Multi-patch and centre-expansion algorithms for phase unwrapping of large InSAR images with dense residues

To recover original full phase values in inherently wrapped output, phase unwrapping has been one of the key techniques in digital image processing. However, to unwrap the phase of a large interferogram with dense residues, a conventional path-following algorithm may produce retrieval errors caused by placing long branch cuts and repetitive connection of residues. In this paper, two unwrapping algorithms, the method of multiple patches connecting opposite residues and the method of centre expansion searching opposite residues, are presented. Some examples of Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) datasets demonstrate improvement compared to conventional methods in Interferometric Synthetic Aperture Radar (InSAR) data processing.