# Efficient Method for Enhancing Reverse-Time Migration Images Using Vertical Seismic Profiling Data
## 4 Results  
### Simple Model  
This section presents the experimental results using the model from the previous section and compares CRRTM with the traditional W-VSP RTM method. All parameters in the model and observation system were consistent with those described in the previous section. All data presented in this section underwent the same processing to eliminate the effects of low-frequency noise and areas outside the theoretical imaging range.  
Figure 13 presents the final imaging results obtained using the conventional W-VSP RTM method. As shown in the figure, the traditional method exhibits significant migration arches around the observation well. Additionally, severe noise is observed at the locations of the observation well.  
Figure 11: Single imaging result in the simple model using CRRTM S-wave imaging.  
Figure 12: Limitation of first-arrival time to the receiver wavefield at different depths.  
To further suppress the noise in the traditional W-VSP RTM method, we modified the imaging conditions for ETC-IC. This approach requires obtaining the first-arrival travel times from the receiver points to each grid point in the model. There are two primary methods for selecting the first-arrival travel times: the maximum amplitude method and ray-tracing method. The first-arrival travel times obtained by these two methods are not identical; the maximum amplitude method generally yields slightly shorter travel times than the ray-tracing method. In this study, we primarily used the ray-tracing method to obtain the first-arrival travel time; the final imaging results obtained using the ETC-IC are shown in Figure 14.  
When using the ETC-IC, the noise around the observation well was significantly reduced. This noise primarily originates from seismic data because its generation time differs from the first-arrival travel times of the seismic waves. Hence, the ETC-IC effectively eliminates this noise. However, modifying the imaging conditions did not significantly reduce the arc noise around the observation well.  
Furthermore, when employing CRRTM, the migration artifacts were relocated to the sides of the effective imaging range. Consequently, in areas of greater interest, the quality  
Figure 14: Final migration results of the traditional W-VSP RTM method and ETC-IC.  
Figure 13: Final migration result of the traditional W-VSP RTM method.  
of the imaging results was notably enhanced. The imaging results obtained using CRRTM are shown in Figure 15.  
We evaluated the imaging quality by comparing the amplitude of the energy within the effective reflection axis with the total energy amplitude in the final imaging results obtained using the three methods. The results are presented in Table 1. These findings indicate that CRRTM effectively suppresses noise, thereby enhancing the imaging quality.  
Furthermore, CRRTM can also be utilized for S-wave imaging, and the final imaging results are depicted in Figure 16. It is observed that, when S-waves are employed for imaging, the resulting images exhibit higher precision.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Methods** & **Energy Ratio (\% Percent)** \\ \hline W-VSP RTM & 86.02 \\ W-VSP RTM with ETC-IC & 85.15 \\ CRRTM with ETC-IC & 98.21 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Imaging quality of three different RTM methods, evaluated based on the energy ratio.  
Figure 16: Final migration results of CRRTM when using S-waves.  
Figure 15: Final migration results of CRRTM and ETC-IC.