Some time ago, I noticed that the controller's screen (CWP) of a particular system in a European ACC. was not updating all the visible tracks at once but it was following this pattern:

The screen appeared as if it was split in invisible rectangles. Starting from the upper left corner, only the tracks in a particular rectangle were updated at a time. Then immediately (I think, there might have been some millisecond delay but I couldn't tell for sure) the next rectangle at the right was updated and once all the rectangles on the row were done, the "scanner" moved to the next raw and so on and so forth.

I've seen a similar pattern in another system (in Europe) as well. Is there some technical reason behind this seemingly complex design? eg. could it be the way the surveillance data processing system (SDPS) functions?

  • $\begingroup$ RE of a particular system – does it cover a very large airspace volume? $\endgroup$
    – user14897
    Commented Jan 15, 2022 at 3:25
  • $\begingroup$ @ymb1 small to moderate I would say. Approximately 80.000 km^2 (around the size of Maine state). But anyway I'm afraid I will have to reword the question. I don't know if this behavior comes from the CWP, or the radar data processor, or any other system and this is not depicted in the question. $\endgroup$ Commented Jan 15, 2022 at 11:46
  • $\begingroup$ Was this in the US? If so, was it terminal or enreoute? Did you see it firsthand or was it a video we can see? $\endgroup$
    – RetiredATC
    Commented Jan 17, 2022 at 4:54
  • $\begingroup$ @RetiredATC No Europe and I saw it firsthand. It was ACC (en-route). If I had a video I would have posted it :) I will update the question. $\endgroup$ Commented Jan 17, 2022 at 5:01

1 Answer 1


I cannot comment on Eurocontrol radar display systems, but in the US, radar data processing is divided into 10NM squares called sort cells. Each sort cell has a preferred radar, normally (but not always) associated with the nearest radar site. Each cell will generally have a second and sometimes a third radar site to provide data if a satisfactory return is not obtained from a higher priority radar.

As the radar antenna turns, the data is digitized and sent to the facility, where ERAM (the enroute ATC computer system) compiles the information and presents it on the controller's display. Since the updates follow the rotation of the radar, you can see a "sweep," but it is not as pronounced as some of the older terminal radar displays.

  • $\begingroup$ In the Terminal environment we now use Fusion mode in STARS, which combines ASR, ARSR, and ADS-B data to create an "average" or "best-guess" for each track. All tracks are updated simultaneously each second (even tracks without ADS-B, which are essentially coasted until the next radar update). If we switch from Fusion to single-sensor mode the targets are not updated simultaneously; the "sweep" is very noticeable even though the sweeping arm running around the scope is no longer present. $\endgroup$
    – randomhead
    Commented Jan 17, 2022 at 10:16
  • $\begingroup$ Anyway, this is all very interesting but (as you say) neither of us can speak to Europe. Your description of ERAM's sort boxes is at least a little bit similar to what OP describes, but it would still be a clockwise rotation for the most part, not a right-to-left row-by-row update. $\endgroup$
    – randomhead
    Commented Jan 17, 2022 at 10:19
  • $\begingroup$ @randomhead If the software is designed to update all the data in each sort cell, send that output to the scopes, and then move to the next sort cell, that’s exactly what you’d see. And I’d assume that’s why the sort cells exist in the first place: divide the multi-input correlation task into more manageable chunks. $\endgroup$
    – StephenS
    Commented Jan 17, 2022 at 17:19
  • $\begingroup$ Also this obviously is not about eurocontrol systems but some other facility in Europe $\endgroup$
    – pcfreakxx
    Commented Jan 18, 2022 at 13:04

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