Development and evaluation of a long range image-based monitoring system for civil engineering structures
Matthias Ehrhart, Werner Lienhart · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2015
Today, many large-scale civil engineering structures are permanently monitored to provide early warnings and to initiate counter actions from structural failure. Total station measurements are commonly used to determine 3D movements of selected points with measurement intervals of several minutes or hours. However, these measurements do not provide information on the vibration behavior of the structures. For this purpose, other sensors like accelerometers have to be installed on the object. In this paper, we present a monitoring system based on a state of the art image assisted total station (IATS) suitable for the measurement of absolute 3D coordinates and the determination of the structure’s natural frequencies. The 3D coordinates can be determined with an accuracy of a few millimeters using conventional total station measurements. For analyzing the structure’s natural frequencies, the telescope camera of the IATS is used in combination with dedicated image processing techniques optimized for artificial and natural targets. While the determination of 3D coordinates based on total station measurements is common practice, the idea of using the total station’s image data for frequency analysis is new. Consequently, investigations on the achievable performance are pending for commercially available products. We therefore evaluate the potential of this technique at a life-size footbridge by comparison with accelerometer measurements. We demonstrate that with our developed monitoring concept and state of the art hardware, accelerometer measurements can be replaced in several monitoring situations by IATS measurements and image processing techniques.