# A Novel Mosaic Method for Spaceborne ScanSAR Images Based on Homography Matrix Compensation
## 5 Experimental Results and Discussion
### Efficiency Analysis
For the traditional feature-based mosaic process (no overlapping area extraction, no scaling compensation or parallel operation), the total mosaic time of six GF-3 ScanSAR images of original size was more than five thousand minutes. After using the improved methods, the mosaic time could easily reach approximately five minutes, which means that the efficiency was improved by nearly a thousand-fold. This indicates that the new method is more efficient. We recorded the time of each processing step in two situations. The scaling coefficient was 0.5 and the number of the parts in parallel was 32. From Table 4, we knew that the registration was the most time-consuming part of the traditional method and its efficiency could be improved greatly by using our proposed method. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Image Name** & **Size** & **Bit Depth/Format** & **Capacity** \\ \hline Azimuth1\_subswath1 & 24,648 \(\times\) 36,092 & 16/TIF & 1.65 GB \\ Azimuth1\_subswath2 & 29,256 \(\times\) 30,016 & 16/TIF & 1.63 GB \\ Azimuth1\_subswath3 & 31,304 \(\times\) 36,532 & 16/TIF & 2.12 GB \\ Azimuth2\_subswath1 & 24,648 \(\times\) 36,092 & 16/TIF & 1.65 GB \\ Azimuth2\_subswath2 & 29,256 \(\times\) 30,016 & 16/TIF & 1.63 GB \\ Azimuth2\_subswath3 & 31,304 \(\times\) 36,532 & 16/TIF & 2.12 GB \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of the six GF-3 ScanSAR images. Figure 9: _Cont._  
To test the effect of the proposed method on multiple large-area image mosaics, six spaceborne ScanSAR images of GF-3 were stitched to a wide image. The scaling coefficient was 0.5, and the number of divided parts was 32. The geolocation results of the six GF-3 ScanSAR images are presented in Table 5, the overlapping rates between adjacent images are provided in Table 6 and the overlapping areas of six images are shown in Figure 10. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multirow{2}{*}{**Registration**} & \multicolumn{2}{c}{**Homography Matrix Calculation**} & \multirow{2}{*}{**Image Projection**} & \multirow{2}{*}{**Image Blending**} & \multirow{2}{*}{**Total**} \\  & & **Calculation** & & & \\ \hline Traditional method & 5200.7 min & 0.5 min & 1.8 min & 1.2 min & 5204.2 min \\ The method we & 1.7 min & 0.5 min & 1.8 min & 1.2 min & 5.2 min \\ proposed & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Time of each processing stage. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Image Name**} & \multirow{2}{*}{**Latitude/Longitude (\({}^{\circ}\)) of the Top-Left Corner**} & \multirow{2}{*}{**Latitude/Longitude (\({}^{\circ}\)) of the Top-Right Corner**} & \multirow{2}{*}{**Latitude/Longitude (\({}^{\circ}\)) of the Lower-Right Corner**} \\  & & **Corner** & & \\ \hline Azimuth1\_subswath1 & 43.043873/ & 41.509605/ & 43.339918/ & 41.802235/ \\ Azimuth1\_subswath2 & 121.062448 & 120.578586 & 119.192047/ & 118.759260 \\ Azimuth1\_subswath3 & 43.218379/ & 41.681016/ & 43.478385/ & 41.939181/ \\ Azimuth1\_subswath2 & 119.982423 & 119.528637 & 118.232633 & 117.824313 \\ Azimuth1\_subswath3 & 43.454342/ & 41.919444/ & 43.656159/ & 42.120934/ \\ Azimuth2\_subswath1 & 118.396638 & 117.985239 & 116.900489 & 116.527078 \\ Azimuth2\_subswath1 & 41.620338/ & 40.083754/ & 41.913187/ & 40.374984/ \\ Azimuth2\_subswath2 & 120.612775 & 120.159869 & 118.789969 & 118.376998 \\ Azimuth2\_subswath2 & 41.792651/ & 40.254233/ & 42.050932/ & 40.511655/ \\  & 119.560996/ & 119.130605 & 117.853522 & 117.461630 \\ Azimuth2\_subswath3 & 42.026978/ & 40.491942/ & 42.228482/ & 40.693604/ \\  & 118.013633 & 117.619156 & 116.552920 & 116.192071 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Geolocation results of the six GF-3 ScanSAR images.