Yasser Maghsoudi, Andy Hooper , Tim J Wright , Homa Ansari , Milan Lazecky 

Interferometric Synthetic Aperture Radar (InSAR) is widely used to measure deformation of the Earth’s surface over large areas and long time periods. A common strategy to overcome coherence loss in long-term interferograms is to use multiple multilooked shorter interferograms, which can cover the same time period but maintain coherence. However, it has recently been shown that using this strategy can introduce a bias (also referred to as “fading signals”) in the interferometric phase, particularly over vegetated areas. We isolate the signature of the phase bias by constructing daisy chain sums of short-term interferograms covering identical 1-year time periods, but using interferograms of different time spans. This shows that the shorter interferograms are more affected by this phenomenon and that different ground cover types are affected differently. We, propose a method for correcting the phase bias, based on the assumption that the bias in an interferogram is linearly related to the sum of the bias in shorter interferograms spanning the same time. We tested the algorithm over a study area in western Turkey by comparing average velocities against results from a phase linking approach that has been shown to be rather insensitive to the phase bias. Our corrected velocities agree well with those from phase linking approach. Our approach can be applied to global compilations of short-term interferograms and offer the possibility of accurate long-term velocities without a requirement for coherence in long-term interferograms.