Automatic mosaicing for airborne SAR imaging based on subaperture processing

The spotlight synthetic aperture radar (SAR) image formation process is beneficially applied to stripmap case by mosaicing of consecutive subpatch images, especially in condition of a highly squinted antenna where most of the stripmap imaging algorithms become inefficient mainly due to the large range migration effects. Furthermore, for an airborne squint mode SAR, the mosaic processing also suffers seriously from the geometric distortions and the border discontinuities in the neighboring images caused by insufficient motion compensations. This paper presents a methodology to generate the continuous full-strip image with automatic and seamless mosaicing processes based on the spotlight subaperture imaging algorithm which is developed to correct the geometric distortion and compensate the spatially-variant phase error. It mainly involves illuminated area divisions, geo-referenced scatterers positioning, geographical coordinate transformation, and the mosaicing of successive images. An evaluation using point-target simulations for a squint angle of 60 degrees is provided. The performances demonstrate its effectivity.