Signal processing for extracting velocity information from spatial filtering signals

Obtaining transient central frequency from non-stationary spatial filtering signals is essential for measuring velocity with spatial filtering technique. According to the property of spatial filtering signal, a method for processing the unsteady spatial filtering signals based on complex-wavelet transform (CWT) was investigated to extract the velocity information, where two Gaussian derivatives with adjacent orders are taken as real and imaginary parts to construct a complex basic-wavelet, and then are employed to implement the CWT. The central frequencies of the spatial filtering signals are derived from the CWTs, enabling to measure the velocities of the arbitrarily irregular materials with some random distributions. The spatial filtering signals of a rotational velocity measurement were utilized to evaluate the accuracy and instantaneity of the signal processing method. The evaluation results indicate that the proposed method is generally prior to the traditional temporal-period method and Fourier-transform-based method, and that it is fit for acquiring the transient central frequencies of unsteady spatial filtering signals.