Derivation of time-dependent two-dimensional velocity field maps for plasma turbulence studies

Time-resolved two-dimensional (2D) velocity maps have been derived for fluctuation measurements in the edge plasma of the National Spherical Torus Experiment (NSTX). The maps have been derived from time sequences of 2D images recorded with the gas puff imaging diagnostic. A hybrid technique combining optical flow and local pattern matching has been implemented to overcome the individual limitations of each when used with data of limited temporal and/or spatial resolution. Local flow velocities of up to similar to 8 km/s and average poloidal flow velocities of up to similar to 5 km/s are found. Results are compared to previous velocity extraction techniques and NSTX results. (c) 2006 American Institute of Physics.