Two-Dimensional Phase Unwrapping For Multi-Baseline SAR Interferograms: Time-Series TSPA

Although the multi-baseline (MB) phase unwrapping (PU) approach does not rely on the phase continuity assumption embedded in the single-baseline (SB) PU approach, it is vulnerable to noise. The two-stage programming approach (TSPA) improves the noise robustness by using the gradient information of the interferogram. However, the TSPA is primarily designed for topography reconstruction. Then, we incorporate the temporal baseline into the TSPA to detect severe deformation, developing the time-series (TS) TSPA (TS-TSPA). The TS-TSPA estimates the absolute phase gradient by combing different temporal baseline lengths and then utilizes the L ¹ -norm optimization model to obtain PU results. Two differential interferograms of 14 April 2021-20 May 2021 and 20 May 2021-1 June 2021 after the Maduo earthquake were showcased. The earthquake had a moment magnitude of Mw 7.4, occurring on 22 May 2021. The quake caused severe surface deformation, deviating or invalidating the phase continuity assumption. With successful PU results by the TS-TSPA, a fault line was identified, and estimated surface displacements ranged from −4.5 to 3.7 m along the line-of-sight (LOS) direction. The PU results of the SB PU method missed the fault line and only detected displacements between 0 and 1.3 m. Therefore, the TS-TSPA effectively detects significant surface deformation where the quake-induced damage could be devastating and outperforms the SB PU method to unwrap phases in damaged areas and fault line delineations.