Time frequency signal analysis of ground vehicle acoustic signatures

The acoustic signatures of various types of ground vehicles are recorded during each vehicle´s transit past a stationary microphone located just above ground level and the acoustic data are analysed using the short time Fourier transform. The spectrogram for each transiting vehicle exhibits a primary set and a secondary set of harmonic lines in the time-frequency domain that can be used for classification purposes. The frequency of each harmonic line varies with time due to the acoustical Doppler effect. The variation with time of the instantaneous frequency of the strongest harmonic line is used to estimate the speed, ground distance at the closest point of approach to the microphone, and engine-firing rate of the vehicle.