surface deformation only and does not incorporate other hydromechanical controls such as dam water level, pore-water pressure, or drainage conditions. Figure 2 – Distribution of sector-scale deformation rates under high-rain and other intervals 3.4 Validation of MT-DInSAR-derived deformation with total station monitoring Ground validation of InSAR over TSFs is often constrained by sparse instrumentation and differing sampling frequencies. Here, MT-DInSAR-derived vertical velocities were compared against total station measurements from eight active control points monitored between June 2023 and July 2025. This comparison is used as a consistency check rather than a formal calibration, as total station accuracy may be influenced by monument stability and survey conditions. Figure 3 shows that four points (5, 6, 7, and 9) lie close to the 1:1 line, with RMSE values of 3.06, 6.66, 7.15, and 4.43 mm/year, all within the typical InSAR validation range of 3-10 mm/year (Chen et al., 2021; Cigna et al., 2021). Three of these points are in the West zone, indicating good agreement despite high local variability. Crest points show greater scatter, likely due to active crest raising and maintenance on the area, while Point 4 in the Toe shows poor agreement, possibly because low coherence dominates where true deformation is small. Figure 3 – Comparison of vertical deformation velocities from total station control points and MTDInSAR 3.5 LightGBM model forecast performance
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