Wohnrade Civil Engineers, Inc. (WCE) was the first UAS operator to successfully map a 1-square-mile area of the Great Sand Dunes National Park & Preserve. The project was a collaborative effort that included Black Swift Technologies, UAS Colorado, and the National Park Service (NPS). The goal was to develop precision mapping using high fidelity remote sensing to monitor change detection and measure dune height in the vicinity of the Star Dune.
The UAS data collection was performed on October 19, 2016 using the Swift Trainer fixed-wing UAS, developed by Black Swift Technologies. A Scientific Research and Collection Permit was obtained from the NPS, with the condition that the takeoff and landing site be located outside the park boundary. As a result, the SwiftTrainer was required to fly beyond visual line of sight 5 miles to the north end of the area of interest. Our crew's efforts also drew the attention of the local press, you can read more details written by the Denver Post.
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). Beyond visual line of sight operations were conducted under FAA Section 333 Exemption rules.
High Resolution Results May Enable New Discoveries
The research staff is very pleased with the results, stating, “It is definitely the best aerial imagery of the dunes to date!” Also, “the accuracy numbers from your survey are impressive.”
They will use the digital terrain model as a baseline for monitoring changes to the sand dunes over time. And even in this early stage, they believe some of the other maps Mary gave them may lead to new discoveries. Thanks to the orthomosaic map, researchers have already picked out linear features on the flanks of the dune that they had never noticed before.
As WCE’s civil engineering workflow shows, drone mapping, combined with adequate ground control points, provides the basis for highly accurate aerial surveys. These surveys not only save considerable time and money, but they also allow for data collection in difficult terrain, providing researchers with high-resolution information that is much more detailed than what they can capture on foot.