LET’S GO FLY A KITE: KITE-BASED STRUCTURE FROM MOTION IN COASTAL SETTINGS

Collecting accurate topographic data is an important component of any research program focused on the study of coastal morphology. Structure-from-Motion (SfM) is an economical alternative to traditional collection methods but because the use of this approach is in its infancy, guidelines have yet to be established. One such guideline is the optimal number of Ground Control Points (GCPs)—locations with known coordinates— necessary to render an accurate topographic map. To address the role of GCP quantity on SfM accuracy we prepared digital surface models of the beach and foredune on Hog Island, VA, USA, a site that contains ~180 high precision GCPs (as the result of an ongoing field experiment). We used a 9-foot single-line delta kite attached to a consumer grade point-and-shoot camera to photograph the field site (~0.25 km²) from a height of 20 m. We then processed the 200+ photographs using Agisoft Photoscan Pro and compared the elevation accuracy of topographic maps rendered using SfM, with varying GCPs, to points surveyed by a total station. Initial results suggest ‘diminishing returns’ when greater than 11 GCPs are used. Results from this study can be used to inform future Structure-from-Motion studies using UAVs or kites in flat, low-sloping coastal environments.