Proof‐of‐concept for low‐cost and non‐contact synoptic airborne river flow measurements

This article presents an example for an image-based method to determine a small rivers’ surface velocity field, bathymetry, and its flow discharge derived thereof. While common river measurement techniques typically need to be in contact with the waterbody, at least to measure transects of water depths, the new approach is completely without direct contact to water. The scenery is recorded by an off-the-shelf action camera mounted to a low-cost quadcopter. During the analysis, image frames are orthorectified and georeferenced by an approach that combines structure from motion and multiview stereo algorithms. Particle image velocimetry based on tracer particles present in the river is utilized to compute flow velocities. Instantaneous surface flow velocity fields are used to compute the mean velocity field as well as to derive water depth estimates by turbulence metrics. The latter provide a basis to verify the bathymetry gained from the reconstructed subaqueous three-dimensional scenery. Finally, flow discharge is estimated based on the above findings. The new method will expand the scientific knowledge on river flows for diverse disciplines such as hydrology, biology, and river engineering. Due to the low cost of the measurement instrumentation being deployed, it has the potential to be applied by a broad user group.