Slope-constrained InSAR reveals 3D deformation and rainfall–deformation associations of the Luoyugou landslide

Three-dimensional (3D) deformation monitoring can clarify landslide kinematics and rainfall–deformation associations where in situ observations are sparse. We integrated ascending and descending Sentinel-1A small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) time series (July 2022–July 2025), a slope-aspect constraint, tangent-angle staging, and statistically tested wavelet analysis for the Luoyugou landslide, China. Deformation concentrated in the central–eastern sector and was dominated by vertical settlement and east–west motion. Rates ranged from −22.94 to 12.59 mm yr − 1 vertically, −16.68 to 21.78 mm yr − 1 east–west, and −10.35 to 5.47 mm yr − 1 north–south. By July 2025, P1 accumulated 63.6 mm eastward and 41.6 mm downward displacement. The slope-aspect constraint sets transverse—not downslope—horizontal motion to zero; matrix condition numbers at P1–P5 were 1.56–1.86 and remained ≤ 2.25 under ± 10 ° perturbations of the slope aspect derived from the digital elevation model (DEM). Six same-day real-time kinematic (RTK) comparisons at P2 yielded component RMSE values of 1.66, 1.52, and 0.60 mm for vertical, east–west, and north–south displacement, respectively. Against a first-order autoregressive [AR(1)] red-noise null, significant 64–128-day rainfall coherence was spatially localized and persisted after removal of linear, annual, and semiannual components. Phase relations varied rather than showing a universal rainfall-leading lag. The results support progressive, rainfall-associated creep, while the constrained north–south component is interpreted as a relative trend and the single-point RTK validation limits field-wide accuracy claims.