LASER SCANNING, DIGITAL IMAGERY AND TACHEOMETRY APPLIED TO DAM SURVEILLANCE

Dam surveillance is intended to detect, by visual inspection and monitoring, phenomenon that can compromise the structural and operating conditions of a dam. Using physical parameters acquired with instrumentation it is possible to understand the behavior of the dam and compare it either to theoretical models or to previous recordings. Visual inspections are also carried out, usually integrated in a monitoring program whose final aim is to evaluate the condition of the dam. Since the early beginning of the past century, geodetic methods have played an essential role in providing, in a Euclidean reference system, horizontal and vertical components of displacement vectors of materialized points deemed representative of the behavior of the dam. By the end of the same century, the miniaturization of Light Detection And Ranging (LIDAR) airborne technology and the availability of inexpensive digital photo-sensors, gave rise to the development of the so called Combined Terrestrial Imaging Systems (CTIS). This combination allowed the fusion of laser data and digital imagery paving the way to bring an unprecedented amount of geometric and radiometric data to the engineer´s office. From these two types of data, geometric and radiometric, collected in a single field campaign, it is possible to deliver the displacement vectors of targeted points, the lines of equal deformation of surfaces and the mapping of deteriorations in the visible dam walls or in any other surrounding and related structures. Besides the discrete displacements provided by the so called geodetic methods, the combination of laser and photo imagery can provide both a spatially continuous map of deformations and some of the information usually collected during traditional visual inspections. This information - cracks, deposits, leaching, leakage, indicators of chemical reactions, spalling, erosion or cavitation - gathered in that combined manner is positionally more accurate, is electronically supported, processed, managed and retrieved, has better quality in terms of chronological and spatial completeness, is less human dependent and less subjective yet, less costly to acquire, when compared to the information collected using traditional methods. Given the fact that from the early recording of the raw data till the final deliveries, the whole process is electronically supported, both the original and the processed data, can migrate directly into an existing information system related to the surveillance of the dam. This system will allow the fast linkage and retrieval of the physical parameters and the graphic information, collected since the preparation of the foundations to the monitoring activities, to the refurbishment ordecommissioning of the dam. In this paper one tries to summarize the experience on the use of the referred technologies within the frame of dam surveillance.

کلیدواژه ها:

dam monitoring ، terrestrial laser scanning ، digital imagery ، combined terrestrial imaging systems ، geodetic methods ، photogrammetry