Analysis of velocimetry data based on continuous wavelet transform: Application to shock wave physics experiments

Interferometry is well established technique for measuring particle velocity in shock wave physics experiments, where velocity information is encoded as the phase of a periodically varying intensity pattern. Conventional phase stepping technique by using a pair of quadrature signals cannot resolve rapid velocity changes and sub-fringe phenomena accurately in most of the velocimetry data. In this report a practical analysis method based on the Continuous Wavelet Transform (CWT) is presented to overcome these difficulties. CWT uses an adaptive time window to estimate the instantaneous frequency of signals. We begin by reviewing the CWT and the time-frequency localization properties of wavelets. The instantaneous frequencies of signal are accurately determined by finding the ridge in the scalogram of the CWT and then are converted to target velocity according to Doppler effects. A performance comparison between the CWT and phase stepping technique is demonstrated by a plate impact experimental data of Al-2024T4 material. Results illustrate that new method is superior in terms of accuracy and analysis simplicity.