Time-Series InSAR Analysis Using PS-InSAR, SBAS-InSAR, and Merged Approach: A Case Study of Khun Dan Prakarn Chon Dam, Nakhon Nayok, Thailand

Abstract

This study compares Persistent Scatterer InSAR (PS-InSAR), Small Baseline Subset InSAR (SBAS-InSAR), and the StaMPS merged processing mode for line-of-sight (LOS) ground-motion screening around Khun Dan Prakarn Chon Dam, Thailand, using 43 ascending Sentinel-1 Interferometric Wide Swath scenes acquired from January 2015 to July 2025. EZ-InSAR, ISCE, and StaMPS were used to generate mean LOS-velocity products and evaluate point density, standard deviation, normalized median absolute deviation (NMAD), mapped interferometric coherence, and agreement on spatially matched points. PS-InSAR produced the smallest velocity dispersion (STD = 0.601 mm/yr; NMAD = 0.513 mm/yr), whereas SBAS-InSAR showed greater dispersion (STD = 1.417 mm/yr; NMAD = 0.882 mm/yr). The merged result provided the greatest spatial sampling (35,143 points; 65.08 points/km2), with intermediate dispersion (STD = 1.002 mm/yr; NMAD = 0.647 mm/yr), and was therefore interpreted as a coverage-precision trade-off rather than a more accurate product. A common-support comparison matched 28,257 merged-PS points within 30 m and yielded an NMAD of velocity differences of 0.334 mm/yr, but weak pointwise association (R² = 0.258), showing that small robust differences do not imply strong equivalence. Most velocities were near zero; however, these relative single-orbit LOS observations cannot independently resolve vertical and horizontal motion or verify structural safety. Residual atmospheric effects, vegetation decorrelation, and viewing geometry limit physical interpretation. Without collocated field observations, the results therefore provide an internal comparison and remote-sensing screening indicators rather than external validation of dam performance.