Abstract
The purpose of this research is to propose a real-time, inexpensive, and portable method for measuring water surface velocities, in which a particle tracking velocimetry (PTV) system is developed by using a smartphone device. The system uses the mobile camera to capture the tracer floating on the river surface, whose movement is expected to represent the velocity of the water surface. The recorded tracer images are identified from the background by using the normalized RGB color model. The magnification ratio, which transforms the distance in pixel to the real distance, is estimated by using the pre-specified mobile height from the water surface, or the characteristic length of the tracer. The proposed system is built based on the iPhone 6s device. The system is tested in two cases. One case is the artificially generated images recording the movement of table tennis, and the relative error does not exceed 3%. The other is the comparison to the velocity measured by acoustic doppler current profilers (ADCP) in the river, and the relative error is not more than 15%. Finally, the limitation of the proposed method is discussed.
Highlights
Velocity is a basic parameter to determine the characteristics of water flow, which plays an important role in hydraulic research
In 2014, the traditional LSPIV method was combined with the smartphone, and multiple ground control points were used to achieve flow rate measurement whose measurement error was less than 10% [13] but the selection of multiple control points was too complicated
Based on the basic principle of particle tracking velocimetry (PTV) technology, the new method of measurement of river surface velocity was established by means of tracer identification
Summary
Velocity is a basic parameter to determine the characteristics of water flow, which plays an important role in hydraulic research. From the practical problem of estimating flood peak to the scientific research of turbulent flow, it is necessary to accurately measure the flow velocity. A large number of teams committed themselves to developing accurate measurement methods of flow velocity. From one-dimensional flow measurement to three-dimensional flow measurement, from steady-state measurement to transient measurement, from local single-point measurement to full-flow measurement, advanced technologies such as ultrasonic technology, laser technology, and image processing technology have been continuously applied to the measurement of surface velocity. The research of velocity measurement moves from lab-scale measurement to field-scale measurement. There are many indoor measurement methods for surface velocity measuring
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