What is the range and accuracy of ATC radar systems?

kaliatech
  • What is the range and accuracy of ATC radar systems? kaliatech

    What is the average range, accuracy, and update frequency of radar systems used to monitor airspace in the USA?

    I'm primarily interested in capabilities for tracking smaller general aviation aircraft without enhanced return data channels like ADS-B, etc.

    Please include sources, if possible. As an example, by looking at TRACON/ASR data exports (CDR), these systems appear to update an aircraft echo at about a 4.7 second frequency, give or take a few tenths. However, I not been been able to source or verify my findings or similar statements made by expert witnesses in litigation cases.

  • This is a general answer, not specific applicable to the situation in the USA.

    There are several types of radars in use to monitor airspace.

    Basically you can distinguish two classes of radar:

    • Primary radar does not require the aircraft to carry a transponder, it is a form of non-cooperative surveillance.
    • Secondary radar on the other hand requires the aircraft to carry a transponder; the transponder replies to interrogations from the radar. This is called cooperative surveillance.

    Radars operate basically by line-of-sight, however due to atmospheric effect the radio waves follow the curvature of the earth to some degree. Aircraft flying low are quickly below the horizon, but aircraft at FL450 can be detected on secondary radar at ranges up to 300NM if the radar is operated for such range. Typically the range is less.

    In general, the further the range that a radar needs to look, the slower it rotates. An airport surface radar may rotate as fast as twice per second, long range en-route radars can go as slow as once per 12 seconds. For typical TMA / TRACON use, 5 seconds would be in the right ballpark, for en-route 8 seconds will be about right.


    The accuracy depends on the type of antenna, whether it is primary or secondary radar, and the distance of the aircraft from the radar head. The distance measurement are not so much affected by the range, an varies from about 5 meters to 300 meters. However, atmospheric circumstances can degrade these figures, especially at long range. The across beam accuracy is very much dependent on the distance from the antenna due to limited angular accuracy of the radar. The further you get, the worse the across beam accuracy becomes.

  • I originally posted this simply as a comment, but I suppose it's more of a partial answer.

    I researched this about six months ago and found that, in the US, 6 seconds was the standard for a TRACON, and 12 seconds for an ARTCC - allowing them to see about a 60nmi and 120nmi radius, respectively. I don't have sources off-hand, but if I come across them, I'll post them.

    Not sure about the accuracy, but when it's a human looking at a screen, discrepancies of even tens of feet is probably not particularly meaningful.

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