Air traffic control radars are devices used to detect, monitor and guide aircraft within a delimited airspace region.
Several types of radars are used in the framework of civil or military air traffic control.
In IVAO, we have one Radar system simulated by specific IVAO software.
The primary radar operates using the electromagnetic waves properties, especially the echo. The primary radar is a turning antenna that emits electromagnetic pulses, meaning a wave front concentrated in time which propagates through air and is reflected by all targets with sizes greater than a given threshold. The radar finally detects the incoming waves after their reflection.
The time difference between the pulse emission and the reflected wave reception is proportional to the distance of the target with respect to the emission antenna. The position of the antenna at the reception, corrected by the fact the antenna is continuously turning, is linked to the azimuthal angle of the target.
Primary radars are unable to detect the altitude of the target.
The emission power of the radar is one of the main specifications which determine the maximum detection range (radar coverage). The introduction of the pulse compression technique has made possible a global reduction of the instantaneous emission power, leading to less expensive devices.
Primary radars are placed in strategic positions within a given region to ensure the largest coverage:
The secondary radar operates using the interrogation technique. The secondary radar transmits a series of electromagnetic pulses, but these pulses are coded in such a way that a transponder system installed inside aircraft system can detect and interpret them.
The transponder of an aircraft detects and decodes the radar pulses (interrogation signal) and emits a series of pulses which code the answer to the interrogation.
The secondary radars operate in "active mode" with respect to primary radars which operate in "passive mode".
The passive answer (primary mode) of the aircraft provides its position while the active answer of the transponder (secondary mode) provides other information (code, altitude, speed...), depending on the type of both the radar and the transponder.
Two types of secondary radars exist:
In IVAO, IVAO ATC software can be considered as Mode S secondary radar.
Radars are able to detect and localize all aircraft within an airspace region.
Radar echoes (eventually coupled to active answers) of a moving aircraft constitute an ensemble of "radar plots" which allow reconstructing a "radar track".
Radar tracks are compiled to generate and display the radar image of the aircraft. All radars placed within a given region have overlapping coverage in order to avoid dead zones. Each of the radars available generates its own image of the aircraft track.
In order to avoid redundant plots in the process of track generation, all radars transmit their plots to a centralized computer which builds up the track. So, the radar image of an aircraft is often produced by the combination of plots coming from several radars, thus ensuring a higher confidence of the displayed information.
In IVAO, we do not have this complex system, IVAO ATC software makes a perfect view of all aircraft plots without any combination of radar images.
Radars are used by air traffic control to provide three types of radar services:
- Radar Surveillance
- Radar Assistance
- Radar Guidance
Radar services can be provided only to aircraft which are "radar identified", which means that the correlation between the radar track and the aircraft is unambiguous.
Some air traffic control units are not able to provide some of the radar services because of their radar performances or the airspace configuration.
Radar is used to identify and determine the position of all aircraft.
In this framework, radar surveillance is meant to:
Pay attention, this service has no communication with the aircraft.
Radar is also used to provide assistance to all aircraft.
In particular, it helps the controller to:
Pay attention, this service does not give any clearance or instructions to aircraft. The air traffic controller only gives advices, information to help the pilot to make a decision.
Radar is finally used to guide aircraft within a controlled airspace. In particular, it helps the controller to:
On IVAO, all controllers dispose of a radar when using IVAO ATC software radar client. Nevertheless, the radar services that can be provided by the ATC depend on the control position he has in charge:
|Radar surveillance service
|Radar assistance service
|Radar guidance service
Other ATC positions can be exceptionally opened in the case of specific events (mostly VFR based):