Relief geometric effects on frequency-domain electromagnetic data

Abstract

A perpendicular transmitter-receiver coils arrangement used in the frequency-domain electromagnetic survey can have deviations in relation to its standard geometric definition due to the relief geometry of the surveyed area when combined with large transmitter-receiver distance and large transmitter loop size. This happens because the local relief characteristics along the transmitter loop wire laid on the ground can deviate the equivalent magnetic moment axis from the vertical, and the global characteristics locate the transmitter and receiver positions at different elevations. A study about that is carried on here substituting the rugged relief by an inclined plane. We have developed a new formulation for the [Formula: see text]-layered model that allowed us to investigate the relief geometry effects on FDEM data but restricting the analysis to the two-layer earth model, considering three cases of transmitter-receiver situations controlled by the relief conditions. The curves representing the Argand diagram and the apparent polarization parameter as a function of the apparent induction number were obtained for each relief model. Such procedures resulted to be very useful to demonstrate their behavior departing from those curves obtained for an inclined and a horizontal ground. These results show that small deviations in the verticality of the transmitter loop axis or in the horizontality of the surficial plane causes significant deviations, even for angles as small as 1°.