I dont think that you would use GPS for pipeline monitoring. You certainly should have cm accuracy for monitoring pipelines. 2cm axial movement can easily mean overstress. That's not lasers, but its way over GPS accuracy.

How are you doing this now?

We recently had some outdoor industrial process piping and their support bents surveyed using LIDAR techniques. This was the first step in a mechanical integrity evaluation for the entire plant. The bents supported from as few as one 24" pipe to as many as 45 pipes and conduits ranging from 1" to 24".

LIDAR is good to about 2 mm accuracy and one model can be easily integrated into another model, so it would work extremely well for monitoring pipe movement over time. The surveyor produced about 1.5B points in less than 8 hours. He was able to determine--while in the field--that one of the two chemical storage tanks the piping serves was ever so slightly out of plumb. He could also tell which part of the pipe support bents were rusted or painted by the type of reflection he saw on his tablet. In addition, he produce a ground surface topo map for us.

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LIDAR can be overkill and works great, but it only works if the pipeline is above ground. Spsaking of which, impeller did not specify?

1503-44...

True. Years ago a water district that abutted a water district I consulted for had a problem with a buried transmission main in a similar situation to what the OP describes. I was told (probably third hand at best) that at several key locations they welded posts to the top of the pipe that extended above ground. Every so often they would survey, by the means available in the 1980s, the elevations of the top of the posts and and any rotation of the posts.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

As far as I know, that's still the procedure. I had a similar problem in North Dakota Badlands about that same time. Pipeline crossing a slope with what appeared to be a water saturated layer of soft coal. We set up a couple of bench marks and monitored horizontal and vertical level movements with chain and level for a year and eventually drilled some dewatering holes into the coal higher up on the slope and it eventually stabilise.

GPS has been used for detecting Earth's crustal motions for nearly two decades. The current generation of GPS receivers can achieve millimeter accuracy. Sparkfun's RTK modules potentially are cheap enough that you can make permanent installations and get real-time data. That all presumes you can either get the RTK corrections or have a fixed base station.
https://www.gislounge.com/using-gps-monitor-earths...
https://www.earthmagazine.org/article/precise-faul...
https://www.sciencedaily.com/releases/2001/03/0103...
https://www.degruyter.com/document/doi/10.2478/jog...
https://www.topcon.co.jp/en/positioning/products/p...
https://learn.sparkfun.com/tutorials/what-is-gps-r...

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Yes, you are right, but I thought it had to have some local enhancement equipment installed. I know they are doing that a lot near active volcanos, Mt Etna and Visuvius.

Then you need a fence and solar power and landowner permission, because you promised all the pipeline stuff would be underground. Besides, its a good excuse to get out of the office once in awhile.

I think that in any case, you need a set of fiducials, or monuments. Conventional total-station survey, lidar survey, or GPS survey all depend on RTK GPS to get the absolute Earth reference. Lidar would seem to ostensibly be the fastest, since you could possibly do it from a single vantage point. I would imagine total-station would require traipsing around to get control points, and GPS would require spending some number of minutes at each monument, although one could possibly drop off a set of receivers and collect data for an hour or so from the array.

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Hi guys, thanks for your thoughts on the matter. My apologies, it is above ground piping and currently, the vendor is using a total station survey. Specifically, use of the total station for horizontal displacement, and digital levels for vertical. A system of control points were set up along the run of the piping, and they'd survey specific points at the top of the piping.
1503-44, you mentioned LIDAR is overkill, so I am assuming this is typically how surveys such as these are performed? Just wondering if there's anything else I can explore to ensure accuracy.

In my experience LIDAR isn't necessary. That will give you a point cloud for leaves on a tree and everything else around there.

You didn't say much about your pipeline, or why you are monitoring it, so its hard to say what kind of accuracy you really need. Normally lengths and levels to a few mm will easily suffice. Why are they having such a hard time with it?

With GPS, you get point clouds of a different sort

Much depends on how old the surveyor's equipment is; the newer, the better, assuming they spent the bucks to get the full benefit of RTK. Nevertheless, some GPS receivers are more capable than others; their designers having taken advantage of essentially "undocumented" features of the GPS constellation and the RF signals therefrom.

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Lidar, GPS and total station are all viable and can be used. Lidar can be filtered so you can turn off the leaves... even some total stations are 'automatic' and don't require an operator... possibly my choice. GPS can operate similar to an automatic total station. Depends on what informaton you need. On the Cornwall Centre the locations of the pile supports were required... I was out on site and the surveyor was measuring the pile locations (prior to total station common use) using a plumb bob... For every main column pile, there were half a dozen 16" friction piles to support the structured slab... I told him precision was only required for the main column piles and that for the friction piles, it didn't matter if the location was an inch or two off... There were hundreds of piles and it likely saved him a lot of work. Depends on the precision you need.

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Right, I see. Well basically, we know the piping would be susceptible to land slippage in this area so we conduct surveys to quantify the displacement. The displacement is then compared to set allowable displacement values so the precision I'm looking for would be to the mm.

I honestly can't say why they're getting so much trouble although, I suspect it's some sort of mistake they made with the data that's throwing everything off. They marked points on the top of the piping to use as measurement points but unfortunately, our painting department decided to re-paint the lines and the measurement points were lost. The contractor re-established monitoring points but upon doing so, we saw vast differences in lateral displacement which we questioned, in the vicinity of 1 - 1.5 meters! The vendor claimed that it was the painting and re-establishing of measurement points that resulted in the differences, but I can't see how that would equate to over a meter in variation. I think they made some other sort of measurement error, or otherwise.

So, I thought maybe there was a better, more efficient way to do the survey to eliminate the possibilty of errors. But, it seems to me that the technique is not the issue, rather the execution.

It would seem to me that the control points shouldn't have moved, since they wouldn't have been on the piping, but possibly located on the periphery of the pad? Were all of the points displaced? or only some? GPS errors are highly dependent on the satellites in view; our subcontractor had their own criteria for the allowable satellites-in-view, to ensure that GPS data was stable.

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It doesn't seem to be a technical problem with the method, but rather the background activities. If the marker targets can't survive, good luck with LIDAR and GPS. You will still need to keep markers in place no matter which method you use. Put a fence around the benchmarks to keep the lift trucks from taking them out and strap some bands around the pipe to hold some new crosshair markers, now that the pipe is freshly painted.

The comparisons need be made from same control points and same pipe marks. If these physically change, then the measurement data is going to be different.
The control points need be outside the influence of whatever geo environment the pipe points are within. Can't have control points moving on a landslide and the pipe points moving likewise too, and data showing no change from prior measurements. There is no issue using a 2-second total station, with targets that are plumb to their pipe targets. Just grab a triple measurement and average, to have a validated value. It wouldn't hurt to have a control station for the control station, as another QA check that the reference control point didn't move.
I personally wouldn't be using gps...due to lack of quality control....the measurement coordinates be slightly different through the day, and only consistent for a QA check is a reoccupy the next day at same time, to have the birds in same geometric pattern, and reading from the same birds again.