*4.2. Coherence Factor Matrix*

As stated in 2.5, the coherence factor (CF) matrix is an effective method to reduce artifacts and interferences in the image. The CF matrix is obtained in the delayed signal. Since the CF matrix is used as a weight to amplify the reflection wave and suppress the artifacts for each shot, it could be theoretically applied into other prestack time domain migration methods. Figure 27 here presents the results when the CF matrix was applied into Kirchhoff migration and DAS beamforming. The results shows that the CF matrix can obviously reduce the artifact caused by surface wave and interference on two sides of the images. However, there was also a contrast reduction at the lower floor in Kirchhoff. This might be a result of different travel time (delay time) calculation algorithm between MVSS beamforming and Kirchhoff migration.

**Figure 27.** Results when the CF matrix was applied into Kirchhoff migration and DAS beamforming. Kirchhoff migration (**a**) without and (**b**) with CF matrix applied. DAS beamforming (**c**) without and (**d**) with CF matrix applied.
