Challenges with Regard to Unmanned Aerial Systems (UASs) Measurement of River Surface Velocity Using Doppler Radar

Surface velocity is traditionally measured with in situ techniques such as probes (in shallow rivers) or Acoustic Doppler Current Profilers deeper water). In the last years, researchers have developed remote sensing techniques, both optical (e.g., image-based velocimetry techniques) and microwave radar). These can be deployed from Unmanned Aerial Systems (UAS), which ensure fast low-cost surveys also remotely-accessible locations. We compare results obtained a UAS-borne radar Particle Image Velocimetry (PIV) different rivers, presented hydraulic–morphological conditions (width, slope, surface roughness sediment material). The was commercial 24 GHz instrument, for static deployment, adapted UAS integration. PIV applied natural seeding foam, debris) when possible, artificial (woodchips) stream where density of particles insufficient. reconstructed profile high accuracy typically order few cm s−1 coefficient determination (R2) larger than 0.7 half cases 0.85), compared acoustic current profiler (ADCP) probe, all investigated rivers. However, measurements show low reliability because vibrations, large instrument sampling footprint, required time difficult-to-interpret quality indicators suggesting that additional research needed to measure radar.