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.

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In this paper the possibility to measure moisture content in roadbeds using multi-channel GPR is described. GPR is a continuous and non-destructive method and its capabilities of providing information on soil and water content is well documented in the past. Most of these earlier described methods involve several time consuming measurements with a variety of antenna settings. A multi-channel radar system can however make more efficient measurements through the use of independently controlled transmitters and receivers in the antenna array.The results, from measurements with a 500 MHz GPR system, show a clear correlation between the GPR data and the soil water content in a Swedish roadbed. Further evaluation is, however, needed to compare different antenna frequencies and to calibrate the equipment together with reference velocity analysis.

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