Improvement of ISAR global range alignment

The global range alignment has a good performance in inverse synthetic aperture radar (ISAR) imaging. The shifts made to the echoes are modeled as a polynomial, and the coefficients of this polynomial are chosen to optimize a quality measure of range alignment. The shift in the time domain is implemented by introducing a phase ramp in the frequency domain in order to remove the limitation of integer steps. However, in this method, the quality measure of range alignment need be calculated in the time domain, which is time consuming. In this paper, we present a new expression for the quality measure of range alignment so that it can be calculated directly in the frequency domain. This raises the computational efficiency of the algorithm significantly.