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Large dynamic range time-frequency signal analysis with application to helicopter Doppler radar data

Despite the enhanced time-frequency analysis (TFA) detailing capability of quadratic TFAs like the Wigner and Cohen representations, their performance with signals of large dynamic range (DNR in excess of 40 dB) is quite poor due to the inability to totally suppress the cross-term artifacts which typically are much stronger than the weakest signal components that they obscure. This paper presents one of two modifications of linear TFA to provide the enhanced detailing behavior of quadratic TFAs without introducing cross terms, making it possible to see the time-frequency detail of extremely weak signal components. The technique described is based on subspace-enhanced linear predictive extrapolation of the data within each analysis window to create a longer data sequence for conventional short-time Fourier transform (STFT) TFA. The other technique, based on formation of a special two-dimensional transformed data matrix analyzed by high-definition two-dimensional spectral analysis methods such as 2-D AR or 2-D minimum variance, is presented in a separate time-frequency textbook under the development editorship of B. Boashash (see Time-Frequency Signal Analysis and Processing, Prentice Hall, 2002).