Particle tracking velocimetry beneath water waves. Part I: visualization and tracking algorithms

A novel particle tracking system working with a high particle concentration for the measurement of flow fields beneath water waves is described. It features a 1-4 cm thick light sheet parallel to the main wave propagation direction so that the seeding particles stay long enough in the illuminated area to enable tracking over several wave periods. An area of up to 14.0 x 10.0 cm super(2) is observed by a CCD camera with up to 200 fields/s. The polychromatic scattering theory of small particles in a light sheet illumination is investigated, enabling the segmentation of individual particles at high particle concentration.