Development of a three-axis accelerometer and large-scale particle image velocimetry (LSPIV) to enhance surface velocity measurements in rivers

Abstract

A three-axis accelerometer was combined with large-scale particle image velocimetry (LSPIV) to obtain nonintrusive and safe surface velocity measurements. Dual cameras were established at the Yu-Feng gauging station of Shimen Reservoir to capture near-field and far-field images and analyze the surface velocity of rivers. Surface velocity measurements were obtained with a flow meter, LPSIV with ground control points, and LSPIV with a three-axis accelerometer to compare the measurement accuracy. The results show that the relative root mean square error (RMSE) values for LSPIV with ground control points and with the three-axis accelerometer are 21% and 18%, respectively. The LSPIV technique with the three-axis accelerometer slightly improved the measurement accuracy of the surface velocity. However a three-axis accelerometer can be utilized to replace the traditional ground control points for yielding the camera pose parameters. Furthermore, the effects of the camera pose, three-axis acceleration, interrogation area (IA), and image resolution on surface velocity measurements were explored. The camera pose parameters, namely, roll (θ) and tilt (τ), and three-axis acceleration parameters, including Xa and Ya, influence surface velocity measurements. If the measurement error of the surface velocity is controlled within ±10%, the acceptable variational ranges of θ, τ, Xa, and Ya are 6.2°, 1.3°, 0.11 g, and 0.02 g, respectively. The IA size and image resolution also significantly affect the accuracy of surface velocity measurements. Therefore, the selection of a suitable IA size and image resolution is crucial for accurately measuring surface velocity.