Development and preliminary assessment of an optical wave gauge

A description and preliminary results are presented for a non-intrusive optical wave gauge based on the principle of optical triangulation. In the proposed implementation, a LASER source beaming vertically downwards generates a spot of scattered light at the water surface. The spot is imaged by an off-axis video camera, and instantaneous wave height measurements are obtained by
processing of the spot images. The spot position on the image is then transformed into a height value using a polynomial best-fit function established by an initial calibration. The gauge geometry is set to give a measurement range of 300mm. The calibration method and apparatus are described. A detailed statistical analysis of the calibration results is presented both for the optical wave gauge and for a conductivity wave gauge used as a
comparison. Dynamic measurements for regular waves of 25mm and 50mm amplitudes at 1Hz are carried out with both probes. The resulting time series data are compared to a theoretical fifth order Stokes solution. While
overall agreement is good for both types of probe, optical wave gauge data are found to provide a better fit to the theoretical solution, especially in the vicinity of wave crests