After RCMC, the energy of the moving target is concentrated into a range gate, and the echo of the moving target can be viewed as a 1-D signal. The Doppler parameters are estimated from the azimuth signal, and the target can be focused and relocated using the estimations.

Since the azimuth signal of the target in SAR can be viewed as a chirp signal, the Doppler parameters can be accurately estimated using the time-frequency analysis algorithms, such as WVD transform, FrFT [22], wavelet transform and so forth.

After the Doppler parameter estimation, motion parameters can be derived. The cross-track velocity can be calculated as

Since the two motion parameters cannot be derived from one Doppler parameter, the cross-track acceleration and the along-track velocity cannot be derived from the Doppler modulation rate at the same time. Thus, the acceleration is neglected in practical applications. The along-track velocity is calculated as

If there are multiple moving targets in the scene, each target must be estimated and focused independently. The flowchart of the whole moving target processing is illustrated in Fig. 2.9.