Nonparametric ISAR autofocusing via entropy-based doppler centroid search

A novel approach to nonparametric entropy-based autofocusing of inverse synthetic aperture radar images is proposed. Kinematics considerations show that the range cell corresponding to the target rotation center has a purely translational Doppler phase. This range cell can be selected by means of entropy criteria, and its phase component used as a measurement of the translational Doppler phase. Concerning the existing techniques, the new one is robust enough to noise and low target reflectivity, whereas provides higher quality output images with low computational load. The quality of the output is further confirmed by resorting to a recently published automatic target recognition algorithm, obtaining a very high success rate on a wide and variegated data set, acquired by the tracking and imaging radar system of the Fraunhofer FHR Institute.