Range-Doppler Inverse Synthetic Aperture Radar Processing
In Chapter 4, the base algorithm for inverse synthetic aperture radar (ISAR) imaging is provided. This algorithm is based on the assumption that the target is stationary and the data are collected over a finite number of stepped look angles. In real scenarios, however, the target is usually in motion and therefore, the aspect diverse data can only be collected if the target’s motion allows different look angles to the radar during the coherent processing time of the radar. The radar usually sends chirp (linear frequency modulated [LFM]) pulses or stepped frequency pulses to catch different look angles of the target. After the radar receiver collects the echoed pulses from the target, the ISAR image can only be formed in the two-dimensional (2D) range-Doppler space since the radar line of sight (RLOS) angle values with respect to target axis are unknown to the radar. This phenomenon will be explained in the forthcoming subsections.
In this chapter, we will examine the ISAR imaging techniques for real-world scenarios when the target is not stationary with respect to radar and the Doppler frequency shift-induced backscattered data are collected by the radar. In particular, commonly used ISAR waveforms, namely the chirp (LFM) and the stepped frequency continuous wave (SFCW) pulse waveforms, are utilized. The 2D range-Doppler ISAR imaging algorithms that employ these waveforms are presented.
6.1 SCENARIOS FOR ISAR ...