Pointwise sampling of the cavern wall
The measuring principle is based on a point-by-point sampling of the cavern wall. In the survey procedure the survey head, with its ultrasonic transducers, is first positioned by servo-control in the required direction with the required angle of tilt. It remains in this position until the point being measured on the cavern wall can be unambiguously determined and all the necessary plausibility checks and correlations have been carried out. This is the only practicable way of obtaining reliable survey records for caverns.

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