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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.

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  • $\begingroup$ I almost wonder if this is more suitable for answering in a foreshortened format, such as focusing on one kind / class of radar system $\endgroup$
    – New Alexandria
    Dec 18, 2013 at 20:51
  • $\begingroup$ Also, I fear you are drifting too close to national security topics. Not that the information should be secret, but that it may be voluntarily non-disclosed. I am guessing, and hope to be wrong $\endgroup$
    – New Alexandria
    Dec 18, 2013 at 20:52
  • $\begingroup$ RE: Scope of question. I suppose depends on how many kinds/classes of radar systems there are in use. I believe the list (at a high level) is very short though. RE: national security. I wondered if this would come up myself. I think it could get questionable if someone were able to provide highly technical details on specific radar systems. However, I think at a high level, this question is asking for knowledge that should be considered public knowledge and might be useful to aviators and those, like me, that are interested aviation accident analysis. $\endgroup$
    – kaliatech
    Dec 18, 2013 at 21:02
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    $\begingroup$ These are too many questions into one. Consider breaking it up. If you ask what is the difference between primary and secondary radar, I am happy to answers, and also if you are interested in difference between Mode A, C and S. But all combined with specific radar types it becomes a bit too much. The basic question in the title I can answer though $\endgroup$
    – DeltaLima ♦
    Dec 18, 2013 at 21:05
  • $\begingroup$ You may get better traction, even just insofar as 'best questions' by posting info about the radar systems you know about, and asking for their differences. $\endgroup$
    – New Alexandria
    Dec 18, 2013 at 21:06

3 Answers 3

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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 effects 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 accuracy of the distance measurement are not so much affected by the range, and 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.

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There are sources online claiming that the terminal Airport Surveillance Radar used by the FAA rotates at 12.5 RPM (one update every 4.8 sec) and the enroute Air Route Surveillance Radar rotates at 5.0 RPM (one update every 12 sec). I have not been able to find official documentation for these figures.

In an article titled "FAA Surveillance Radar Data as a Complement to the WSR-88D Network" Mark Weber includes the following unsourced table:

TDWR (Raytheon) ASR-9 (Northrop Grumman) ASR-11 (Raytheon) ARSR-4 (Northrop Grumman)
Transmitter
Frequency 5.5 - 5.65 GHz ~ C Band 2.7-2.9 GHz 2.7-2.9 GHz 1.2-1.4 GHz
Polarization Linear Linear or Circular Linear or Circular Linear or Circular
Peak Power 250 KW 1.1 MW 20 kW 60 kW
Pulse Width 1.1 μs 1.0 μs 1.0 μs, 80 μs 150 μs
PRF 2000 (max) 2 CPIs (~ 1000 Hz avg.) 4 CPIs (~ 1000 Hz avg.) 9-pulse CPI at variable spacing (288 Hz avg)
Receiver
Sensitivity 0 dBz @ 190 km 1m2 @460km 0 dBz @ 20 km 1m2 @111km 0 dBz @ 20 km 1m2 @111km* 0 dBz @ 10 km 1m2 @370km
Antenna
Elevation Beamwidth 0.55 Degrees (min) 5 Degrees 5 Degrees 2 Degrees (stacked)
Azimuth Beamwidth 0.55 Degrees 1.4 Degrees 1.4 Degrees 1.4 Degrees
Power Gain 50 dB 34 dB 34 dB 35 dB (transmit), 40 dB (receive)
Rotation Rate 5 RPM (max) 12.5 RPM 12.5 RPM 5.0 RPM

He does not provide citations for this information but there is no reason to doubt it.

The FAA's ASR-11 Test and Evaluation Master Plan document does not mention rotation rate (that I can see) but does list some detailed "Critical System Characteristics" beginning on page 16, for example:

PSR Probablity of Detection (Pd)
The PSR shall be capable of detecting a 1.0 m2 Radar Cross Section (RCS), Swerling 1 target to a range of 55 nmi in the clear and at the nose of the beam with a single scan Pd of 0.8 and a Probability of False Alarm (PFA) of 10-6.

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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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    $\begingroup$ As a side note, we definitely need to get some controllers engaging in this site. $\endgroup$
    – Bret Copeland
    Dec 19, 2013 at 1:03
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    $\begingroup$ I'll try and convince some to join $\endgroup$
    – DeltaLima ♦
    Dec 19, 2013 at 10:36
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    $\begingroup$ Thanks. This answer is closer to my findings. In all fairness, I already have some specific data regarding ATC radar capabilities. However, I've never been able to source it or verify it beyond statements by expert witnesses in litigation cases, and by watching actual radar echos in recorded data. As an example, according to CDR data exports, TRACON/ASR systems appear to update an aircraft echo at about a 4.7 second frequency, give or take a few tenths. I'll update my question with this note. And I agree, having ATC controllers engaged on this site would be beneficial to everyone. $\endgroup$
    – kaliatech
    Dec 19, 2013 at 12:46

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