Structural monitoring of a large dam by terrestrial laser scanning

ABSTRACT: This paper presents some first results of a project aimed to access the feasibility of monitoring deformations of large concrete dams by terrestrial laser scanning. For this purpose a test field has been established on the dam of the Cancano Lake (Valtellina, Italy). This is made up of a geodetic network materializing a local datum for georeferencing all data acquired at different times. A large number of retro-reflecting targets have been positioned and measured by a total station in the local datum. Moreover, targets have been measured also in captured scans. Some of these have been placed on the dam structure to be used as independent check points, the others in the surroundings to play as ground control point. Three measurement campaigns have been accomplished so far by using two laser scanners: a long range Riegl LMS-Z420i and a medium range Leica HDS 3000. Reported analyses are focused on two main problems: the first one is the accuracy and the stability of georeferencing, which is fundamental to make comparisons between different multi-temporal scans; the second one is the computation of deformation based on the acquired point-clouds.