A lightweight small-loop TEM instrument for rapid near-surface mapping: Development and Case Studies

Shallow subsurface geology, often referred to as the critical zone, is fundamental to groundwater evaluation, aquifer recharge, environmental site investigations, and mining applications. Accurate characterization of this zone is required to identify infiltration pathways, low-permeability barriers, buried valleys, and channel structures, and to support decisions related to well placement, remediation, and resource management. Conventional methods such as electrical resistivity imaging (ERI) and ground conductivity meters are widely used but can be constrained by limited survey speed, discontinuous spatial coverage, sensitivity to near-surface disturbances, and logistical complexity in the field.

To overcome these limitations, a new transient electromagnetic (TEM) system, TEM2Go, has been developed for rapid, high-resolution shallow subsurface characterization. The system is optimized for depths from the surface to approximately 50–75 m while providing continuous lateral coverage along survey profiles. Acquisition speeds of 15–20 minutes per kilometre enable efficient mapping of large areas at high spatial density. A distinguishing feature of TEM2Go is real-time data processing and inversion, allowing near-instant visualization of subsurface conductivity during field operations. This enables adaptive survey design, where line spacing, follow-up measurements, and data density can be adjusted immediately based on observed results.

TEM2Go is the result of several years of research and development and incorporates multiple hardware innovations aimed at maximizing data quality while maintaining field practicality. The system design balances transmitter moment, receiver bandwidth, transmitter turn-off characteristics, and pulse repetition rates to achieve high resolution in the shallow subsurface. Both transmitter and receiver coils measure 65 × 65 cm and are designed for backpack-mounted operation. Each fully assembled unit weighs less than 12 kg, allowing deployment by a small field crew and enabling surveys in areas with limited or no vehicle access.

During data acquisition, the transmitter–receiver offset is continuously monitored, with a recommended operational offset of 15–20 m. This configuration supports continuous profiling while maintaining sufficient depth of investigation and resolution for near-surface applications. Real-time processing is fully integrated into the acquisition workflow. Recorded voltage decay curves are processed and inverted on-site, and conductivity models are displayed directly in the control software. Immediate access to inversion results improves quality control by revealing coupling effects, cultural noise, or offset inconsistencies as they occur, and provides rapid geological context to guide ongoing survey decisions.

The conference presentation describes the research and development process behind TEM2Go, highlighting key design choices and performance trade-offs. Case studies from collaboration with the Central Denmark Region are presented, where TEM2Go was used to map complex geology associated with point-source contamination. These examples demonstrate how rapid, high-resolution TEM profiling can improve identification of conductive pathways and geological controls on contaminant transport, supporting more targeted site characterization and remediation planning.