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GPS Around Airports

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Ben Purvis
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Anyone had any GPS difficulties when working in close proximity to airports? I collected a geodetic monument at around .30 feet off and using Javad equipment I had never seen this before.

 

 

 
Posted : January 23, 2023 12:46 pm
Rover83
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If you're able to collect data, there's likely not a problem.

Very rarely will there be interference that will skew your data but still allow you to store a point.

My Occam's Razor theory is that the published position is off.

 
Posted : January 23, 2023 1:07 pm
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Jitterboogie
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what time of day was it collected?

Sometimes the constellation offers up crap data, recently in Colorado it's been later afternoon

And that migrated across the chronological and constellation daily and weekly evolutions.

 
Posted : January 23, 2023 1:12 pm
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Rover83
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@jitterboogie

That's a good point, if we're talking two short(ish) occupations at very different times of the day, one with really screwball geometry, that could account for the deltas.

But generally speaking you should see a corresponding degradation in position quality if the constellation is that poor.

 
Posted : January 23, 2023 1:28 pm
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MI-Other-Left
(@michigan-left)
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FNT E (AA8102) in Flint, MI (Bishop Airport) is challenging.

https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=AA8102

After 9/11, they erected a 10' high chain link fence around the airport property perimeter, but placed the fence such that the monument was still accessible to the public. 

If you type the coordinates into google earth and zoom in, you can clearly see the mark, where the initial fence was built after 9/11, and what looks like as though the fence has been repositioned again.

The photos from the datasheet link are from FNT C, not FNT E. Not sure how that happens?

Anyway, you could set up a CORS on that mark, but never get the published value because of the fence being so close to the monument. Putting the antenna at 12' didn't really work well either. In fact, I remember that we could not even get fixed while occupying it.

So, to answer the OP question directly, yes, have had problems. But not likely for the reasons OP is having.

We did lots of control surveying and HARN in the 90's in MI, and I always enjoyed working in/around airports. Back then it was a breeze, and you got to meet the most interesting characters working Operations for airports.

 
Posted : January 23, 2023 1:32 pm
Jitterboogie
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@rover83

I'm not even bringing the whole truckload of stuff like equipment used, horizons from hangars, proximity to vehicles, EMF, ETC ETC ETC.

  I've fallen back to loving the absolutely super tight and amazing reproducible data of the total station and try to find excuses to not use GPS even when it's way faster.

I'm weird and like precise accuracy, yeah go ahead, poke fun, I'm thick skinned and got enough GPS to live a second lifetime.

Just a tool in the box, sometimes it's better sometimes it's not.

Get off my lawn!

 

 

 
Posted : January 23, 2023 1:34 pm

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OleManRiver
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Uhmmmm is that monument in line with a glide slope by chance.  Yes yes yes you can have issues with gps data around airports also around truck drivers and others that use jamming and spoofing technology to hide from employers. At one time the faa had a map and a place to report irregularities. It will not always happen fyi. Don’t stand to close to a glide slope it will make your babies be born naked. 😂 

Is this a commercial or military or both airport. You could possibly go back out and never see the issue again. It could be a bad published point. Or you caught some bad multipath from the frequency shredder known as a chain link fence. Etc. 

 
Posted : January 23, 2023 6:01 pm
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Steinhoff
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Posted by: @olemanriver

Don’t stand to close to a glide slope it will make your babies be born naked.

Your babies are born clothed?

Uh... be right back. Need to talk to the wife.

 
Posted : January 23, 2023 6:05 pm
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OleManRiver
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@steinhoff I am only repeating what I was told 😂.

 
Posted : January 23, 2023 6:37 pm

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holy cow
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From personal experience of being in the delivery room, all babies are born female with blonde peach fuzz for hair.

 
Posted : January 23, 2023 6:40 pm
MI-Other-Left
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@olemanriver

The interference is multipath, etc. from the fence.

For years prior to 9/11, the monument was about 68' away from the original fence. It was one of the "go-to" points in the area because you could drive right up to it with all your gear, set up, and leave everything running without worry. Plus it was a PACS/CBN mark, which are/were even better than regular marks of the time.

 
Posted : January 23, 2023 6:51 pm
OleManRiver
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@michigan-left Good old PACS and SACS. I have set a few of these over the years. I hope it’s figured out. I can tell you chainlink fences are about as bad as it can get at times for gps signals. Glide slopes depending when they were made and how much power they are pushing at any given time is not good either. Had a PACS once we ran static on continuously 24/7 non stop for 2 weeks straight i bet we got only a few days worth of decent data out of that set up. We could compare the reports of when and direction glide slope and output power with gps data. I never set another pacs in the main line of a glide slope again. A sacs yes but never a pacs. Now commercial  airport might be somewhat different than military. But a lot of the same technology was on them. I have no idea how close or far that chainlink fence is from the station now nor if it is powered chainlink fence. Just trying to throw out suggestions is all. Things it might be. Gps signals are not very strong. Our recievers have become better at listening though through better antennas and such.

 
Posted : January 23, 2023 7:40 pm
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On_Point
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multi-path? Chain link fence first comes to mind at an airport but I suppose there are many things at an airport that can cause multi path. 

 
Posted : January 23, 2023 7:54 pm
paden cash
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I've done a good amount of GPS work around APs, both civil and military.  While multipath from fences and hangars can be a factor at times the few difficulties I've experienced had to do with my Topcon equipment's UHF (400 MHz) radio and not the unit's ability to receive signals from the SVs. 

Like Rover83 noted; if you're able to collect data, there's probably not a problem. 

 
Posted : January 23, 2023 8:16 pm
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Jitterboogie
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@olemanriver 

I liked working at the airport.  Esp that day when I was on the apron and the Guardrail platform was taxiing toward the truck we were using to camera the 1100 feet of storm with no manholes...

It was close enough to touch the wing tip pod while I stood between it and the not so good idea of making contact with our truck.  I was tempted snap a video and pictures but decided I didn't want to be debriefed by the Spooks from the Agency and the Army.

Neat planes.  Flying everything along the border of Texas NM and the rest.

Also watched the White knight 2 fly the runway for line up.  Airport work is fun, if you're not being distracted by planes...lol

 

 

no secrets here... these things hear anything they want to hear....

 

 
Posted : January 23, 2023 8:24 pm
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