Simultaneous velocity and size measurements are of great importance for resolving the dynamics of polydispersed multiphase flows. This effort explores novel sub-resolution particle center estimation algorithms for Digital Particle Image Velocimetry (DPIV) and Particle Tracking Velocimetry (DPTV). In addition these schemes provide direct measurements of the apparent particle image diameter using the same DPIV/DPTV recordings. Three novel fitting schemes were developed and compared with established methods such as center of mass, three-point Gaussian fit estimator and a least-square fit method. The new methods consist of two variations of a four point gaussian estimator and a variation of the conventional least-squares fit estimator. The new methods eliminate the bias error due to pixel discretization, thus significantly reducing the total error in the position and sizing measurement compared to the classic three point and least squares Gaussian estimators. In addition, the accuracy of the least-squares fits were essentially independent of the true particle diameter and significantly reduced the particle position error compared with current estimation schemes.

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