Applications of UAV-SfM Remote Sensing in Monitoring Morphodynamic Processes in Sedimentary Cliffs of Pacheco Beach, Northeast Brazil

Leisner, M.M.; Paula, D.P.; Albuquerque, M.G.; Façanha, M.C.; Vasconcelos, Y.G., and Morais, J.O., 2024. Applications of UAV-SfM remote sensing in monitoring morphodynamic processes in sedimentary cliffs of Pacheco beach, Northeast Brazil. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 558-563. Charlotte (North Carolina), ISSN 0749-0208. Cliffs are steep morphologies, sculpted by the erosion of different types of rock and subject to mass movements. This study aims to evaluate the morphodynamic changes in a 700 m stretch of sedimentary sea cliffs located in northeastern Brazil using high-resolution images collected by UAV-SfM techniques to understand the geomorphic changes of the coastal landscape. The study used the Geomorphic Change Detection (GCD) method and CloudCompare's M3C2 algorithm applied to short-term monitoring. These tools use photogrammetric products (Elevation Models and Densified Point Clouds) to determine morphological changes in terms of erosion and deposition. The difference grid models are acquired by UAV-based remote sensing, which can accurately and efficiently provide very high-resolution images and digital surface model data to measure volumetric changes. The multi-temporal analysis revealed significant volumes of erosion throughout the cliff area during the study period. In the first interval (July/2023 - January/2024), the cliff recorded erosion in 18% of its area, with volumetric rates - 6,241 ± 1,230 m3 of erosion. In the second period (January/2024 to April/2024), more severe erosion rates were observed on the cliff, reaching -10,603 ± 1,504 m with 30% of its area eroded. This research has shown that sedimentary cliffs in northeastern Brazil are undergoing significant morphodynamic changes, with erosion rates increasing over time. The application of advanced remote sensing techniques, such as UAV-SfM and the GCD and M3C2 tools, reveals clear erosion patterns that vary according to the seasonal climatic processes (e.g., marine and subaerial) acting in the region under study. The results obtained are essential for understanding the geomorphological risks associated with coastal cliffs. In addition, they highlight the effectiveness of using UAVs for coastal monitoring, providing valuable information for the sustainable management of these vulnerable environments.