{ "abstract": "Rip currents cause most surf-beach lifeguard rescues and most beach drowning incidents, yet automated detection relies on costly instrumentation that scales poorly across the many beaches that lack lifeguards. We propose an end-to-end pipeline producing pixel-level rip-current likelihood maps directly from raw unmanned aerial vehicle (UAV) video without manual ground-control points — to our knowledge the first to do so from uncalibrated drone video, prior automated approaches operating at video-clip granularity or requiring surveyed camera installations. The pipeline composes (i) dense optical-flow estimation with five classical algorithm variants; (ii) a sphere-aware projection mapping pixel coordinates to local-isometric ground coordinates, with a tilt-aware Jacobian correction of per-pixel velocity; (iii) a CNN six-class scene parser (sky/sea/land/foam/structure/void), trained on frames verified by dense pixel-matching to contain no extraction from either evaluation video; (iv) a per-pixel temporal accumulator flagging pixels whose flow direction agrees with the locally-estimated offshore direction within ±90∘ — the physical boundary of seaward-directed flow, shown robust in an 18-scene sensitivity sweep; and (v) post-processing by Gaussian smoothing (σ=25 px) and a normalized cross-algorithm ensemble. We evaluate on two UAV-captured rip-current videos at Palm Beach and Haulover Park, Florida, annotated by consensus among three coastal-science domain experts. At the physically-neutral T=90∘ default the framework attains precision-recall AUC 0.636 at Palm Beach and 0.660 at Haulover; per-scene selection — of the angular tolerance, ensemble membership, mixing weight, sphere tilt, and which modules are engaged — against the same expert annotation used for evaluation raises these to 0.7066 and 0.7040, reported as an optimistic upper bound rather than an expected-performance estimate. We release the source code, the trained sea-mask refiner, a YOLOv8m-seg deep-learning baseline, and the evaluation scripts. Evaluation is limited to these two expert-annotated scenes, and the method requires visible surface tracers (foam, dye, or sediment fronts) advected by the current.", "abstract_shown": true, "affiliations": [ "Department of Mathematics, University of Miami, Coral Gables, Florida, United States of America.", "Department of Earth and Environment, Florida International University, Miami, Florida, United States of America.", "Department of Electrical and Computer Engineering, University of Miami, Coral Gables, Florida, United States of America." ], "article_type": "Research Article", "arxiv": null, "author_total": 3, "authors": [ { "affs": [ 0 ], "name": "Kaiqi Yang" }, { "affs": [ 1 ], "name": "Stephen B Leatherman" }, { "affs": [ 2 ], "name": "Anchen Sun", "orcid": "0000-0003-3633-6385" } ], "bibtex": "https://research.draconitic.com/paper/5cm57y2m0rn04.bib", "cited_by": 0, "doi": "10.1371/journal.pone.0360672", "fulltext_url": "https://europepmc.org/articles/PMC13718950", "id": "5cm57y2m0rn04", "issns": [ "1932-6203" ], "landing_url": "https://doi.org/10.1371/journal.pone.0360672", "language": "eng", "licence": "CC-BY", "licence_label": "CC BY", "licence_source": "article", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "heading", "Aquatic Environments" ], [ "heading", "Biology and Life Sciences" ], [ "heading", "Bodies of Water" ], [ "heading", "Cameras" ], [ "heading", "Classical Mechanics" ], [ "heading", "Cognitive Psychology" ], [ "heading", "Cognitive Science" ], [ "heading", "Computational Pipelines" ], [ "heading", "Computational Techniques" ], [ "heading", "Earth Sciences" ], [ "heading", "Ecology and Environmental Sciences" ], [ "heading", "Engineering and Technology" ], [ "heading", "Equipment" ], [ "heading", "Foams" ], [ "heading", "Geomorphology" ], [ "heading", "Landforms" ], [ "heading", "Marine Environments" ], [ "heading", "Marine and Aquatic Sciences" ], [ "heading", "Materials" ], [ "heading", "Materials Science" ], [ "heading", "Motion" ], [ "heading", "Neuroscience" ], [ "heading", "Oceans" ], [ "heading", "Optical Equipment" ], [ "heading", "Perception" ], [ "heading", "Physical Sciences" ], [ "heading", "Physics" ], [ "heading", "Psychology" ], [ "heading", "Research Article" ], [ "heading", "Research and Analysis Methods" ], [ "heading", "Sea Water" ], [ "heading", "Sensory Perception" ], [ "heading", "Shores" ], [ "heading", "Social Sciences" ], [ "heading", "Topography" ], [ "heading", "Velocity" ], [ "heading", "Vision" ], [ "plos", "/Biology and life sciences/Neuroscience/Cognitive science/Cognitive psychology/Perception/Sensory perception/Vision" ], [ "plos", "/Biology and life sciences/Neuroscience/Sensory perception/Vision" ], [ "plos", "/Biology and life sciences/Psychology/Cognitive psychology/Perception/Sensory perception/Vision" ], [ "plos", "/Earth sciences/Geomorphology/Topography/Landforms/Shores" ], [ "plos", "/Earth sciences/Marine and aquatic sciences/Bodies of water/Oceans" ], [ "plos", "/Engineering and technology/Equipment/Optical equipment/Cameras" ], [ "plos", "/Physical sciences/Materials science/Materials/Foams" ], [ "plos", "/Physical sciences/Mathematics/Applied mathematics/Algorithms" ], [ "plos", "/Physical sciences/Physics/Classical mechanics/Motion/Velocity" ], [ "plos", "/Research and analysis methods/Computational techniques/Computational pipelines" ], [ "plos", "/Research and analysis methods/Simulation and modeling/Algorithms" ], [ "plos", "/Social sciences/Psychology/Cognitive psychology/Perception/Sensory perception/Vision" ] ], "openalex": null, "pdf_url": "https://europepmc.org/articles/PMC13718950?pdf=render", "pmcid": "PMC13718950", "pmid": "42956000", "published": "2026-10-29", "publisher": "Public Library of Science", "ris": "https://research.draconitic.com/paper/5cm57y2m0rn04.ris", "sources": [ { "first_seen": "2026-10-30T12:17:17Z", "native_id": "10.1371/journal.pone.0360672", "source": "plos", "url": "https://doi.org/10.1371/journal.pone.0360672" }, { "first_seen": "2026-11-01T00:20:36Z", "native_id": "MED:42956000", "source": "europepmc", "url": "https://europepmc.org/article/MED/42956000" }, { "first_seen": "2026-11-02T12:22:52Z", "native_id": "PMC13718950", "source": "pmc", "url": "https://doi.org/10.1371/journal.pone.0360672" } ], "subjects": [ { "field": "biology", "origin": "plos:neuroscience", "subfield": "neuroscience" }, { "field": "chemistry", "origin": "plos:materials science", "subfield": "materials-polymers" }, { "field": "earth", "origin": "plos:geomorphology", "subfield": "geology-geochemistry" }, { "field": "physics", "origin": "heading:Physics", "subfield": "general" } ], "title": "Rip current detection in nearshore areas through UAV video analysis using optical flow and almost local-isometric embedding techniques on the sphere", "title_text": "Rip current detection in nearshore areas through UAV video analysis using optical flow and almost local-isometric embedding techniques on the sphere", "type": "peer-reviewed", "updated_at": "2026-11-02T12:22:52Z", "url": "https://research.draconitic.com/paper/5cm57y2m0rn04", "venue": "PLOS One", "versions": [] }