Measurement of Flow Velocity Using Video Image of Spherical Float

Abstract In this study flow velocity measurement using video images of a float was designed to measure flood discharge during heavy rainfall. A spherical float was used to obtain video image being not distorted according to oblique angle. The drifting distance of the spherical float was calculated by the inscribed and circumscribed vertical lengths of spherical float image from the center line based on geometric image interpretation. The flow velocities computed from Spherical Float Image Velocimetry (SFIV) coincided approximately with the real velocities in the open channel. The velocity coefficient value, the mean velocity by flowmeter to flow velocity of SFIV ratio, was 0.925 with standard deviation of 0.030. The results presented that SFIV may be utilized to determine the mean velocity and discharge in rivers.