## 3 Theoretical Analysis and Experiment
### Experiment
#### 3.2.1 Experimental Equipment and Environment  
The layout of each module of the UAV magnetic exploration system used in this experiment is shown in Figure 7. The fluxgate magnetometer and the OPM were installed at the nose position. The fluxgate magnetometer was used to measure the geomagnetic field vector in the UAV coordinate system. The OPM was used to measure the magnetic total field. The batteries are located at the rear side of the wing, which supplies power to the OPM, fluxgate magnetometer, flight control inertial navigation module, engine and other modules through the power supply line. The current sensor was installed at the main power supply line to measure the total current output by the batteries. The schematic diagram of the circuit principle of the UAV magnetic exploration system is shown in Figure 8.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Technical Index** & \multicolumn{2}{c}{**Parameters**} \\ \hline
**Magnetic Sensor** & **Fluxgate Magnetometer** & **OPM-CAS-18-VL** \\ \hline Measuring range & \(\pm\)100,000 nT & 10,000–105,000 nT \\ Noise level & 6 pT/sqrt Hz at 1 Hz & 0.3 pT/sqrt Hz at 1 Hz \\ Size & 32 \(\times\) 32 \(\times\) 152 mm & \(\sqrt{253\times 78}\) mm \\ Weight & 160 g & 500 g \\ Orthogonality error & 0.5\({}^{\circ}\) & \\ Resolution & 0.1 nT & 0.0001 nT \\ Maximum error & 10 nT & 2.5 nT \\ \hline \hline \end{tabular}
\end{table}
Table 1: Fluxgate magnetometer and optical pump magnetometer parameters.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Current Sensor Parameters** & **Value** \\ \hline Measuring range & \(\pm\)150 A \\ Accuracy at 100 A & \(\pm\)0.45\% \\ di/dt accurately followed & \(>\)200A/ μs \\ Offset current & \(\pm\)0.1 mA \\ Linearity & \(<\)0.15\% \\ Size & 36.5 \(\times\) 27.2 \(\times\) 14.3 mm \\ Weight & 18 g \\ \hline \hline \end{tabular}
\end{table}
Table 2: Current sensor parameters.  
Figure 6: (a) UAV magnetic exploration system; (b) the cesium optical pump magnetometer.  
A three-axis parallel fluxgate magnetometer, which is what we used in this work, consists of an excitation module, a pickup module and a signal processing module for each axis. There are a pair of excitation coils with ferromagnetic wires as cores in them in each excitation module. The larger coil surrounding the excitation coils is the pickup module. The ferromagnetic core is a cobalt-rich amorphous wire (Co\({}_{68.2}\)Fe\({}_{4.3}\)Si\({}_{12.5}\)B\({}_{15}\)) 100 \(\upmu\)m in diameter and 20 mm in length. The function of the signal processing module includes generating the excitation signals and demodulating the induction signals. The diagram of the fluxgate sensor is shown in Figure 9. The photograph of the fluxgate magnetometer is shown in Figure 10. The parameters of the fluxgate sensor are listed in Table 3[25].  
Figure 8: Schematic diagram of the circuit principle of UAV magnetic exploration system.  
Figure 7: Layout of each module of UAV magnetic exploration system.  
For accurately measuring the magnetic interference generated by UAV electronic equipment, the experimental region was in an open field far away from town and with a stable magnetic field. As shown in the Figure 11 There were no interference magnetic sources such as buildings and high-voltage lines around.