Railroad Bridge Out of Plane Displacement Estimation Using Camera-Laser-IMU System

Abstract

Transverse displacement, or lateral out-of-plane movement of a railroad bridge, is an important factor in evaluating railroad bridge condition. Excessive movement in this direction can signal potential issues leading to structural failure or an increased risk of derailment. To ensuring the structural stability and safety of railroad bridges, it is critical to monitor the lateral movement of Railroad Bridge. Traditional displacement measurement methods, are usually contact-method often involve complex installation processes that are costly, time-consuming, and pose safety risks, particularly near active train tracks. To address these challenges, this study introduces a non-contact approach for transverse displacement estimation integrating camera, laser, and inertial measurement unit (IMUs). Cameras provide precise position measurements by detecting visible features, while IMUs capture high-frequency movements that cameras may miss. Additionally, camera data corrects drift and long-term errors in IMU readings, improving accuracy. So, to benefit from the strength of both sensor, this study investigate the use of Extended Kalman Filter (EKF) for data fusion and enhancing the estimation accuracy. The effectiveness of this system was evaluated through controlled laboratory experiment simulating bridge pier movements ranging from 1 mm to 25 mm. The UAV movement is simulated in the laboratory considering random translation and rotational movement that may happen because of hovering motion or UAV flying. The system’s performance was validated against reference measurements from LVDTs and ground-based laser sensors. Results demonstrated that fusing IMU and camera data yielded more accurate displacement estimates than using camera or laser alone, confirming the advantages of sensor fusion in bridge motion tracking. The developed system will eventually be mounted on a UAV to enable remote and non-contact railroad bridge monitoring, improving accessibility to difficult-to-reach locations. This advancement enhances safety, reduces costs, and increases efficiency in railroad bridge inspections.