Surveying the Great Sand Dunes National Park Overview
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The Great Sand Dunes National Park and Preserve Unmanned Aircraft System Aerial Survey [email protected] [email protected] 720 259 0965 720 638 9656 wcecivil.com BlackSwiftTech.com 11582 Colony Row 2100 Central Ave., Ste. 102 Broomfield, CO 80021 Boulder, CO 80301 Figure 1: Final data product combining three dimensional data products with orthophoto collected by the Black Swift Technologies SwiftTrainerTM UAS Introduction • The placement and surveying of ground control points using GPS in an area inac- cessible to vehicles. A landmark set of Unmanned Aircraft System (UAS) operations were conducted in the Great • Conducting a mission over an Area of In- Sand Dunes National Park and Preserve as part terest (AOI) several miles from the launch of a collaborative project to produce accurate, site while maintaining safe operations three-dimensional maps of the area. This re- through constant voice communications quired the combined eorts and expertise of between visual observers and the Pilot in Wohnrade Civil Engineers (WCE), Black Swift Command (PIC). Technologies (BST), UAS Colorado, and the National Park Service (NPS). Two flights were • Variable environmental factors, most no- successfully completed on October 19th 2016, tably gusting wind and contrasting shad- making Wohnrade Civil Engineers of Broomfield, ows. Colorado the first FAA licensed operator to use • The use of photogrammetry to process a an UAS to conduct a sanctioned mission over relatively homogeneous scene where fea- the Great Sand Dunes. Additionally, the photos ture detection and correlation across pho- collected during the flights allowed the team to tos was dicult. generate first-of-its-kind data products over a 1-square-mile area of the park. The focus of this white paper is to provide The Great Sand Dunes National Park is a details about the encountered issues as well as very unique environment, resulting in many the solutions the team employed to overcome technical challenges for aerial data collection. them. It will demonstrate how the team’s ex- Specifically these include: perience and calculated approach ensured the 2 720 259 0965 720 638 9656 wcecivil.com BlackSwiftTech.com 11582 Colony Row 2100 Central Ave., Ste. 102 Broomfield, CO 80021 Boulder, CO 80301 Figure 2: Photo of the visual observer stationed on top of the Star Dune. work culminated in a successful and safe flight- sand deposited by the prevailing southwest- deployment as well as a valuable data product erly and westerly winds. Although the sand on for the NPS. the surface of the Great Sand Dunes is of late Holocene age, most of this massive sand body is a complex of deposits that accumulated episod- 1 Purpose of the Study ically for more than 130,000 years.”[1] Although the dunes system as a whole is The primary purpose of this work was to pro- fairly stable, changes still occur within the vide meaningful data to the National Parks Ser- field. According to the NPS, “Currently, there vice. “The Great Sand Dunes contain the tallest is enough vegetation on the valley floor that dunes (maximum height about 750 feet, or there is little sand blowing into the main dune- 230 m) in North America. These dunes cover field from the valley. However, even today there an area of 72 square kilometers (28 square are still some small parabolic dunes that orig- miles) and contain an estimated 10-13 billion inate in the sand sheet and migrate across cubic meters (2.4 to 3.1 cubic miles) of sand. grasslands, joining the main dunefield. At The dunes accumulated in an embayment that other times, some of these migrating dunes be- formed where the trend of the Sangre de Cristo come covered by grasses and shrubs and stop Range changes from southeasterly to south- migrating.”[2] Additionally, although the larger westerly. They owe their exceptional height formations, such as the Star Dune and the High to a combination of factors including range- Dune, have maintained their shape for hundreds front geometry, topography, an abundant sand of years, they will commonly change locations supply from the nearby basin, a complex wind based on shifts in weather patterns. regime, and the Sangre de Cristo Range, which One of the fundamental tenets of the Na- prevents continued eastward migration of dune tional Park Service is the study and understand- 3 720 259 0965 720 638 9656 wcecivil.com BlackSwiftTech.com 11582 Colony Row 2100 Central Ave., Ste. 102 Broomfield, CO 80021 Boulder, CO 80301 Figure 3: Flight path of the two flights conducted over the Star Dune area of interest. Note the straight flight tracks and significant distance between the AOI and takeo and landing location. ing of the resources they are charged with pro- the limited resources available for the collect. tecting. For the Great Sand Dunes system, this Specifically, this size of survey would generally involves remote and in situ sensing to monitor require up to 24 ground control points (GCPs) change detection. Work to date largely involved to provide an absolute reference for the photo labor intensive traditional surveying methods, set, as well as several check points (CPs) to consuming valuable resources from an already use in error analysis of the final data product. over-constrained workforce. In an eort to al- However, the AOI was inaccessible by vehicle leviate these issues, this investigation was con- and required travel by foot, which consequently ducted to develop precision mapping capabili- meant the establishment of GCPs and collec- ties through the use of UAS. Specifically, a de- tion of their individual GPS x,y and z coordinates sire exists to measure terrain height in the vicin- would take significantly longer than usual. ity of the largest park feature, the 750ft (229m) tall Star Dune, as well as provide change detec- tion for the dune itself. Over a period of eight hours on October 18, 2016, a combined total of seven surveyed GCPs 2 Mission Planning and check points CPs were set by a two man crew from Wohnrade Civil Engineers. Although 2.1 GPS Ground Control Points well short of the desired 24, this was the maxi- mum number achievable by a two man team in The AOI for the project consisted of an one the period allotted for the mission. Measures square mile rectangle, centered on the Star were taken to ensure that the GCPs did not shift Dune (Figure 3). This size and shape were cho- on the dune or become covered in sand before sen to balance the requirements of the NPS with the collect could take place. 4 720 259 0965 720 638 9656 wcecivil.com BlackSwiftTech.com 11582 Colony Row 2100 Central Ave., Ste. 102 Broomfield, CO 80021 Boulder, CO 80301 2.2 Flight Path Generation The flight paths were generated using the SwiftTabTM user interface software from BST. This software allows for the simple creation of mapping plans based on only a few speci- fied parameters from the operator. Specifically these include the height above ground level for the mapping mission and percent overlap of the photos. Tracks are automatically generated to achieve these parameters, and photo trigger lo- cations are based on GPS location, eliminat- Figure 4: Launch of the SwiftTrainerTMTM UAS from a ing incorrect spacing due to strong tail or head small dirt road. winds. One of the challenges for this particular The SwiftTrainerTM provides industry- project was the collection of data over very di- leading AOI coverage through the uniform verse terrain, given the area of interest con- spacing of images, tight flight tracking, and tained terrain variations of up to 750ft (229m). consistent overlap pattern. These factors are TM Use of the SwiftTab app greatly simplified the essential for producing an image set capable mapping plan generation process as it makes of deriving accurate geospatial data from. This use of digital elevation maps to 1) ensure the was especially important for this particular data waypoints remain within a specific height of set, given the incredibly limited number of fea- the ground (thus maintaining a uniform ground tures that could be extracted from the dunes sample distance for the photos taken through- themselves. out the flight) and 2) inform the operator if any One of the conditions of the NPS Scien- flight paths will intersect particularly sharp ter- tific Research and Collecting Permit was to lo- rain features. cate the launch and landing site outside of the Great Sand Dunes National Park boundary. This not only extended the collection time con- 3 Aerial Data Collection siderably, but also required operations from a very short dirt road. The hand launch capabil- 3.1 The SwiftTrainerTM UAS ity and automated landing functionality of the SwiftTrainerTM proved invaluable in being able The UAS team of Wohnrade Civil Engineers and to conduct the missions given the NPS con- Black Swift Technologies chose the fixed-wing straints. SwiftTrainerTM (Figure 4) for the Sand Dunes The 1-square mile AOI was flown in 2 hours project for its ease of use, accurate ground and 30 minutes over two flights, collecting tracks, accurate geotagging of images, ex- 1,755 images. The automated "resume map- tended range, and ability to map large areas in a ping" feature of the SwiftTrainerTM was used to single flight (up to 2.25 sq-mi). The SwiftTrainer ensure proper overlap between the data sets. A is a small, fixed-wing UAS that is sold by BST total of 1,289 images were collected during the to primarily conduct these sorts of aerial cam- first flight, and 466 images were collected dur- paigns. ing the second. 5 720 259 0965 720 638 9656 wcecivil.com BlackSwiftTech.com 11582 Colony Row 2100 Central Ave., Ste.