Pulse Impedance: A New Approach to Defining Apparent Resistivity of Electrical Source Transient Electromagnetic Data

The definition of apparent resistivity is a critical aspect of electromagnetic methods, particularly in the context of the electrical source transient electromagnetic (ESTEM) method, which has not been well resolved. This study presents a novel concept termed pulse impedance for ESTEM, which is defined as the ratio of the first-order time derivative (pulse response) of the horizontal electric field to the vertical magnetic field. This innovative definition facilitates the derivation of a clear and explicit expression for apparent resistivity that maintains accuracy across the entire range of periods. The pulse impedance approach notably eliminates the source term from the calculations, resulting in an apparent resistivity that is independent of source parameters, thus enhancing the robustness and reliability of the resistivity estimations. The efficacy of this approach was corroborated through the analysis of data obtained from both numerical simulations and field measurements.