Cross-range scaling for aircraft ISAR images based on axis slope measurements

Inverse synthetic aperture radar (ISAR) has been highly exploited for target recognition due to its high resolution imaging capability. Scaling of the ISAR image is a necessary step to the reliable target recognition. Usually, the target motion is unknown. The amount of rotation during the observation cannot be determined, so it is difficult to perform the cross-range scaling. In this paper, a technique aiming at achieving cross-range scaling of aircraft ISAR images is developed. The rotation rate of the aircraft is firstly estimated from the under-scaling image by measuring slopes of the aircraft’s two axes, i.e. the fuselage axis of symmetry and the cross (pitch) axis. Then, with the generally known observation time, the cross-range scale factor can be determined. Since all the operations are performed in the image domain, the scaling technique is used with ease. Moreover, the aircraft orientation relative to the radar line of sight (RLOS) and its flying velocity can be roughly estimated simultaneously. Results of real data processing confirm the effectiveness of the proposed technique.