In-situ accuracy/precision test of UAV-based photogrammetry method of shallow water bottom considering refraction of light at water surface

Abstract

In UAV photogrammetry on shallow water bottoms, there is a problem that the water depth is underestimated due to the influence of water surface refraction. To overcome this issue, a method had been proposed that solves the multi-view and two-media triangulation problem, thereby simultaneously estimating the coordinates of submerged points, water surface elevation, and slope. In this study, we conducted the first field experiment of this method to evaluate the accuracy/precision of this method under ideal conditions. As a result, it was confirmed that the coordinates of submerged points can be estimated with an RMS error of less than 0.1m in the vertical direction. On the other hand, an estimation error of about 0.2m was detected for the water surface elevation, and was attributed mainly to the estimation error of the input camera parameters. Since the true (optimal) camera parameters are unknown in the field experiments, further studies are needed in the future about the effect of errors in camera parameters.