3-D Measurement of Objects in Unknown Aquatic Environments with a Laser Range Finder

In this paper, we propose a three-dimensional (3-D) measurement method of objects in aquatic environments whose refractive indices or boundary shape of the refraction are unknown with a laser range finder. When applying vision sensors to measuring objects in liquid, we meet the problem of an image distortion. It is caused by the refraction of the light on the boundary between the air and the liquid, and the distorted image brings errors in a triangulation for the range measurement. Therefore, 3-D measurement of objects in liquid requires a geometrical analysis that takes refraction effects into account. In the analysis, it is indispensable to know the boundary shapes that have discontinuity of refractive indices, and refractive index of liquid. Our proposed method takes refraction effects into account and estimates these unknown parameters to measure accurate 3-D shapes of objects in liquid. Experimental results have shown the effectiveness of the proposed method.