Tomography method for adjacent channel frequency shift of transmitted in-Seam waves

In-Seam Seismic is one of the main detection methods for small geological structures in the coal mining working face. In this method, the energy attenuation feature of in-seam waves is mainly utilized. In case of any significant geological anomaly or receivers coupling difference in coal working face, the energy distribution of the in-seam wave at different frequency bands will be significantly affected, and the stability and accuracy of in-seam wave detection results will be decreased. Using the centroid frequency change features of the in-seam wave signals for inversion imaging is an innovative, effective method. However, for this method, there are difficulties in eliminating diversity influence of seismic source. Therefore, the tomography method base on the adjacent in-seam frequency shift of transmitted in-seam waves, for the estimation of the relative variety of the centroid frequency, was proposed. On the basis of the theoretical analysis, the formula for calculating relative variation of the centroid frequency shift (M_i) based on the adjacent in-Seam transmitted channel waves was derived; the positive linear correlation between M_i and the propagation distance of in-seam wave was verified by two-dimensional numerical simulation; and the normal and new imaging results of field test signals were compared and analyzed. As demonstrated by the above experiment results, there is a frequency shift in in-seam wave signals, and the tomography method with the M_i value is effective. The above method overcomes the effects that are caused by the source difference and the improper artificial selection of source centroid frequency on imaging results, providing a new approach for the processing of in-seam wave data.