Unexplained variation in reported positions

I see a large variation in the number of positions in relation to the number of aircraft between different days. Yesterday there were > 1000 positions/ac and a couple of days ago I had just above 400 positions/ac. These cases are a bit extreme, but the quotient varies quite a lot all the time. I have not changed anything during that time and there has been no network problems as far as I know.

Any ideas?

A lot depends on your atmospheric conditions and various forms of interference. Weather, air density, temperature, and other factors all play a role in determining signal strength from a source. Distance also plays a factor: many of these aircraft will be broadcasting from 300km away. If you have more distant traffic and poor atmospheric conditions, then you’re going to receive fewer positions.

There’s also the factor that your receiver may be set to dynamic amplification (someone please correct me on that terminology if I got it wrong). Often immediately following an upgrade (such as my recent upgrade to PiAware 7.2) I find that I have a wide variation from day to day and week to week on the number of positions reported. That’s because I have dynamic amplification turned on, and my receiver is trying to figure out the optimal setting.

I find that usually about a week after an upgrade or other outage, my receptions increase about 150%. I’m located between KMKC and KMCI, so as the amplification lowers I get more positions from aircraft at the two nearby airports but lose some of the positions from more distant aircraft flying over, for example, KOMA and KICT. At least, that’s what I think is happening.

You are of course right that the conditions and the amplification influence the result. Also interference, of course, but I have a quite good band-pass filter which should eliminate most of the out of band interference.

The dates I am comparing are March 26 and March 30. From the diagrams you can see that there was not much variation in range (about 250 nm) or amplification (during most of the day the same in both cases)*. Well, slightly after midnight there is no traffic at all to be seen within about 250 nm (so range is 0) and the gain goes up to maximum. But that is always the same, so it is a variation during the day not between days.

To conclude, I don’t think that in this case the variations in conditions and gain can explain a factor of 2.5 between positions per aircraft count when different days are compared.

  • Unfortunately you don’t because it seems I can’t upload pictures. Curious, the are quite small.

Let’s see if the graphs will be uploaded now.

Here is what I see.

I agree the positions reported has increased recently if you are in the Stockholm area like we are. I offer three things to consider. Two are factual, the other complete supposition. Feel free to add to the list or debunk my guess. I have no hard answers, either.

  1. Airlines started flying new schedules with the time change last weekend. More planes in the air as they try to get back to normal ops after two years of COVID.

  2. Closure of Russian and Ukranian airspace has changed routing significantly, so depending on your location you could see more or less or the same level of traffic.

  3. Air traffic controllers may be a bit rusty having worked at much reduced levels due to the dip in traffic because of COVID. So, based on #1 and #2 occurring at the same time, radars are interrogating more often to provide better situational fidelity to help the controllers out. This in turn leads to more messages being seen.

Edit: I will add a fourth item. The marked increase in miltary traffic (Swedish, Finnish and NATO) in response to the invasion of Ukraine and related to the Cold Response NATO exercise in Norway likely has a role.

have you been using Sky Aware Anywhere?

I checked the development for a site nearby. It seems that his quotient also went up somewhat after March 26, but far from what I am seeing. Strange.

  1. I think that the number of planes we have seen here has gone up after March 26, but just compared to that date, not compared to the days before as you can see from the second diagram.
  2. Yes, it has changed significantly, but that happened much earlier, just a few days after the new war started.
  3. Interesting idea, but my neighbouring site does not see much of that.

Yes, I have. Actually all the time. If FA has increased the update frequency for SkyAware Anywhere it could explain what we see.

here is a quote from OBJ “If you’re also using skyaware anywhere (your logs imply you are) then the report rate gets artificially increased while it’s in use to improve the interactive experience there, which unfortunately also shows up on the stats page.”

Maybe then that FA varies the update frequency, perhaps depending on the load on their servers. I have used SkyAware Anywhere during the whole period.

Yes, using SkyAware Anywhere can almost double your positions reported. That said, my positions for the past week compared to the previous are up 25% without using it. You are probably seeing a combination of increased traffic and use of Anywhere.

I don’t know if there is a relation but after @obj restarted the MLAT server in the EU region ( If I understood correctly) I saw an increase in positions.
See this post Problem with MLAT? - #7 by triggers
That restart brought the number of positions back to normal
After I had to reboot some receivers last friday they returned to the lower values again.
The number of aircraft remains the same on average, but the postions really fluctuate.

As said, this is an assumption but It looks like the serverside issue is still there.
I can’t explain why the number of positions has dropped to a 1/3 of the previous days.

And yes I do use Skyaware Anywhere permanently, I have a display of the radarview from an Intel Nuc on a screen.

What a difference! But it seems you have very few, if any, MLAT positions?

Between 5000-7000 on a normal day. Living under an approach towards EHAM so the ADSB traffic is usually much higher then the MLAT traffic :slightly_smiling_face:

This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.