Abstract
The Arctic is a region that is expected to experience a high increase in temperature. Changes in the timing of phenological phases, such as the onset of growth (as observed by remote sensing), is a sensitive bio-indicator of climate change. In this paper, the study area was the central part of Spitsbergen, Svalbard, located between 77.28°N and 78.44°N. The goals of this study were: (1) to prepare, analyze and present a cloud-free time-series of daily Sentinel-2 NDVI datasets for the 2016 to 2019 seasons, and (2) to demonstrate the use of the dataset in mapping the onset of growth. Due to a short and intense period with greening-up and frequent cloud cover, all the cloud-free Sentinel-2 data were used. The onset of growth was then mapped by a NDVI threshold method, which showed significant correlation (r2 = 0.47, n = 38, p < 0.0001) with ground-based phenocam observation of the onset of growth in seven vegetation types. However, large bias was found between the Sentinel-2 NDVI-based mapped onset of growth and the phenocam-based onset of growth in a moss tundra, which indicates that the data in these vegetation types must be interpreted with care. In 2018, the onset of growth was about 10 days earlier compared to 2017.
Highlights
IntroductionIn Svalbard [1,2,3]
Accepted: 29 July 2021Global temperature is increasing, and so in Svalbard [1,2,3]
In order to monitor climate-induced change in vegetation, time-series of optical satellite data can be used to map a range of different biophysical parameters, and such data have been used in Svalbard to map phenological stages such as the onset and peak of the growing season, as well as plant productivity [6,7,8]
Summary
In Svalbard [1,2,3]. This has strong impacts on terrestrial ecosystems. In order to monitor climate-induced change in vegetation, time-series of optical satellite data can be used to map a range of different biophysical parameters, and such data have been used in Svalbard to map phenological stages such as the onset and peak of the growing season, as well as plant productivity [6,7,8]. Cloudiness in Svalbard, as well as in the other arctic islands, has caused problems when monitoring the different phenological stages using satellite data [7,9]. Frequent events with fog, low solar elevation angles, short growing seasons, and weak vegetation responses characterize Svalbard, and make
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