Video-Based Estimation of Surface Currents Using a Low-Cost Quadcopter

Abstract

Video imagery of surface waves recorded from a small off-the-shelf quadcopter with a self-stabilizing camera gimbal is analyzed to estimate the surface current field. The nadir looking camera acquires a short image sequence, which is geocoded to Universal Transverse Mercator coordinates. The resulting image sequence is used to quantify characteristic parameters (wavelength, period, and direction) of short (0.1-1 m) surface waves in space and time. This opens the opportunity to fit the linear dispersion relation to the data and thus monitor the frequency shift induced by an ambient current. The fitting is performed by applying a spectral energy-based maximization technique in the wavenumber-frequency domain. The current field is compared with measurements acquired by an acoustic Doppler current profiler mounted on a small boat, showing an overall good agreement. The root-mean-square error in current velocity is 0.09 m/s with no bias.