Brücker, C. Experiments in Fluids (1996) 21: 312. doi:10.1007/BF00190682
Coding of the light-sheet in depth with different colors and recording with color-sensitive films or CCD cameras enables three-dimensional correlation analysis to obtain the out-of-plane velocity component in 3-D PIV. In the system used, two overlapping light-sheets of different color are recorded simultaneously and the particles' images of the separate sheets are discernible by color splitting. For only two successive exposures as usual in cross-correlation PIV, the resulting images allow for cross-wise plane-to-plane correlations between the separated sheets. This yields altogether three independent correlations. In addition to the usual procedure to obtain the in-plane component, one can determine the out-of-plane velocity component from the three correlation peak values by an appropriate fit of the correlation profile in depth to determine the maximum location with higher accuracy compared to previous methods. In addition, there is no need of a third exposure at a third moment which increases the accuracy for time-varying flows.