Evaluation of Discharge Measurement Uncertainty of a Surface Image Velocimeter

This study aims to develop a framework for evaluating the uncertainty of a surface image velocimeter (SIV) based on the Guide to the Expression of Uncertainty in Measurement (GUM) standard. To achieve this, the uncertainty factors of the SIV were thoroughly reviewed and categorized into those that can be directly incorporated into the functional equation for surface velocity calculation and those that cannot. Factors that can be included in the velocity calculation equation primarily involve image displacement measurement and the accurate determination of the time interval between successive stationary images. Conversely, parameters and image quality were identified as uncertainty factors that are not directly integrated into the velocity calculation equation. Based on the GUM standard, equations for calculating the uncertainty of surface velocity, depth-averaged velocity, and flow discharge measurements were developed. Furthermore, using the results from the standard uncertainty evaluation, assessments were performed for the velocity uncertainty of both surface velocity and depth-averaged velocity, as well as the flow rate measurement uncertainty of the SIV. We anticipate that the velocity and flow rate measurement uncertainty framework and the uncertainty analysis results for the SIV presented in this research will enhance the reliability of SIV-derived flow rate measurements, thereby contributing to more dependable flow rate determination.