Preprint Article Version 1 This version is not peer-reviewed

Assessing the Use of Sentinel-2 Time Series for Monitoring Cork Oak Decline in Portugal

Version 1 : Received: 27 September 2019 / Approved: 28 September 2019 / Online: 28 September 2019 (15:01:45 CEST)

A peer-reviewed article of this Preprint also exists.

Navarro, A.; Catalao, J.; Calvao, J. Assessing the Use of Sentinel-2 Time Series Data for Monitoring Cork Oak Decline in Portugal. Remote Sens. 2019, 11, 2515. Navarro, A.; Catalao, J.; Calvao, J. Assessing the Use of Sentinel-2 Time Series Data for Monitoring Cork Oak Decline in Portugal. Remote Sens. 2019, 11, 2515.

Journal reference: Remote Sens. 2019, 11, 2515
DOI: 10.3390/rs11212515

Abstract

In Portugal, cork oak (Quercus suber L.) stands cover 737 Mha, being the most predominant species of the montado agroforestry system, contributing for the economic, social and environmental development of the country. Cork oak decline is a known problem since the late years of the 19th century that has recently worsen. The causes of oak decline seem to be a result of slow and cumulative processes, although the role of each environmental factor is not yet established. The availability of Sentinel-2 high spatial and temporal resolution dense time series enables gradual processes monitoring. These processes can be monitored using spectral vegetation indices (VI) once their temporal dynamics are expected to be related with green biomass and photosynthetic efficiency. The Normalized Difference Vegetation Index (NDVI) is sensitive to structural canopy changes, however it tends to saturate at moderate-to-dense canopies. Modified VI have been proposed to incorporate the reflectance in the red-edge spectral region, which is highly sensitive to chlorophyll content while largely unaffected by structural properties. In this research, in-situ data on the location and vitality status of cork oak trees are used to assess the correlation between chlorophyll indices (CI) and NDVI time series trends and cork oak vitality at the tree level. Preliminary results seem to be promising since differences between healthy and unhealthy (diseased/dead) trees were observed.

Subject Areas

Quercus suber; cork oak decline; sentinel-2; time series; vegetation indices

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