A quicklook processor for an airborne SAR

This paper reports on the quicklook processor algorithm implemented for the airborne iSAR system. Range compression is performed prior to quicklook processing. A quasi-focussed algorithm, based on the principles of unfocussed SAR, is used to meet the azimuth resolution requirements in real-time. The algorithm is suited to the production of medium resolution imagery. The azimuth data is divided up into subaperture pairs, each of which is processed as an unfocussed SAR. The subaperture pairs become smaller at the edges of the processing aperture due to the phase runout. Thus the resolution using the quasi-focussed algorithm is better than that achievable with an unfocussed SAR, but the computational advantages of unfocussed SAR are largely retained. Squint correction is also addressed. Range lines are fed in real time into the processing aperture at one end and discarded at the other end using a shift-and-discard technique. An array of nine Transputers^TM is used for the processing.