InSAR closure: a simple and novel approach for identifying phase unwrapping errors using an interferogram and its reversal

Phase unwrapping errors are a major source of uncertainty in Interferometric Synthetic Aperture Radar (InSAR) and are difficult to detect and correct. In time-series InSAR, the closure phase method is commonly used to identify phase unwrapping errors, but it requires three or more interferograms generated from multiple Synthetic Aperture Radar (SAR) images. However, for two-image InSAR, no effective method exists for identifying phase unwrapping errors beyond visual inspection. In this study, we extend the closure phase concept to two-image InSAR by swapping the reference and secondary images. Our results show that this swap induces significant changes in the interferometric phase, resulting in both global offsets and speckle-like deviations. The global offsets can be removed by subtracting the mode, while speckle-like deviations alter the values of phase unwrapping errors, which can be detected through threshold segmentation of the summed results. Our method enables the identification of phase unwrapping errors without the need for additional data or subjective visual interpretation. We validated the method’s effectiveness across L-, C- and X-band datasets, demonstrating its capability to detect phase unwrapping errors in both deformation and elevation measurements. These results confirm the method’s versatility and robustness for multi-band radar applications.