Moloney, J.G.; Hilton, M.J.; Sirguey, P., and Simons-Smith, T., 2018. Coastal dune surveying using a low-cost remotely piloted aerial system (RPAS).

Monitoring coastal morphodynamics is important for understanding the response of coasts to short-term storm events, for understanding coastal response to long-term environmental change, and for managing beach-dune systems. Remotely piloted aerial systems (RPAS), or “drones,” present new opportunities for coastal monitoring. They are inexpensive and efficient, require minimal expertise, and provide high-resolution aerial imagery. This paper investigates the efficacy of low-cost RPAS for coastal foredune monitoring. Comparisons among total station, real-time kinematic global navigation satellite system, terrestrial laser scanner, and RPAS surveys were made based on the efficiency of point acquisition, cost, accuracy of the output surface, and the method's sensitivity to atmospheric and environmental limitations. Temporal elevation and volumetric changes in sand were quantified using RPAS photogrammetry and conventional survey methods. An intentionally notched section of foredune was monitored over a 12 month period. The RPAS survey was the most efficient method and had a high level of accuracy. The digital surface model (DSM) derived from the RPAS survey had a vertical root mean square error of 8 cm. However, RPAS was more sensitive to environmental and atmospheric conditions, although the survey rapidity means undesirable weather conditions can be avoided. The RPAS did not accurately quantify total sand deposition downwind of the notches due to an elevational offset caused by vegetation, which is dense throughout the study site. Comparison of the DSMs derived from RPAS surveys indicated a decrease in elevation (between 10 and 20 cm) during the survey period. The method affords the advantages of point acquisition efficiency and flexibility. However, low-cost red-green-blue RPAS is more suited to quantifying the morphology of bare sand or sparsely vegetated areas, quantifying large-scale changes, or for long-term morphologic monitoring due to its inability to penetrate vegetation. It is expected that future sensors capable of penetrating vegetation will become more accessible for low-cost platforms.