Wohnrade Civil Engineers, Inc (WCE) began using drones in their work eighteen months ago. Led by principal engineer Mary Wohnrade, P.E., the company combines DroneDeploy’s deliverables with the Autodesk suite and other engineering software to create accurate aerial surveys. The firm uses this information to provide their clients with a range of professional services, including pre-development site reconnaissance, digital elevation models, topographical mapping and volumetric calculations.
Mary belongs to UAS Colorado, a business league that supports the use of UAVs in professional services. It was through this group that she heard about an opportunity to map the Great Sand Dunes. In October, 2016 Mary and her team used drone mapping to conduct an aerial topographic survey of the dunes.
Drones Provide Access in Difficult Terrain
Like with any sand dunes, those at Great Dunes National Park shift and migrate with the wind. As part of their ongoing research into the geology and ecosystem of the park, researchers keep year-over-year data on this shifting landscape. But, because the difficult terrain makes a full ground survey extremely lengthy, if not impossible, the research team has in the past relied mostly on hand measurements of selected points on the dunes. In 2011, the entire park was mapped from a plane using LiDAR, as part of a larger US Geological Survey project that sought to survey Colorado’s San Luis Valley. But except for this one occasion, year over year the research team has relied on a handheld GPS unit to annually measure twelve index dues scattered around the main dune.
Looking for a way to gather accurate, comprehensive data annually, the park staff reached out to UAS Colorado, who put them in touch with Mary Wohnrade and her engineering firm. WCE mapped a one-square mile section of the dune field, centered on the Star Dune, the tallest of the group.
Regulations usually prohibit flying drones in national parks, but Constantin Diehl at UAS Colorado secured the Scientific Research and Collecting Permit from the NPS to do so. Mary and her team flew the area with a fixed-wing SwiftTrainer that was equipped with a custom platform and flight management system operated by Jack Elston of Black Swift Technologies. They used a 75/75 overlap and obtained 1,755 images. The one square mile area was flown in moderately windy conditions and took two and a half hours to fly. Flight time was longer than usual because their permit specified that they could not take off or land the drone within park boundaries, meaning they had to launch five miles away from the area of interest (AOI).