ARCHAEOLOGICAL EXPLORATION AT THE HOVEY LAKE SITE AIDED BY GROUND PENETRATING RADAR (GPR)

Ground penetrating radar (GPR) is a noninvasive subsurface imaging technique that uses electromagnetic waves in the 10- to 1000-MHz frequency band to detect changes in the dielectric properties of subsurface material. Such changes are often associated with archaeological features. Lower frequencies offer deeper penetration, while higher frequencies yield better resolution. Sensors & Software 500, 250, and 200 MHz cart-based systems were used at Hovey Lake and other sites because they offered the best balance between penetration and resolution. Grids were surveyed using parallel lines spaced at 1.5-ft intervals. Field data were processed and maps showing anomalies at varying depths were created using Sensors & Software EKKO Mapper or GPR –SLICE software packages.

At Hovey Lake, near Mt. Vernon, Indiana, the archaeological site consists of a large, fortified village containing many small houses arranged around a central plaza. The site was occupied by prehistoric people of a Mississippian culture known as “Caborn-Welborn,” from about 1400 A.D. to 1650 A.D. Because GPR is noninvasive, rapid, provides intuitive field data, and is sensitive to archaeological features, it was used in conjuction with standard soil coring, the predominate method for locating prehistoric structures. Different surveys of the same area produced different results, if soil moisture at the time of the surveys varied; the lower the moisture, the more distinct were the GPR anomalies. Different processing of the same data sets sometimes produced different results, with anomalies shifting by 50 to 100 cm. Burned soil produced the most striking GPR anomalies.

Subsurface images created from GPR surveys at Hovey Lake helped to plan excavations and answer research questions. Several house and fortification wall structures, some quite subtle, were found precisely where indicated by GPR anomalies, demonstrating the value of GPR.