Range instantaneous Doppler ISAR imaging based on combined spectrogram

Range instantaneous Doppler (RID) techniques based on time frequency transforms (TFT) can significantly improve the image quality of targets with complex motion. With the improvement of radar image resolution, the migration through resolution cells (MTRC) cannot be ignored. Consequently, there may exists spurious scatterers in the RID image due to the limited time-resolution. In this paper, the RID imaging method based on the combined spectrogram is proposed. For the proposed method, a better time-resolution is achieved via short time Fourier transform (STFT) with a short frequency smoothing window (FSW), meanwhile a better frequency-resolution is obtained by STFT with a long FSW. The high time-frequency resolution desired is obtained by combining the advantages of the two STFTs. Results of the experiments demonstrate the effectiveness of the new method proposed.