Absolute phase determination in SAR interferometry

High resolution extended DEM can be obtained from interferometric SAR image pairs. In order to evaluate the elevation of a pixel with respect to a slant-range reference plane, its absolute interferometric phase is required and this is usually derived unwrapping a 2D interferometric fringe pattern. Different methods have been suggested for phase unwrapping, based on local or global approaches. In both cases, phase incostistencies (residues) in SAR interferograms due to noise and topography determine unwrapping errors which appear as discontinuities in the computed absolute phase field. In this paper, results are reported on our experiment addressed to improve the output of phase unwrapping techniques by means of a residue classification procedure, according to their origin. Working on both simulated and real phase fields, we have found some differences between the spatial configurations of phase fields around singular points due to noise or linear discontinuities. A practical method has been developed to solve some ambiguities in the phase unwrapping of real SAR interferograms, useful for the linear integration approach as well as for global methods.