Fig. 1.
(a) Location of the Lena River Delta in northern Siberia. (modified from Vegetation zones in the Arctic – UNEP/GRID-Arendal Maps and Graphics Library). (b) Near-infrared Landsat mosaic of the Lena River Delta. The third terrace of the delta is outlined in orange and the second terrace in red, with the remaining area representing the first terrace. The yellow star indicates the location of Samoylov Island on the first terrace. (c) Aerial image mosaic of Samoylov Island with a flood plain in the West and an elevated river terrace in the East. The red dotted line indicates the total mapped area of ice-wedge polygonal tundra.
Fig. 2.
Scaling approach. Left-hand side: Upscaling land cover from (A) field-based mapping to (B) high-resolution land cover classification from aerial images and (C) satellite imagery. Domains (A), (B) and (C) show the effect of scale on extent and resolution as investigated in the study – from the plot scale with a high resolution but limited spatial extent (A, B) to the regional scale with low resolution but a large coverage (C). Right-hand side: Upscaling evapotranspiration (ET) rates from (D) plot measurements (ms) to eddy covariance measurements (E) through aerial land cover classification of the eddy footprint.
Fig. 3.
(a) Aerial land cover classification of the ice-wedge polygonal tundra on Samoylov Island, showing the polygonal pattern of low-lying centres of wet tundra and polygonal ponds, separated by elevated polygonal rims of dry tundra. Locations of measurement stations are marked in red. The red circle indicates the approximate footprint area of the eddy covariance station. (b) Close-up view of a near-infrared aerial image showing a typical lysimeter and soil moisture measurement set-up with one lysimeter installed in a wet polygon centre and another one on a dry polygon rim. (c) Close-up view of the eddy footprint area and the measurement stations within.
Table 1. Observation periods and the number of plots for field measurements of volumetric water content (VWC), evapotranspiration (ET) and vegetation surveys in wet tundra and dry tundra. Details of aerial and satellite data, including image acquisition dates.
Table 2. Volumetric water content (VWC) of the upper surface (10 cm), plant functional types and key species for wet and dry tundra, derived from field measurements. The VWC is shown as the range of surface moisture (in percentages) across all plots, for dry tundra and wet tundra
Table 3. Land cover percentages and ET ratio for the eddy footprint, the total mapped area on Samoylov Island and the Lena Delta. Land cover percentages of the Lena Delta represent the subpixel-scale heterogeneity as derived from Fig. 7. Land surface percentages exclude water bodies with surface areas greater than 0.1 ha, i.e. water bodies that can be mapped directly with Landsat data. ET ratio is the contribution of the different land cover types to the areally weighted evapotranspiration based on the mean daily ET rates for the whole observation period as well as for the summer and fall period (Fig. 6).
Fig. 4.
Cumulative percentage plots of surface areas (broken lines) and frequencies (continuous lines) for water bodies and wet tundra patches. Vertical lines indicate the pixel size of CHRIS/PROBA data (17×17 m) and Landsat data (30×30 m).
Fig. 5.
Daily precipitation, net radiation and evapotranspiration (ET) from wet (ET wet) and dry tundra (ET dry) and evaporation from water bodies (E water) during the observation period from July 21 to September 14, 2008. Summer and fall are represented by light grey and dark grey backgrounds, respectively.
Fig. 6.
ET rates for wet tundra, dry tundra and water surfaces during summer and fall, as derived from plot measurements. The size of the arrows is proportional to the ET rates.
Fig. 7.
Mean subpixel-scale land cover percentages for the total mapped area on Samoylov Island, shown for each k-means class from (a) CHRIS/PROBA data collected on July 23, 2008 and (b) Landsat-7 ETM+ collected on July 23, 2000, of the total mapped area on Samoylov Island. Vertical lines indicate the lower 10%- and the upper 90%-quantile for the relative proportions of subpixel-scale open water and dry tundra. Open water and overgrown water (quantiles not shown) show a good separability from dry tundra in both CHRIS/PROBA and Landsat data. Subpixel-scale ratios of wet tundra (quantiles not shown) can be clearly separated from the other land cover classes in Landsat but not in CHRIS/PROBA data. (c) and (d) Grey bars show the percentage of the total mapped area covered by each of the k-means classes for (c) CHRIS/PROBA and (d) Landsat.
Fig. 8.
Percentage of subpixel-scale open water for each of the nine k-means classes in the Lena Delta. The spectral grouping of the k-means classes is determined by the relative proportions of subpixel-scale open water versus dry tundra as shown in Fig. 7. White areas were not included in the classification as they are not spectrally representative of the ice-wedge polygonal tundra on Samoylov Island. Orange boundaries indicate the second terrace, red boundaries the third terrace of the Delta. The remaining area belongs to the first terrace.
