LÖDÖSEHUS: GEOPHYSICAL METHODS FOR DESCRIBING ARCHAEOLOGY AND NEAR-SURFACE GEOLOGY AT THE SITE OF A MEDIEVAL CASTLE IN LÖDÖSE, SW SWEDEN
Sammanfattning: Near-surface geophysics is a well established method for mapping the geological conditionsin the subsurface. The use of geophysics is also a commonly used method in archaeologicalsurveys, although traditionally not as much in Sweden. Ground-penetrating radar(GPR) is however gaining more popularity and is arguably the most used method in archaeologydue to the amount of data that can be gathered in a short amount of time and withlittle effort. This study was done mostly with GPR together with a resistivity and inducedpolarization (IP) survey with the aim to compare the methods with each other. Data gatheredwith the GPR can be visualised in 2D and 3D and it is therefore of great interest tocompare these data forms. The study area is located in Lödöse, SW Sweden, which was oneof the most important cities in medieval Sweden. The survey presented in this thesis wasdone over the former courtyard and outer bailey of a castle with a triple moat system oncecalled Lödösehus. Today there are no visible remains of this castle and only a small part ofthe outer bailey has been excavated. The 3D GPR data showed previously excavated structuresalong with two larger, previously undiscovered structures. The 2D GPR data showedreflections from two of the moats and identified anomalies in the 3D data as postholes andstructures. The resistivity survey potentially identified an unexcavated moat and showed thatthe top 5 meters of the soil has unusually high resistivity values for clay. This indicates ahigh degree of leaching of salts or thick deposits of anthropogenic waste which could explainthe exceptional penetration depth with the GPR in an area of clay. The IP survey showedan area of electrical chargeability in connection to the potential moat that was found in theresistivity survey, indicating the possibility of metallic objects in the area. This study hasgreatly increased the archaeological knowledge of Lödösehus and provides exact locationsof previously excavated structures. Furthermore, new areas of interest have been identifiedfor future excavation in order to learn more about the history of one of the largest cities inmedieval Sweden.
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