All photos were collected during a single flight on 24 February 2011 (Austral Summer). During UAV data acquisition 12 circular, aluminium reference disks with a 22 cm diameter, bright orange rim, and a clearly defined centroid (visible as a single black pixel in the images) were laid across the study area for georeferencing purposes. Another 30 aluminium orange disks with a 10 cm diameter were spread out for independent accuracy assessment (Fig. 1). Both types of ground control points (GCPs) could be easily identified on the collected imagery. Their exact locations were measured directly after UAV image acquisition using a Leica 1200 DGPS system in dual frequency real-time kinematic mode, providing centimeter positional and height accuracies (2–4 cm).