TEM Technology
The TEM geophysical method explained: principles, benefits, applications, and limitations.
What is TEM?
The Transient Electromagnetic (TEM) method is a non-invasive way to “see” underground without requiring extensive groundwork. The TEM method is a highly efficient technique for locating groundwater and minerals, as well as for applications such as geological mapping and environmental surveys. The TEM method helps us understand the many different layers of soil and rock beneath the surface.
TEM works a bit like sending a pulse or “ping” into the ground and then listening to how the earth responds. Different underground materials react in various ways. For example, wet clay or polluted zones allow the signal to move more easily, while dry rock blocks it and causes the signal to fade quickly. By studying these responses, TEM builds a picture of what’s hidden in the subsurface.
Non-invasive & efficient investigation
Carry out subsurface mapping without drilling or ground disturbance. Cover extensive areas in days, not weeks, while reducing project costs and environmental impact.
Comprehensive depth range & resolution
TEM instruments can explore the subsurface from about 100 meters to over 600 meters deep in a single survey. TEM can also detect thin layers and changes across an area that single point measurements might overlook. This gives a more complete, 3D picture of what lies beneath the surface.
Risk reduction & investment protection
Avoid costly surprises and protect capital investments. Mapping subsurface conditions before construction or drilling can prevent expensive project delays and budget overruns.
Real time data & decision making
Get immediate results in the field with instant data processing. Make informed decisions during surveys and provide preliminary results to stakeholders without office delays.
How TEM works: The Physics made simple
Understanding TEM is like imagining what happens when you drop a stone in water and watch the ripples spread outward. When we abruptly shut off a strong electrical current in a wire loop, we create electromagnetic “ripples” that spread through the ground like smoke rings.
Step 1
The transmitter loop (red) is placed on the ground and carries an electrical current. A small receiver coil “listens” for signals. The layout can be in a central position (as shown) or slightly offset, depending on the survey goal.
Step 2
When current flows through the transmitter loop, it creates a magnetic field that penetrates the ground. This stage is called the “on-time,” where the system starts the process, but no measurements are taken yet.
Step 3
As the transmitter is switched off, the magnetic field disappears, and this change generates currents in the ground in the form of circular smoke-rings. These currents spread down and outward, creating an additional magnetic field. The receiver coil records how this signal changes over time.
Step 4
The receiver measures how the signal changes over time. The early part of the signal comes from shallow ground, while the later part comes from deeper layers. When the data is processed, it helps identify the different subsurface layers such as clay, aquifers, or solid bedrock.
Step 5
By repeating TEM measurements along a survey line, we can build a cross-section of the subsurface. Colors in the image represent different resistivities. For instance, in the image below the purple/pink resistive zones show sandy aquifers, while the blue/green conductive zones (low resistivity zones) indicate clay layers that block water flow. Together with borehole data, this creates a reliable picture of where groundwater is located and how it is contained.
Applications: where TEM excels?
From mapping groundwater in water-scarce regions to monitoring saltwater intrusion in coastal areas, TEM solutions deliver critical subsurface intelligence across diverse environments and geological conditions.
Managed Aquifer Recharge and Climate Resilience
TEM technology enables effective monitoring of Managed Aquifer Recharge (MAR) projects, tracking how artificial infiltration improves groundwater resources and ensuring optimal placement of recharge facilities for climate-resilient water management strategies.
Groundwater Solutions for Water-Scarce Regions
In regions with limited surface water access or seasonal contamination issues, TEM technology excels at locating suitable aquifers by distinguishing water-bearing layers from dry zones and differentiating between fresh, saline, and contaminated water before expensive drilling begins.
Saltwater Intrusion Monitoring
In coast-near areas, saltwater intrusion poses significant risks to freshwater aquifers. Our geoscanners excel at mapping saltwater boundaries in areas prone to flooding, rising sea levels, or affected by artificially lowered groundwater levels, enabling proactive management of this environmental threat.
Permafrost Mapping
When accessing remote and challenging terrains where ground remains frozen for consecutive years, understanding permafrost distribution becomes essential. Mobile TEM systems can effectively map permafrost boundaries and seasonal variations in these harsh environments where traditional survey methods face significant limitations.
Understanding TEM limitations
Know about how some environments can be unsuitable for TEM investigations.
Electromagnetic noise sensitivity
TEM measurements can be affected by electromagnetic interference from power lines, electrical infrastructure, and urban environments. Active industrial facilities, transmission lines, and densely built areas may generate noise that degrades data quality or makes surveys impractical.
Limited lateral resolution
TEM is very good at showing underground layers in depth (vertical resolution). However, it’s not as strong at spotting narrow features that run sideways or sudden changes from one material to another. This is because the method averages the signals from a wide area, which can smooth out or hide small details such as thin cracks or narrow zones.
Surface access & terrain constraints
While mobile TEM systems improve accessibility compared to traditional methods, certain terrain conditions still present challenges. Extremely steep slopes, dense vegetation, or areas with significant surface obstacles may limit survey coverage or require specialized deployment strategies.
Case studies: TEM in action
See how TEM helps solve real-world subsurface challenges.
Case Study - Potential of Managed Aquifer Recharge Site in California US
Evaluation of Potential Recharge Site, Central Valley, California
Using tTEM to assess feasibility: Managed aquifer recharge, where excess water is used to recharge the groundwater aquifers, has been proposed as a means of curbing groundwater depletion in the Central Valley. However, locating new fields for recharge is difficult. The challenge is to map out the subsurface to understand where water might move, allowing water agencies to better prioritize and plan for recharge. Study by Stanford University and Aarhus University.
Case Study - Searching for groundwater in Western Tanzania
Well siting in Tanzania
The HydroGeophysics Group, at Aarhus University carried out well siting campaign western Tanzania, where a two day tTEM survey in the village Makere ended up with recommendation of two sites well locations. The first target was a location with a potential for a thick unconfined aquifer to be present, while the second target was a confined aquifer system at greater depth, present in boreholes from nearby villages. The tTEM survey confirmed the extension of the system.
Case study - Fractured Bedrock Boreholes in Togo
Siting boreholes in Togo – Fractured bedrock
A well-siting campaign was carried out in Togo in 2022 using tTEM which resulted in recommendations of multiple borehole sites. The survey was conducted by HydroGeophysics Group, Aarhus University together with local partners, with the purpose of resolving the geology and finding potential sites for drilling water giving boreholes. The tTEM results located a several fracture zones which resulted in very successful boreholes.
Discover our product range
TEMcompany’s geophysical scanners are built to meet the requirements of geophysics professionals. Engineered for portability, our geoscanners are compact, easily transported in rugged cases, and ready for deployment by air or land, on water, in deserts, and frozen landscapes.
sTEM family
sTEM10
If you are looking for a compact yet powerful system for targeted groundwater exploration and mineral mapping, delivering accurate results in diverse conditions, then you should consider the sTEM10.
sTEM family
sTEMprofiler
If you are looking for an efficient solution for large-scale subsurface investigations, providing continuous depth profiling for groundwater and geological surveys, then you should consider the sTEMprofiler.
tTEM family
FloaTEM
If you are looking for a unique floating TEM system designed for mapping underwater geology and sediment layers in lakes, rivers, and coastal areas, then you should consider the FloaTEM.
tTEM family
tTEM
If you are looking for a high-resolution tool for near-surface imaging, perfect for aquifer characterization, environmental assessments, and agricultural applications, then you should consider the tTEM.
