TEM Technology

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.

Benefits of TEM technology

Understand what makes TEM effective in the field

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.