Photogrammetric surveying forests and woodlands with UAVs: Techniques for automatic removal of vegetation and Digital Terrain Model production for hydrological applications

The purpose of this study is the photogrammetric survey of a forested area using Unmanned Aerial Vehicles (UAV), and the estimation of the Digital Terrain Model (DTM) of the area, based on the photogrammetrically produced Digital Surface Model (DSM). Furthermore, through the classification of the height difference between a DSM and a DTM, a vegetation height model is estimated, and a vegetation type map is produced. Finally, the generated DTM was used in a hydrological analysis study in order to determine its suitability compared to the usage of the DSM. The selected study area was the forest of Seih-Sou (Thessaloniki). The DTM extraction methodology applies classification and filtering of point clouds, and aims in the production of a surface model including only terrain points (DTM). The method yielded a DTM which functioned satisfactorily as a basis for the hydrological analysis. Also, by classifying the DSM DTM difference, a vegetation heights model was generated. For the photogrammetric survey, 495 aerial images were used, taken by a UAV from a height of ~ 200m. A total of 44 ground control points were measured with an accuracy of 5cm. The accuracy of the aerial triangulation was approximately 13cm. The produced dense point cloud, counted 146,593,725 points.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author