The right way to use radiometric data with a digital elevation model (DEM)

Gamma-ray spectrometry sees only the top tens of centimeters of the ground (about 30–45 cm). This makes it extremely sensitive to what happens at the surface — and the surface is governed by terrain. That is why interpreting radiometrics without looking at the Digital Elevation Model (DEM) is a common mistake that leads to wrong conclusions.

Why terrain matters so much

The radiometric signal reflects not only the rock; it also reflects surface processes:

• On slopes, material is transported — the signal may come from rock that does not outcrop there;
• In lowlands and plains, sediments accumulate and "mask" the underlying rock;
• On hilltops and lateritic crusts, certain elements (such as thorium) concentrate through supergene processes.

Ignoring this can make the interpreter confuse a geomorphological control with a real geological anomaly.

The DEM as a context layer

Combining radiometrics with the DEM helps answer essential questions:

• Is this thorium anomaly on a lateritic hilltop (supergene enrichment) or on in-situ rock?
• Is this potassium low hydrothermal leaching or just sedimentary cover in a valley?
• Do the radiometric lineaments follow structures or only the drainage?

Terrain therefore works as a plausibility filter to separate geology from landscape.

Best practices in practice

Some recommendations when integrating the two datasets:

1. Overlay the radiometrics (especially the ternary) on the DEM's shaded relief;
2. Check whether the anomalies respect geological contacts or only contour lines;
3. Use the DEM to identify cover and weight the confidence of anomalies;
4. Combine with magnetometry, which "sees" at depth and is not affected by surface effects.

Automated integration

Aligning radiometrics, DEM, magnetometry and geology on the same base requires data preparation and a consistent projection. Automating this integration ensures all layers arrive georeferenced and ready to overlay — which reduces interpretation errors and speeds up analysis.

How Lithogeo helps

This is exactly the kind of work the Lithogeo platform automates. From an ANM process number or a polygon of your area, it processes and integrates the public data — magnetometry, gamma-ray spectrometry, geology, terrain and mineral occurrences — and delivers the products described here ready for analysis, in minutes and right in the browser.

Educational content. The DEM is an indispensable context, but the final interpretation must consider the complete geological model.