Although displacement measurement is essential for many civil infrastructure applications, the precise estimation of structural displacement remains a challenge. In this study, a structural displacement estimation technique was developed by fusing asynchronous acceleration and computer vision measurements using a Kalman filter. First, the scale factor, which converts translation from vision measurements (in pixel units) into displacement (in length units), is automatically computed using a natural target (i.e., without any artificial target or any prior knowledge of the target size). Second, an improved feature matching algorithm was developed to better trace the natural target within the computer vision. Third, an adaptive multirate Kalman filter was formulated such that asynchronous computer vision and acceleration measurements with different sampling rates could be seamlessly combined to improve displacement estimation. The feasibility and effectiveness of the proposed displacement estimation technique were validated by performing shaking table, four‐story building model, and steel box girder pedestrian bridge tests. In all tests, the proposed technique was able to accurately estimate displacements with root mean square errors of less than 3 mm.

A displacement measurement system fusing a low cost real-time kinematic global positioning system (RTK-GPS) receiver and a force feedback accelerometer is proposed for infrastructure monitoring. The proposed system is composed of a sensor module, a base module and a computation module. The sensor module consists of a RTK-GPS rover and a force feedback accelerometer, and is installed on a target structure like conventional RTK-GPS sensors. The base module is placed on a rigid ground away from the target structure similar to conventional RTK-GPS bases, and transmits observation messages to the sensor module. Then, the initial acceleration, velocity and displacement responses measured by the sensor module are transmitted to the computation module located at a central monitoring facility. Finally, high precision and high sampling rate displacement, velocity, and acceleration are estimated by fusing the acceleration from the accelerometer, the velocity from the GPS rover, and the displacement from RTK-GPS. Note that the proposed displacement measurement system can measure 3-axis acceleration, velocity as well as displacement in real time. In terms of displacement, the proposed measurement system can estimate dynamic and pseudo-static displacement with a root-mean-square error of 2 mm and a sampling rate of up to 100 Hz. The performance of the proposed system is validated under sinusoidal, random and steady-state vibrations. Field tests were performed on the Yeongjong Grand Bridge and Yi Sun-sin Bridge in Korea, and the Xihoumen Bridge in China to compare the performance of the proposed system with a commercial RTK-GPS sensor and other data fusion techniques.

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In this paper, dynamic displacement is estimated with high accuracy by blending high-sampling rate acceleration data with low-sampling rate displacement measurement using a two-stage Kalman estimator. In Stage 1, the two-stage Kalman estimator first approximates dynamic displacement. Then, the estimator in Stage 2 estimates a bias with high accuracy and refines the displacement estimate from Stage 1. In the previous Kalman filter based displacement techniques, the estimation accuracy can deteriorate due to (1) the discontinuities produced when the estimate is adjusted by displacement measurement and (2) slow convergence at the beginning of estimation. To resolve these drawbacks, the previous techniques adopt smoothing techniques, which involve additional future measurements in the estimation. However, the smoothing techniques require more computational time and resources and hamper real-time estimation. The proposed technique addresses the drawbacks of the previous techniques without smoothing. The performance of the proposed technique is verified under various dynamic loading, sampling rate and noise level conditions via a series of numerical simulations and experiments. Its performance is also compared with those of the existing Kalman filter based techniques.

Lock-in thermography, penetrant inspection, and scanning electron microscopy for quantitative evaluation of open micro-cracks at the tooth-restoration interface M Streza, I Hodisan, C Prejmerean et al. Feature extraction using normalized cross-correlation for pulsed eddy current thermographic images A R Al-Qubaa, G Y Tian, J Wilson et al. Wireless ultrasonic wavefield imaging via laser for hidden damage detection inside a steel box girder bridge Yun-Kyu An, Homin Song and Hoon Sohn Vertical cracks characterization using lock-in thermography: I infinite cracks N W Pech-May, A Oleaga, A Mendioroz et al. A reference-free micro defect visualization using pulse laser scanning thermography and image processing View the table of contents for this issue, or go to the journal homepage for more 2016 Meas. Sci. Technol. 27 085601