This study compared the reliability of discontinuity orientation data collected in 2016 using unmanned aerial systems (UAS) with traditional transit compass data as a control, to evaluate UAS-generated results for rock slope stability analysis. The 2016 UAS operations were primitive by 2020 standards. Lessons learned are reviewed and related to UAS procedures common today. Two sites in Virginia were selected: a cut slope along State Route 629 (Site 1) and an abandoned shale quarry below Cove Mountain (Site 2). For logistical reasons, a different UAS was used at each of the two sites. Overlapping images from UAS flights were used to create point clouds from which discontinuity orientation data were extracted. Discontinuity data from both UAS and transit compass methods were imported into Dips 7.0, RocPlane 3.0, and Swedge 6.0 software for stereonet, statistical, and kinematic analyses. Statistical evaluation of the data sets suggested better overall reliability of UAS results for Site 2 than for Site 1. Compared to transit compass data, Site 1 UAS results are reliable for plane failure analysis only, whereas Site 2 UAS results are reliable for analyzing all types of failure. Possible reasons for this include different drone systems used at the two sites with different navigation and camera characteristics, interference from high-voltage electrical transmission lines at Site 1, and biases in human versus artificial interpretations. Compensating for some identified factors is now simpler by adding surveyed ground-control points to the model. Representative compass data should always be acquired for quality assurance.

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