Devils Tower National Monument in Wyoming
Devils Tower rises 867 feet above the surrounding landscape, and is a prominent monolith of igneous rock. The tower is the monument’s primary resource, as identified in its enabling legislation, yet its vertical aspects and summit can only be seen by those with technical rock climbing experience. High resolution imaging allow the park staff to discern fine details of the tower surface, including erosional cracks, and provide a snapshot-in-time document of rock quality conditions. This dataset is used as a baseline to evaluate potential rock fall areas of concern. The digital 3D model also allows the park to display climbing routes, pre-plan for rescue operations, and examine nesting sites commonly used by peregrine falcons.
In October 2016, the USGS and the NPS set out to collect the high resolution imagery required to generate the 3D digital dataset of the tower. Prior to the actual flights, NPS personnel climbed the tower to place several ground-control targets and conducted ground-truth surveys of ground texture and vegetation. The UAS flights were conducted with a 3D Robotics Solo quadcopter utilizing a Ricoh GR II camera payload. Sections of the viewing trail were closed for public safety while UAS flights were conducted. Twenty flights, over a three-day period, yielded more than 2,000 overlapping photos. The data was processed using photogrammetry (structure-from-motion) algorithms with surveyed ground control targets and scale markers to georeference the model in three dimensions.