Imaging skeletal remains with ground-penetrating radar: comparative results over two graves from Viking Age and Medieval churchyards on the Stóra-Seyla farm,northern Iceland

Detailed ground-penetrating radar surveys were conducted at separate Viking Age and Medieval churchyards on the Stóra-Seyla farm in Skagafjörður, northern Iceland. Surveying over a previously unknown site (ca. AD 1000) that is located just a few meters above the Skagafjörður valley bottom delineated the remnants of a buried circular turf wall that encloses a church structure and several graves. The radar profiles over the graves contain strong hyperbolic reflections that emanated from the skeletal remains. Over one of the graves, an air-filled void within the chest cavity had been detected as noted by reflections with normal polarity which indicated a boundary towards increasing microwave velocity. During excavation, the soil surrounding an intact rib cage collapsed thus confirming the presence of the void. In general, the skeletal remains were very well preserved and yielded strong reflections which permitted the orientation of the body to be determined. Conversely, the radar profiles over a grave from a more recent churchyard (ca. AD 1200) show ground disturbance but lack hyperbolic reflections. Upon excavation, only teeth were recovered. The poor preservation of the skeletal remains is attributed to increase contact with infiltrating groundwater from an overlying gravel layer. Interpretations were aided by time-slice overlay imaging, forward modeling and analysis of the reflection coefficient.