Fourth-order Spectra Of Sonar Signals

In active sonar, when a long pulse is transmitted the return echo is usually amplitude modulated from target dynamics, Doppler spreading, Or medium effects. Uncler these conditions, the spectrum can be severly distorted making detection and classification inlpossible. Using an amplitude modulated coded pulse train, it is shown in the paper that the fourth-order spectrum can extract range and Doppler information while for the same conditions the spectrum cannot.