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 te chnique is of the order of only 0.04 pixels. However, a large interrogation window, typically 32 x 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. I nitially, the pixel unit displacement is detected by the iterative method. Then, the sub-pixel displacement is evaluated by the use of the gradient me thod instead of the three-point Gaussian peak fitting technique. The error of the proposed technique is analytically assessed by Monte Carlo simulatio ns. The RMS error is of the order of 0.01 pixels even with a small interrog ation window, for instance 13 x 13 pixels or less. Thus, the method can ach ieve high sub-pixel accuracy and high spatial resolution compatibility.