TERRA: Terrain Extraction from elevation Rasters 6 through Repetitive Anisotropic filtering 7 8 9

Anton Pijl (1) , Jean-Stéphane Bailly (2, 3) , Denis Feurer (3) , Mohamed Amine El Maaoui (4) , Mohamed Rached Boussema (4) , Paolo Tarolli (1)

1 TeSAF - Department of Land, Environment, Agriculture and Forestry
2 AgroParisTech
3 UMR LISAH - Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème
4 ENIT - Ecole Nationale d'Ingénieurs de Tunis

19 Over the past decades, several filters have been developed to derive a Digital Terrain Model (DTM) from a Digital Surface 20 Model (DSM), by means of filtering out aboveground objects such as vegetation. In this filtering process, however, one 21 of the major challenges remains to precisely distinguish sharp terrain features, e.g. ridges, agricultural terraces or other 22 anthropogenic geomorphology such as open-pit mines, riverbanks or road ramps. Hence, loss of elevation data around 23 terrain edges (and consequent smoothing) is very common with existing algorithms. In terraced landscapes, the 24 preservation of precise geomorphology is of key importance in digital terrain analyses, such as hydrologic and erosion 25 modelling, or automatic feature recognition and inventorying. In this work, we propose a new filtering method called 26 TERRA (Terrain Extraction from elevation Rasters through Repetitive Anisotropic filtering). The novelty of the algorithm 27 lies within its usage of terrain aspect to guide the anisotropic filtering direction, therefore maximising the preservation of 28 terrain edges. We derived six DTMs from DSMs using UAV Structure from Motion (SfM) photogrammetry, laser 29 altimetry and satellite sources (grid resolutions ranging from 0.1−1.0 m). The results indicated a close agreement of DTMs 30 filtered using the TERRA algorithm and reference DTMs, while terrace risers were well preserved even under thick 31 canopies of vines and trees. Compared to existing filtering approaches, TERRA performed well in minimising Type I 32 errors (false ground removal), while Type II errors occurred locally where vegetation was covering the terrace edges. 33 Given the promising filtering performance, and supported by the minimal requirements of parameterisation and 34 computation, the TERRA algorithm could be a useful tool in DTM preparation for digital terrain analysis of agricultural 35 terraces and similar hillslopes characterised by a complex mosaic of sharp terrain and non-terrain features. 36

Mots clés: vegetation removal; edge preservation 37; Digital Terrain Model (DTM) extraction; terraces; anisotropic filtering

Domaines: Milieux et Changements globaux; Science des sols; Géomorphologie

Anton Pijl, Jean-Stéphane Bailly, Denis Feurer, Mohamed Amine El Maaoui, Mohamed Rached Boussema, et al.. TERRA: Terrain Extraction from elevation Rasters 6 through Repetitive Anisotropic filtering 7 8 9. International Journal of Applied Earth Observation and Geoinformation, 2020, 84, pp.101977. ⟨10.1016/j.jag.2019.101977⟩. ⟨hal-02316912⟩