A New Subpatch Focusing Algorithm for Spotlight SAR Processing of Large Scenes

Space-variant phase error is the source of defocusing in spotlight SAR image for large scenes. The well-known autofocus techniques cannot easily overcome this type of error. This error limits the scene size of the SAR image. Subpatch technique can be used to focus the large scenes. In this paper, a new subpatch technique based on re-centering phase computation of previously recorded raw data is proposed. First, range compressed raw data is re-centered to a reference point for each subpatch. Then, polar format algorithm is applied to each subpatch. The angularly distorted subpatch images are then assembled by using an angular interpolation and mosaicking process to form a full scene focused image. Our simulation result shows that a well focussed spotlight SAR image of large scene can be obtained by choosing predefined focussing criteria.