Thermographic imaging of shear flow at a wind-driven water surface

Thermographic imaging is applied to measure the shear flow at a wind driven water surface, an essential parameter to understand exchange of momentum, heat and mass between the atmosphere and the oceans. Only a thin line less than 1 mm thick perpendicular to the wind direction is heated with a penetration depth matched to the thickness of the shear layer at the water surface. With pulsed irradiation the shear can be estimated, while continuous irradiation is suitable to measure the orbital velocities of the wind waves. Motion fields and shear are computed by a generalized optical flow approach.