Effective unwrapping of complicated phases by exploiting multiple interferograms: a case study of the 2016 Kumamoto earthquake
Abstract
Synthetic aperture radar (SAR) interferometry can measure ground surface deformation with high accuracy and spatial resolution, in the form of phase change in an interferogram. The phase is observed modulo 2π (i.e., wrapped), and unwrapping is necessary to obtain the absolute amount of deformation. Although several advanced automatic unwrapping algorithms and approaches have been proposed, unwrapping errors can occur, especially in complicated phases. Manual adjustment of the integration path in the unwrapping may improve the unwrapping result. However, sometimes, it tends to be challenging even for an expert. In this report, I describe an effective unwrapping approach for complicated phases to obtain a reliable unwrapping result using multiple interferograms. A common integration path guide is created from geocoded interferograms and their phase noise coherence estimates, which reduces/eliminates the effort involved in manual adjustment and greatly reduces unwrapping errors. The remaining unwrapping errors were detected from residuals between the unwrapped phases of multiple interferograms and corrected based on isolated components. A case study was taken up in the northwest of the outer rim of the Aso caldera. Here, plenty of displacement lineaments were generated by the 2016 Kumamoto earthquake, resulting in severely complicated interferometric phases to correctly unwrap by any existing approaches. Therefore, the proposed approach effectively and efficiently retrieves reliable unwrapped phases and subsequent significant interpretations of the displacement lineaments. This effective unwrapping approach may reveal complicated deformations and unrecognized mechanisms in future earthquakes or other deformation-causing geophysical phenomena.
- Publication:
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Earth, Planets and Space
- Pub Date:
- December 2022
- DOI:
- 10.1186/s40623-022-01595-5
- Bibcode:
- 2022EP&S...74...33M
- Keywords:
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- Synthetic aperture radar;
- Phase unwrapping;
- 2016 Kumamoto earthquake;
- Displacement lineament