Multiresolution phase unwrapping for SAR interferometry

An approach to two-dimensional (2D) phase unwrapping for synthetic aperture radar (SAR) interferometry is presented, based on separate steps of coarse phase and fine phase estimation. A technique called adaptive multiresolution is introduced for local fringe frequency estimation, in which difference frequencies between resolution levels are estimated and summed such that a sufficiently conservative phase gradient field is maintained. A coarse unwrapped phase of the full terrain height is then constructed using weighted least-squares based on coherence weighting. This coarse phase is used in a novel approach to slope-adaptive spectral shift filtering and to reduce the phase variation of the interferogram. The resulting interferogram can be more accurately multilooked and unwrapped with any algorithm. In this paper, fine phase construction is done with weighted least-squares and with weights determined by simple morphological operations on residues. The approach is verified on a simulated complex interferogram and real SAR data.