COLLOCATED AND SIMULTANEOUS MEASUREMENT OF SURFACE SLOPE AND AMPLITUDE OF WATER-WAVES

We demonstrate by experiment that, in addition to the local surface slope, local surface elevation can also be directly measured using the refracted light beam traversing an air-water interface, thus showing the feasibility of a new surface slope and wave height amplitude gauge for use in studying water waves. We have achieved surface height resolutions as small as 40 mum for the range of surface wavelengths lambda approximately 1.2-2.4 cm used in the present experiments. This measurement principle is readily adaptable to waves of different scale. The available dynamic range defined by the ratio of maximum wave amplitude to minimum resolvable amplitude need only be limited by the useful dynamic range of the photodetector when matched to a laser of suitable frequency and sufficient power.