Utilizing the towed Transient ElectroMagnetic method (tTEM) for achieving unprecedented near-surface detail in geological mapping

Abstract

The subsurface in areas affected by the Pleistocene glaciations often reveal very complex architectures and because of this, the near-surface geology is generally difficult to map and model in high detail. A number of geophysical methods focus on the uppermost part of the subsurface and are capable of mapping details, but no single method has hitherto been able to provide the detail, the data density and the resolution required to map the near-surface Quaternary geology in 3D. Driven by the demands for high detail in the uppermost parts of the subsurface related to for instance surface water and groundwater vulnerability assessments and climate-change related projects, a new high-resolution electromagnetic survey method, tTEM, has been developed. We present examples and discuss the method and its applicability in four study areas where data from tTEM surveys has been combined with geological data and knowledge to map near-surface geological features that could not be resolved in 3D using other geophysical methods focusing on the deeper subsurface or methods with a wider data spacing. • A new geophysical method (tTEM) for high-detailed mapping of the uppermost 50–70 m. • The method provides a high data coverage combined with a considerable penetration depth. • New and improved possibilities for modelling complex near-surface geology in high detail. • Especially useful in aquifer mapping, surface water and groundwater vulnerability assessments, climate change adaptation projects, mapping of aggregates, and risk assessments at contaminated sites.