Determination of rail vehicle speed with acoustic signal processed using continuous wavelet transform

The paper presents the course of research and analysis on the possibility of using time-frequency methods of acoustic signal processing to determine the speed of moving rail vehicles. An experiment was conducted in the form of a trackside pass-by test of the acoustic pressure emitted by passing trams representing the rolling stock of the Municipal Transport Company in Poznan. The recorded signal was then processed using the Continuous Wavelet Transform (CWT), resulting in a scalogram that is a variation of the time-frequency characteristics. This made it possible to identify in the signal the travel time of individual bogies and their wheelsets, as well as the most sensitive value of the scale parameter. The waveform of the scalogram fragment for the selected value of the scale parameter was processed using the RMS envelope, and then the peak values were identified. Juxtaposing the obtained results with the knowledge of the structural dimensions of the tested vehicle, it was possible to determine its moving speed. To validate the results of the experiment, photocells located on both sides of the measurement track were used, which generated voltage when the test vehicle passed between them, allowing the determination of its average moving speed. The result of the study was the formulation of a method that can be used to determine the speed of a vehicle based on the time elapsed between the identification in the signal of the components corresponding to the passage of successive sets of wheels.