{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,28]],"date-time":"2026-02-28T10:38:30Z","timestamp":1772275110285,"version":"3.50.1"},"reference-count":52,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2022,3,5]],"date-time":"2022-03-05T00:00:00Z","timestamp":1646438400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100012774","name":"Innovation Fund Denmark","doi-asserted-by":"publisher","award":["8087-00002B"],"award-info":[{"award-number":["8087-00002B"]}],"id":[{"id":"10.13039\/100012774","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100012774","name":"Innovation Fund Denmark","doi-asserted-by":"publisher","award":["7048-00001B"],"award-info":[{"award-number":["7048-00001B"]}],"id":[{"id":"10.13039\/100012774","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Surface velocity is traditionally measured with in situ techniques such as velocity probes (in shallow rivers) or Acoustic Doppler Current Profilers (in deeper water). In the last years, researchers have developed remote sensing techniques, both optical (e.g., image-based velocimetry techniques) and microwave (e.g., Doppler radar). These techniques can be deployed from Unmanned Aerial Systems (UAS), which ensure fast and low-cost surveys also in remotely-accessible locations. We compare the results obtained with a UAS-borne Doppler radar and UAS-borne Particle Image Velocimetry (PIV) in different rivers, which presented different hydraulic\u2013morphological conditions (width, slope, surface roughness and sediment material). The Doppler radar was a commercial 24 GHz instrument, developed for static deployment, adapted for UAS integration. PIV was applied with natural seeding (e.g., foam, debris) when possible, or with artificial seeding (woodchips) in the stream where the density of natural particles was insufficient. PIV reconstructed the velocity profile with high accuracy typically in the order of a few cm s\u22121 and a coefficient of determination (R2) typically larger than 0.7 (in half of the cases larger than 0.85), when compared with acoustic Doppler current profiler (ADCP) or velocity probe, in all investigated rivers. However, UAS-borne Doppler radar measurements show low reliability because of UAS vibrations, large instrument sampling footprint, large required sampling time and difficult-to-interpret quality indicators suggesting that additional research is needed to measure surface velocity from UAS-borne Doppler radar.<\/jats:p>","DOI":"10.3390\/rs14051277","type":"journal-article","created":{"date-parts":[[2022,3,6]],"date-time":"2022-03-06T20:40:02Z","timestamp":1646599202000},"page":"1277","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Challenges with Regard to Unmanned Aerial Systems (UASs) Measurement of River Surface Velocity Using Doppler Radar"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8470-2493","authenticated-orcid":false,"given":"Filippo","family":"Bandini","sequence":"first","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]},{"given":"Monica Coppo","family":"Fr\u00edas","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]},{"given":"Jun","family":"Liu","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]},{"given":"Kasparas","family":"Simkus","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]},{"given":"Sofia","family":"Karagkiolidou","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9861-4240","authenticated-orcid":false,"given":"Peter","family":"Bauer-Gottwein","sequence":"additional","affiliation":[{"name":"Department of Environmental Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark"}]}],"member":"1968","published-online":{"date-parts":[[2022,3,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"289","DOI":"10.1002\/esp.319","article-title":"On the correspondence between morphological and hydrodynamical patterns of groyne fields","volume":"27","author":"Sukhodolov","year":"2002","journal-title":"Earth Surf. 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