Optimization of Space Magnetic Gradient Anomaly for Ground-Airborne Frequency-Domain Electromagnetic Detection in Complex Terrain

Ground-airborne frequency-domain electromagnetic (GAFDEM) rapid imaging method holds the potential for swiftly detecting underground anomalies in complex terrains at great depths. However, the current GAFDEM rapid imaging methods have not yet achieved satisfactory detection results in actual complex terrains. This is primarily due to two reasons: 1) the detection environment in complex terrain involves nonhorizontal land and significant relief caused by the presence of mountains. However, current GAFDEM rapid imaging methods fail to consider the influence of terrain on imaging effectiveness, and 2) in controlled-source electromagnetic detection, the design of the observation scheme directly affects the detection effectiveness of imaging methods. In actual detection, terrain constraints limit the design of observation schemes. For GAFDEM, the design of its transmitting sources is greatly influenced by terrain since these sources need to be deployed on the ground. Addressing these issues, this study analyzes the challenges faced by the space magnetic gradient anomaly (SMGA) in complex terrains, which exhibit effective detection under a horizontal ground model. Based on the analysis results, an optimization method for SMGA in complex terrains is proposed. This method achieves rapid correction of the background field in SMGA, thereby enhancing its detection efficacy in complex terrains and enabling the effective identification of underground electrical anomalies. Furthermore, performance testing of the optimized SMGA (O-SMGA) demonstrated that O-SMGA exhibits excellent applicability. Subsequently, an examination is conducted on multiple parameters of the transmitting source assessing their effects on the imaging performance of O-SMGA. Based on the analysis results, design guidelines for GAFDEM transmitting sources in complex terrains applicable to O-SMGA are provided to further enhance its detection effectiveness in actual detection. Finally, a synthetic test of O-SMGA and the transmitting source design guidelines is conducted using models with actual terrain data and actual experimental results. The results indicate that these methods still exhibit excellent performance in actual detection applications.