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Open AccessArticle

Improved Mapping of Mountain Shrublands Using the Sentinel-2 Red-Edge Band

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Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, LECA, F-38000 Grenoble, France
2
Centre de Recherches sur les Écosystèmes d’Altitude (CREA), Observatoire du Mont-Blanc, F-74400 Chamonix, France
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CESBIO, Université de Toulouse, CNES/CNRS/INRA/IRD/Université Toulouse III-Paul Sabatier, F-31000 Toulouse, France
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CBNA, National Botanical Conservatory of the Alps, 148 rue Pasteur, F-73000 Chambéry, France
5
Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, LTSER Zone Atelier Alpes, F-38000 Grenoble, France
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(23), 2807; https://doi.org/10.3390/rs11232807
Received: 10 October 2019 / Revised: 20 November 2019 / Accepted: 26 November 2019 / Published: 27 November 2019
Shrub encroachment into grassland and rocky habitats is a noticeable land cover change currently underway in temperate mountains and is a matter of concern for the sustainable management of mountain biodiversity. Current land cover products tend to underestimate the extent of mountain shrublands dominated by Ericaceae (Vaccinium spp. (species) and Rhododendron ferrugineum). In addition, mountain shrubs are often confounded with grasslands. Here, we examined the potential of anthocyanin-responsive vegetation indices to provide more accurate maps of mountain shrublands in a mountain range located in the French Alps. We relied on the multi-spectral instrument onboard the Sentinel-2A and 2B satellites and the availability of red-edge bands to calculate a Normalized Anthocyanin Reflectance Index (NARI). We used this index to quantify the autumn accumulation of anthocyanin in canopies dominated by Vaccinium spp. and Rhododendron ferrugineum and compared the effectiveness of NARI to Normalized Difference Vegetation Index (NDVI) as a basis for shrubland mapping. Photointerpretation of high-resolution aerial imagery, intensive field campaigns, and floristic surveys provided complementary data to calibrate and evaluate model performance. The proposed NARI-based model performed better than the NDVI-based model with an area under the curve (AUC) of 0.92 against 0.58. Validation of shrub cover maps based on NARI resulted in a Kappa coefficient of 0.67, which outperformed existing land cover products and resulted in a ten-fold increase in estimated area occupied by Ericaceae-dominated shrublands. We conclude that the Sentinel-2 red-edge band provides novel opportunities to detect seasonal anthocyanin accumulation in plant canopies and discuss the potential of our method to quantify long-term dynamics of shrublands in alpine and arctic contexts. View Full-Text
Keywords: optical remote sensing; anthocyanin; dwarf shrubs; European Alps; land cover mapping; NARI optical remote sensing; anthocyanin; dwarf shrubs; European Alps; land cover mapping; NARI
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Bayle, A.; Carlson, B.Z.; Thierion, V.; Isenmann, M.; Choler, P. Improved Mapping of Mountain Shrublands Using the Sentinel-2 Red-Edge Band. Remote Sens. 2019, 11, 2807.

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