Reducing Thermal Reflections for Infrared Thermography Applications on Tunnel Liners with Reflective Finishes

Infrared thermography (IRT) has been employed as a non-destructive evaluation (NDE) method to detect delaminations in bridge decks by ASTM standards since 2003. Compared to other NDE methods, IRT is fast in data acquisition and processing. In addition to applications on bridge decks, IRT can be employed to detect defects in other structures such as roadway pavements and tunnel liners. Recent IRT applications on tunnel liners with reflective finishes such as ceramic tiles show that the IRT results can be severely contaminated by infrared reflections of the vehicles and the illuminating systems in the tunnels. In this study, an algorithm is developed to mitigate the contamination caused by the thermal reflections in the IRT results. The reflection is reduced by combining thermal data from multiple thermographs. Perspective projection is employed to map thermal data to the same coordinates if the thermographs are taken with an infrared camera moving in the space. The algorithm is proved to be successful by the results from the lab experiments and field tests. The algorithm can work with IRT data collected by vehicle-mounted infrared cameras to achieve high-speed IRT for tunnel liners with reflective finishes.