Optical water waves measuring techniques

Optical wave slope gauges offer several advantages in comparison with conventional wire gauges:    They do not disturb the water surface, can measure even high frequency capillaries without disturbance and damping, and the wave slope covers a much smaller range than does the wave height: all waves, independent of the frequency, roughly have the same maximum slope. We developed a refraction technique and tested its performance thoroughly. Slopes up to 1.2 can be measured. The wave height influence on the slope signal is 0.25%/cm. For slopes less than 0.5 the signal is linear to the slope with an overall accuracy of 3%. Larger slopes are reduced by up to 5-15% in amplitude. We demonstrate that correlation measurements even in the capillary region are possible with an oscillating laser beam position. We further developed a slope visualisation technique. This technique seems promising in view of the mass transport mechanisms through the aqueous viscous boundary layer.