Automatic Velocity Measurement in River using Unmanned Surface Vehicle

We developed an automatic measurement system for free-surface velocity and direction in natural rivers using an autonomously controlled unmanned surface vehicle (USV). Oncoming mainstream velocity was measured by the propulsion force required for the USV in order to preserve the position at a measurement point. Indoor tests were conducted under several hydraulic conditions by varying streamwise velocity, and the calibration formula was obtained by interrelating the oncoming velocity magnitude with the propulsion force at the target point. Field tests were also performed to examine the reliability and accuracy of the present automatic flow measurements in a river. Both local velocity and direction in the river flow could be measured well by the USV. The present USV was found to possess a sufficient ability to meet practical performance for the flow measurement in a calm river.