Tree cover mapping based on Sentinel-2 images demonstrate high thematic accuracy in Europe

• Published in: International journal of applied earth observation and geoinformation Vol. 84; p. 101947
• Main Authors: Ottosen, Thor-Bjørn, Petch, Geoffrey, Hanson, Mary, Skjøth, Carsten A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.2020; International Institute for Aerial Survey and Earth Sciences; Elsevier
• Subjects: Band combinations; Copernicus; Sentinel-2; Tree cover; Unsupervised classification; Copernicus; Unsupervised classification; Tree cover; Band combinations; Sentinel-2
• ISSN: 1569-8432; 1872-826X
• DOI: 10.1016/j.jag.2019.101947

•A tree map was created using unsupervised classification for six Sentinel-2 tiles.•The combination with highest agreement with the NFI was the bands 2, 3, 6 and 12.•Good qualitative agreement between the present map and the NFI.•The map shows between 8% and 79% greater tree cover compared to previous estimates.•The overall accuracy of the present map was assessed to be up to 90%. The spatial and temporal distribution of trees has a large impact on human health and the environment through contributions to important climate mechanisms as well as commercial, recreational and social activities in society. A range of tree mapping methodologies has been presented in the literature, but tree cover estimates still differ widely between the individual datasets, and comparisons of the thematic accuracy of the resulting tree maps are rather scarce. The Copernicus Sentinel-2 satellites, which were launched in 2015 and 2017, have a combination of high spatial and temporal resolution. Given that this is a new satellite, a substantial amount of research on development of tree mapping algorithms as well as accuracy assessment of said algorithms have to be done in the years to come. To contribute to this process, a tree map produced through unsupervised classification was created for six Sentinel-2 tiles. The agreement between the tree map and the corresponding national forest inventory, as a function of the band combination chosen, was analysed and the thematic accuracy was assessed for two out of the six tiles. The results show that the highest agreement between the present tree map and the national forest inventory was found for bands 2, 3, 6 and 12. The present tree map has a relative difference in tree cover between 8% and 79% compared to previous estimates, but results are characterised by large scatter. Lastly, it is shown that the overall thematic accuracy of the present map is up to 90%, with the user’s accuracy ranging from 34.85% to 92.10%, and the producer’s accuracy ranging from 23.80% to 97.60% for the various thematic classes. This demonstrates that tree maps with high thematic accuracy can be produced from Sentinel-2. In the future the thematic accuracy can be increased even more through the use of temporal averaging in the mapping procedure, which will enable an accurate estimate of the European tree cover.