Surface wave profile measurement by image analysis

A way of measuring the geometrical characteristics of progressive steep water surface waves is to use a visualization technique connected with image analysis processing. In the laboratory, visualization of wave profiles can be realized with quite simple procedures: a previous paper (Bonmarin and Ramamonjiarisoa 1985) has described a technique allowing such a visualization in a large water tank 40 m long, 3.2 m wide and about 1 m deep. This paper reported also on a manual process for analysing the wave pictures obtained. In the present paper, we describe an automated image analysis method which is complementary to the manual process mentioned above. It uses a video technique and allows analysis of a large number of pictures leading to statistical measurements.List of symbols L total wave length - H total wave height - crest elevation above still water level - trough depression below still water level - wave steepness = H/L - crest steepness = /L - F₁ forward horizontal length from zero-upcross point (A) to wave crest - F₂ backward horizontal length from wave crest to zero-downcross point (B) - crest front steepness = /F₁ - crest rear steepness = /F₂ - vertical asymmetry factor = F₂/F₁ (describing the wave's asymmetry with respect to a vertical axis through the wave crest) - horizontal asymmetry factor = /H (describing the wave's asymmetry with respect to a horizontal axis: SWL) - L₃ vertical asymmetry factor = L₂/L₁ (describing the asymmetry between the crest and the trough) - E_p potential energy of the wave - e₊ ratio between the potential energy located in the crest and the total potential energy of the wave