a second rotating antenna, often mounted on the primary antenna, which communicates with aircraft transponders to receive data such as identification, altitude, and emergency status.
The current generation of ASR, ASR-9, can detect weather and aircraft with the same beam and display them on the same screen. ASR-9 has a digital Moving Target Detection (MTD) processor, using doppler radar and a clutter map to eliminate ground and weather clutter and track targets.
While radar systems have improved significantly, limitations remain. Radar coverage may be limited at lower altitudes near some airports, and obstructions, terrain, and the Earth's curvature can block radar signals. Additionally, certain aircraft without transponders or with malfunctioning equipment may not be detected by radar systems.
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Frequently asked questions
Airport radar systems, also known as Airport Surveillance Radars (ASR), are used to detect and display the position of aircraft in the terminal area. The primary radar consists of a large rotating parabolic antenna dish that sweeps a vertical fan-shaped beam of microwaves around the airspace surrounding the airport.
The position of the aircraft is detected with the help of microwaves reflected back to the antenna from the surface of the aircraft. The secondary radar has a second rotating antenna that is mounted on the primary antenna and interrogates the transponders of the aircraft, transmitting a radio signal back.
Air Traffic Controllers monitor the radar screens and direct traffic by communicating with aircraft pilots via radio. They are responsible for maintaining a safe and orderly flow of traffic and adequate aircraft separation to prevent mid-air collisions.
Airport Surveillance Radars (ASR) are divided into two types: primary and secondary radar systems. The current generation of radar is the ASR-9, which was first installed in 1989 and is capable of tracking a maximum of 700 aircraft simultaneously. ASR-11 is another type of airport radar system that has completed deployment.
