BURIED BY WIND: GEORADAR SHEDS LIGHT ON ANCIENT FORESTS AND SETTLEMENTS ENTOMBED BY RAPIDLY MIGRAING DUNES

In recent decades, identification, mapping, and 3D visualization of coastal archaeological sites have been revolutionized by the application of ground-penetrating radar (GPR) imaging. One of the key aspects of site characterization is the ability to both detect and resolve in situ cultural features related to sediment removal (graves, hearths, post holes) and accumulation (structures, middens, artifacts, debitage). Even in areas where attenuation by saltwater or thick clay is not a limiting factor, high-amplitude hyperbolic diffractions from archaeological remains may be cluttered by point-source signal return from buried vegetation or bioturbation structures. New algorithms for enhancing signal-to-noise ratio in B-scans and depth slices, as well as polarity reversal patterns, aid in distinguishing targets with similar dielectric properties. Here we present examples of high-resolution (200-800 MHz) georadar surveys proximal to several important archaeological sites and rapidly buried ecosystems in temperate (USA, Lithuania, Latvia) and tropical settings (The Bahamas). A site in coastal Maine offers an example of rapid entombment of man-made structures by migrating sand following vegetation removal. Along the Baltic Sea coast, ongoing sand invasion into forest and pediturbation by large ungulates act as potential contributors to near-surface signal clutter. At Bahamian sites, active carbonate dunes have substantially greater numbers of unfilled burrows (land crabs, lizards, iguanas) and undecayed vegetation (trunks, roots, phytodetritus) than their lithified analogs (aeolianites). Target density varies highly even along a single profile, with mean values (5-m running average) of up to 2.6 m^-1 . Our research demonstrates how visualization of known targets and attribute analysis of radargrams (amplitude, velocity, and polarity structure) helps improve the ability to discriminate between diffraction patterns of diverse origin.