Underground surveying embraces the survey operations performed beneath the surface of the earth in connection with tunneling, exploration and construction in subterranean passageways. It is quite different from surveying on the surface. The following peculiarities of underground surveys indicate how they differ from surface surveys:
- Artificial illumination is required to view instrument crosshairs, to read verniers, to sight targets etc. Because of poor lighting.
- Working space in passageways is often cramped.
- Instrument stations and benchmarks for levelling must often be set into the roof of a passageway to minimize disturbance from the operations being carried on in the workings.
- Instrument stations are set with some difficulty since plugs must be driven into drill holes in rock.
- In many instances the underground workings arc wet, with considerable water dripping from the roofs of passage ways and running along the floors.