Autofocus for high resolution ISAR imaging

Abstract:
This paper investigates autofocus techniques for high resolution airborne Inverse SAR (ISAR) imaging of ground moving vehicles. The FHR PAMIR instrument which can be mounted onboard a Transall C-160 provides high resolution range data with resolutions in the order of 10 cm. ISAR images of even private cars may be acquired in this way. For the generation of such images translational and rotational motion components of the target must be known. These can be either derived from GPS data which is usually not available or from combining range tracking and road information. Errors in the geometrical data lead to a defocusing of the images and severe image degradation. If at least the rotational motion component is known accurately enough remaining translational motion components may be estimated from the data using autofocus techniques like prominent point processing (PPP), phase gradient autofocus (PGA) or image contrast based autofocussing techniques (ICT). This paper shows some of the known autofocus techniques and compares results achieved with real data.