The use of ISAR imagery for Automatic Target Recognition is seriously hampered by the difficulty of target motion compensation. Phase perturbations that result from target maneuvers during the processing interval need to be corrected for. In a previous paper, we demonstrated the use of the local Radon transform for estimating the radial velocity of a target. This estimate can then be used to align a sequence of range profiles prior to cross-range compression. In this paper, we make a quantitative comparison of the results that are obtained using different types of local Radon transformations. In the second part of this paper we outline an algorithm for compensation of phase perturbation that are caused by non-uniform target rotation. The algorithm has been tested on simulated data.
The use of the Radon transform and the Wigner-Radon power spectrum for ISAR motion compensation is described. It is shown that the local Radon power spectrum is closely related to the Cohen's class of quadratic time-frequency representations in a similar way as the Radon and Fourier transform are related. The peak of the local Radon transform is used as a measure for the velocity towards the radar of a moving target. The velocity estimate can be used to align the range profiles and perform target radial motion correction. Another application of the Radon transformation is the correction for time-variation of Doppler frequency of the signal during the Coherent Processing Interval. The Radon transform of the cross-range time-frequency representation of the signal is used for focusing an ISAR image that has been blurred due to non-uniform target rotation.