Geophysical survey is a non-destructive and non-invasive investigation of a site widely used in archaeology in order to identify below-ground anomalies that are human made, such as building foundations, ploughed-over graves and other buried structures. And this is why it was obvious for me to use this technique before the actual archaeological excavations at the site. As a matter of fact, one of my purposes in choosing the geophysical survey as a part of my investigations at Kvarnbo was to facilitate the future choice of where to put the excavation trench(es) 😉
We used Ground Penetrating Radar technique at Sa 14.9 and it was Dr Andreas Viberg from Stockholm University (specialized in geophysical methods) operating the instrument as well as interpreting the results. And you can read more about the variety of projects Andreas is involved in on his webpage – http://www.andreasviberg.se/ (in Swedish). Andreas had the most wonderful weather here on Åland and the whole of 3 eager assistants at his disposal, including Professor Frands Herschend from Uppsala University and Kim Darmark from the Museum of Åland (and me); furthermore, our work was followed by the local media – the attention that the site definitely deserves and we only welcomed 🙂
In short, the ground penetrating radar instrument consists of an antenna and a processing unit. The technique comprises sending an electromagnetic pulse down into the soil while the antenna slides over the ground and then measuring the time until this pulse is returned to the surface after reflecting back from different layers and/or objects in the ground. The thing is that whenever this electromagnetic pulse hits a layer or an object of different electromagnetic character than the layer above, part of the signal is reflected and sent back and this signal is received while the time elapsed is measured. Then, using this travel time and depth information, the data is processed into three-dimensional (underground) map of the surveyed area – and this map can be viewed as horizontal slices in the desired depths.
In total, about 4000 m² were surveyed at Kvarnbo distributed into four areas of investigation that were all connected to each other. The survey grids were physically marked on the ground and the instrument slidden back and forth inside the grid.
The results from the survey are now being processed and I am pretty sure that these will help me to plan future investigations at Kvarnbo. But -you know what- while working in the field we might have discovered more houses in the area by visual inspection!! 😉