Enhanced measurement capability of a digital particle holographic system for flow field measurements

To enhance the capability of digital particle holography as a tool for flow field measurements, several effective methods are developed. The correlation coefficient method was used to accurately locate the focal plane of particles and the optimal factors of this method were discussed. To remove noises and improve the quality of holograms and reconstructed images, the Wiener filter was adopted. The two-threshold and image segmentation methods were used to obtain high quality binary images from which we can get good results of particle extraction. Based on the above methods, an in-line digital particle holographic system was applied to channel flow field and the axial velocities of channel flow were measured. The feasibility of these methods is verified by quantitative measurement results which are in good agreement with the theoretical predictions.

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► Correlation coefficient method is used to accurately locate the focal plane of particles.
► To remove noises and improve the quality of holograms and reconstructed images, Wiener filter is adopted.
► Two-threshold and image segmentation methods are used to obtain high quality binary images.