Direct estimation of the wall shear rate using parametric motion models in 3D

We present a new optical-flow-based technique to estimate the wall shear rate using a special illumination technique that makes the brightness of particles dependent on the distance from the wall. The wall shear rate is derived directly (that means, without previous calculation of the velocity vector field) from two of the components of the velocity gradient tensor which in turn describes the kinematics of fluid flows up to the first order. By incorporating this into a total least squares framework, we can apply a further extension of the structure tensor technique. Results obtained both from synthetical and real data are shown, and reveal a substantial improvement compared to conventional techniques.