For my last query this year, I was at Moorgate and at either end were big green things which I guess we're cameras. They were on long poles at the tunnel entrance and swiveled around mainly focusing on the tracks in the tunnel. I'm guessing they were cameras but really remind me of surveyor's equipment.
I might be wrong, but I think those are related to Crossrail. They, along with laser trackers, keep track of subsidence in the ground from tunneling works, and with their tunneling in the area they use them to know where to pump grout and revert subsidence.
If you ventured above ground, the entire area around Liverpool Street and Moorgate is covered with laser monitoring equipment fixed to buildings as part of Crossrail works which constantly measure movement.
Finsbury Circus and adjacent pavements are particularly interesting. Many of the metal gates/frames in front of the buildings around the perimeter have sheered and I noted a few days ago that some of the stonework around the steps to buildings to the south western section of the oval circus have cracked.
The whole area is being constantly surveyed by engineers and given the substantial works which are ongoing immediately underneath building movement is inevitable.
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Yes, as said they are monitoring any movement due to Crossrail works ...... and boy, there are some big cracks opening up! I think those green things are still called theodolites.
Did you know there are 5 levels of railway at Moorgate! At the top the Met, one level down First Capital Connect(or what ever it's now called) down again the Northern Line, below that Crossrail and next .... The post Office Railway
Yes, they are for the monitoring. You will see them hidden in a lot of the stations. There are a few in Farringdon station. I have also seen them in Paddington station on the District line. Basically anywhere where the building are really old you will see them. If you walk out of Farringdon station towards Barbican you will see 10+ on the buildings there.
If you go to this site (http://akshatrathi.com/2014/08/02/10-reasons-why-digging-a-tunnel-under-london-is-an-epic-endeavour/) and look at the third point you can see what exactly they are doing and how.