Extracting subtle IP responses from airborne time domain electromagnetic data

Induced polarization (IP) effects observed in airborne time domain electromagnetic (TEM) survey data offer information on the chargeability of the subsurface in addition to conductivity derived from TEM data. However the IP effect is generally weak and obscured in the total TEM response. As a result, the typical inverse transient associated with IP effect does not always manifest itself in the EM response. This causes difficulty for algorithms that rely on the inverse transient to estimate the chargeability of the subsurface. We have developed a robust method that decomposes the total electromagnetic response into a fundamental (inductive) and a polarization component and we estimate apparent chargeability from the polarization component. In this paper, we discuss the method and illustrate its effectiveness with examples