An archaeological excavation is a little like eating a layered cake: once you have removed a layer, you cannot put it back.
The problem becomes even trickier if two layers look almost exactly the same.
Researchers from Aarhus University and Moesgaard museum in Denmark have now developed a relatively inexpensive multispectral imaging system that gives archaeologists more ways of looking at the soil before they dig into it.
Instead of illuminating an excavation with ordinary white light, the prototype uses LEDs at 16 different wavelengths, ranging from near-ultraviolet through visible light to near-infrared.
Different materials absorb and reflect these wavelengths differently. Two deposits that both look like rather similar brown or black soil to the human eye may turn out to be quite different when viewed in another part of the electromagnetic spectrum.
“We wanted to make things faster, clearer and better in the field – and at a cost that makes sense for archaeology. One way of doing that is simply to rethink the light,” says Associate Professor Søren Munch Kristiansen from the Department of Geoscience at Aarhus University.
The study is published in the Journal of Archaeological Science .
The researchers tested the first prototype at Sorte Muld on the Danish island of Bornholm.
Sorte Muld – literally “Black Soil” – is an archaeologically rich Iron Age site with more than a metre of dark cultural deposits created by centuries of human activity.
For archaeology, that richness comes with a problem. Many of the layers are thin, irregular and very similar in colour, making it difficult to determine exactly where one deposit ends and another begins.
The LED multispectral imaging system, or LEDMSI, photographed the same section repeatedly while illuminating it with the 16 different wavelengths.
The resulting images were then analysed using statistical methods that combine the spectral information and enhance differences between materials.
And differences emerged that were difficult to distinguish in normal colour photographs.
“The images looked almost psychedelic when we took them, and we only really saw what we had when we analysed them back at the computer,” says Søren Munch Kristiansen. “Then we could see new layers and changes in the fill that we simply could not see with the naked eye.”
One of the features revealed by the analysis may represent an old ground surface and therefore a break in activity at the site. The researchers stress that the interpretation remains to be confirmed, but it illustrates what the system can do: point the archaeologist towards differences that might otherwise go unnoticed.
That matters because archaeological soil rarely resembles a neat pile of pancakes. People dig holes, fill them in again, move soil around and build on top of earlier activity. Two objects found in apparently separate layers may therefore be contemporary, while neighbouring deposits may represent very different events.
Seeing those differences more clearly can improve both documentation and decisions about where to take samples for dating and other analyses.
The experiment revealed another useful trick.
When illuminated with ultraviolet light, small bone fragments fluoresced and became easier to distinguish from the surrounding soil.
Normally, fluorescence photography requires optical filters to separate fluorescence from reflected light. The researchers showed that useful information could also be extracted without such filtering, simplifying the equipment needed in the field.
This may eventually help archaeologists locate material worth sampling for scientific analyses. Previous research has linked fluorescence in archaeological bone to collagen preservation, which in turn can be relevant when selecting material for ancient DNA and protein analyses.
The present study does not demonstrate that LEDMSI can automatically select the best DNA samples. But it shows that fluorescent material can be detected quickly and with comparatively simple equipment.
The prototype is also considerably cheaper than hyperspectral imaging systems previously used for similar archaeological purposes – roughly 20 times cheaper according to the researchers.
The system has already moved on from the version tested at Sorte Muld.
A second-generation prototype with a better camera and two LED units has recently been tested at Fredbjerg in northern Jutland, Denmark, where archaeologists are excavating a cemetery dating from the late Viking Age and early Christian period.
Preservation there is poor. In some graves, very little skeletal material remains, and the bodies are visible mainly as faint shadows in the soil.
“We’re trying to see if there is information present in the graves that is not otherwise apparent,” says archaeologist David Stott from Moesgaard, one of the developers of the LEDMSI system.
During the Fredbjerg excavation, the researchers used the multispectral data to help decide where to take samples for further analyses.
The new version can acquire its series of images in around 30 seconds, compared with up to about five minutes for the first prototype. The researchers are now working towards processing the results on site almost immediately on a computer – and eventually on a phone or other field device.
Another goal is to add machine-learning software that can learn the spectral signatures of different materials and help archaeologists work out what they are looking at.
“The difficult part is teaching an algorithm what is what. At the moment, the archaeologist and I, as a geologist, basically have two settings: glasses on or glasses off. This gives us many more ways of seeing,” says Søren Munch Kristiansen.
He does not expect algorithms to replace the trained archaeological eye.
The ambition is to give that eye some assistance.
“I hope that in ten years, bringing a system like this to an excavation will be as normal as bringing a digital camera,” Søren Munch Kristiansen adds.
Journal of Archaeological Science
Seeing the past in a new light: LED multi-spectral imaging as an interpretative aid for archaeological excavation
20-Jun-2026