Wavelet-Based Optical Flow Estimation of Instant Surface Currents From Shore-Based and UAV Videos

Estimation par flux optique sur bases d'ondelettes de courants de surface instantanés à partir de vidéos prises depuis la rive et par UAV

Pierre Dérian (1) , Rafael Almar (2)

1 FLUMINANCE - Fluid Flow Analysis, Description and Control from Image Sequences
2 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales

Instant fields of surface current are retrieved from shore-based and unmanned aerial vehicle videos by an optical flow (OF) method named “Typhoon”. This computer vision algorithm estimates dense two-dimensional 2-component velocity fields from the observable motion of foam patterns in the surf zone. Despite challenging image data resolution and quality, comparison of OF surface current estimates with measurements by an acoustic Doppler velocimeter reveals its ability to capture both wave-to-wave fluctuations and low-frequency variations. The method is also successfully applied to the monitoring of a “flash rip” event. Our study shows clearly the high potential of this method in the nearshore, where the rapid development of webcams and drones offers a large amount of applications for swimming and surfing safety, engineering and naval security and research purpose, by providing quantitative information.

Mots clés: Remote sensing; Sea surface; Sea coast; Image motion analysis; Geophysical inverse problems; Wavelet transforms; Unmanned aerial vehicles; Rip currents; Shore dynamics; Optical flow; Motion estimation

Domaines: Vision par ordinateur et reconnaissance de formes [cs.CV]; Océan, Atmosphère; Traitement des images [eess.IV]; Mécanique des fluides [physics.class-ph]; Traitement du signal et de l'image [eess.SP]

Pierre Dérian, Rafael Almar. Wavelet-Based Optical Flow Estimation of Instant Surface Currents From Shore-Based and UAV Videos. IEEE Transactions on Geoscience and Remote Sensing, 2017, pp.1 - 8. ⟨10.1109/TGRS.2017.2714202⟩. ⟨hal-01573715⟩