APPLICATION OF AIRBORNE LIDAR TO GEOLOGIC MAPPING IN CENTRAL TEXAS

Field mapping in the Central Texas region encounters several major problems including limited access to private land, limited outcrop, dense and variable vegetative cover, and indistinguishable carbonate facies. Airborne LiDAR data can be a useful tool in overcoming some of these obstacles. The data can be processed in Geographic Information Systems (GIS) to generate a Digital Elevation Model (DEM), effectively creating a bare-earth model of the land surface, which can be further processed into derivative products such as slope raster maps. LiDAR data was acquired from the Texas Natural Resources Information System (TNRIS) for the Driftwood, Mountain City, and Signal Hill quadrangles in Central Texas and used to generate a 2.1 meter resolution DEM. The Cretaceous units in Central Texas feature prominent tread-and-riser geometries in their bedding, which are best displayed in GIS as a slope raster generated from the DEM. The slope raster map, which displays the slope of the landscape at each raster cell, was calibrated and correlated to a measured section from the field area demonstrating it can resolve riser beds down to the sub-foot scale. Distinct and continuous patterns on the slope raster map delineate treads and risers of the contacts between the Glen Rose Fm., Walnut Fm., and Edwards Group, which can be mapped directly in GIS. Breaks in these patterns represent mappable faults. These patterns generated from LiDAR are not apparent in other elevation data sets (topographic maps, National Elevation Dataset, Shuttle Radar Topography Mission) and more traditional remote mapping techniques, such as stereo photo pairs. The contacts traced from slope raster maps generated from LiDAR showed improvement on previous work. Combined with traditional field mapping and calibration to measured sections, this technique can be a useful mapping tool for certain geologic settings.