Land cover classification of Samoylov Island and Landsat subpixel water cover of Lena River Delta, Siberia, with links to ESRI grid files

Ignoring small-scale heterogeneities in Arctic land cover may bias estimates of water, heat and carbon fluxes in large-scale climate and ecosystem models. We investigated subpixel-scale heterogeneity in CHRIS/PROBA and Landsat-7 ETM+ satellite imagery over ice-wedge polygonal tundra in the Lena Delta of Siberia, and the associated implications for evapotranspiration (ET) estimation. Field measurements were combined with aerial and satellite data to link fine-scale (0.3 m resolution) with coarse-scale (upto 30 m resolution) land cover data. A large portion of the total wet tundra (80%) and water body area (30%) appeared in the form of patches less than 0.1 ha in size, which could not be resolved with satellite data. Wet tundra and small water bodies represented about half of the total ET in summer. Their contribution was reduced to 20% in fall, during which ET rates from dry tundra were highest instead. Inclusion of subpixel-scale water bodies increased the total water surface area of the Lena Delta from 13% to 20%. The actual land/water proportions within each composite satellite pixel was best captured with Landsat data using a statistical downscaling approach, which is recommended for reliable large-scale modelling of water, heat and carbon exchange from permafrost landscapes.忽略北极土地覆被的小规模异质性，可能会对大尺度气候与生态系统模型中的水、热及碳通量估算造成偏差。我们针对西伯利亚勒拿河三角洲的冰楔多边形苔原区域，分析了CHRIS/PROBA与Landsat-7 ETM+卫星影像中的亚像元尺度异质性，并探讨了其对蒸散发（ET）估算的相关影响。研究中将野外实测数据与航空及卫星数据相结合，实现了精细尺度（分辨率0.3米）与粗尺度（最高分辨率30米）土地覆被数据的关联匹配。占总湿苔原面积80%、总水体面积30%的斑块，其尺寸均小于0.1公顷，无法通过卫星影像识别。夏季时段，湿苔原与小型水体的蒸散发量约占区域总蒸散发量的一半；秋季时，这两类地物的贡献占比降至20%，此时干苔原的蒸散发速率反而成为最高值。纳入亚像元尺度水体后，勒拿河三角洲的总水面占比从13%提升至20%。采用统计降尺度方法结合Landsat数据，可最优还原每个合成卫星像元内实际的陆/水占比，该方法被推荐用于可靠开展多年冻土景观的水、热及碳交换大尺度模拟。