A highly accurate iterative PIV technique using a gradient method

An iterative PIV technique in which the combination of the iterative cross-correlation technique and three-point Gaussian peak fitting for a sub-pixel analysis has been used can improve the spatial resolution and accuracy of measurement. It is reported that the root-mean-square (RMS) error of the technique is of the order of only 0.04 pixels. However, a large interrogation window, typically 32 × 32 pixels or larger, should be taken, resulting in a low resolution, in order to achieve the high sub-pixel accuracy. The high accuracy is not compatible with high spatial resolution. In this paper, a new high-resolution PIV technique based on a gradient method is proposed. Initially, the pixel unit displacement is detected by the iterative method. Then, the sub-pixel displacement is evaluated by the use of the gradient method instead of the three-point Gaussian peak fitting technique. The error of the proposed technique is analytically assessed by Monte Carlo simulations. The RMS error is of the order of 0.01 pixels even with a small interrogation window, for instance 13 × 13 pixels or less. Thus, the method can achieve high sub-pixel accuracy and high spatial resolution compatibility.