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Open AccessArticle

Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone

1
U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, Field Research Facility, Duck, NC 27949, USA
2
Oak Ridge Institute for Science and Education, Oak Ridge, TN 37830, USA
3
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
*
Author to whom correspondence should be addressed.
Current address: Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, NC 27607, USA.
Academic Editor: Kristen Splinter
Remote Sens. 2021, 13(4), 690; https://doi.org/10.3390/rs13040690
Received: 14 January 2021 / Revised: 8 February 2021 / Accepted: 10 February 2021 / Published: 13 February 2021
(This article belongs to the Special Issue Advances in Remote Sensing in Coastal and Hydraulic Engineering)
Complex two-dimensional nearshore current patterns are generated by feedbacks between sub-aqueous morphology and momentum imparted on the water column by breaking waves, winds, and tides. These non-stationary features, such as rip currents and circulation cells, respond to changing environmental conditions and underlying morphology. However, using fixed instruments to observe nearshore currents is limiting due to the high costs and logistics necessary to achieve adequate spatial sampling resolution. A new technique for processing surf-zone imagery, WAMFlow, quantifies fluid velocities to reveal complex, multi-scale (10 s–1000 s meters) nearshore surface circulation patterns. We apply the concept of a wave-averaged movie (WAM) to measure surf-zone circulation patterns on spatial scales of kilometers in the alongshore and 100 s of meters in the cross-shore. The approach uses a rolling average of 2 Hz optical imagery, removing the dominant optical clutter of incident waves, to leave the residual foam or water turbidity features carried by the flow. These residual features are tracked as quasi-passive tracers in space and time using optical flow, which solves for u and v as a function of image intensity gradients in x, y, and t. Surf zone drifters were deployed over multiple days with varying nearshore circulations to validate the optically derived flow patterns. Root mean square error are reduced to 0.1 m per second after filtering based on image attributes. The optically derived patterns captured longshore currents, rip currents, and gyres within the surf zone. Quantifying nearshore circulation patterns using low-cost image platforms and open-source computer vision algorithms presents the potential to further our understanding of fundamental surf zone dynamics. View Full-Text
Keywords: nearshore currents; hydrodynamics; surf zone; drifters; optical flow; Argus; Coastal Image Research Network nearshore currents; hydrodynamics; surf zone; drifters; optical flow; Argus; Coastal Image Research Network
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MDPI and ACS Style

Anderson, D.; Bak, A.S.; Brodie, K.L.; Cohn, N.; Holman, R.A.; Stanley, J. Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone. Remote Sens. 2021, 13, 690. https://doi.org/10.3390/rs13040690

AMA Style

Anderson D, Bak AS, Brodie KL, Cohn N, Holman RA, Stanley J. Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone. Remote Sensing. 2021; 13(4):690. https://doi.org/10.3390/rs13040690

Chicago/Turabian Style

Anderson, Dylan; Bak, A. S.; Brodie, Katherine L.; Cohn, Nicholas; Holman, Rob A.; Stanley, John. 2021. "Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone" Remote Sens. 13, no. 4: 690. https://doi.org/10.3390/rs13040690

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