Investigating induced polarization in Floatem Data

This case study explores how induced polarization (IP) can be investigated using FloaTEM data, even when classic IP signals (like sign changes in decay curves) are not visible. The FloaTEM system, a boat-based transient electromagnetic (TEM) setup, was used to survey 65 km in IJssel Lake, Netherlands—a site with known geology: a freshwater layer, a clay layer, and a deeper saline aquifer. Using the EEMverter inversion tool, the data were inverted both with and without accounting for IP, using a specialized method called the Maximum Phase Angle (MPA) reparameterization of the Cole-Cole model. While both resistivity-only and IP-aware models produced similar general results, the IP inversion revealed something more: a clear polarizable layer matching the known clay zone beneath the lake. This demonstrates that even when traditional IP signatures aren’t obvious, subtle IP effects can still be detected with advanced modeling, offering additional insight into subsurface materials—especially useful in mapping clay layers in aquatic environments.