Source influences of grounded-wire transient electromagnetic soundings: A systematic review and investigation

Abstract

Grounded-wire sources serve as critical transmitting elements in the transient electromagnetic method (TEM). Despite the sustained interest in understanding the impact of grounded-wire sources on the data collected, there remains a notable deficiency in thorough research and discourse on this topic. This study employs numerical simulations and field measurements to investigate the various factors that influence the effects of grounded-wire sources on TEM soundings, particularly focusing on aspects such as size, shape, shallow local anomalies, and the turn-off effect. The findings indicate that the dimensions of the source can significantly affect the early signals observed. Neglecting the actual shape of the source may lead to considerable deviations in the inversion results. Furthermore, local electrical heterogeneities beneath the source can produce overprint effects, resulting in substantial distortions of the observed signals. The turn-off time of the grounded-wire source exhibits a positive correlation with both the source length and the transmitting current, while it shows a negative correlation with grounding resistance. It is recommended that practitioners meticulously document the shape and position of the source. Additionally, it is advisable to position the source in regions characterized by simple and flat geological formations whenever feasible. The design of the source length and the intensity of the transmitting current should be carefully calibrated to accommodate the varying detection requirements for both shallow and deep targets. The implications of this research are significant for the construction, data processing, and interpretation of TEM soundings that utilize grounded-wire sources.