# Three-Dimension Inversion of Magnetic Data Based on Multi-Constraint UNet++
## 5 Inversion of Real Data  
The measured area for the actual data is located in Suqian City, Jiangsu Province, covering a small section of the Tanlu fault zone, which is the largest developed fault structure in eastern China. Due to its complex crustal structure, strong tectonic movement, and active seismic activity, the Tanlu fault zone has become a hot spot of attention and research in the field of geoscience [21; 22; 23]. Magnetic anomaly data were obtained from the measured data after a series of processing steps, such as diurnal variation correction, normal field correction, and magnetic pole correction. Then, the measured data were gridded into two-dimensional plane data with a size of 32 \(\times\) 32, and the size of the gridded unit was 93 m \(\times\) 156.8 m, as shown in Figure 22a. After the magnetic anomaly plane data were input into the multi-constraint DL UNet++ network, the predicted results were output, as shown in Figure 22b. It can be seen that the output results contain two large abnormal bodies, which indicates that there are two large bars with high-magnetic-susceptibility abnormal bodies in this test area.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Model** & **Method** & \begin{tabular}{c} **Model Fitting** \\ **Difference** \\ \end{tabular} & \begin{tabular}{c} **Data Fitting** \\ **Difference/nT** \\ \end{tabular} \\ \hline Composite test model I & \begin{tabular}{c} single-constraint DL \\ multi-constraint DL \\ \end{tabular} & 0.0334 & 0.9511 \\ \hline Composite test model II & \begin{tabular}{c} single-constraint DL \\ multi-constraint DL \\ \end{tabular} & 0.0248 & 0.7481 \\ \hline Composite test model III & \
\begin{tabular}{c} single-constraint DL \\ multi-constraint DL \\ \end{tabular} & 0.0225 & 0.4285 \\ \hline Composite test model III &
\begin{tabular}{c} single-constraint DL \\ multi-constraint DL \\ \end{tabular} & 0.0113 & 0.0932 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The composite test model evaluation index summary.  
Figure 22: The real data: (**a**) a contour map of magnetic anomaly data; (**b**) the multi\(-\)constraint DL inversion results.  
Figure 23a shows the magnetic anomaly data obtained from the forward modeling of the network prediction results, and Figure 23b shows the magnetic anomaly data obtained from the forward modeling of the inversion results by subtraction of the real magnetic anomaly data, with the overall difference within 5 nT, which meets the requirements of high-precision magnetic measurement according to the Geological and Mineral Industry Standard of the People's Republic of China. According to the previous geological exploration data, we know that there are three north-south faults in the survey area. Because the core at the fault location often changes, we can judge the specific location of the faults through aeromagnetic measurement.  
Figure 24 shows the prediction results of the multi-constraint DL inversion method. We projected the fault structure position in the measured area onto the magnetic anomaly plane data and the multi-constraint DL inversion results. According to this, we found that the predicted results were in good agreement with the actual fault conditions, and the magnetic anomalous bodies were basically distributed in the middle of the F1 and F2 fault zones, and to the right of the F3 fault zone. This indicates that the multi-constraint DL inversion successfully inverts the spatial location of the underground magnetic anomaly, and we can obtain a more accurate fault location according to the inversion results of this method. This provides guidance for subsequent research into the Jiangsu section of the Tanlu fault.  
Figure 23: Data –fitting effect of multi –constraint DL inversion of real data: (**a**) forward magnetic anomaly data of inversion results; (**b**) data –fitting difference of real data.