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

We demonstrate by experiment that, in addition to the local surface sl ope, local surface elevation can also be directly measured using the r efracted light beam traversing an air-water interface, thus showing th e feasibility of a new surface slope and wave height amplitude gauge f or use in studying water waves. We have achieved surface height resolu tions as small as 40 mum for the range of surface wavelengths lambda a pproximately 1.2-2.4 cm used in the present experiments. This measurem ent principle is readily adaptable to waves of different scale. The av ailable dynamic range defined by the ratio of maximum wave amplitude t o minimum resolvable amplitude need only be limited by the useful dyna mic range of the photodetector when matched to a laser of suitable fre quency and sufficient power.