Untersuchungen statistischer und geometrischer Eigenschaften von Windwellen und ihrer Wechselwirkung mit der wasserseitigen Grenzschicht

Using color image processing a refraction based technique for retrieving the slope of a water surface covered with waves has been substantially improved. This multichannel technique is similar to photometric stereo analysis for opaque surfaces. The three independend channels of a color camera allow simultaneous detection of both surface gradient components. The third information is used for normalization to the total illumination intensity for every individual pixel, leading to an increased linearity and enhanced robustness. Errors due to inhomogeneous illumination or disturbance by small particles in the water can be corrected almost completely. For combined measurements the technique can be reduced to two colors. Measuring only one slope component normalization is still possible. At two wind/wave facilities statistical and geometrical information for small scale waves were obtained and compared to results from authors using other techniques. Two combined experiments were conducted. At different scales the wave field and the underlying flow field were observed simultaneously. Hering [1996] computed kinetic energy density and vorticity of the flow field in a 10cm x 10cm frame. In the second combined experiment Münsterer [1996] measured concentration profiles of a tracer gas in a 4cm x 4cm section in the viscous boundery layer. Both experiments provided new insights in the interaction between capillary waves, turbulence in the flow field and in the boundary layer respectively.