  This article presents a flow visualization method for wind-waves, as well as
a technique to measure flow field on two sides of interface by stereoscopic
particle image velocimetry (PIV) simultaneously. The new flow visualization
method applied a special illumination setup to enhance reflection and weaken
refraction on interface, which improves contrast and detail performance of
photos. The concatenation of flow visualization photo along flow direction is
able to demonstrate the scenario from capillary waves to gravity-capillary
waves at the early stage of wind-waves. After that, time-resolved stereoscopic
PIV is employed in vertical planes on both sides of interface with two camera
pairs. Two kinds of tracking particles with different scattering performance
are spread in air or water separately. Then interface detection algorithm is
designed to separate different particles and determine interface position.
Adaptive min-max normalization and near-wall image preprocessing is used to
improve near-wall and main stream PIV result. Finally, clip arts of results
show the flow field in the same time in air and water near interface.
