Land Subsidence Assessment of an Archipelago Based on the InSAR Time Series Analysis Method

The lack of resources on islands leads to their extremely rapid development, and this can result in frequent geological disasters involving island subsidence. These disasters not only destroy the ecological environment and landscape of islands but also pose massive threats to the safety of residents' lives and property and can even affect the country's maritime rights and interests. To meet the demands of island stability and safety monitoring, in this study, we propose a large-area, full-coverage deformation monitoring method using InSAR technology to assess island subsidence based on a comprehensive analysis of conventional monitoring techniques. The working principle and unique advantages of InSAR data are introduced, and the SBAS InSAR key interpretation processing flow are described in detail. The GPU-assisted InSAR processing method is used to improve the processing efficiency. The monitoring results showed that the southern island group of the Miaodao Archipelago was relatively stable overall, with an annual average deformation rate of 3 mm. Only a few areas experienced large-magnitude surface deformation, and the maximum annual deformation magnitude was 45 mm. The time series deformation results of the characteristic points of the five inhabited islands in the southern island group showed that the subsidence trends of the two selected points on Beichangshan Island (P1 and P2) were slowly declining. The P3 point on Nanchangshan Island experienced a large deformation, while the P4 point experienced a relatively small deformation. The selected points (P5, P6 and P7) on Miaodao Island, Xiaoheishan Island and Daheishan Island were stable during the monitoring period. InSAR data can be used to accurately identify the millimetre-scale microdeformations experienced by island groups, thus demonstrating the high-precision deformation monitoring capability of these data. In addition, the accuracy of these data can meet the needs of island and archipelago subsidence monitoring, and the proposed method is an effective means to monitor the spatial deformation of island targets. This study is conducive to further enriching and improving island stability and safety monitoring technology systems in China and to providing data and technical support for identifying and mastering potential island risks, protecting and utilizing islands and preventing and reducing disasters.