Nearshore Bathymetry Estimation from Drone Video Using PIV Technique
Abstract
This research introduces a novel method to estimate nearshore bottom topography
using an unmanned aerial vehicle (UAV), or drone. The UAV was manipulated over the
area of interest to film video, and the Particle image velocimetry (PIV) technique was then
applied to analyze the video frames in order to retrieve the wave speeds. Under the shallow
water conditions, the wave dispersion relation can be simplified in a manner such that
when the wave speed is known, the water depth can be inferred. In other words, when
wave speed is known, water depth can be inferred. After combining the inferred water
depths at multiple points from within the area of interest, the bathymetry was constructed.
To validate the method, individual waves were recorded in the nearshore breaking
zone during two trials at Freeport, Texas, USA. We measured the significant difference in
intensity across the recorded images, as the intensity had a larger signal-to-noise ratio, and
this improved the implementation of the PIV algorithm. We then compared the PIVestimated
water depth with field measurement and observations, finding that the water
depth was overestimated by 13.5%, which was primarily explained by non-linear wave
breaking effects. We then introduced a correction factor, reducing the estimation error to
within 6% of the true observed water depth.
Though there are limitations, this new approach can lower the cost of developing
bathymetric maps in the nearshore and result in greater flexibility across space and time.
Further improvements in equipment and work on developing better correction factors may
result in still greater precision.
Citation
Sun, Shih-Heng (2017). Nearshore Bathymetry Estimation from Drone Video Using PIV Technique. Master's thesis, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /169616.