High resolution GPR mapping of Late Bronze Age architecture at Kalavasos-Ayios Dhimitrios, Cyprus

a r t i c l e i n f o At the Late Bronze Age site of Kalavasos-Ayios Dhimitrios in southern Cyprus, the subterranean remains of previously unknown buildings were recently discovered and mapped with ground-penetrating radar (GPR). Though the fine-grained calcareous substrate at the site was not necessarily ideal for GPR—exhibiting a high clay fraction, significant volumetric water content, and scattering rubble—the buildings were mapped in excellent resolution with sufficient detail to indicate walls, entry-ways, and other architectural details. This was achieved with a somewhat lower frequency antenna (250 MHz center frequency) than is commonly recommended in archeological geophysics. The 250 MHz system was employed in order to mitigate the potentially negative effects of the lossy substrate, which had proved problematic for past research using higher frequency antennas. Our work showed that excellent GPR results were possible in this substrate by simply lowering the antenna frequency, and that electromagnetic attenuation likely improved spatial resolution allowing for the detection of greater detail than might be expected. The resulting GPR findings offer a fresh perspective on this important archeological site, while indicating that conservative antenna selection is not only sometimes warranted, but may be crucial in some archeological GPR investigations. Recent GPR surveys have successfully delineated a number of important architectural features at the Late Bronze Age site of Kalavasos-Ayios Dhimitrios (K-AD) in southern Cyprus (Rogers et al., 2012; Urban et al., 2013). The site exhibits a clay-rich, alkaline substrate with substantial embedded rubble and significant soil moisture content (as high as 27% VWC at 0.4 m). It has been previously noted in the archeological GPR literature that substrate conditions such as described above are poorly suited for GPR investigations (Conyers, 2013: 203–204), and it has long been known that electromagnetic attenuation, α, is more pronounced with higher antenna frequencies, often leading to greatly reduced penetration depths In order to mitigate the anticipated effects of α, in addition to scattering losses expected with the substrate at K-AD, a 250 MHz GPR system was employed for the investigation at hand; a somewhat lower antenna frequency than is most often recommended in archeological geophysics. While decreasing the antennae frequency may mitigate the effects of α, however, it does so at the expense of spatial resolution (e.g. Jol, 1995). This approach is therefore generally viewed as a compromise where greater probing depth is gained only at a loss of spatial detail. The majority …