Improved spectrograms using the discrete Fractional Fourier transform

The conventional spectrogram is a commonly employed, time-frequency tool for stationary and sinusoidal signal analysis. However, it is unsuitable for general non-stationary signal analysis [1]. In recent work [2], a slanted spectrogram that is based on the discrete Fractional Fourier transform was proposed for multicomponent chirp analysis, when the components are harmonically related. In this paper, we extend the slanted spectrogram framework to non-harmonic chirp components using both piece-wise linear and polynomial fitted methods. Simulation results on synthetic chirps, SAR-related chirps, and natural signals such as the bat echolocation and bird song signals, indicate that these generalized slanted spectrograms provide sharper features when the chirps are not harmonically related.