Sequential Covariance Fitting for InSAR Phase Linking

Traditional phase-linking (PL) algorithms are known for their high cost, especially with the huge volume of synthetic aperture radar (SAR) images generated by Sentinel-1 SAR missions. Recently, a COvariance Fitting Interferometric Phase Linking (COFI-PL) approach has been proposed, which can be seen as a generic framework for existing PL methods. Although this method is less computationally expensive than traditional PL approaches, COFI-PL exploits the entire covariance matrix, which poses a challenge with the increasing time series of SAR images. However, COFI-PL, like traditional PL approaches, cannot accommodate the efficient inclusion of newly acquired SAR images. This article overcomes this drawback by introducing a sequential integration of a block of newly acquired SAR images. Specifically, we propose a method for effectively addressing optimization problems associated with phase-only complex vectors on the torus based on the majorization–minimization framework. The proposed approach demonstrates comparable performance to the offline COFI-PL method while achieving a reduction in computation time of approximately 15% in both simulations and real data experiments. Moreover, it outperforms state-of-the-art sequential approaches in terms of both accuracy and speed.