## 3 Experiments and Analysis
### Comparison of Fusion Criteria
#### 3.2.3 Combination of Low and High Frequency Fusion Criteria  
In order to verify the combined performance of the superior low and high frequency fusion criteria mentioned above, experiments are performed using measured Data 3. The combined fusion criteria are shown in Table 5. The fused image (Figure 10) is highlighted by L1-L6 areas, and the characteristics of each region are used to analyze the performance of the combined fusion criteria. In addition, some objective indexes are applied to evaluate the algorithm's ability, as shown in Table 6. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Criterion** & **Energy\_Max** & **Dire\_Contrast\_Max** & \begin{tabular}{c} **PCNN** \\ **(NSML)** \\ \end{tabular} & \
\begin{tabular}{c} **IDPCNN** \\ **(MSF)** \\ \end{tabular} &
\begin{tabular}{c} **IDPCNN** \\ **(NSML)** \\ \end{tabular} \\ \hline AG & 9.7983 & 5.6267 & 9.8573 & 9.8565 & 9.8580 \\ E & 7.0776 & 6.9663 & 7.0835 & 7.0835 & 7.0836 \\ RCE & 0.0409 & 0.0429 & 0.0438 & 0.0441 & 0.0439 \\ FD & 13.3184 & 7.3078 & 13.3596 & 13.3582 & 13.3608 \\ Q\({}^{AB\!F}\) & 0.6783 & 0.4031 & 0.6814 & 0.6817 & 0.6818 \\ IFQI & 0.7361 & 0.3585 & 0.7470 & 0.7474 & 0.7474 \\ WFQI & 0.8894 & 0.4604 & 0.9003 & 0.9003 & 0.9004 \\ EFQI & 0.0409 & 0.0429 & 0.0438 & 0.0441 & 0.0439 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Objective evaluation indexes of the rich terrain fused image (Data 2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Criterion** & **Energy\_Max** & **Dire\_Contrast\_Max** & \begin{tabular}{c} **PCNN** \\ **(NSML)** \\ \end{tabular} & \
\begin{tabular}{c} **IDPCNN** \\ **(MSF)** \\ \end{tabular} &
\begin{tabular}{c} **IDPCNN** \\ **(NSML)** \\ \end{tabular} \\ \hline AG & 6.6622 & 3.9657 & 6.7027 & 6.7025 & 6.7031 \\ E & 6.9263 & 6.8291 & 6.9261 & 6.9263 \\ RCE & 0.0895 & 0.0527 & 0.0825 & 0.0822 & 0.0822 \\ FD & 9.5084 & 5.3125 & 9.5364 & 9.5366 & 9.5373 \\ Q\({}^{AB\!F}\) & 0.6362 & 0.4134 & 0.6414 & 0.6417 & 0.6417 \\ IFQI 1 & 0.7732 & 0.3769 & 0.7834 & 0.7826 & 0.7834 \\ WFQI 2 & 0.9092 & 0.5074 & 0.9242 & 0.9247 & 0.9247 \\ EFQI 3 & 0.4545 & 0.3793 & 0.4756 & 0.4793 & 0.4813 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Objective evaluation indexes of the fused aircraft debris image (Data 1). Figure 10: Fused image information of overlapping areas between adjacent strips. (**a**) Criterion 1. (**b**) Criterion 2. (**c**) Criterion 3. (**d**) Criterion 4. (**e**) Proposed criterion 5. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Fusion Technique** & **Low Frequency** & **High Frequency** \\ \hline Technique 1 & IDPCNN (NSML) & IDPCNN (NSML) \\ Technique 2 & EOL Filtering & IDPCNN (MSF) \\ Technique 3 & EOL Filtering & IDPCNN (NSML) \\ Technique 4 & SMLF & IDPCNN (MSF) \\ Proposed Technique 5 & SMLF & IDPCNN (NSML) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Combination method of low and high frequency fusion criteria. Compared with each area in Figure 10, different features and information are displayed comprehensively. In the image edge area L1 and the terrain fluctuation area L4, the phenomenon of incomplete fusion and discontinuous shadows are generated by the processing of combined technique 1, 2, and 3, and the combined technique 4 is unable to availably extract the information and topographic relief change characteristics of this area. For the L2 and L3 areas with incomplete detection information, the combined technique 4 and 5 fully absorb the complementary information of the two strips, showing a clear overview of the slope and boundary characteristics. In addition, the combined technique 1, 2, and 3 have no capacity for weakening the interference effect of residual error in the L5 area, and the fused image still retains the error traces after the subsea tracking processing. As for the edge contour area L6, the combined technique 5 proposed in this paper can effectively fuse the missing information of adjacent strips in the overlapping area, and the shadow trace of fused discontinuous discrimination is not produced.