Time-frequency characterization of micro-multipath signals in over-the-horizon radar

A challenging task in over-the-horizon radar (OTHR) is the tracking of target altitude. It has been shown that the micro-multipaths due to ocean/ground reflections may reveal important information about the elevation maneuvering of a target. The Doppler signature of such micro-multipath signals is typically composed of three components having close nonlinear time-frequency behaviors. In this paper, we develop novel time-frequency analysis techniques for the characterization of Doppler effect of micro-multipath signals. The proposed method is based on the local analysis of the signal phase, followed by a stationarization operator. In the warped representation domain, the multi-component nonlinear Doppler signatures become stationary, thus allowing the application of spectral analysis tools. The results presented are based on real data and illustrate the potential of the proposed methods.