Semi-automatic detection of charcoal kilns from airborne laser scanning data

Øivind Due Trier, Lars Holger Pilø

Abstract


This paper presents new methods for the semi-automatic detection of charcoal kilns from airborne laser scanning (ALS) data.

The 17th century saw the establishment of a number of iron works in Norway, based on the need of the Danish king for iron for ships, armaments and other military purposes. The iron works at Lesja, Oppland County, was established 1660. Surveys in connection with cultural heritage management work have pointed to the presence of large numbers of charcoal kilns in the area surrounding the Lesja Iron Works. It was not known, however, what the total number of preserved kilns was, if they showed sign of reuse, and how they were distributed throughout the landscape.

In 2013 the entire forested valley in Lesja was mapped by ALS with five first returns per m2. The initial visual interpretation of the ALS data, focusing on the central area, yielded about one thousand possible charcoal kilns. All were round, with a diameter between 10 and 20 m. However, the edge of the kilns had a varied topographical expression. Some kilns had a ditch surrounding them, some had pits, and some had a combination of the two. In addition some kilns had a low mound inside the ditch/pits or even pits inside the circumference.

In order to conduct a complete mapping, covering the different shapes of charcoal kiln, several detection methods are used: (1) mound detection, (2) pit detection, (3) circular ditch detection, and (4) partial ditch detection. Although many individual charcoal kilns are missed by the automatic detection methods, many are also detected, leading the archaeologist to look for additional charcoal kilns nearby. In conclusion, the automatic detection methods are improving the quality of visual interpretation of the ALS data, and make the field work more efficient.