An Objective Approach to Defining Earthwork Geometries Using Subdecimeter Digital Elevation Models

摘要

Alligator Mound, a ca. 800-year-old effigy earthwork located in central Ohio, lies within a 2000 m2 area on the edge of a steeply sloping bluff. This earthwork, with a maximum local relief of approximately 1.5 m, blends into the underlying natural topography, complicating the extraction of measurements of its geometry. To overcome this limitation, a 5 cm × 5 cm gridded digital elevation model (DEM) of Alligator Mound was developed from 2,534,774 elevation points collected from 11 survey locations using a terrestrial light detection and ranging system. This subdecimeter DEM and a derivative local relief model (LRM) capture the subtle topography at this site so that the natural landscape can be objectively filtered from the earthwork. The resulting geometric data (i.e., perimeter, lengths, area, and volume) are compared with subjective historical depictions of this partially denuded earthwork. The results show the value of subdecimeter scale DEMs and LRMs for characterizing subtle features constructed on complex underlying topographies, and for monitoring and/or mitigating long-term natural and anthropogenic earthwork degradation.