Method for Measuring the Surface Velocity Field of a River Using Images Acquired by a Moving Drone

Hovering drones use ground control points to measure the surface flow velocity of rivers. This study aims to use only GPS data and images captured by a drone to extract the flowrate at a designated absolute position. Using GPS data, the moving directions of the drone and of the image were calculated, and each image point was converted into a physical UTM (Universal Transverse Mercator) coordinate system. After determining the range of observation by selecting the start and end frames, all images of the measurement cross section were divided into reference frames (measurement subsections), and the flowrate was calculated with spatiotemporal volume obtained by gathering images for 1 sec (30 frames) for all measurement subsections. The results were comparable with those obtained using the existing hovering drone image analysis method.