Quantitative Visualization of Three-Dimensional Free Surface Slopes and Elevations

Abstract

A new technique that integrates optics, colorimetry, and digital image processing is developed to measure the three-dimensional surface slope and elevation for time-evolving flows. The setup requires that a lens be placed at a distance of its focal length away from a diffuse, uniform, white light source which is covered with an appropriate transparent color palette. This setup then produces a system of color rays where beams of the same color are parallel to themselves, yet oriented in different directions with respect to beams of other colors. This arrangement is used in one of two modes. In the first mode, the reflective mode, the arrangement is set to illuminate the free surface from above the free surface. A three-chip color camera placed far above the free surface captures the reflected rays from the free surface (hence the name reflective mode). In the second mode, the refractive mode, the arrangement illuminates the free surface from below the free surface. A three-chip color camera placed far above the free surface captures the refracted rays from the free surface (hence the name refractive mode). For both modes, each of the three RGB color signals from the color camera is recorded onto separate laser disk recorders. These modes then allow for measurements of the free surface slope by creating a one-to-one correspondence between different colors and the free surface slopes. These data can then be integrated to derive the free surface elevation. Applications to various problems are discussed.