Goaf area detection using high-precision wavefield imaging method of ground-airborne transient electromagnetics

The coal goaf areas are the main cause of accidents involving water intrusion in coal mines. The ground collapse caused by water intrusion in goaf areas poses major threats to further coal mining as the conventional ground-based transient electromagnetic method is difficult to perform due to the hilly terrain in the Loess Plateau. In this study, a ground-airborne transient electromagnetic method for detecting coal goaf areas on the Loess Plateau was presented. First, a numerical model was built using the geological data of the study area. The transient electromagnetic method (TEM) responses of the coal goaf area were determined by forward modeling. Then, the high-precision wavefield transformation method was applied to image the forward model. It was found that compared with the apparent resistivity definition method, the results of the high-precision wavefield transformation method more accurately represented the subsurface structures and the volume effect was avoided. Finally, the high-precision time sweep wavefield imaging method was applied to process the field data. The results revealed that the high-precision wavefield imaging method was able to accurately determine the locations of the goaf areas. In addition, the upper and lower interfaces of the strata and the goaf areas were clearly identified.