# Method of Suppressing Rayleigh Waves Based on the Technology of Time-Domain Differential Detection
## 4 Engineering Validation of the Differential Detection Method
### Pipeline Detection  
Based on geological conditions, a natural gas transmission pipeline with a diameter of 1 m is situated approximately 4.5 m beneath the surface within the Quaternary clay layer.  
Figure 5: Comparison and local magnification of two adjacent channel original records after surface wave suppression. (**a**) Two adjacent records (color) and differential results (black). (**b**) Local amplification of two adjacent records and differential results.  
Figure 6: Comparison of bilateral shot gather records before and after Rayleigh wave suppression. (**a**) Records of bilaterally aligned artillery sets prior to stripping. (**b**) Records of stripped bilaterally aligned artillery sets.  
During shallow seismic exploration, the survey line runs perpendicular to the pipeline's direction. Initially, shot gather records were acquired with a lateral offset of 1 m and an inter-trace spacing of 0.5 m. An 18-pound hammer was utilized to activate the source, and 36 magnetic velocity sensors with a frequency of 28 Hz were deployed, with a data sampling interval of 50 \(\upmu\)s. The 18 th recording trace is positioned directly above the gas pipeline. Figure 7a shows the original shot gather record, while Figure 7b illustrates the shot gather record after time-domain differential processing. Figure 7b depicts that the energy of the Rayleigh wave is effectively suppressed, enhancing the direct longitudinal waves, refracted waves, and reflected or diffracted waves from the gas pipeline. Figure 8 compares trace 9 and 10 signals before and after differential processing, further highlighting the suppression of the Rayleigh waves.  
Two equal-offset seismic profiles were acquired using 4 m and 4.5 m shot offsets, to illustrate the effectiveness of the time-domain differential method. Figure 9a shows the far shot equal-offset profile without differential processing, while Figure 9b demonstrates the equal-offset profile after time-domain differential processing. The Rayleigh wave energy is extremely strong in the unprocessed record (Figure 9a), with reflections or diffracted waves from the surface of the gas pipeline almost completely obscured, complicating the detection of the gas pipeline's presence or position in the original seismic equal-offset profile. In contrast, the diffracted wave signals above the gas pipeline can be identified relatively without additional processing using the time-domain differential suppression method (Figure 9b).  
Figure 8: Comparison of signals before and after the 9 th and 10 th adjacent two differentials.  
Figure 7: Comparison between the original record of the gun set above the natural gas pipeline and the record after differential wave detection. (**a**) Record of the original collection of guns. (**b**) Post-differential gun set recording.  
A comparison of Figure 6a,b and Figure 8a,b reveals that the dominant frequency of the seismic waves in the records significantly increases after the application of the time-domain differential detection method.