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

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 2-D 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-towave fluctuations and low-frequency variations. The method is also successfully applied to the monitoring of a "flash rip" event. This paper shows clearly the high potential of this method in the nearshore, where the rapid development of webcams and drones offers a large number of applications for swimming and surfing safety, engineering and naval security, and research purpose, by providing quantitative information.