Lidar remote sensing datasets have become commonplace tools for many archaeologists. In Finland, NLS datasets offer an excellent starting point in planning and conducting archaeological surveys. Elevation model data is vital in studying the Stone Age, for example, as features located in prehistoric coastal areas can be tens of metres higher than the current coastline as a result of land uplift. In addition, Lidar datasets help find previously unidentified ancient monuments before any fieldwork.
See the forest from the trees
The most useful datasets in archaeology include digital surface and topographic models, i.e. bare earth models, from which any aboveground vegetation is filtered out.
There are many approaches to visualising Lidar datasets. The most commonly used analytical hill shading has its limitations. In them, the light source is usually placed northwest to produce a realistic illusion of 3D topography. If the light source was placed southeast, we would interpret the results the other way around – holes would be mounds, and vice versa. In addition, any line features parallel to the light source often disappear. To solve these problems, methods have been developed especially for the interpretation of Lidar datasets, including the local relief model and the sky view. The relief model highlights tall or low features that stand out from their background, while the sky view examines the surface area of the sky that can potentially be seen from each point – simply put, a smaller part of the sky can be seen from the bottom of a hole than from the top of a mound.
Stone Age coastal areas: pit-houses and stone walls
In the Stone Age, people lived in pit-houses, i.e. houses built in depressions in the ground, in many parts of Finland. They can still be identified in forests as shallow depressions. These depressions range from a few metres all the way to features of roughly twenty metres and features that resemble terraced houses.
Pit-houses can easily be identified in Lidar datasets, as they often stand out when visualised using simple hill shading. People interested in prehistory have identified hundreds of pit-houses using elevation models of the NLS which have enabled them to be engaged in the targeting of fieldwork.
A giant’s church is another Stone Age feature, which has been examined using Lidar datasets. Giant’s churches are stone enclosures built at the tops of hills in the coast of Ostrobothnia. Their size varies from a few to several tens of metres. They date back some 4,000–5,000 years, but their purpose remains unclear. A potential giant’s church has also been identified in Pielinen, outside the previously identified area, using Lidar datasets.
20th century archaeology: military trenches and Nazis
Lidar datasets are also useful in studying more recent features. In Finland, 20th century conflict archaeology has been studied especially in Helsinki, Hango and Lapland. One of the difficult themes of Finland’s recent history has been investigated in Hanko and Lapland: the presence of the Wehrmacht in Finland, which was also the topic of my doctoral dissertation at the University of Helsinki. My studies focus on the internal organisation of military camps. Other projects have identified the defensive positions of the Germans in Enontekiö, among other locations.
In Helsinki, we have also tested the semiautomatic identification of features with encouraging results. Recently, Lidar mapping using drones has also increased: for example, an accurate elevation model has been prepared for the ancient Rapola hill fort. Photogrammetry models of German features in Lapland have been produced based on drone photos.
Commonplace in the future
Lidar datasets offer an excellent tool for targeting archaeological surveys and protecting cultural heritage. The use of Lidar datasets in Finland could be advanced through open access analysis services customised for the datasets of the NLS. They could be automated online services.
In the midst of all the technology, we should keep in mind that the analysis of Lidar datasets is only one preparatory phase. Fieldwork carried out by professional archaeologists will continue to be invaluable considering research, ancient monument management and land use planning.
Author: Oula Seitsonen is an archaeologist and geographer who works in the Domestication in Action project at the University of Oulu and heads the Archaeology of the Mannerheim Line project at the University of Helsinki. His doctoral dissertation “Digging Hitler’s Arctic War. Archaeologies and Heritage of the Second World War German military presence in Finnish Lapland” is available in the digital archives of the University of Helsinki. His current project is called “Vaakunakylä: Contemporary archaeological perspective on the inequalities of the welfare society”.