Noise-robust phase-unwrapping method in radar interferometry

Synthetic aperture radar (SAR) interferometry is a technique based on the exploitation of the interference pattern of two SAR images acquired in similar geometric conditions, at two different dates. This technique has a very broad range of applications. It is used to generate digital elevation models (DEM). It also can detect centimeter-size changes on the ground surface. In order to extract topography from interferograms, the interference pattern has to be unwrapped and transformed into altitude. Phase unwrapping is one of the most difficult parts of the process and has become one of the most studied subjects in the interferometric community. In this paper, we present a new phase unwrapping method, based on a global analysis of the interferogram. The interferogram is divided into surface elements that can be modeled by local slopes. A model of the unwrapped phase is computed thanks to these elementary surfaces. We show that the interferogram can be unwrapped using the computed model as soon as the differences between the model and the interferogram are smaller than half a fringe on the entire image. Then, we present two algorithms based on this method, an automatic one and an interactive one. We discuss the performances of each algorithm on test sites. We show that the automatic algorithm is very efficient in noisy areas, and that the interactive one can be of interest in areas with shadow or overlay. Finally, possibilities of improvements are discussed.