An Integrated UAV Magnetometry Workflow for Magnetic Anomaly Detection and Environmental Assessment in Cascais (Portugal)

High-resolution unmanned aerial vehicle (UAV) magnetometry has emerged as a promising technique for shallow subsurface investigation, environmental monitoring, and infrastructure assessment. However, many existing studies primarily focus on data acquisition and magnetic anomaly mapping, with limited attention to uncertainty quantification and reproducible interpretation workflows. This study presents an integrated methodology for high-resolution UAV-based magnetic surveying applied to the coastal environment of Cascais (Portugal). A multirotor UAV equipped with dual fluxgate magnetometers acquired more than 3.16 million georeferenced magnetic measurements over a 0.68 km² study area. The proposed workflow combines magnetic compensation, quality control, temporal correction, Monte Carlo uncertainty propagation (10,000 realizations), variogram modelling, ordinary kriging interpolation, and density-based spatial clustering (DBSCAN) for automated anomaly detection and source characterization. Cross-validation demonstrated excellent interpolation performance, with a mean prediction error of -0.3 nT, a root-mean-square error of 4.2 nT, and a correlation coefficient of 0.987 between observed and predicted magnetic values. Seven high-confidence magnetic anomaly clusters were identified, corresponding to probable buried metallic objects and elongated subsurface infrastructure. The integration of geostatistical modelling with uncertainty analysis significantly reduced interpretation subjectivity and provided quantitative confidence estimates for anomaly localization and spatial extent. Compared with conventional magnetic surveys, the proposed methodology offers high spatial resolution, operational flexibility, and a fully reproducible framework for objective subsurface characterization. These results demonstrate the potential of UAV magnetometry combined with advanced spatial analysis to support environmental auditing, coastal management, infrastructure monitoring, and near-surface geophysical investigations.