I. Introduction
In recent years, the DFRFT [7]–[9], [6] has become a useful time-frequency tool for multiple chirp parameter estimatiolin [5] and in particular it has been successfully applied to the problem of vibration estimation using SAR [2]–[4]. Direct DFRFT based estimation of the vibration frequency involves application of the DFRFT to the target return signal, peak coordinate location and translation of the peak coordinates to center-frequency and chirp-rate estimates using the peak-to-parameter mapping. This direct approach works well when the SNR is high and the SCR is high and above 15 dB. However in the presence of significant clutter produced from reflections of surrounding objects, accurate location of the peak becomes difficult due to the presence of clutter-induced side-lobes in the DFRFT spectra.