Tracer particles are necessary for Ultrasonic Doppler Method (UDM) as reflectors of the ultrasonic wave. Though the nylon powders are used as reflectors in the experimental apparatus, the use of them is difficult in the measurement of the actual rivers. Therefore, the coverage of UDM is limited. Then, we think that microbubbles can be used for the flow rate measurement of the actual rivers as reflector of UDM, as their follow is good in the flow field. In addition, they have profitable characteristics like the water quality purification and the physiology revitalization of the aquatic life. This research' mixed microbubbles with open channels, and measured with UDM. And we experimentally obtained the flow velocity distribution, and the relation between the bubble diameter distribution and the amount of inhalation air.
