LAUSR

A sailing ship can produce significant disturbances on the water surface, but the perturbation generated by a moving submerged source is much smaller due to the physical property of the free surface, as represented by the rigid-lid assumption, with the geometric displacement barely observed or measured. Based on the stereo imaging principle, an experimental system for the three-dimensional measurement of the surface perturbation is built by assembling two charge coupled device (CCD) sensors, to measure the surface waves generated by a small submerged sphere, including the small-scale vertical displacements and the flow field on the water surface. The obtained results are consistent with those obtained by the theoretical analysis, and the measurement accuracy for the vertical displacements is improved by 50% compared to that of the direct optical method based on the image grey levels. Additionally, the present measurement technique can be efficiently and precisely applied to other measurements of small-scale disturbances on a free surface.