Abstract
The Arctic-Boreal regions experience strong changes of air temperature and precipitation regimes, which affect the thermal state of the permafrost. This results in widespread permafrost-thaw disturbances, some unfolding slowly and over long periods, others occurring rapidly and abruptly. Despite optical remote sensing offering a variety of techniques to assess and monitor landscape changes, a persistent cloud cover decreases the amount of usable images considerably. However, combining data from multiple platforms promises to increase the number of images drastically. We therefore assess the comparability of Landsat-8 and Sentinel-2 imagery and the possibility to use both Landsat and Sentinel-2 images together in time series analyses, achieving a temporally-dense data coverage in Arctic-Boreal regions. We determined overlapping same-day acquisitions of Landsat-8 and Sentinel-2 images for three representative study sites in Eastern Siberia. We then compared the Landsat-8 and Sentinel-2 pixel-pairs, downscaled to 60 m, of corresponding bands and derived the ordinary least squares regression for every band combination. The acquired coefficients were used for spectral bandpass adjustment between the two sensors. The spectral band comparisons showed an overall good fit between Landsat-8 and Sentinel-2 images already. The ordinary least squares regression analyses underline the generally good spectral fit with intercept values between 0.0031 and 0.056 and slope values between 0.531 and 0.877. A spectral comparison after spectral bandpass adjustment of Sentinel-2 values to Landsat-8 shows a nearly perfect alignment between the same-day images. The spectral band adjustment succeeds in adjusting Sentinel-2 spectral values to Landsat-8 very well in Eastern Siberian Arctic-Boreal landscapes. After spectral adjustment, Landsat and Sentinel-2 data can be used to create temporally-dense time series and be applied to assess permafrost landscape changes in Eastern Siberia. Remaining differences between the sensors can be attributed to several factors including heterogeneous terrain, poor cloud and cloud shadow masking, and mixed pixels.
Highlights
The Arctic-Boreal domain is currently undergoing extensive environmental changes
We focus on three sub-objectives: (1) comparison of the spectral characteristics of corresponding bands from Landsat-8 and Sentinel-2 data of same-day acquisitions for three individual study sites in Eastern Siberia that broadly differ in ecosystem and land cover characteristics; (2) defining spectral band adjustments between Landsat-8 and Sentinel-2 data for each of the three study sites; and (3) determining a set of spectral band adjustments that is applicable to Eastern Siberia generally and comparing them to the application of the global Harmonized Landsat Sentinel-2 product
The overall objective of our study was to compare the spectral characteristics of Landsat-8 and Sentinel-2 across Arctic-Boreal permafrost regions and to assess their compatibility and potential use in a combined time series
Summary
Mean annual air temperatures increased by up to 1.5–2 ◦C over the 1960–2009 period [1], and precipitation increased, with climate models showing further precipitation increases with additional warming [2]. Both the increase in air temperatures and precipitation affect the thermal state of permafrost, which is defined as ground that remains at or below a temperature of 0 ◦C for at least two consecutive years and is very widespread in this region [3]. A multitude of landscape-scale changes, such as active layer deepening, thermokarst and talik formation, soil erosion, and changes in vegetation composition and surface hydrology can be linked to permafrost thaw [12,13,14,15]
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