The Swedish UNESCOWorld Cultural Heritage site ofthe Birka and HovgÔrden Iron Age settlementsiswellsuitedfor the testing of high-resolution archaeologicalprospection methods.In May 2006 ground-penetratingradar (GPR) and magnetometer test measurementswere conducted at Birka, resultingin data ofoutstanding qualityand new archaeological discoveries, but also demonstrating the need for increased spatial sampling regarding GPR prospection at complex Scandinavian sites. Therefore Birka was selected as a testing ground for a pilot study investigating the suitability of thenovelmultichannel GPRarray system MIRA (MAL-Imaging Radar Array) forefficient, large-scale GPR surveyswith very dense spatial sampling. The study was conducted in May 2008 by MAL-Geoscience AB in collaboration with the archaeological prospection unit of the Swedish National Heritage Board. The very high-resolution three-dimensional GPR pilot survey demonstrated that it is possible to survey 1ha and more per day with 8 cm cross-line spacing, mapping archaeological structures in unprecedented resolution, such as postholes of only 25 cm diameter.This paper describes the tested technology and methodology as well as the fieldwork and the results of the study.
We present an example of a so‐called array GPR investigation outside the Cathedral of Uppsala, Sweden. The aim of the investigation was to reveal historically interesting features in surroundings where excavations are not allowed. In the investigation, 17 different GPR antennae of the same frequency were used to obtain measurements in 16 parallel profiles simultaneously. When several separate transmitter and receiver antennae are combined into one single antenna array unit, exactly positioned parallel profiles are obtained, resulting in a seamless high‐resolution 3D picture of the subsurface. Processing the radar data into the resulting images involves several steps, such as aligning traces, removing static shifts and matching the mean response. Radar data are merged with geometry data from a total station (used to track the position of the antenna array) and then gridded and migrated. In the Uppsala case presented here, the resulting pictures in the form of time slices gave archaeologists very valuable help in understanding the subsurface and mapping historical anomalies. The findings indicate former paths and early medieval streets, among other features.
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