In order to evaluate the correlation correctly with a single pass, the correlation function must be small with respect to the displacement correlation peak. This is accomplished when the following requirements are fulfilled:

1. There should be at least 7-10 particle image pairs in each interrogation spot.

2. The in-plane displacement should be limited to 1/4 of the size of the interrogation region.

3. The out-of-plane displacement should be limited to 1/4 of the thickness of the light sheet.

4. The displacement difference over the interrogation volume should be less than 3-5% of the size of the interrogation region.

Recording of the particle images

Besides particle dynamics, the registration, storage and read-out of the individual particle images are other key elements in PIV. This is because the accuracy of the technique is strongly depends upon the precision with which the image displacement can be related to particle locations and their respective particle displacements. The continuous intensity distribution of the particle image is transformed into a discrete signal of limited bandwidth. When the discretization of the image signal matches the minimum sampling rate, the frequency contents of the original signal, and thus the particle location as well, can be reconstructed without any losses. According to the well-known Nyquist criterion of signal processing, the bandwidth limited signal can be perfectly reconstructed from its discrete samples when the sampling rate of the signal is at least twice the signal bandwidth.