Contactless river discharge from Unoccupied Aerial Systems hydrometry: performance evaluation using a large and diverse set of river cross sections
Year: 2025
Type: preprint
Abstract: Unoccupied Aerial Systems offer promising opportunities for monitoring inland water hydrometry. UAS-borne Doppler radar, water-penetrating radar, and radar altimetry enable contactless observation of key hydraulic variables, providing valuable data under hard-to-access or critical conditions. However, a systematic assessment of UAS-based river discharge estimation across diverse river types is still lacking. To address this gap, we present a framework for estimating discharge from UAS-derived water surface velocity, water surface elevation, and river bathymetry with local water surface slope computed from the water level profile. Four surface-to-bulk velocity conversion methods: 0.85 method, log law method, power law method and entropy method were applied. The overall accuracy of UAS discharge estimation algorithm was benchmarked at 46 cross-sections across four river systems with gauge records. We quantified uncertainty propagation from each input variable, assessed their relative contributions, and performed an error propagation experiment with ±30% perturbations to simulate high-bias measurement scenarios. To identify factors controlling performance, we calculated Spearman’s rank correlations between discharge bias, uncertainty metrics, and cross-sectional properties. Results show that, across most sites, at least one method achieved discharge bias within 30%, though no single method consistently outperformed the others. The 0.85 method proved most robust overall, with performance patterns linked to morphology: 0.85 and entropy methods generally better at larger rivers, while high water surface slopes reduced the accuracy of the log law and power law methods. Correlation analysis revealed that surface velocity uncertainty dominated to discharge uncertainty in deep rivers, whereas water surface elevation was more influential in shallow ones.
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W4414205041