Addressing how spatial resolution affects image velocimetry outputs: implications for measurements from space

Image velocimetry (IV) methods for measuring river flow have gained significant attention, with growing interest in satellite imagery applications. Despite this potential, challenges exist in identifying surface features critical for IV at the coarser spatial resolutions of satellite imagery (1–3 m px−1), compared to near-field imagery (e.g. uncrewed aerial systems). Here we evaluate IV performance across resolutions ranging from 0.02 to 3 m px−1, examining the surface features required for successful Satellite IV (SIV). Results indicate that IV accuracy depends on scene characteristics, with high-contrast, well-distributed surface tracers essential at coarse resolutions. Using suitable scenes with spatial resolutions up to 3 m px−1, discharge estimates are comparable to both original-resolution results and reference data (±5%). This study demonstrates the viability of SIV using 1-second image pairs and, provided that sufficient trackable surface features are present, highlights its potential to support river discharge monitoring, particularly in remote or ungauged regions.