Three-component polarization migration of channel waves for prediction ahead of coal roadway

When excavating roadways in coal mining, it is critical to predict any geological anomalies that lie ahead of the excavation in advance. Channel waves can be used for this purpose; however, the mirror imaging artefacts in the diffraction migration of channel waves must be overcome. When mixed with a Rayleigh channel wave, the polarization migration of a two-component Love channel wave is no longer possible. In this paper, the polarization situations in three-dimensional channel waves are comprehensively summarized and a new three-component channel wave polarization migration technique is proposed to remedy the deficiencies in current migration methods. The proposed technique has directional selectivity and filters out other interfering waves during the migration process, eliminates the artificial mirror phenomenon, and provides a higher imaging accuracy than other methods. However, the polarization of three-component channel waves is very complex. For example, the fundamental mode of a Rayleigh channel wave in the center of a coal seam is vertical-linearly polarized instead of elliptically polarized. In addition, the Love and Rayleigh channel waves mix easily as the group velocities of their fundamental modes are similar, and separating these necessitates the use of a special polarization filter. When two types of channel waves mix, a suitable polarization filter can be applied to suppress one or the other; however, this can produce two migration images of Love and Rayleigh channel waves. The most economical and practical means to overcome this is to record the two horizontal components at the center of the coal seam using a Love channel wave polarization migration that is independent of the Rayleigh channel wave. The proposed method was validated by way of a numerical simulation, and the results confirmed its superiority over conventional methods.