Comparing induced polarization effect on semi-airborne and airborne transient electromagnetic data: A numerical study

In a transient electromagnetic (TEM) survey, when a chargeable body presents, its induced polarization (IP) will generate an additional electromagnetic field that further superposes on the TEM data. If the added fields are not considered properly when designing a TEM survey or inverting the TEM datasets, erroneous results may be obtained. Thus, we compare the IP effects on the airborne and semi-airborne TEM methods in this study. One big difference between the two methods is that the semi-airborne method mainly uses the ground-based galvanic source and the airborne method utilizes the air-based inductive source. To fully illustrate this difference, we calculated the IP-TEM coupled responses at a time range of 10(-6) s to 10 s. Despite the commonly known reversal of signs in the transient, we found that in some cases of airborne TEM response, the sign will reverse twice. The relative errors caused by the IP effect are further demonstrated. A minimum peak at the early time that is closely related to the IP parameters is revealed, indicating that the IP fields will drop rapidly at the early time and then decay slowly. Finally, a misfit space analysis is performed, showing that both methods can well resolve the resistivity and the IP parameters of a conductive target, while it is difficult to recover the IP parameters of a resistivity target.