A Novel UAV-Based Ground–Airborne Frequency-Domain Electromagnetic System Using Triaxial Induction Core Sensors

The Ground-Airborne Frequency-Domain Electromagnetic (GAFDEM) method utilizes a ground-based transmitter and an airborne receiver, offering high transmission power and efficient data acquisition. It is particularly suited for rapid subsurface exploration in geologically complex regions. However, current UAV-based coil-type EM systems suffer from high background noise and significant measurement variability, which hinder accurate field measurements under large transmitter–receiver offsets. To overcome these challenges, we developed a novel UAV-compatible three-component GAFDEM system (JLU-3D-II) based on magnetic-core sensor technology. A quantitative evaluation method based on repeated flight experiments was proposed and implemented. The system’s performance was assessed through laboratory tests and field repeatability experiments. Indoor tests demonstrated that JLU-3D-II achieves nearly a 30-fold reduction in noise within the 10–1000 Hz frequency band, compared to air-core coil sensors of equivalent weight. Field experiments showed that the root mean square relative error of the vertical magnetic component across repeated flights decreased from 18% to below 2%, indicating a substantial improvement in measurement accuracy. Compared to the typical operational radius (approximately 1.5 km) of mainstream international UAV-based EM systems, this experiment achieved more than double the effective detection distance, verifying the system’s adaptability and data stability in long-offset detection scenarios.