Towards terahertz imaging applications at Stonehenge for identification of prehistoric carvings

Prehistoric carvings on the stone surfaces of Stonehenge may lie undiscovered beneath shrubby layers of lichen. We assess the suitability of terahertz time domain imaging as a subsurface imaging technique for archaeologists to identify carvings obscured by lichen. In a lab setting, we show that lichen at low water content does not completely obscure carvings on stone using terahertz imagery, and that the fainter returns from the stone surface can still be leveraged to give a basic view of the stone topography beneath lichen.