HOW CLOSE IS CLOSE ENOUGH? A COMPARATIVE STUDY OF VIRTUAL SURVEY MEASUREMENTS FROM LIDAR TO TRADITIONAL, IN-PERSON, GROUND-BASED MEASUREMENTS OF GEOLOGIC STRUCTURES OF THE DEVONIAN MILLBORO SHALE

GIS paired with remote sensing has led to new frontiers in understanding, analyzing and mapping geological landscapes. LiDAR and virtual surveying can potentially enhance the efficiency and flexibility of geologic and engineering fieldwork, e.g. instead of manually surveying with measuring tapes and total stations, geologists today can remotely observe phenomena and perform data collection using a variety of ground-based and UAV-assisted techniques and virtual 3D models. However, a key question is how accurate are virtual geologic survey measurements derived from remote sensing techniques compared to measurements gathered in person. In this study LiDAR was used to create a virtual 3D terrain model of the Middle Devonian, Millboro Shale exposed near Radford in Southwest Virginia. This shale outcrop was chosen because it contains a variety of geologic structures including tectonically-induced deformation, lamination, bioturbation, bedding planes, fractures, pyrite mineralization, occurrence of concretionary intervals/strata, and in-filled joints and fractures in addition to human-made, saw-cuts for sampling.

Simultaneous Localization and Mapping LiDAR (SLAM-L) scans, and high-resolution imagery from the ground and UAVs were used to create 3D models, which were used to collect virtual measurements of 19 geologic features. These measurements were compared to the ground-scaled measurements obtained with a traditional measuring tape. Both vertical and horizontal measurements were analyzed using various statistical methods, including repeated measures, 2-tail T tests, and ANOVA.

We present results that answer key questions including: 1) are the vertical measurements of geologic structures more accurate and precise in comparison to the horizontal measurements? 2) are there any geologic structures that showed a statistically significant difference between measurements obtained via LiDAR versus ground surveys? Our findings support virtual surveying but pose some interesting questions relating to the vertical and horizontal aspects of common geologic structures. Our results raise questions about the innate fuzziness and uncertainty of boundaries between different geologic structures and how such uncertainties can impact interpretation of data collected through virtual 3D models.