Archaeological prospection of forested areas using full-waveform airborne laser scanning

Airborne laser scanning (ALS) is a potential tool for recognising and measuring topographic earthwork features in wooded areas. To explore its potential for archaeological reconnaissance in a densely forested area, a test scan covering an Iron Age hillfort in the eastern part of Austria was carried out during the first phase of a research project. ALS sensors can penetrate vegetation canopies allowing the underlying terrain elevation to be accurately modelled. The latest generation of airborne laser scanners was used in the project. This sensor digitally records the entire waveform of the received laser echoes. We argue that the digital terrain model (DTM) generated from entire waveform ALS data could be classified with greater confidence providing a more accurate DTM than with previous ALS devices. The processing algorithms used to create the interpretative DTM are discussed in detail. Using the described procedures it was possible to remove most of the forest canopy and understorey (brushwood and low level vegetation) covering the archaeological features. The ALS DTM was compared with a detailed topographic mapping of the visible archaeological traces collected by a terrestrial survey. Significantly, very low earthwork features, which were not recognized by the trained surveyors in the field, were identified in the ALS-derived DTM. Therefore, in this study area ALS has been demonstrated as an important tool for systematic archaeological prospection in vegetated areas. There are, however, some restrictions, which are discussed in the paper.