Abstract: A reference-based autofocusing procedure is particularly suited to existing and future interferometric SAR systems, though the principles are generally applicable to signal processing systems for which there are two partially correlated data sets having relative spectral errors. In an airborne or spaceborne system, the technique only requires some additional steps in the ground processor functions. The invention takes advantage of the fact that in a bistatic system, one antenna phase center both transmits and receives with the usual common-mode cancellation, and can thus be expected to form a reasonably well-focused image. In the second system, with the degraded phase error response, the image provided by the first system is used as a coherent reference to aid the estimation and removal of the relative phase errors between the two.

Abstract: A method of phase unwrapping is described along with an efficient UNIX/C implementation. From selected reference or starting points in a phase-wrapped image, the phase gradients with respect to the nearest neighbors of the starting pixels whose correlation is above the first correlation threshold are examined and a path representing the smallest phase difference is chosen as the first step in the creation of a path. The process is continued and, with each step, a maximum of three new neighbors is added to a list of possible path extensions. The list is sorted by step size, and the smallest step size is selected as the next path extension. This continues until all pixels that can be reached by paths containing only pixels with correlation above the first correlation threshold are on a path. In the same way, the paths are then extended to include all pixels with correlation above the next lower correlation threshold.