Extraction of archaeological features from high-resolution LIDAR data

Ralf HESSE

(State Office for Cultural Heritage Management Baden-Württemberg, Esslingen am Neckar, Germany)

Outline: The poster presents the scope, aims, methods and first results of the LIDAR-based archaeological mapping project of Baden-Württemberg.

In May 2009, the State Office for Cultural Heritage Management Baden-Württemberg launched a three-year project aimed at the complete archaeological mapping of Baden-Württemberg using high-resolution airborne LIDAR (Light Detection And Ranging) data, covering an area of 35751 km2. The goal is the verification and extension of the existing archaeological data base.
Several data processing steps are applied to create a suitable mapping basis and extract small- scale (detail) topographic features for archaeological interpretation: After the creation of the digital elevation model (DEM) at a pixel size of one metre from the LIDAR point data, a low pass filtered DEM representing the large-scale landscape forms is subtracted from the DEM. This difference represents a local relief model (LRM) reflecting the elevation of the desired small-scale topographic features relative to the large-scale landscape forms. However, because small-scale features are smoothed rather than eliminated by the low pass filter, the LRM derived by this approach is biased towards small features, i.e. the local relief elevations are progressively underestimated as their spatial extent increases. Therefore, in a further processing step, a purged DEM is created from the DEM point elevations along the zero-metre contour lines in the LRM. Subtraction of this purged DEM from the original DEM results in an enhanced LRM which reflects less biased elevation information of small-scale features relative to the landscape at large.
As the enhanced LRM reflects only the small-scale topography, it is an improved basis for the mapping and prospecting of archaeological features such as burial mounds, linear and circular earthworks, sunken roads, agricultural terraces, ridge and furrow fields, kiln podia and mining sites. It provides further possibilities for analysis such as local elevation profiles and volume measurements.
The poster presents first results of the project. They confirm the feasibility of using LIDAR for the archaeological mapping of very large areas and the value of the LRM approach.

Keywords: LIDAR, laserscan, archaeological mapping, feature extraction