L2-Norm Quasi 3-D Phase Unwrapping Assisted Multitemporal InSAR Deformation Dynamic Monitoring for the Cross-Sea Bridge

Interferometric fringes containing noise with complex distributions significantly contribute to phase unwrapping (PhU) failures in synthetic aperture radar interferometry (InSAR) technology. The study proposes an L²-Norm Quasi 3-D PhU-assisted multitemporal InSAR strategy. Initially, the L²-norm quasi 3-D PhU (first spatial 2-D and then temporal 1-D PhU) is employed to reduce the phase gradient of interferograms with optimized networks. The advantage of this methodology is that the wrapped residual phase satisfies the phase triangle, thereby making it suitable for existing widely-used 2-D or 3-D PhU techniques. Subsequently, a popular PhU method is applied to the residual phase, which is smooth and continuous, thereby improving the accuracy of subsequent spatial PhU. The deformation rate, time series and number of PhU triplet closures demonstrate the reliability of the proposed method for the Pingtan Straits Rail-cum-Road Bridge and the Hong Kong–Zhuhai–Macao Bridge in China using the sentinel-1A SAR dataset. The deformation results demonstrate that the bridge deformation is temperature-dependent, with the location of deformation being contingent upon the structural configuration of the bridge.