Surface currents retrieved from airborne video
2017
Within this paper, we describe a methodology to retrieve very high-resolution ocean surface currents from short video sequences of water
surface waves. The video sequences were acquired in the range of visible light with a small, nadir looking 4k
video cameraattached to an off the shelf
quadcopter. The
quadcopteris equipped with an actively controlled
gimbalfor stabilization of the
video camera. Furthermore, the
quadcopteris equipped with a logger that records all the flight information, which is used to
geocodethe video data. In a first step, the video data are corrected for the distortion of the lens and are then
geocodedto a rectilinear coordinate system at water level. The resulting video data allow for measuring
surface waveproperties such as wave direction and length as well as
phase velocity. These properties of the waves enable to estimate the surface current vector, which results from the difference of the observed
phase velocityto that given by the linear dispersion relation of
surface gravitywaves. For testing purposes, the method was applied to video data, which were collected over the Elbe River in vicinity of a
weir. The resulting surface current field nicely represents the surface flow and indicates the overall applicability of the method.
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