FD4 Correlation is an algorithm developed for the Time Resolved PIV. FD4 Correlation offers the frequency analysis of the velocity fluctuation at each PIV grid and the sophisticated spatiotemporal validation.
In the conventional in-plane (2D) PIV analysis, outliers are detected using spatial validation and flip the value by the interpolation. In the Time Resolved PIV, each vector map is very close in time; thus it is possible to apply a temporal validation before or after applying a spatial validation.
FD4 Correlation offers more advanced spatiotemporal validation. The spectrum of each grid is analyzed by applying an FFT. Then the high frequency noise is filtered out and then an inverse FFT is applied to get the time domain velocity date back without high frequency noise. Using this velocity fluctuation curve, outliers are replaced with the best estimated value at each time and grid.