ISAR Imaging of Ship Based on the Modified 4th Order Time-Frequency Distributions with Complex-Lag Argument

ISAR imaging method, based on conventional time-frequency distribution, can not meet the requirements of the ISAR ship imaging, due to the complexity of the ship´s movement. Time-frequency distribution with complex-lag argument (CTD) is a new kind of time-frequency distribution which has good time-frequency concentration. Methods of reducing the cross terms of CTD for multi-component FM signals have been proposed for recent years. In this paper, based on the analysis of a cross-term reduced 4th order CTD (CTD4) algorithm, the scale problem and the image-truncation problem of the original algorithm have been pointed out and their modified algorithm is proposed. This modified CTD4 can be applied to the ISAR Range-Instantaneous Doppler (RID) imaging. The imaging experiments using simulation signal and real data of ship have shown the effectiveness of the modified algorithm.