UAV-Based Survey of the Earth Pyramids in Kuklica Geosite (North Macedonia)

This paper presents methods for a UAV-based survey of the site "Kuklica" near Kratovo, North Macedonia. Kuklica is a rare natural complex with earth pyramids, and because of its exceptional scientific, educational, tourist, and cultural significance, it was proclaimed as a Natural Monument in 2008. However, after the proclamation, the interest in visiting this site and the threats of its potential degradation rapidly grew, increasing the need for a detailed survey and monitoring. Given the site's small size (0.5 km2), the freely available satellite images and digital elevation models do not allow comprehensive analysis and monitoring, especially of the individual forms. Instead, new tools are increasingly used, including UAV (Unmanned Aircraft Vehicles) and LiDAR (Light Detection and Ranging). Since professional LiDAR is very expensive and still poorly available, we used a low-cost UAV (DJI Mini 4 Pro) for a detailed survey. First, the flight path, the altitude of the UAV, the camera angle, and photo recording intervals were precisely planned and defined. Also, the ground markers (checkpoints) were carefully selected. Then, the recorded drone photos are aligned and processed through the Agisoft Metashape software, producing a digital elevation model and orthophoto imagery with very high (sub-decimeter) resolution. Following this procedure, more than 120 earth pyramids are delineated, ranging in height from 1-2 m to 30 m of the highest. In this stage, a very accurate UAV-based 3D model of the most remarkable earth pyramids is made (accuracy is checked with the iPhone 14 Pro LiDAR module), and their morphometrical properties are calculated. Also, the site's erosion rate and flash flood potential are calculated, showing high susceptibility. The final goal is to follow the changes and to minimize the degradation of the unique land-scape, thus protecting the geosite and its values much better.