USING UAV BASED DIGITAL PHOTOGRAMMETRY AND CLASSICAL TECHNIQUES TO MAP STRUCTURAL FEATURES EXPOSED IN THE HANSON-2 QUARRY, SYLVANIA, OH

The Hanson-2 quarry in Sylvania, Ohio, maintained by the Olander Park System, contain numerous exposed, yet previously undocumented structural features. Three regional joint sets exist in NW Ohio, trending NW-SE, NE-SW, and NNE-SSW. These joint sets may have formed through repeated activity of the N-S trending Bowling Green Fault (BGF), but may also be an orthogonal joint set formed through flexure of the Findlay Arch, predating the BGF. These joint sets are exposed and preserved mainly in quarries.

Unmanned Aerial Vehicles (UAVs) have been used previously in quarries to document excavated volumes and to map exposed structural features, allowing for interpretation in areas unreachable or unsafe using classical techniques.

Three geologic questions were asked for this study. Do the joint sets measured in the Hanson Quarry match the regional joints sets in Ohio? Does the aid of UAVs to map this quarry allow for accurate measurements in inaccessible areas? What image resolution can be generated to accurately map structural features exposed in the bedrock outcrops?

A total of 86 joint measurements were made over 6 separate areas of the quarry using a Brunton Pocket Transit. Two major joint sets were resolved: 310˚-320˚ (NW-SE), and 40˚-50˚ (NE-SW). These joint sets trend similarly to those found regionally.

A Phantom 3 Professional UAV was flown over a set of transects forming a grid of vertical air photos with 60% overlap across the quarry. These were complemented by an additional set of low angle oblique photos acquired below the quarry rim. This set of over 800 images span a rectangular area of roughly 31.6 hectares. The data collected was processed into a series of Point Cloud (.las) files, and then processed to generate a Digital Elevation Model (DEM).

The DEM, orthophoto, and point cloud presented ~1.5 cm scale resolution for analysis, allowing for higher accuracy in measurements of visible structural features, as well as provided the potential to view features not able to be fully recognized from ground level. UAVs provide new ground for high level accuracy using photogrammetric techniques, resulting in more accurate measurement and interpretation, when related to field data collected using classical techniques.