Paper No. 23-4
Presentation Time: 2:40 PM
COOKIE CUTTER: ASSESSING THE PLANFORM OF 500 CAROLINA BAYS IN LIDAR DIGITAL ELEVATION MAPS
Over the past ten years, our Carolina Bay Survey (Survey) has performed the precise measurement of over 50,000 Carolina bay landforms. Six common planform archetypes have been identified, each associated with different geographies of the USA. The most common archetype - named by us as bayCarolina - has been assigned to over 26,000 gentle depressions in Virginia, North Carolina, and South Carolina. While the match of the archetype to the actual depression's encompassing rim is occasionally subjective when inspecting bays whose major axis are under a 800 meters, the overwhelming majority of larger bays are robustly correlated to the archetype. We present digital elevation maps of 500 bays from the Survey’s 2,100 bayCarolina-shaped landforms larger than 800m. Google Earth is used for interactive visualization and static map creation, allowing the viewing of our seamless bare-earth terrain imagery in situ. The Survey’s elevation maps are generated in the Global Mapper GIS platform using publicly available LiDAR datasets. When considering a relief of only 1 to 5 meters across kilometer-scale landforms, identifying the true shape of those basins is enhanced by our use of a 20x elevation exaggeration and high gain hsv-shading during map creation. Google Earth's groundOverlay supports the manipulation of a templated PNG image representing the archetype, and enables the operator to obtain an optimal fit to the bay’s actual rim. The template can be stretched or shortened to accommodate the variations in eccentricity and scale seen in the Survey, but cannot be “distorted” in any other fashion. Once created, the overlay’s XML structure allows for the efficient extraction and documentation of a bay’s spatial metrics, which are stored in a geospatially referenceable Google Fusion database (https://goo.gl/EHR4Lf). To accentuate any variations from the archetype across the 500 bays, each is presented in an individual LiDAR-derived elevation map in which the applied scale and orientation have been normalized. The bayCarolina shape is basically a geometric oval, but with an observable flattening on one side. Many Carolina bays exhibit raised rims along segments of their periphery, but we emphasize that these landforms are often merely depressions in a pediment, where an enclosing escarpment fully encircles a shallow basin.