Unseeded and seeded PIV measurements of river flows videotaped from a helicopter

A new PIV method for measuring river surface flows using videotaped images taken from a helicopter has been developed. In this method, shifting of background images while videotaping was effectively corrected using the known coordinates of fixed points on the image. In low flow conditions, river surface flows were visualized using rice crackers, while in flood flow conditions surface ripples generated by the effects of near surface turbulence and pressure fluctuation were used as natural unseeded tracers. The performance of the presented method was verified through its applications to the actual river flow measurements.