## 3 Real Date
### Data Analysis  
Shot 1 is taken as an example and is effectively received by 50 two-component receivers. Four groups of waves are evident in the seismic records, as shown in Figure 9 (listed in order from top to bottom). The record shows that after the refracted direct P-wave and S-wave arrive, two waves arrive at different times on the x and y components, indicating that both can carry the complete channel wave information of the extra-thick coal seam, which is a distinctive characteristic, different from thin and moderately thick coal seams.  
The first and second waves to arrive are the refracted P- and S-waves, respectively, whose calculated velocities are 4200 m/s and 2300 m/s. The velocity of the third wave group is 1100 m/s, and that of the fourth and last wave group is 900 m/s. The amplitude characteristics of the third wave group on the y component are more obvious than those on the x component, the overall continuity of the third wave group is relatively good, and extra-thick coal seams highlight the total reflection propagation characteristics. The actual  
Figure 8: Channel wave transmission survey layout.  
Figure 9: Shot 1 raw record.  
data are consistent with the characteristics of the wavefield snapshot in the area of the weak dispersion area. The third wave with the velocity is stable, and the fourth wave group is the channel wave, indicating that both can carry the complete channel wave information of the extra-thick coal seam, which is a distinctive characteristic different from thin and moderately thick coal seams.  
The propagation characteristics of channel waves can also be studied by dispersion analysis. We compare the shot seismic record with the dispersion curve of channel waves (Figure 10) and take the x and y components of the 33 rd channel of shot 1 as an example. The left panel in Figure 10 shows the single-channel data and an enlarged view of the record, where the vertical axis represents the travel time, and the horizontal axis is the amplitude value. The abscissa of the dispersion curve is the frequency, and the ordinate is the velocity (time scale). The velocity value is stable, and the velocity corresponding to the propagation of the channel wave is consistent with that of the single-shot seismic record.  
We find that two wave groups (Figure 10a) appear at 360 ms and 430-480 ms on the time axis, which is similar to the general times when the channel waves appear, and the time-frequency characteristics are consistent with those of the dispersion curve. In the first wave group in the red box, the amplitudes of the x and y components are obvious, and the y component has a stronger amplitude than the x component. The waves characterized by a short duration, a shape similar to a body wave, and weak dispersion characteristics are defined herein as apparent channel waves, and their velocity value is equal to the shear wave velocity of the coal seam.  
In the second wave group in the red box, the x component displays many phases, a long duration, and relatively obvious dispersion characteristics, which are in line with the characteristics of channel waves (Figure 10b).  
From the characteristics of the dispersion curves, we discover that the corresponding velocities of the first wave group in the red box are stable with increasing propagation  
Figure 10: Dispersion analysis of the x and y components of the 33 rd channel of shot 1. (a) x-component. (b) y-component.  
distance, and the frequency and energy are constant, all of which are consistent with the characteristics of the weak dispersion region in the wavefield snapshot.