Robust optical displacement measurement of bridge structures in complex environments

Abstract

A robust optical displacement measurement method is proposed herein for long-span bridges by considering complex environmental interference, such as illumination changes, system disturbances, and remote calibrations. First, to reduce the centroid shifts caused by lighting changes from the ambient or target itself, a center detection algorithm with an area-consistency constraint was applied. Optimized algorithm can reduce the noise variance by about half in the static laboratory experiment, which shows better illumination robustness than the adaptive threshold-based method. Second, to overcome the lower accuracy of 6-D camera pose tracking in remote measurements and limited correction effects of the widely used relative displacement method, a novel correction method with better implementability as well as accuracy was proposed for typical environmental vibrations. Third, an integrated real-time standing optical displacement sensor was developed for outdoor tests. In particular, a system combining a kilometer-level rangefinder and high-power laser designator was designed to achieve fast and fine object distance calibrations. Finally, the proposed method was applied to a short-span concrete bridge and a long-span steel bridge. The extracted displacement time histories at multiple points and deflection shapes at certain moments are expected to provide rich data for further performance evaluations.