Aerial Drone Magnetometry for the Detection of Subsurface Unexploded Ordnance (UXO) in the San Gregorio Experimental Site (Zaragoza, Spain)

Unexploded ordnance (UXO) poses a significant hazard in controlled outdoor testing/training areas. This paper assesses the effectiveness of aerial drone-mounted magnetometry for detecting buried UXO located outside the designated landing areas of the National Training Center (CENAD) of San Gregorio (Zaragoza, Spain), considered the largest manoeuvre area in Europe. To this end, a high-resolution aeromagnetic survey was conducted using a GEM GSMP-35U proton magnetometer mounted on a hexacopter drone. Data were collected at flight heights of 7 m and 2 m above ground level along a grid with 1 m line spacing. For its validation, eleven UXOs were deliberately buried at known coordinates to evaluate the system’s sensitivity and spatial resolution under operational conditions. The results demonstrate the capability of aerial drone-based magnetometry to detect small magnetic anomalies (with amplitudes between 2 and 18 nT) associated with buried UXO in complex environments characterised by high ferromagnetic noise, achieving signal-to-noise ratios greater than 5 (SNR > 5) at 2 m height and a geolocation accuracy of approximately 0.5 m. These findings support the use of unmanned aerial magnetometry as a viable tool for identifying hazardous remnants in military training ranges and field scenarios, enabling coverage of 0.53 ha in less than one hour of effective flight time.