Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems
This paper examines the potential of an optical flow video-based technique to estimate wave-filtered surface currents in the nearshore where wave-breaking induced foam is present. This approach uses the drifting foam, left after the passage of breaking waves, as a quasi-passive tracer and tracks it...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-05-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/13/10/1874 |
| _version_ | 1797534520069586944 |
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| author | Isaac Rodríguez-Padilla Bruno Castelle Vincent Marieu Philippe Bonneton Arthur Mouragues Kevin Martins Denis Morichon |
| author_facet | Isaac Rodríguez-Padilla Bruno Castelle Vincent Marieu Philippe Bonneton Arthur Mouragues Kevin Martins Denis Morichon |
| author_sort | Isaac Rodríguez-Padilla |
| collection | DOAJ |
| description | This paper examines the potential of an optical flow video-based technique to estimate wave-filtered surface currents in the nearshore where wave-breaking induced foam is present. This approach uses the drifting foam, left after the passage of breaking waves, as a quasi-passive tracer and tracks it to estimate the surface water flow. The optical signature associated with sea-swell waves is first removed from the image sequence to avoid capturing propagating waves instead of the desired foam motion. Waves are removed by applying a temporal Fourier low-pass filter to each pixel of the image. The low-pass filtered images are then fed into an optical flow algorithm to estimate the foam displacement and to produce mean velocity fields (i.e., wave-filtered surface currents). We use one week of consecutive 1-Hz sampled frames collected during daylight hours from a single fixed camera located at La Petite Chambre d’Amour beach (Anglet, SW France) under high-energy conditions with significant wave height ranging from 0.8 to 3.3 m. Optical flow-computed velocities are compared against time-averaged in situ measurements retrieved from one current profiler installed on a submerged reef. The computed circulation patterns are also compared against surf-zone drifter trajectories under different field conditions. Optical flow time-averaged velocities show a good agreement with current profiler measurements: coefficient of determination <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msup><mi>r</mi><mn>2</mn></msup><mo>)</mo><mo>=</mo></mrow></semantics></math></inline-formula> 0.5–0.8; root mean square error <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><mi>RMSE</mi><mo>)</mo></mrow></semantics></math></inline-formula> = 0.12–0.24 m/s; mean error (bias) <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>=</mo><mo>−</mo><mn>0.09</mn></mrow></semantics></math></inline-formula> to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mn>0.17</mn></mrow></semantics></math></inline-formula> m/s; regression slope <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>=</mo><mn>1</mn><mo>±</mo><mn>0.15</mn></mrow></semantics></math></inline-formula>; <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>coherence</mi><mn>2</mn></msup></semantics></math></inline-formula> = 0.4–0.6. Despite an underestimation of offshore-directed velocities under persistent wave breaking across the reef, the optical flow was able to correctly reproduce the mean flow patterns depicted by drifter trajectories. Such patterns include rip-cell circulation, dominant onshore-directed surface flow and energetic longshore current. Our study suggests that open-source optical flow algorithms are a promising technique for coastal imaging applications, particularly under high-energy wave conditions when in situ instrument deployment can be challenging. |
| first_indexed | 2024-03-10T11:31:42Z |
| format | Article |
| id | doaj.art-6873e13a10574ea998be06627553991b |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T11:31:42Z |
| publishDate | 2021-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-6873e13a10574ea998be06627553991b2023-11-21T19:13:06ZengMDPI AGRemote Sensing2072-42922021-05-011310187410.3390/rs13101874Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical SystemsIsaac Rodríguez-Padilla0Bruno Castelle1Vincent Marieu2Philippe Bonneton3Arthur Mouragues4Kevin Martins5Denis Morichon6CNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceCNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceCNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceCNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceCNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceCNRS, UMR 5805 EPOC, Université de Bordeaux, 33615 Pessac, FranceSIAME-E2S, Université de Pau et des Pays de l’Adour, 64600 Anglet, FranceThis paper examines the potential of an optical flow video-based technique to estimate wave-filtered surface currents in the nearshore where wave-breaking induced foam is present. This approach uses the drifting foam, left after the passage of breaking waves, as a quasi-passive tracer and tracks it to estimate the surface water flow. The optical signature associated with sea-swell waves is first removed from the image sequence to avoid capturing propagating waves instead of the desired foam motion. Waves are removed by applying a temporal Fourier low-pass filter to each pixel of the image. The low-pass filtered images are then fed into an optical flow algorithm to estimate the foam displacement and to produce mean velocity fields (i.e., wave-filtered surface currents). We use one week of consecutive 1-Hz sampled frames collected during daylight hours from a single fixed camera located at La Petite Chambre d’Amour beach (Anglet, SW France) under high-energy conditions with significant wave height ranging from 0.8 to 3.3 m. Optical flow-computed velocities are compared against time-averaged in situ measurements retrieved from one current profiler installed on a submerged reef. The computed circulation patterns are also compared against surf-zone drifter trajectories under different field conditions. Optical flow time-averaged velocities show a good agreement with current profiler measurements: coefficient of determination <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msup><mi>r</mi><mn>2</mn></msup><mo>)</mo><mo>=</mo></mrow></semantics></math></inline-formula> 0.5–0.8; root mean square error <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><mi>RMSE</mi><mo>)</mo></mrow></semantics></math></inline-formula> = 0.12–0.24 m/s; mean error (bias) <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>=</mo><mo>−</mo><mn>0.09</mn></mrow></semantics></math></inline-formula> to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mn>0.17</mn></mrow></semantics></math></inline-formula> m/s; regression slope <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>=</mo><mn>1</mn><mo>±</mo><mn>0.15</mn></mrow></semantics></math></inline-formula>; <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mi>coherence</mi><mn>2</mn></msup></semantics></math></inline-formula> = 0.4–0.6. Despite an underestimation of offshore-directed velocities under persistent wave breaking across the reef, the optical flow was able to correctly reproduce the mean flow patterns depicted by drifter trajectories. Such patterns include rip-cell circulation, dominant onshore-directed surface flow and energetic longshore current. Our study suggests that open-source optical flow algorithms are a promising technique for coastal imaging applications, particularly under high-energy wave conditions when in situ instrument deployment can be challenging.https://www.mdpi.com/2072-4292/13/10/1874optical flowvideo imagerysurf zonesurface currentsrip currents |
| spellingShingle | Isaac Rodríguez-Padilla Bruno Castelle Vincent Marieu Philippe Bonneton Arthur Mouragues Kevin Martins Denis Morichon Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems Remote Sensing optical flow video imagery surf zone surface currents rip currents |
| title | Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems |
| title_full | Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems |
| title_fullStr | Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems |
| title_full_unstemmed | Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems |
| title_short | Wave-Filtered Surf Zone Circulation under High-Energy Waves Derived from Video-Based Optical Systems |
| title_sort | wave filtered surf zone circulation under high energy waves derived from video based optical systems |
| topic | optical flow video imagery surf zone surface currents rip currents |
| url | https://www.mdpi.com/2072-4292/13/10/1874 |
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