A reference-consistent UAV–total station framework for multi-temporal tilt and corrosion monitoring of slender tubular towers

Wind turbine towers in coastal environments are exposed to geometric misalignment and surface corrosion, yet these condition indicators are commonly assessed separately and without a consistent reference across inspection epochs. This study develops a reference-consistent structural health monitoring framework that integrates total-station surveying and multi-temporal unmanned aerial vehicle imagery for concurrent monitoring of view-dependent image-space inclination indicators and visible corrosion. A baseline lower-segment reference axis is established in a fixed geodetic coordinate system. The geodetically controlled baseline image configuration is transferred to subsequent epochs through covariance-weighted control-image constraints, while RTK-GNSS and inertial observations support exterior-orientation estimation. The angular difference between the projected reference axis and an image-derived visual symmetry axis defines the inclination indicator. The combined single-view standard uncertainty is 0.041°, the expanded uncertainty is 0.082°, and the engineering monitoring threshold is 0.098°. Five UAV epochs acquired between October 2024 and June 2025 yield first-to-final angular-change magnitudes of 0.030° to 0.074° across eight fixed viewing directions. These values remain below the single-view expanded-uncertainty reference magnitude and are therefore interpreted as monitoring-level observations rather than statistically confirmed structural deformation. An independent total-station re-survey at the final epoch yields validation residuals from −0.032° to +0.044°, with a mean absolute residual of 0.017° and a root-mean-square residual of 0.023°, supporting monitoring-level consistency between the UAV-derived and projected total-station changes. Visible corrosion is segmented using YOLO11-seg and normalized with respect to the valid, observable tower-surface region. The independent test set yields a precision of 79.6%, a recall of 88.0%, and an F1 score of 0.84. The visible corrosion extent index increases from 0.04 to 0.12%, corresponding to a descriptive transition from ASTM D610 grade 8 to grade 7. The framework provides a reference-consistent and uncertainty-aware basis for maintenance-oriented monitoring of slender tubular towers.