A theoretical study on electromagnetic probing of permafrost terrains

Abstract

A theoretical analysis has shown that a portable double dipole multifrequency electromagnetic system can be a viable tool for mapping the permafrost terrains of the northern areas for engineering purposes. In this analysis, the theoretical response of a two-layer permafrost terrain (with the frozen layer at the top underlain by the unfrozen sediments) has been obtained for three coil arrangement systems. Available data on the frequency variations of the electrical properties of the permafrost and the unfrozen layers have been considered in the simulations to make the models realistic.The performance of the horizontal coplanar system is seen to be the best for mapping purposes, closely followed by that of the inclined-parallel system which is a null-coupled configuration. The study also considers the effects of the presence of a transition layer between the permafrost and unfrozen layers. The results indicate that the effects are greater when the parameters in the transition layer vary in an exponential fashion rather than in a linear fashion. The quadrature parts of the mutual coupling ratios are, in all cases, less affected by the transition layer than the in-phase parts. However, the resolution is better for the in-phase part when the permafrost thickness and frequency values are large.