Validation of Drone-Borne Aeromagnetic Surveys Using Multi-Altitude Measurements in Rugged Terrains, Taiwan

Geothermal energy is an essential renewable resource whose effective development relies on subsurface structure, particularly in regions with high geothermal potential. Magnetic surveying serves as a fundamental geophysical tool in this context, enabling the identification of concealed intrusions, estimation of source depths, and delineation of buried dykes or faults. While regional airborne campaigns offer efficient coverage, their resolution is often limited by wide survey-line spacing and high flight altitudes. Conversely, ground-based surveys, though detailed, are frequently hindered by rugged terrain and accessibility issues. Drone-borne aeromagnetic surveys address these limitations, providing high-resolution datasets in areas with complex topography.

In this study, we utilized a total-field scalar magnetometer integrated with a multicopter Unmanned Aerial System (UAS) to acquire magnetic measurements. The UAS followed pre-programmed survey lines defined by GPS waypoints and employed terrain-following flight modes at constant altitudes no higher than 120 m above ground level, which are substantially lower than those of conventional airborne surveys and allow measurements to be acquired closer to subsurface magnetic sources. Surveys were conducted at multiple altitudes to calculate vertical magnetic gradients, which serve as essential constraints for modeling subsurface magnetic susceptibility distributions. The data processing workflow comprised spike removal, International Geomagnetic Reference Field (IGRF) correction, and diurnal correction. The processed data were subsequently gridded using the natural neighbor interpolation method to generate magnetic anomaly maps.

Our drone-borne aeromagnetic surveys in volcanic regions have demonstrated strong consistency with existing aeromagnetic datasets while offering significantly enhanced spatial density. This study extends the application of drone-borne aeromagnetic surveying to a metamorphic formation with lava flows. Distinct magnetic anomaly patterns are observed at different flight altitudes. Ongoing research involves the application of computational methods and modeling to analyze these altitude-dependent phenomena and refine the interpretation of subsurface magnetic source distributions.