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TradiTIonal velocity measurement techniques, such as hot-wire and laser Doppler anemometry (LDA) and standard ParTIcle Image Velocimetry (PIV), are unable to provide velocity informaTIon in such thin films. The Forward Scattering ParTIcle Image Velocimetry (FSPIV) technique developed by Ovryn and Hovenac (1993) offers the most promise. In this scheme, shown schematically in Figure 1, a partially coherent light beam back illuminates a mono-disperse suspension of spherical particles seeded in a fluid which ideally follow the fluid pathlines. A video microscopy system is used to view and record the forward scattered and transmitted light. Ovryn et al. has demonstrated that the light scattering produces a unique diffraction like image of the particle in the image plane for each de-focus position of the particles. This characteristic was exploited to determine the particle de-focus distance and the paraxial velocity if the time between the video frames is known. Simultaneously the transverse velocity (normal to the optical axis) was calculated by finding the particle centroid trajectories over time.
