Monitoring of Hwanggang Dam using Time-Segmented Compressed SAR (TS-ComSAR) Algorithm

Monitoring the structural integrity of dams in politically sensitive and physically inaccessible regions is critical for disaster risk reduction and national security. This study presents a long-term structural stability assessment of the Hwanggang Dam in North Korea using time-series Sentinel-1 synthetic aperture radar (SAR) data acquired between 2017 and 2025, processed with interferometric SAR (InSAR) techniques. Two key technical challenges associated with long-term dam monitoring in the absence of in situ reference data are addressed: (i) the loss of persistent scatterers (PS) over multi-year observation periods due to temporal decorrelation, and (ii) the need to maximize the density of coherent measurement points within a single, spatially isolated structure. To overcome these limitations, a time-segmented Compressed SAR (TS-ComSAR) approach is employed, in which InSAR processing is performed in annual segments and subsequently stacked to construct a nine-year displacement time series. By constraining the temporal baseline, this strategy enables consistent identification and tracking of stable PS points across multiple years. In addition, a full-stack nine-year time-series dataset is processed using the conventional Compressed SAR (ComSAR) approach to enable a direct comparison with TS-ComSAR results. The analysis indicates that the Hwanggang Dam remains structurally stable over the observation period; however, the concrete dam section exhibits a persistent uplift trend, with cumulative displacement on the order of 20–30 mm. In contrast, the embankment (fill) dam section shows a pronounced long-term subsidence trend, with cumulative displacement reaching approximately 60–80 mm over the monitoring period. These results demonstrate the effectiveness of TS-ComSAR for infrastructure safety monitoring and highlight its capability for remote structural health assessment of strategic dams in restricted regions where ground-based observations are unavailable. The proposed integration of time-segmented and full-stack ComSAR provides a robust framework for long-term stability assessment of critical infrastructure under data-limited conditions.