Effect of dielectric continuity of media in immediate proximity to the generator loop on results of near-field transient electromagnetic sounding in the microsecond range

Background. The method of near-field transient electromagnetic sounding (TEM) involves the study of transient fields excited in the earth under the action of changes in the source current. Initially, transient measurements were conducted at times from 100ms and greater; however, in the 1990s, an active study of transient fields in the microsecond range began. Since the microsecond range corresponds to frequencies close to 1 MHz, some parameters of installations, which had been previously neglected, began to attract attention due to their significant contribution to the measured signal. In the 1990s, research was initiated to assess the effect of various installation parameters on measurement results in the microsecond range. At the same time, the effect of the dielectric constant of media in immediate proximity to the generator loop has not been evaluated. Aim. Experimental evaluation of the effect of the dielectric constant of a medium in immediate proximity to the generator loop on the measured transient process. Materials and methods. Field experiments and analysis of the results obtained. Results. The results of measuring transient fields at various parameters of the medium located in immediate proximity to the generator loop are presented. Their analysis is carried out. Conclusion. (1) When working at early (0.1—10 ms) times by the TEM method using an ungrounded current loop as a source, it can be possible to receive signals distorted by processes occurring in the loop itself due to the external parameters of the medium in which the generator loop is located. (2) The shunt resistance should be selected depending on both the size of the generator loop and the effective parameters of the medium in which the generator loop is located.