Design and field validation of a large-volume reference system for inspecting underwater hydroelectric structures

This paper presents the validation of a reference system for the inspection of large underwater hydroelectric structures. The reference system is part of a comprehensive solution for underwater inspection previously presented by the authors. The reference consists of a set of vertical wires forming a virtual plane of reference for a 3-D laser scanner. The geometrical characteristics of the reference are achieved through the use of a specially designed five-degree-of-freedom table and statically balanced universal joints. Key mechanical, electronic and software elements of the design are described. Field trials carried out on the site of a Hydro-Québec hydroelectric dam show that the approach is practicable. Trial results are compared to those from an alternative measurement system.